Selecting motors for the MechMate

[Gerald_D]

There has been some evolution on this topic. A number of posts in this thread were edited and/or deleted Nov 14, 2008. The earlier version of the thread is archived here (http://www.mechmate.com/forums/showthread.php?t=1112).

Today's (Nov 14, 2008) first choice in motor is a geared stepper motor from Oriental Motor Corporation available as a simple secure on-line purchase at around US$250.
It is the Vexta-Step type PK296A2A-SG7.2 (http://catalog.orientalmotor.com/item/all-categories/pk-series-stepping-motors/pk296a2a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0):

http://catalog.orientalmotor.com/item/all-categories/pk-series-stepping-motors/pk296a2a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0#
Geared motor

Most MechMate builders use this motor and are happy with it. (has (http://www.mechmate.com/forums/showthread.php?t=887)some backla (http://www.mechmate.com/forums/showthread.php?t=887)sh (http://www.mechmate.com/forums/showthread.php?t=887)). It works well with Geckdrives (http://www.geckodrive.com/products.aspx?n=546875) 201,202,203,250,251,540 However, it is an expensive motor, and difficult to obtain outside the USA. The equivalent motor in Europe is the Oriental Motor PK296AE-SG7.2 (http://www.oriental-motor.co.uk/uk/sites/produkt_4.php?ida=3&idser=69&idpr=1240&sgid=72)

Second choice is to use an un-geared Nema34 size stepper motor directly driving the pinion on the rack. Have past personal experience with Oriental Motor Vexta-Step type PK299-01AA (http://catalog.orientalmotor.com/item/stepping-motors--1068/pk-series-stepping-motors/pk299-01aa?&plpver=11&origin=keyword&by=prod&filter=0) motors ($205). Less expensive than the first choice geared motors, but less shaft torque and a slightly rough cut quality. Still produces a very passable CNC router. The smallish price difference does not make an un-geared Oriental Motor attractive, unless you want to start out with a well-known motor to add a non-backlash belt reduction (http://www.mechmate.com/forums/showthread.php?t=366) later. If you want to go this route, the Oriental Motor Vexta-Step type PK299-F4.5A (http://catalog.orientalmotor.com/item/stepping-motors--1068/pk-series-stepping-motors/pk299-f4-5a?&plpver=11&origin=keyword&by=prod&filter=0) is probably a better choice than the PK299-01AA that I used before.

http://www.mechmate.com/motor2.jpg
Un-geared (direct) motor

Third choice is still to use an un-geared Nema34 size stepper motor directly driving the pinion on the rack, but to go for something much less expensive than the premium "Oriental Motor" brand. MotionKing (http://www.mechmate.com/forums/showthread.php?t=1845) 34HS9801 (http://www.mechmate.com/forums/attachment.php?attachmentid=1511&d=1212750637) is being used happily and can be imported direct from China. The price over there, without shipping/tax charges is under $60. One of these inexpensive motors, with a belt reduction added at a later stage, will rival the performance of the "first choice" geared Oriental Motors mentioned right at the top. Even before adding belt reductions, you will have an income producing CNC router. You will be spending a little more time on sanding the slightly rough edges of your cuts though. :)

What to look for when selecting a motor:

1. Only consider a square body motor - the round body motors are older technology with a lot less torque.

2. Use at least a Nema34 size, meaning that the square body is 85x85mm [3.4x3.4"]. Smaller sizes will be under-powered.

3. Do not be tempted to use bigger than Nema34 motors - they will not fit the standard mountings provided for in the design. Besides, bigger motors bring other problems (http://www.mechmate.com/forums/showthread.php?t=255).

4. Nema34 motors are available in different lengths, depending on whether the rotor magnetics are single, double or triple stacked. For geared (or beltdrive) motors, a single stack (motor length about 66mm [2.6"]) is enough. When used un-geared, you will need a double-stacked motor at about 96mm [3.78"] long. Avoid motors much longer than this - see point 3 above.

5. For the MechMate mechanical design, the motor shaft must be at least 12mm [0.5"] in diameter to carry the spring load and not bigger than 14mm so that a small pinion gear can still be fitted. The shafts must be at least 32mm long to reach the rack, but not longer than 40mm otherwise they will collide with the rail supports.

6. The best wiring configuration for our router driving application is "half-coil". (this gives the most torque at high speed while keeping the motor temperature within limits). To wire a motor half-coil, it must have 6 or 8 lead wires.

7. If you want the motor to be compatible with a certain range of drives, the motor inductance must match. For Geckodrives, the inductance must typically be somewhere between 1.5 and 6mH. (The Gecko 250/540 wants around 3mH). Very low inductance motors cannot be driven properly by Gecko's, while very high inductance motors need very high voltage drives that are not easy to obtain.

8. If looking at a motor already integrated with a gearbox, watch out for the backlash. The "first option" geared motor above has an acceptable backlash for general board cutting and cabinet making work. It will not pass for fine precision clock-making (but then you shouldn't be looking at a MechMate anyway). Belt reductions give the fine resolution without backlash.

9. Consider getting motors with rear shaft extensions, so that encoders could be fitted. Geckodrive has a drive under development that will pull more power out of a stepper motor if it has an encoder (ala servo motor). Not a new technology (Oriental Motor has the Alpha-Step series, for example), but there is a talk of a retro-fittable feedback /drive system at an economical price, within a year or so. . . .

10. Bear in mind that geared motors have a higher detent torque. ie. they can hold a higher load when power is removed. If you are going to have a very unbalanced z-axis, a geared motor might be able to hold it up when you switch off the power.

[Dirk Hazeleger]

According to Oriental, the 7.2:1 gearbox has less backlash than the 3.6:1. It is still a single stage gear reducer. The standard gearbox sold on Oriental's site is a Spur Gear reducer, which can produce from 60 to 90 arc minutes backlash, the Tapered Hob is 15 arc minutes. This is all according to Oriental, others claim it is a very tight reducer. It may loosen up after running a while. I noticed John Forney had one of the original spur Gear reducers and I checked it and didn't notice any play.

I would choose the Pk296A2A over the PK296A1A. The torque curve is much better.

http://www.mechmate.com/Forum/messages/15/1909.jpg


The following is the torque curves, notice the B designation is just for a double ended shaft

http://www.mechmate.com/Forum/messages/15/1910.jpg http://www.mechmate.com/Forum/messages/15/1911.jpg

[Gerald_D]

That "tapered hob" issue: A hob is a tool for cutting a gear, why is Oriental practically the only company in the world that makes an issue of the tool with which the gear is cut? Its like saying my house was built with a 2lb claw hammer - why is that supposed to make a difference?

[Dirk Hazeleger]

I have no idea as far as the tapered hob issue. They don't publish the spur gear spec, and I think the rep was guessing when I asked him. It would be interesting to break down both reducers and see what the real difference is.

[Gerald_D]

The "taper hob gear" is actually a "taper gear". From a newsletter:


http://www.mechmate.com/Forum/messages/15/2039.gif


I suppose the pitch diameter is an average across the width of the gear.


http://www.mechmate.com/Forum/messages/15/2041.gif

[eric thomas]

http://www.xylotex.com/4AxSysKit-425.htm
can you use this system for the mechmate?
why, why not

[Gerald_D]

Sorry, too small and underpowered.

[Thomas M. Rybczyk]

Loren,

For a very good motor from an excellent supplier between $69-$89 follow this link. http://www.kelinginc.net/

I have been using this model KL34H280-55-4A (http://www.kelinginc.net/KL34H280_55_4A.pdf) on my current cnc machine http://accurate-inspections.com/pr%20cnc%20upgrade/ for about six months with excellent results.

These are not geared so you will have to go the gear box route for better resolution, but even at 1-1 I have done some very nice v-carving with these.

Tom

[Mike Richards]

Generally, current relates to torque and voltage relates to speed. For a given motor, the more current that it has available (up to the maximum rating for the drive) the more work it can do. And in the same way, the more voltage available to a motor (up to the maximum allowed by either the stepper driver or the maximum recommended by Gecko, i.e. 20X or 25X of the rated voltage), the faster the maximum speed will be.

Recent tests on my test bench have shown that a moderately sized motor (PK296B2A-SG3.6) can be spun faster than a larger motor, so, if gearing is available, the PK296 (300 oz*in) or PK299 (600 oz*in) seem ideal for the job. Even without gearing the PK299 size seems to be a very good match.

[glenn Crawford]

Hi,
New member here trying to gain some knowledge and insight on building a CNC and converting 2 convential machines o CNC. My question is what size motor would you think I would need for a 9" South Bend Lathe and a small Enco knee mill? I'm not well vrsed in electronics so this is pretty much all new to me. Also is there a means of compensating for the backlash in the lead screws without going to ball screws?
Thanks to all you really got an interesting site here and I hope to learn a lot from it.

[Gerald_D]

Hi Glenn, I'm sorry to tell you that we specifically want to cover only "big" CNC routers on this site.

However, having looked at your profile, I feel jealousy (you have a Multicam) and sympathy (you are a schoolteacher(I think)).....

Non-CNC routers are tools that need 2 hands to push around. Small non-CNC lathes and mills can be operated with one hand. Therefore you are needing smaller motors to replace the humans for small lathes/mills than for routers. (Big lathes and mills are a different story). Where we are using NEMA 34's for routers, you should be okay with NEMA 23.

www.cnczone.com (http://www.cnczone.com) would really be the right place for you to get all your answers. Good luck.

[Shopteacher]

Hi Gerald,
Sorry to tell ya, you ain't getting rid of me that easy. LOL I have a second Multicam coming in the next school year (yes I am a school teacher and I appreciate your sympathy). In addition to converting the two machined above I intend to build a mechmate for home. I downloaded your plans and haven't had time to fully review them, but what I have seen and read really look great.
My biggest weakness in in the setup and understanding of the motors and the controls, but have been getting a better understanding from sites like yours.
Glenn

[Frank D]

AHHHHHHHHHHH!!!! whew, i feel better now. All this stepper vs servo stuff is making me go bananas. After i posted the above message, i read the servo vs stepper thread. Ok, I need to know a little more before committing to a motor.

How much hand finishing would be required on a circle cut using a mechmate with properly sized and configured stepper motors?

I am believing that a geared stepper motor can hold the stationary axis stationary. Is this correct?

Ok, originally i was typing the desired accuracies of the machine, then i divided out the fraction and realised that even the most basic control system will be more than accurate enough.

So I guess as long as i'm not gonna hafta spend an hour filing or sanding cut parts, it's steppers and little green lizards for me!

[Gerald_D]

Hi Frank

I was hoping that somebody else would chime in here since you all must be very tired of hearing my biased opinions.......http://www.mechmate.com/Forum/clipart/happy.gif

To answer the easy question first; We have un-geared steppers on two tables and we don't have problems holding the stationary axis stationary. My impression is that the people who have reported problems in this area are using Oriental Motors Alpha controller's with feedback from the motors, and that these motors "hunt" to hold a fixed position (The I in PID?).

The tricky question, "how much sanding on circles". It won't help you if I honestly replied that we never sand any circles, because we simply don't do any post-cutting finishing service. Our clients do that themselves and we don't compete on their turf. The few times that I have made things for myself, and have wanted to remove the chatter marks that occur on parts of circles only, I reckon that it took about 10 strokes with 80grit paper?? Can anyone else give a better answer to this valid question?

Realising that we have direct drive motors, the general client feedback is that they are happy with MDF and softwood cut for them, but that they want better for acrylic plastic (perspex). If we had gearboxes, we could probably also satisfy the plastics guys.

[Loren Gameros]

Hi,

Here is my 2 cents.
I don't really know how much "mill mark" there will be when cutting circles using ungeared motors since I haven't used them yet so in that respect I can't comment.

How about someone posting some pics with wood and plastic?

I do know this, if was to cut circles say with my bandsaw, I would have a considerable amount of sanding with a power sander then alot of hand sanding. If all I have to do is sand 10 strokes with 80 grit sand paper, I will be most pleased. I have purchased the ungeared motors from Oriental (as recomended) and will using them. I will play around with them when I get them moving. I would think that no hand held or hand propelled power tool would be able to hold any kind of smooth transition through a radius. I don't know if this is a better answer but I will take a router cut over my bandsaw any day much less my jig saw.

[Frank D]

Guys, thanks for the info. I agree with the notion that 10 strokes of sandpaper is nothing, I always dress cuts anyway. And Gerald, your opinions are what got me thinking i could build one of these things. And the guys in this forum reaffirm that. So anyhoo, I guess now I'm on the hunt for some motors. Any thought on the gecko drive? 202 v 203. Can't figure out what the differences are from the blurbs on there site. I'll keep reading and can't wait to start posting pics.

[Robert Masson]

Hi all, Gerald.,

Can?t seem to find posts on the MechMate speed ( ipm) subject.
I?d like to know more on the possibilities of its cutting & transient speed capabilities of a tipical MechMate set up. Don?t get me wrong here, I?m not hopping to get anything like this ?Tim Allen type? worthless supersonic speed !!
No?no, just curious on what to expect and hopping to find out more & the how on the ipm achievable?
Thanks, Robert http://www.mechmate.com/Forum/clipart/happy.gif

[DocTanner]

Robert,
A search of (ips) will find the topics.
Never have been sure which to quote - IPS or IPM

I use 7.2 reduction and a 35 tooth pinion.
It will surface the spoilboard at 400 ipm
At 575 ipm it loses steps.
The Mechmate is able to cut much faster than I am comfortable with.

DocTanner

[Robert Masson]

Thanks doc,
It?s what I was hopping to get!! http://www.mechmate.com/Forum/clipart/happy.gif
Later, Robert

[IN-WondeR]

Is this motor enough to drive the Mechmate... it's rated at 3.33Nm so it should be strong enough, or am I missing something...
http://motioncontrolproducts.co.uk/product_info.php/cPath/10_14_34/products_id/83

KM

[Gerald D]

Kim, the smallest one is 3.33Nm which is a bit light. You should be looking at FL86STH80-4208 at 4.51Nm minimum. They are calling it Nema 23, but the sizes look like the Nema 34?

Frank, if you are still reading this, you may want to look here (http://www.mechmate.com/forums/showthread.php?t=14) for pics of various cut qualities with different machines and speeds. We normally get much better than the best of those with the MechMate.

[IN-WondeR]

Thx Gerald....

I will go with the 4.51Nm version then, it's only £42 a piece, which is very cheap... Maybe I'll even go with the 6.5Nm version to get bigger torque... And possibly more control of the gantry...

[Gerald D]

I don't know what the shipping costs are like, but it might be worthwhile to buy only one of each now and test them. Put the "worst" motor on the z-axis where it doesn't work so hard, and get the better motors for the other axes. :)

[Alan_c]

Doc
Have you any further comment on your setup with the 7.2 geared motors? Is the 1A sufficient or do you see the possibility of needing a 2A motor? What sort of jog speeds, and move speeds while cutting are you achieving?
I am getting close to making a decision on motors and would appreciate your input.

[domino11]

In browsing the oriental motor website, I noticed that they now have 9, 10, 18 and 36 to 1 gear ratios available in this motor line. Gerald, or anyone for that mater, what do you think about going higher than 7.2 : 1? The higher torque might give a better cut quality.

Also, the 2 amp motor seems to have a lower voltage coil and a lower inductance. Seems to me that if your driver can handle the 2 amps, then maybe this would be a better choice than the 1 amp? Lower inductance should mean better acceleration and torque?

Any comments anyone?

[Gerald D]

High ratios could be useful if:
- There is a true higher torque. Even the 7.2 gearbox doesn't allow you to use 7.2 times the torque of the ungeared motor. Mechanical limitations on bearing loads, shaft strengths, etc.
- There isn't any additional backlash.
- Your computer/controller/drive can run at the higher frequency required.
If you want to do some experimenting, let us know what you find :)

The 1 Amp motor with 3.6:1 gearbox developed sufficient torque to break 1/2" cutters. Can't see an obvious reason why a 2 amp motor would be "better".

[domino11]

Gerald,
Do you think the 3.6 geared motor provides better resolution and better cut quality than the direct motor? I was thinking of the 10 : 1 motor as it would be a nice divisor and provide more resolution for better cut quality?

[Richards]

The main problem with high gear ratios is the number of steps per second that it takes to move along an axis. For instance, using the popular 30 tooth pinion that has a pitch diameter of 1.5 inches, moves the axis 1.5 X pi or 4.71 inches. Because a Gecko G20x stepper driver requires 2,000 pulses to rotate the shaft one time, each stepper pulse on a 1:1 (non-geared) motor would move the axis 4.71/2000 or 0.002355 inches, which is also 424.628 steps per inch. If we were to use a 3.6:1 geared stepper motor, it would take 424.628 X 3.6 = 1528.6608 pulses to move an inch. Mach 3 has a top speed through the parallel port of 45,000 pulses per second (on my computer). That means that Mach 3 could move/jog an axis at 29.43 inches per second with a motor geared 3.6:1 (if the ramping was perfect and no gremlins were active on that particular day; however, getting 1/2 that speed would still be a notable feat).

Going to 10:1 gear reduction would require 4246.28 steps per inch. Top jog speed would be reduced to about 10 inches per second (with 5-ips being more realistic).

More importantly, as Gerald pointed out, the gearboxes used on the PK296A1A-SG series motors are NOT famous for being particularly strong or accurate. The are limited in the amount of torque that they can handle and they have some backlash. For most normal CNC work, I would pick the 3.6:1 gearbox or the 7.2:1 gearbox. Personally, I have four of the 3.6:1 gearboxes on my test bench. If and when I ever get around to building a MechMate, I'll most likely use those motors.

[Gerald D]

Gerald,
Do you think the 3.6 geared motor provides better resolution and better cut quality than the direct motor?

Going by all reports, and following common logic, the 3.6 geared is better than direct, though I have no personal experience of it. The 7.2 seems to be the even better option (again, going by reports). 10:1 is not spoken of, and it is not even slightly important to use "nice" numbers.

Added Nov 14 2008: Have since converted from direct-drive to geared 7.2:1 motors. VERY happy with the results. Cuts are now smooth.

[Gerald D]

Mike, Art Fenerty recently found a way to get much higher speeds out of his Mach engine, which is apparently standard now. (Something like 100khz without changing the PC?)

[Richards]

Gerald,

Thanks for the info about the higher Mach 3 speeds. I haven't downloaded anything from Art since the stable G100 plugin became available. (I receive dozens of Mach forum messages every night, but usually I just quickly scan the headers to see if there's anything I need - somehow I totally missed the higher speed pulse rate.) At any rate, I've just downloaded the latest software and will soon be testing it at my test bench.

[Richards]

Mach 3, at 100kHz, is wonderful! For the first time, I can make the motors on the PMDX/Gecko G202 test bench act as though they were the motors on the G100/G203 test bench.

At 100kHz, gear ratios higher than 7.2:1 could be used, but, in my opinion, either the 3.6:1 or the 7.2:1 would still be my preference.

Edited: We need to remember that, even though Mach 3 at 100kHz can spin the motors much faster, the torque requirements on a motor will probably dictate that the motor be used at moderate speeds, the speed range where a stepper motor has the most torque. What I am thinking about, however, is that higher ratio geared motors could be used if good quality gear boxes were used (expensive, more than $800 per gear box) or that brushed servos could be used (also expensive because the ones I've tested are useless without a high ratio gear box). The advantage to using servo motors is that the torque curve seems to be constant throughout the motor's speed range, but the available torque is only a fraction of that available from a smaller and lighter stepper motor. For instance, I have a 34-size brushed servo (ID33004) that is long and heavy and has only 170 oz*in of torque at 70V. However, at 70V, that motor can run all day long at 2,200 RPM. So, with a 7.2:1 or 10:1 gear box to multiply the torque and to divide the speed, that particular motor might be useful on a CNC router. The problem of course is that even though the motor and Gecko G320 servo driver costs almost the same as a Gecko G20x stepper driver and a 600 oz*in stepper motor, the servo requires a gearbox - meaning that a MechMate with servos would probably cost at least $4,000 more than a MechMate with steppers.

[javeria]

Hi All,

How about http://www.linengineering.com/site/products/8718.html , i have a quote from them for model 8718S-05P around 250 USD each. Do you all think vexta is better, i think i should find a dealer for vexta here in bangalore

rgd
IRfan

[Gerald D]

Suggest you first find the Vexta price before you decide which company is the better supplier. On paper, the motors are very similar.

[javeria]

Suggest you first find the Vexta price before you decide which company is the better supplier. On paper, the motors are very similar.

I got the quotes from Vexta distributers its almost 300USD for the ungeared and around 365USD for the geared (3.2) without taxes.

ho ho.............

[Gerald D]

Have you considered importing from Motionking, China? They might even tell you they have a stockist/agent in India.

[joepardy]

Gerald,

I think that I have read through every post on motors, gearboxes, controllers, and drivers in this forum over the last few days - and though it may not be conflicting - it can get confusing :confused:.

I am looking at building a MechMate with a BC head. Ultimately I would like to build a 4x8 machine with a 24" Z axis. I have designed and am about to begin building the BC head. I have selected the following hardware/Software so far:

(1) Gecko GRex-100 Controller (6 axis)
(6) Gecko G203V Drivers
(4) PK296A2A-SG (3.6 or 7.2) Series Oriental Motors (X,X,Y,Z Axis)
(2) PK264A2A-SG (7.2 to 36) Series Oriental Motors (B,C Axis)
Mach 3 Software with G100 Firmware Upgrade

I beleive that this configuration will "work", but I would like to have your input.

Also, with this configuration, can you recommend a "pre-built" power supply? At a minimum, I would like it to be able to handle the power requirements of the controller, drivers, and stepper motors.

I do plan on adding some other "bells and whistles" in the future (vacuum table, motor on/off, etc.) so a little extra would power for the control relays wouldn't hurt.

I am much more "mechanically" inclined than I am "electrically" proficient - hence the hesitation to build my own power supply.

Again, your wisdom & knowledge would be greatly appreciated.

[Richards]

Joe,
I know that you addressed your post to Gerald, but, if you don't mind, I'll give you my input (and it certainly won't hurt my feelings if Gerald advises something different).

First off, you've made an excellent choice of motors, Gecko stepper drivers and pulse generator. I have almost the identical parts on hand on my test bench and have had absolutely no problems with any of the parts.

To determine which power supply will work best, you must decide whether you want to wire the motors Bipolar Series or half-coil. I strongly suggest that you choose half-coil to get much better response at higher speeds, but you will lose about 30% of the low-speed torque if you choose half-coil. Assuming that you decide to use half-coil wiring, the PK264A2A-SGxx motor will determine the maximum voltage. That motor is rated at 1.4mH (half-coil), so 1000 * SQRT(0.0014) = 37VDC MAXIMUM. I've had excellent results with a 27VDC power supply with the PK295B2A-SG3.6 motor (which is just the PK296A2A-SG3.6 motor with dual shaft). Current requirements would be ((4 X 3A) + (2 X 2A)) * 0.66 = about 11A MINIMUM. And 11A X 30VDC = about 350VA. I would select a 500VA power supply to give some margin.

If you decide to wire the motors Bilevel Series, then the forumula for the PK264A2A-SGxx motor is: 1000 * SQRT(0.0056) = 75VDC MAXIMUM. Personal experience dictates that a power supply voltage of 50V to 70V will work fine, with my personal preference being a power supply that is closer to 50V than to 70V. Current requirements would be ((4 X 2.1A) + (2 X 1.4A)) * 0.66 = about 7.5A MINIMUM. And 7.5A X 60VDC = about 500VA. I would select an 700VA or 800VA power supply to give some margin.

AnTek has a PS-5N30 power supply (30V @ 500W) for $100. They also have the PS-8N54 (54V @ 800W) for $120, which is only $10 more than the PS-6N54 (54V @ 600W).

The G100 comes with its own wall-wart power plug to generate the necessary voltage, so you won't need any other voltages unless you add other unspecified parts and pieces.

[Gerald D]

Mike is the right guy to speak to regarding the electrics. :)

[larry1larry]

Hi Guys,
This is my first post after reading everything on the forum about stepper motors.
My brain is fried for the moment,so I will make some unqualified statements.
If confused,should I just use a 4 wire motor?
Different wireing schemes result in half voltages or current or whatever.Perhaps the variable is how big a power supply you build.
I read many times in posts of the power supply pushing current to the motors. I thought power supplies provided current to the motors and the motors drew current from the supply,with the gecko's limiting the current.
The geared oriental motors have less torque than the un geared motor?
For the moment my brain is wired bi-polar series,100volts/20amps/80c.
After cooldown things may be clear.
BTW great forum,Thanks
Larry

[Richards]

Larry,
Keep reading, just keep reading.

[smreish]

Mike....funny how you mention reading...just keep reading. I was soldering the harness connections on my motor's last night while the kids were busy watching Nemo....just keep swimming...
The kitchen table project has so many parallels :)

- Almost ready to put power to the box for a test run. Waiting for paint to dry so I can reassemble the cabinet.

Sean

[larry1larry]

Information overload.
Sorry my brain is still overloaded but I will try to make some assumptions.
From what I have read here,.66 is OK as all 4 steppers are never fully on at one time.the others act as a current dump.
I like the low current and sealed cabinet.For higher current you could cut a hole in the box and mount the Gecko's to an external heat sink.
Larry

[Richards]

Larry,

Although 66% is generally accepted as enough current, I always go 100%. Power supplies are cheap compared to the material that might be wasted if the motors can't do their job.

As far as heat goes, the G203v doesn't generate much heat. A slightly oversized power supply doesn't generate much heat. I run G203v all the time on my test bench. They've always stayed at, or very near, room temperature. The various toroidal transformers that I use also stay at or very near room temperature.

As to whether a device 'pulls' current from the power supply or whether the power supply 'pushes' current through a device is kind of a loaded question. Sometimes it's easier if we think of a power supply as a device that can produce pressure (voltage) and volume (current). If you've ever played with water, you know that the higher the pressure, the more volume - in a fixed amount of time. So, a power supply can 'push' electricity out to various devices, as long as the various devices can't allow passage of more current than the power supply is able to produce. That brings us to the device. If we use the water analogy again and think of each device as a certain size of hose, it is easy to visualize what is actually happening. Lets say that device A has a 1/4-inch hose and device B has a 3/4-inch hose. Using that example, it is easy to understand that device B will allow more current to pass at a given pressure than device A allows to pass. The same thing is happening with power supplies and electrical components. The power supply is able to push out electricity at a certain pressure as long as the various devices connected to that power supply allow less current to pass than the power supply is able to supply. So, to bring this long analogy to an end, if a power supply can supply 10A of current and all of the devices connected to that power supply can only allow 8A of current to pass, then the power supply can be considered adequate to handle the job. On the other hand, if the power supply could only handle 6A of current and all of the devices connected to that power supply can allow 8A of current to pass, then the power supply would be considered inadequate to handle the job (just like running too many sprinklers off of one water line causes pressure to fall to the point that the sprinklers can't do their job).

[Gerald D]

Mike, an early New Year's resolution of mine is to do some measurements of these lovely vague concepts we spend hours talking about. . . . .

1. Put a logging amp-meter on the output of the power supply driving motors which are doing various types of cutting (3D, cabinet doors, etc.). This will tell us if the 0.66 factor is okay.

2. Take a variable transformer powering a recommended motor via a g202 and g203V and log motor temperature versus voltage. This will tell which voltage is the limit for the motor.

But, if Santa has been kind while I am away on holiday, there will be lovely graphs and test reports waiting in my stocking when I get back. ;)

[revved_up]

Ok, I am about to commit to the build and start buying hardware etc. I have read this thread 3 or more times and agree with many of the posters before me that this can be quite confusing and thankyou Gerald for updating your postings and keeping everything current. Is it a possibility that someone that has tested different motor control combinations could possibly post a spreadsheet to make it easier to compare and list pros and cons. Maybe if possible leave it open for people to add their specs of what they have working on their machines in the future so everything could be in one consise location. I know this may be asking for alot for somebody to take the time for this as time is my most precious asset but it would help all of us with less experience to make good decisions.

[turnerseng]

Who is a good source for servo motors in South Africa? and what would the model number be for the replacement to the Oriental steppers PK296A1A.

[Alan_c]

Try CNC Direct (http://www.cncdirect.co.za)in JHB, their prices are not bad, but nobody on this forum has used their motors. The OM motors are available from Varispeed but their pricing is truly laughable if not downright criminal.

[Doug_Ford]

Andy,

If you are planning on using them on a MM, a servo won't work. It spins too quickly.

[Marc Shlaes]

Doug,

I am surely no expert, but, it seems that with transmissions such as those that JR and I designed and built, they would work.

Today, JR and I should be posting the DXFs as well as a description of just how the cutting of the 1/2 inch aluminum worked.

[Doug_Ford]

You may be right Marc. I hadn't thought of that. Sure sounds like a lot of work and extra money especially when we're not sure it is needed. My machine has power to spare. If I changed my pinion from a 35 tooth to a 20tooth, I don't think I would ever lose a step and it would still probably go fast enough to scare me.

[smreish]

...Doug...it doesn't go that fast with 20Tooth......but it does a fine job.
I seem to cut in the 180-225ipm band comfortably all day long. I do think I am going to "upsize" slightly next month when I move the machine. I need a "little" quicker fast moves between parts. I need to shave about 4 minutes off each cut cycle to get a better part/price yield.

[Kevin]

I think you will need a lot more than 3:1 reduction for a servo motor to work on a MechMate...

Kevin

[Marc Shlaes]

Kevin, please elaborate. This is something I wanted to learn about for a while. Maybe it is just curiosity. Maybe it won't go anywhere but I would love to know more about servos.

Thanks in advance.

[Richards]

The servo motor that I've had for several years is an ID3004. With the Gecko G320/G340 type servo driver, it spins at about 2,200 RPM and gives about 225 oz*in torque. The motor is about 10-inches long.

As you can see, there are two problems, 2,200 RPM with a 20/20 pinion and rack would mean that the axis would move 2200 / 60 X 3.14 inches per second, or 115.13 inches per second. The second problem is that 225 oz*in is only about 1/3 the torque that I would consider adequate.

Most of my cutting is done at 8-inches per second or slower. My preferred jog speed is 12-inches per second. So, 115/12 = 9.58:1 gearing. With belt-driven transmissions, that means you would need a multi-stage transmission, and that means you're going to have a very bulky transmission. The smallest practical pulley on the 5/8-inch motor shaft is 20-tooth and the largest commonly available pulley on the drive shaft is 72-tooth, which gives 3.6:1 reduction, meaning that you would have to use a two-stage transmission. Remember that a transmission will also multiply the torque, so a 9:1 or 10:1 transmission will give about 2,000 oz*inches of torque.

Servo motors are quieter than stepper motors. They have constant torque. Their resolution depends mostly on the encoder that you use. (I use a 500 line encoder that gives 4 X 500 lines or 2000 "steps" per revolution.) However, if something happens to the encoder, the servo is going to run away. A servo also has jitter at rest. And, the servo that I've listed would require a separate 70VDC power supply per motor.

If 7.2:1 to 10:1 gearboxes were available at a reasonable price, I would switch to servo motors, but when the decent quality gearboxes cost around $1,000 each, using a servo motor with a rack and pinion drive is too expensive for my use.

Every CNC router that I've seen that uses servo motors also uses ball-screws. Ball-screws introduce many more possible problems. Dirt and dust are a big problem. "Whip" can be a problem at CNC router speeds. Cost is much higher than rack and pinion. Maintenance is also an issue.

On the other hand, when compared to servo motors, stepper motors are inexpensive, easy to use, maintenance free, and easy to use with rack and pinion. They can be used direct drive or with gearboxes/transmissions. From what I've seen on the forum, the PK296A2A-SG7.2 motors are an excellent match with the Mechmate.

On my machine (Shopbot), I started with direct drive 600 oz*in motors, then added 3:1 belt-drive transmissions to the X and Y axes, and finally switched to 7.2:1 gearbox motors on the X and Y axes. Using either the 3:1 or the 7.2:1 geared motors gave much smoother edges than the direct drive motors that came with the machine; however, the 7.2:1 motors gave hardly any improvement over the 3:1 motors.

[Kobus_Joubert]

Yes PLEASE..more servo info. I can lay my hands on some MOOG G4x3 servo motors. If these servo's can be used on a MM, this will be great.:D

Thanks Mike, we were typing at the same time.

[Doug_Ford]

Sean,

What are you upgrading? Bigger motors or larger pinions? Or something else?

[smreish]

Doug,

An associate of mine is building a servo based CNC plasma machine at this time and I am paying close attention to his progress to learn a little. The real reason is I plan on building a plasma table in the very near future. I haven't fully decided if I will convert the Mechmate that I just finished to the plasma since it's a classic version. I would prefer to build another MM with Mamba parts and spindle. Just easier to start from scratch then retrofit the existing machine. The cost is about the same!

With regard to your earlier post

"I am going to "upsize" slightly next month when I move the machine. I need a "little" quicker fast moves between parts. I need to shave about 4 minutes off each cut cycle to get a better part/price yield

I will change the pinion size next month to a slightly larger for quicker jogs and fast moves.

[Marc Shlaes]

Came across this just a few moments ago. Pretty good info on this topic. Check it out.

http://www.cnczone.com/forums/showthread.php?t=52090

[Doug_Ford]

I'd love a CNC plasma cutter too but I don't have the room in my garage for another machine. Good luck with it.

[Robert M]

Marc, thank you for sharing this valuable link.
Robert

[PEU]

I have a question regarding the Vexta PK292A2A-SG7.2 motor, as suggested in the 1st post Im thinking about purchasing them with a rear shaft for an encoder.
Reading the vexta catalog for series PK2 page C231 I read that the doubleshaft model is the PK296B2A but next to the part number it says its unipolar, am I reading it correctly? or what should be the doubleshaft equivalent of the PK296A2A-SG7.2?

Or it refers on how one wires them? in this case the PK296B2A-SG7.2 should be the motor I need.

Im confused :)

Thanks!

[Richards]

The PK296B2A-SGxx is the motor that has the shaft extended out the back. I have four PK296B2A-SG3.6 motors on my test bench. The PK296A2A-SGxx motor is the standard motor without the shaft extension.

Both the A2A and the B2A have the same electrical specifications and the same six wires per motor. Either can be wired full-coil or half-coil, depending on your needs.

[domino11]

Mike,
I have looked on the oriental motor site for an equivalent pk296a2a with 8 wires but dont see any. I was wondering if they had one so you could run a paralell combination. Or do you think parallel is not needed?

[Gerald D]

My guess is that since that family of geared motors is limited for torque by their gearboxes, it doesn't make sense for them to give you 8 wires so that you can increase the torque with parallel coils.

[Richards]

Gerald is right.

A six wire motor can be wired series or half-coil when connected to a Gecko stepper driver. You need an eight wire motor if you need parallel coils.

[sprayhead]

Someone able to tell me how much force/Weight a 5N.m motor can hold (holding torque) @ 25mm from the center of it's shaft?

The PK296A2A-SG7.2 gives out 5N.m from 0rpm to ~100rpm.

I am wondering what kind of push (in kilograms) this thing is able to put on the racks, so I can have a better idea of what's really going on.

thanks
Francis

[Gerald D]

5 N.m = 5 Newton.meter = 0.5 kilogram.meter = 500 kilogram.millimeter

which is 20 kilogram at 25mm

[sprayhead]

20.41Kg :p

Recalculated using G accel.

They are quite good these little motors huh!!! makes me feel good.

Thanks
Francis

[Gerald D]

Sounds like you are starting to believe us :)

[sprayhead]

For a heavier Z unit... say it is an extended version, or it is carrying a heavier spindle of a different kind or just some gadget of a different nature...

What are the thoughts of the people on using the PK296A2A-SG18 ?? It has a lot more holding torque then the PK296A2A-SG7.2.... It might even be interesting to use this motor and not use a gas shock on the original project? Proceed?

Francis

[domino11]

Francis,
Dont forget the reason most people dont go to the higher gear ratios are the fact that to get any decent speed, the computer and paralell port cannot keep up. Mach3 is also limited to the pulse stream it can handle. I would look carefully at the calculations and limitations of the hardware and software first. See Mike Richards post in this thread for more info.

http://www.mechmate.com/forums/showthread.php?p=4368&postcount=64

[joepardy]

As it so happens, I am not in the process of working on my Z axis. My machine is not the conventional Mechmate design, however, I may have some insight. My Z axis is about 24" long, and weighs about 80#. I originally tried the PK296A2A-SG72, and it would not lift it. I also tried the PK296A2A-SG36 - again, without success. In both cases, either the spur gear slipped on the gear rack, or (when locked into place), the motor bogged down - lifting it a fraction of an inch - then dropping it. I am therefore working with a combination of gas springs to counterbalance the weight. When I installed a single spring (and limited the travel to 13") the SG72 model worked great.

In my case, to offset the 80# weight, I am installing 100# springs.

[gmessler]

Hi Francis,

Take a look at Mike's response to my post in this thread. Valuable information on holding torque.:)

http://mechmate.com/forums/showthread.php?t=56

[Gerald D]

When your motor is de-energised, the holding torque disappears and the router falls . . . . .

A typical solution for loooong z-slides is a pneumatic cylinder, adjustable pressure regulator and a compressor.

[sprayhead]

Jeopardy,

Do you use any parts of the MechMate on your Z axis? Same spider plate and Z slide perhaps? or it all had to be modified to fit both the gas springs? I am scratching my head thinking how to use 2 springs and get them to work together to be effective for the whole length.


Boys,

As far as speed and lack of pulse frequency that should be fine because I intend to use the smoothstepper anyways. My application won't require much in terms of speed from the Z axis, so no visible problems there yet.

Gerald,

I obviously didn't realize that when you turn the motors off the Z slide slides and goes baang, if there is nothing extra to hold it. :p

[Gerald D]

There apparently are big systems with electric/spring brakes. . . when the system is de-energised, the springs apply brakes to fight the gravity that never de-energises. :)

[sprayhead]

like a Stepper Motor with electromagnetic break? I think I have seen that on Servos.

Another thought I had why the PK296A2A-SG18 would be good is when the Gecko drops to 70% the torque... recirculating.

If one could attach an electromagnetic break to the PK296A2A-SG18 that would be a good solution, I guess.

This thread then drifted to other counterbalance methods:
http://www.mechmate.com/forums/showthread.php?t=1026 (http://www.mechmate.com/forums/showthread.php?t=1026)

[Gerald D]

A newbie opening this current thread for the first time was confronted with a confusing first post. Two years have taught us a lot about motors and we have settled onto some comfortable choices. I have rewritten that first post and edited/pruned some of the subsequent posts. However, the earlier version of this thread is here (http://www.mechmate.com/forums/showthread.php?t=1112) in the Archive.

[domino11]

Gerald,
That is a great summary. I especially like the links to other threads on motors, belt reduction and the like. Excellent. :)

[Gerald D]

My apologies. I had a couple of posts here about confusion of motor specs. I do believe now that the links in the first post go to valid spec pages. There is a grey area with specs from other Oriental Motor sites showing something different, but let me check around a bit before making a storm in a teacup.

[Gerald D]

Here is Oriental Motor's numbering system for motors in some countries.

2715
-----Direct motors --------------------------- Geared Motors-----

The "Rated Voltage" numeral (where the 1 is used in the above examples) is what causes the confusion . . .

If a PK296-03AA motor is coupled to a 7.2:1 gearbox then it becomes a PK296A2A-SG7.2 motor. The 3 becomes a 2 and the voltage rating drops from 2.8 to 2. Since the resistance and inductance values stay the same, the reason for de-rating the voltage is not known. (Some have observed that the geared motors run hotter than ungeared motors - might be because they aren't de-rating the voltage?)

An earlier post (http://www.mechmate.com/forums/showthread.php?p=14503&postcount=83) in another thread adds to the confusion.

[gt68]

What are the calculations needed to end up choosing a Stepper Motor?
If possible, can someone give me a real example so that I can understand the
procedure?
I'm new in this field so I would prefer a simple procedure wthout alot of c
complicated mathematics.
Thanks in advance.

[Richards]

Sometimes it's easier to just use what others are using. The Oriental Motor PK296A2A-SG7.2 motors are popular. The Gecko G203v stepper driver works well with that motor. A 35VDC power supply is almost ideal when you wire the motor half-coil.

With that motor, you'll get adequate torque, adequate speed and adequate resolution for your cuts. The motors, drivers and power supply will cost about $1,800.

Testing and evaluating stepper motors takes time and some expertise. I can guarantee the it will cost much more than just buying those parts that I've listed.

One of the problems with building a one-of-a-kind machine is that you need to be the chief engineer - the chief electrical engineer, the chief mechanical engineer. Gerald has done all of the mechanical engineering for you and all of the essential electrical. All that is left to do is to scour the forum for the threads that explain why you should do something in some particular way.

If, after reading, you still have some why questions, post your question and those of us who have already traveled that road with help you find your way.

[Gerald D]

George, it is a waste of time doing the calcs unless you know:

1. The speed range through which you want to work the machine.

2. The cutting loads, plus cable and hose drag loads you are going to impose at all points in the speed range.

3. The friction forces versus speed imposed by your lnear bearing arrangement.

* * * * all the above needed for "static" calcs.....then the dynamic calcs:

4. The masses of the moving parts

5. The rate at which you want to change speeds (desired accel / decel.)

* * * * * and then to pick a motor:

6. The full torque vs speed curves of the range of stepper motors that you might be interested in buying.

Have too often seen that guys do "calculations" based only mass, max speed and motor's torque at zero speed.

[skippy]

What is the difference between "USA Option" and non USA Option IE PK296A2A-SG7.2 and the PK296A2-SG7.2?

As Australia is in the Asia selling region for Oriental Motor and the web site is in Singapore and only lists the PK296A2-SG7.2 see below. I don't think there is any difference but I what to be 100% sure before ordering.

[Gerald D]

Paul, can you give a link to the catalogue where you got that info from?

[skippy]

Gerald, Here is the link

http://www.orientalmotor.com.sg/images/series/PDF/07072PhaseMotor.pdf

The chart is on page 3 and the specs are on page 18 of the pdf

[Richards]

The electrical specifications on page C-179 for the PK296A2-SG7.2 motor match the specifications on page C-231 for the PK296A2A-SG7.2 motor. The inductance is the same. The resistance per phase is the same. The current per phase is the same. The voltage is the same. Both motors have 6-leads. (Page C-231 has a column listing the leads. Page C-180 shows the number of leads in the dimension drawing.)

Note that the gearbox shaft is different on the two motors. The A2A has a 0.500-inch shaft (12.7mm) with one flat ground into the shaft. The A2 motor has a 12mm shaft with a single key-way ground into the shaft. Also, the rear shaft extension on the B2A motor is 0.500-inch with two flats ground into the shaft. The rear shaft on the B2 motor has a 14mm shaft with two flats ground into the shaft.

[Gerald D]

The motors do look similar electrically (I can't see an inductance value?). Mechanically it will fit.

[Richards]

I've just received an e-mail from Grant Beebe at Oriental Motor who verified that the two motors are the same - electrically.

[gorantec]

Hi i like to build CNC machine with dimensions 2400x2000mm and i found some motors and i like to know are this is good for my machine the motors are : VEXTA- A4496 – 9215K 0.72DEG/STEP DC 2.9A 0,23 OHM 8mm 5 -PHASE ORIENTAL COMPANY MOTOR LTD and if this motors are small for my machine please let me know which size is preffered for this motors ?

[Gerald D]

If the shafts are 8mm then they are too small - we need 12mm to 14mm. The body of the motor must be about 90mm square and 90mm long if you do not have gearboxes.

[gorantec]

If the shafts are 8mm then they are too small - we need 12mm to 14mm. The body of the motor must be about 90mm square and 90mm long if you do not have gearboxes.

the problem is only with dimensions of the motors or the motors will dont have power ?

[Gerald D]

Dimensions and power are the same thing. A motor with small dimensions has a lower power than a a bigger motor - it is as simple as that. I have looked at many motor specifications and have learned to look only at the size of motor that I have suggested.

[bradm]

Also, those are 5 phase steppers, which require special drivers. 5 phase steppers are arguably an obsolete technology branch these days; if you inherit a set with matched drivers that fits your application, fine. If not, you likely don't want to engineer a new design with them.

[gorantec]

hi

will this motors MT34FN26 be good for machine with dimensions of 2400x1400x150 mm ?

MT34FN26
Phase voltage Vdc = 2.45
Phase current A = 4.3
Phase resistance Ohm ±10% = 0.57
Phase induttance mH±10% = 1.7
Bipolar holding torque Nm±10% = 3.4
Rotor inertia g.cm² = 1000
Detent torque Nm = 0.08
Max. radial force N = 220
Max. axial force N = 60
Step angle = 1.8° ±5%
Front shaft diameter mm = 12.7
Terminal or lead wires = 8 lead wires of 400 mm
Protection = IP30 (IP54 for motor with terminal box option)
Ambient temperature ° C = - 40 ~ + 55
Insulation class ° C = B, 130
Dimensions mm = 86 x 86 x 65
Weight Kg = 1.70

[Richards]

The MT34FN26 motor has specifications somewhat similar to the Oriental Motor Pk296-F4.5 motor, so it would probably work well IF you added a belt-drive gearbox to it. With about 480 oz*in torque, it does not have as much torque as the Oriental Motor PK299 series of motors that have been used without a belt-drive or gearbox.

If you use Gecko stepper drivers and if you connected the motor using parallel or half-coil connections, you could use a power supply up to about 41VDC. A standard 35VDC power supply should work fine. If you connected the motor using series connections, you could use a power supply up to the Gecko's 80V maximum. 70VDC would be my preference with a series connection.

[Gerald D]

Gorantec, they will work if you have 3:1 ratio belt drives or gearboxes. Their torque will be too low for direct drive.

(The 86x86 millimeter is good, but the 65mm is too short. You need about 90mm length if you want direct drive. See the MT34FN31)

[gorantec]

Gorantec, they will work if you have 3:1 ratio belt drives or gearboxes. Their torque will be too low for direct drive.

(The 86x86 millimeter is good, but the 65mm is too short. You need about 90mm length if you want direct drive. See the MT34FN31)

What about MT34FN47 its 6A and have 8.5 Nm torque and the body is 86x86x118 ?

Please advice

[Richards]

The MT34FN47 motor might be too large. At 8.5Nm (1,200 oz*in) it produces a lot of torque. Look at the thread "Why a stepper motor should not be too large (http://www.mechmate.com/forums/showthread.php?t=255)".

The motors that seem to work best are in the 2.5 Nm (with gears or belt-drive) to 4.5 Nm range (may be used without a gearbox or belt-drive). My personal experience is that even a 4 Nm motor works much better with a belt-drive transmission (3:1). The quality of the cut was much better with the belt-drive transmission. Right now, the two x-motors and the one y-motor have 7.2:1 gear boxes and the quality is very good compared to an un-geared motor.

[Gerald D]

Gorantec, our friend in India, Vishnu, is going to try some 114mm long motors soon - see his post here today:
http://www.mechmate.com/forums/showthread.php?t=973

I am a bit concerned that the range of motors (http://elyapimiprojeksiyon.com/viewtopic.php?t=5577&sid=25fd98cd2e27f336eedf0892890b7c37) you have found (MT34FN26, MT34FN31, MT34FN47 . . . . . ) have lower inductances, which gives lower voltages and higher currents than the more common motors in this size range. This could change the decisions a bit - maybe those motors are good, maybe they are too rough.

[Gerald D]

You might notice from these numbers MT34FN26, MT34FN31, MT34FN47 that the motors are 3.4 inches square and that the lengths are either 2.6 inches, 3.1 in, or 4.7 inches. The motor length is an important factor in motor choice.

[gorantec]

What about MT34FN47 its 6A and have 8.5 Nm torque and the body is 86x86x118 ?

Please advice

Please advice i have scheme for 5A driver but my motor is 6A will work in 5A driver and what will louse only torque or ?

[Richards]

Some of the older motors that I first tried with Gecko G202 stepper drivers were poorly matched to the Geckos, but they still ran just fine. The old round PH299 motors and the round Superior Electric motors ran rough when compared to the square PK299, PK296 and PK268 motors that I now use.

All of the motors were accurate and dependable. They never missed a step when properly loaded, but they sounded rough and felt rough when I held a hand to them while they ran.

The difference would be like comparing a new well-tuned car to an old car that needs its timing adjusted. Unless you drove both cars, you might not realize how nice the new car was.

Even now with Oriental Motor AS series Alpha 7.2:1 geared motors (with Oriental Motor's Alpha stepper drivers) on my Shopbot, when I run a true 3-D pattern, the motors sound very rough when compared to the long cuts that I normally make when cutting parts for cabinets.

[gorantec]

what about this motors http://www.marelmakina.com/files/msm34H280-3IP.pdf

[TimWerding]

Hi,
I have been reading and researching for a while and am now getting ready to start ordering parts. By the way, thank you everybody for providing long nights of interesting reading.

The Oriental Motor series PK296A1A goes all the way up to 36:1. Do I understand correctly, that there is a sacrifice of speed for accuracy in going up the gear ratio? Why is the choice a 7.2:1?

Another question I have is, Gerald in the first post in this thread recommends the PK296A2A-SG7.2, the post is from 2006. Since then is there nothing new and worthwhile on the market?

Thank you,
Tim

[Gerald D]

Going up the ratio means:
1. the PC must run faster to generate the higher pulse rate
2. risk of increased backlash in the gearbox
3. the only possible benefit is a smoother cut, but we already have a good smooth cut at the 7.2 ratio.

Nothing else has even come close to the OM PK296A2A-SG7.2 when we look for an already packaged motor/reduction combination with proven low enough backlash. At $260 each, they are very expensive but convenient. Belt-driven are better (lower backlash), but are restricted to about 4:1 ratio at most, and are not ready packaged.

[Richards]

Tim,

There is a huge difference in performance between the PK296A2A-SGxx motor and the PK296A1A-SGxx motor. The A2A motors have lower inductance which means that they perform better at the voltages that the Gecko stepper drivers can handle.

The PK296A2A-SGxx motor requires a 70VDC (to 80V) power supply if wired bipolar series and a 35V (to 40V) power supply if wired half-coil. I ALWAYS wire the PK296A2A-SGxx motor half-coil. The extra torque produced by wiring it bipolar-series cannot be used by its gearbox and the extra speed produced by the half-coil wiring can be used by the gearbox.

The PK296A1A-SGxx motor would require a power supply of 150V to 177V if wired bipolar series and a 80V to 90V power supply if wired half-coil. You could wire the PK296A1A-SGxx motor half-coil and use a 70V to 80V power supply and get excellent results, but I would still choose the PK296A2A-SGxx motor for my own use.

[TimWerding]

Thank you all.
I will try to stick as closely as possibly to drawings. It is going to be little difficult to get some of the things here in Mexico. I am a lot further south than the other two Mexican builders.
I will go with the PK296a2a-sg7.2, the 203V Geckos and the PMDX122.

[ChiknNutz]

Hello all. I have found a local person with some motors that may be a good deal. I want to post for review what they are to see if they would work or not. I compared some of the suggested specs and they seem to be similar to what is suggested with the exception of them being round cases and not square. They are new/unused and about 4 yrs old (for a CNC project that never happened). Thanks for any assistance.

Ametek Brush-type DC Servo motors with encoders that you can run with Step and Direction signals, just like a stepper motor. If you’re used to working with steppers, you will not believe the performance from this motor. It is compatible with the low-cost ($114) and high-performance Geckodrive G320 servo drives, G340 servo drives(www.geckodrive.com), as well as other brush-type servo drives including the Rutex R990H (www.rutex.com) which has some really nice features including step multiplying.
This is a great solution to upgrade a stepper machine to servos, or retro-fit a medium to large size mill or lathe with CNC controls. If you’re building your own CNC Router, this is by far the most economical way to go for high performance.

The motor body measures 4” diameter X 4-7/8” long with a 3.25” diameter, 4-bolt hole circle on the face. The shaft mounting surface is .625” diameter X 1” long, with a shoulder of 7/8” X 3/8” long. Overall length with the 1000 CPR (4000 pulse per revolution) Renco encoder is 7”.
Advantages over comparably sized stepper motors are:
• Closed loop control- The encoder feedback ensures that the motor is in position, but doesn’t require an expensive control system that uses analog signals. When used with the Geckodrive, you only need step & direction signals.
• High Speed and torque- High peak torque allows for faster acceleration and deceleration, and better continuous torque at cutting and rapid speeds than steppers. Torque doesn’t suddenly drop off at medium speed as with steppers.
• Smoother operation- Because these motors don’t rely on the “steps” that you feel when turning a stepper motor shaft, they run much smoother and quieter than stepper motors.
SPECIFICATIONS:
• Torque Constant 44oz-in/amp
• Voltage Constant 32.5 V/1000RPM
• Nominal Voltage 40 VDC
• Maximum Voltage 60 VDC
• No-Load Current <.51A
• Demagnetization current >20A
• Terminal Resistance 2.60 ohm
• Mech Time Const(max) 18.3 msec

[Gerald D]

That motor will not have enough holding torque unless you add a very significant belt/gear reduction.

See Servo versus Stepper motors (http://www.mechmate.com/forums/showthread.php?t=261)

[gorantec]

Hi

i have 3 step motors now with torque of 8.5 Nm and i planing to build machine with dimenzion X=2100 Y=1200 mm cutting area im planing to put only one step motor on X axis will be enough ? Since the motors are with big torque ?

[Gerald D]

You need 2 motors on the x-axis to hold it square with the table. The 2 motors are exctly synchronised by Mach3.

[gorantec]

You need 2 motors on the x-axis to hold it square with the table. The 2 motors are exctly synchronised by Mach3.

what will happen if i put only one motor ? will not work or ? please let me know more ? Becuse i can not find another motor it will be hard since i was waithing 3 months to get these :(

[Gerald D]

It will only work for very light cutting if you use one motor on the x-axis, and it will have a low accuracy.

[gorantec]

It will only work for very light cutting if you use one motor on the x-axis, and it will have a low accuracy.

i need these machine only for making some simple desing for mdf doors i think will work for theat or im laing my self :o

[Gerald D]

Sorry, but it won't really work for MDF doors. :(

[hennie]

It starts with a little design and ends up with something big.Use two on the x-axis one on the y-axis and get another smaller one for he z-axis.

[gorantec]

ok it's me again :o will this motor MT34FN26 http://www.tinel.com/products/pdf/MT34FN_GB.pdf be good for z axis or ?

[Richards]

The data sheet for the MT34FN26 motor looks similar to the data sheet for the Oriental Motor PK296-F4.5. With about 450 oz*in of torque, it is a motor that I would normally use with a belt-drive (3:1 or 3.6:1). Assuming that you use a Gecko G201, G202 or G203v, the motor should work well with a 35VDC to 40VDC power supply if you wire it bipolar parallel or unipolar (half-coil). You would need a 70VDC power supply if you decide to wire it bipolar series.

I don't think that I would use that motor without a belt-drive, even on the Z-axis.

[gorantec]

hi are any one have expirience with this driver http://www.routoutcnc.com/10ampdrivecard.pdf my motors are MT34FN47 http://www.tinel.com/products/pdf/MT34FN_GB.pdf will be good this ? Since Gecko are only 7A and my motors need 8A in bipolar parallel conection ?

[Richards]

The data sheet for the MT34FN47 motor shows that the 035x8yy motor has 8.3mH, making unsuitable for the driver you listed. (To get full speed and power, you would need a power supply of over 250VDC). The 060x8yy motor has 3mH inductance, which would require a power supply up to 55VDC to get maximum performance out of the motor.

I prefer to use a motor that has about 1.5mH to 2.5mH inductance, which would allow the use of a 35VDC power supply (1.5mH) or a 48VDC power supply (2.5mH).

[Gerald D]

Let us look at the basics - this is from the document you linked:

4680

It looks like the MT34FN47 motors are supplied in two versions: 035x8yy and 060x8yy. Which version have you got on your table? (I don't want to waste time discussing the wrong motor).

[gorantec]

hi Gerald thanks for answer

my motors are 060x8yy they are 6A in unipolar if you wire in bipolar series need 4.2A and if you wire in bipolar parallel need 8A driver i like to connect in parallel i have made some 5A driver and connect in series but performance was not good .

Please prefer some driver

[Gerald D]

Which driver did you use for your test? What was the supply voltage?

You say the performance was not good . . . . . not enough torque, or not enough speed?

[gorantec]

i have made this driver http://www.fisertek.it/images/schema%20ponte%20H%204%20amper.gif there was no torque and also slow speed and power suply was 30V

[Gerald D]

Okay, now I understand the poor performance.

I do not agree that you have to go for a bipolar parallel connection to get a good performance. With a good driver and a good voltage you will get a nice performance from half-coil connections. There will not be as much torque at low speed as with the parallel connection, but the router does not need much torque at low speed. At the high speed side, the torque of parallel and half-coil is nearly the same. If you wire half-coil, a 6 Amp driver at 55 volts is going to give you a very good performance.

[gorantec]

So Gecko drive will be excellent for this motors :D

[Gerald D]

Yes, I think so. But maybe you can find a driver nearer to you?

[gorantec]

Gerald will this stepper be good for Z axis 86HS2802 http://www.driver-motor.com/ProductContent.aspx?ID=47 this is from Claudia web site or please preffer some step motor from theat in the list since i will order 4 drivers from there and i like to oreder just one for Z

[Gerald D]

Gorantec, you already have 3 motors of 3.0 mH inductance and that will decide the power supply voltage. Now you need a number 4 motor and you will run it off the same power supply, so it must also have about 3 mH inductance.

Then, for the z-axis, you need some detent torque, so that the router/spindle does not drop when you switch the motors off. This means that the z-motor must be about the same size as the x and y motors.

If your z is also direct drive then I agree on the 86HS2802 motor (the motor weight is probably 3.8kg and not 1.8 as the web page shows)

It is very difficult working with the specification sheets you have given because of some strange differences between them. It looks like the 150mm long motor of Deitech has the same torque performance of the 118mm motor of Tinel and I don't believe the difference will really be that big. That is why I agree on the 126mm motor of Deitech.

[waleednazar]

hi every body,

I have this stepper motors
I brought 5 stepper motors from old printers :

SANYO DENKI
3,25A
1,8° DEG v=1.9v
type 103H7124-1041 FH6-1177 01, six wire.

I search alot in the web there is no data sheet for this motor.this all what i know.
Can I use this motors FOR THE Mechmate. Six wire motors are unipolar(Iam right?) if yes, can i connect it pipolar? sorry for my ignorant.:confused:
help me plz.

waleed

[Gerald D]

http://db.sanyodenki.co.jp/stepping_e/two/pdf/2step_e_079-086.pdf

They are too small.

[anton]

Hi Gerald,
Would the pk296a2a-sg10 motors make any difference in performance to the standard mechmate, considdering I am planning on using the mechmate to route aluminuim?

Anton

[domino11]

Anton,
I had the same idea when I first started looking at the MM. The problem is that Mach3 can only output pulses so fast. The additional gearing in the 10:1 gearbox puts you out of the Mach3 limit. This forces you to go too slow with the additional gearing. Check out Mikes post here
http://www.mechmate.com/forums/showthread.php?p=25770&postcount=2 that talks about gearing, step resolution and backlash to see if it really would make a difference to you. The backlash seems like it will be more than the resolution at 7.2, so going further wont really get you that much perhaps.

[obuhus]

Hello, Gerald. My name is Dmitriy, I from Russia.

I am going to build MM and now I select stepper motors. In Russia the motors Vexta, unfortunately, are difficultly accessible and very dearly.
I have found analogue in China. I plan to use Geckodrive and,maybe, belt-drive transmission (3:1).
It is my choice.

LDO-86STH80-4208A

Size - Nema34
Rated Voltage - 2.4V
Current/Phase - 4.24A
Resistance/Phase - 0.75ohms
Inductance/Phase - 3.4mH
Holding Torque - 46Kg.cm
Leads Number - 8
Rotor Inertia - 1400g.cm2
Approx. Weight - 2.3Kg
Detent Torque - 1.2Kg.cm
Body Length - 80mm

( http: // www.ldomotors.com/st86.htm)

Say please, I on a correct way?

[Gerald D]

Those motors are definitely okay for belt drives, and I think just okay for direct drive. For direct drive I like to see a motor about 3 kg in mass. Maybe this sounds strange, but there is a direct relationship between the size of the motor, its mass and its torque. The direct drives we have used have always been 96mm long and 3kg in mass - 80mm and 2.3kg is quite a bit lighter.

The length and the mass are easy to check, and a supplier cannot tell lies about those numbers. But, they can give us false numbers for the torque, and we cannot check it easily.

If you are definitely going to run direct drive, then I would take the LDO-86STH118-4208A.

[lumberjack_jeff]

They appear to be the same motors I am using on mine, except mine are branded "Fulling Motor".

They are available with gearboxes.
http://www.mechmate.com/forums/showthread.php?p=25054&postcount=13

[obuhus]

Thanks, Gerald.

You very much have helped to me.
But your variant not too large?
"... at about 96mm [3.78"] long. Avoid motors much longer than this - see point 3 above. (bigger motors bring other problems) "

[Gerald D]

No, not too large. 118mm is not too much larger than 96mm. I was actually surprised to see the results of the guys in Brasil with very much longer motors. See the pictures and videos near the end of thread:

Cutting small gears and 3D puzzles! - Curitiba, PR, Brazil (http://www.mechmate.com/forums/showthread.php?t=1298)

and:

Building control desk #17 - Sao Caetano do Sul, SP, Brasil (http://www.mechmate.com/forums/showthread.php?t=963)

[obuhus]

Thanks, Gerald.

The job of these guys looks nice.

Once again thanks for the help.

[m_leblanc]

Hi everybody, and congratulation for this great forum, very informational. I have been reading quite a few treads and always want to take a look at the next one or link.
About choosing the right motor, Gerald, you started this tread on oct 2006, if you had to buy new motors would these choices be the same today.
Thank you

[Gerald D]

I update the first post of this thread every time there is significant change in ideas. It was last changed 7 months ago and there have been no new ideas since.

[m_leblanc]

Thank you, I have been through the post and haven't seen it

[sprayhead]

Wondering how the PK299-F4.5a (NEMA 34, ~860 oz/in) runs at very slow speeds? I suspect that it would have at least decent linearity, since it is from O.M. It should have a much "better than typical chinese" manufacturing processes.
If I am right, the OM motors are made in Japan?

Thanks,
Francis

[Richards]

I run the PK299-F4.5A wired half-coil on my test bench and as an auxiliary motor on my Shopbot all the time. It runs very well at all speeds; however, I haven't specifically tested it at "very slow speeds". All stepper motors resonate at certain (usually slow) speeds. It is a characteristic of a stepper motor but the G203v has a trimpot that does a very good job of canceling out that problem.

The Oriental Motor factory is in Japan. Here in the United States, most of the motors are assembled in Torance, California. I visited the plant several years ago and spent a few hours on the assembly line watching them assemble the motors. They impressed me to the point that I have not bought any other brand since that visit. They use quality parts, quality people, and quality methods. Most importantly, each person does a quality check before passing the partially assembled motor to the next person in line. They teach the concept that the "customer" is that next person in line, meaning that each assembler's job is to insure that his "customer" is satisfied. On some stations, that "satisfaction guarantee" was as simple as orienting the motor so that the next assembler could pick it up without wasting time turning it in another direction.

The PK299-F4.5A motor is my favorite motor. I wire it half-coil and use a 48VDC power supply to drive it. It runs about 65-degrees C with that power supply and the load that I require it to drive. If you prefer a six wire motor, the PK299-03AA motor has the same electrical specs.

[sprayhead]

Wow, that's nice facts, it makes me think even more about going Oriental Motors, increased peace of mind.

on a new note:
I was having a read on this thread at the beggining and trying to find out more facts about the PK296a2a-sg7.2 and how to size the power supply for it, when wiring it half-coil and using a Gecko 203v.

Still unsure what inductance value I have to use on the formula to calculate the optimum power supply voltage for the motor, for half coil wiring. (32 * (√mH inductance) = Power Supply Voltage)
Is it the bipolar series inductance rating divided by 2? or is it the unipolar rating?

Would it be a problem if I go over the limit with the voltage given by the formula by a small ammount?

thanks,
francis

[Richards]

Francis,

The PK296A2A-SG7.2 has 1.5mH Inductance unipolar (or half-coil) and 6mH Inductance bipolar series. Inductance is 'caused' by the number of coils and how they are connected. Data sheets always show the half-coil rating as 1/4th of the bipolar series rating and the bipolar series rating as 4X the unipolar rating.

In this case the formula is: 32 * SQRT(1.5 mH) = 39.19 V = MAXIMUM voltage.

Voltage causes heat. The higher the voltage, the great the amount of heat. Mariss determined that a modern 'square' motor is rated at 100-degrees C, so he selected a maximum voltage that will keep the motor slightly under that limit (85 C). If our shops were always 25 C or lower, we could safely use the maximum voltage, but, at least in my shop, summer-time temperatures often rise above 45 C in the afternoon (that's where my thermometer pegs, so I don't know how hot it really gets).

I de-rate the maximum voltage by about 15% to 20% so that I'll never have a motor that gets above its rated temperature.

[sprayhead]

Mike I cannot thank you enough for your help on this forum;)

BTW, talking about heat generated by a stepper, here's something that looks like will be very nice, and allow us to keep our stepper motors nicer and cooler and yet more powerful...

THE G203X..........
http://www.cnczone.com/forums/showthread.php?t=79500


Mariss is also working on another, even more audacious project, the StepperServo...

just love it
F.

[skippy]

I just got a quote on the PK296A2-SG7.2 here in Australia at about AUD $ 620 each :eek: which is about USD $510 and I need five for a four Axis

WE can not get PK296A2A-SG7.2 in Asia and it's equivalent is PK296A2-SG7.2

below is the link for the USA

http://catalog.orientalmotor.com/item/stepping-motors-/pk-series-stepping-motors/pk296a2a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0

Which are USD $257 each. I might need someone int the USA to send me them instead ;)

Regards

Paul

[anton]

You can order straight of the Oriental Motor website, and have it couriered with UPS to Aus.

Anton

[skippy]

You can't order from the USA Oriental Motor website outside of the USA. Someone PM me suggesting to try a different region that maybe able to send to Australia that I'm looking in to.

Regards

Paul

[domino11]

Paul,
Check out the marketplace area. I posted a link for a distributor in Canada, He might be able to ship to you. Very helpful. I got my motors from him. He is an authorized distributor.

[Ticapix]

Hi,

This is my first post and my english is not very good.
I have read with a great interest major part of posts concerning : the choice motors.

I have understand that a big motor is not a good choice.
My question is:

With the new drivers who can make µsteps, is it possible to use bigger ( i.e. nema 34 - 7 amp - 1200 oz ), direct drive motor, without disadvantages ?

[Gerald D]

Drivers making µsteps are not new. Most of the things written in this thread: Why a stepper motor should not be too big (http://www.mechmate.com/forums/showthread.php?t=255) were written by people who only produce drivers that make µsteps.

[Ticapix]

Ok, thank you Gerald.

I thought , that drivers technology, had changed the past two years.

Regards

Thierry

[Polder48]

Gerald and all interested.

In my efforts to complete our preparation for the MM build, I had an interesting discussion with a familiar supplier of drivers. He is the distributor of STÖGRA drivers. These drivers start with a Nema 58 size and they calling them "small" drivers.

After informing me that he could supply me a driver similair to the PK296AE-7.2, he advised me against his driver, because it wasn't "explosion safe", which was definitly the case with the OM driver!

This gave me sort off a blow on the head, because I never considered explosion safety an item, while never read anything about it on this and other fora. Contact with OM confirmed me that the PK series are explosion safe.

Is this of any interest for you? I stop searching for an alternetive driver and definitly go for the OM.

cheese from polder

[Gerald D]

Polder, you have me confused!

1. I think you used the word "driver" when you really wanted to say "motor"? The whole discussion is about motors and Stögra makes motors. (The drive(r) is the electronic circuit that gives power pulses to the motor).

2. This is the very first time that I see "explosion proof" mentioned in relation to CNC routing in the typical woodwork workshop.

In electrical terms, "explosion proof" means that the device is completely enclosed so that a spark inside cannot cause an explosion of the gases around the device. If you think of the coal mines with methane gas, or the fuel pumps at the gas station, there you need explosion proof motors and other electrics (such as lights and switches). However, in our workshops we normally use routers, saws, grinders, drills which are definitely NOT explosion proof. I see no need for our MechMates to be explosion proof if the other equipment is not.

[Besser]

Skippy, dont waste your money!
Look here: http://www.oceancontrols.com.au/ocean_catalogue.pdf page 56. You get the whole kit (four sets) for $1600 AUD

They are 630oz ,motors, power supplies and drivers (all matched)
While I think it's still expensive, it's the best I've found so far for us OZI's

Who can beat that?

[KenC]

The Chinese...

[Polder48]

Gerald, excuse for the confusion.

You're right ofcourse, I meant motors, not drivers, my English thinking is not straight yet. Glad you consider explosion proof not to be an item in a typical woodwork workshop. In my relation with the Stögra salesman there where a lot of chemicals (nasty stuff) involved, that's why he probabely made a point of it.

Never the less if the OM is a good thing on this point I'am not going to argue against it. Last weekend a ship in our harbour burnt down, due to an electrical circuit breaker that didn't do what it supposed tobe doiïng, breaking the electrical circuit. I hate fire.

cheese polder

[Gerald D]

Hey, that ship burnt on 30 July! (unless you have these electrical ship fires every week?) :D

I am sure that you are talking of the Prins Willem fire (http://images.google.co.za/images?rlz=1T4IRFA_enZA279ZA280&um=1&q=Prins+willem+fire&start=0)

[BartDeckers]

Gerald,

You mention a price of about 250 USD for the PK296A2A-SG7.2 stepper motor.

I got a price quotation of 391 USD in Belgium for the PK296AE-SG7.2.
This price is tax included (+25%). Price without tax is 314 USD.

Is your price of 250 USD tax included?

Regards,

Bart

[Polder48]

Gerald,

The Prins Willem burned down on august 8! A remarkeble day since I was in Den Helder that day returning from a sailing trip with my wife to the Shetland Isles.:)

The yacht I talked about was also a historical wooden ship, an one of build from 1923, based on a "gauntlet". A big loss because it was a very fast sailing yacht, 18-22 knots with 7 bgt winds, and steady as a rock. Loved it like a MM.

happy sailing polder:D

[Polder48]

Bart,

Wait 2 more days. I will have a confirmation on a offer for the PK296AE-SG7.2, which is the European equifalent of the PK296A2A-SG7.2. Its less then 250 euro if everything works out right. Will keep you informed if you wish so.

cheese polder

[BartDeckers]

Polder,

That sounds like a very good price. Please keep me informed.

Thanks,

Bart

[Greeny]

I am currently sourcing items and came across this Stepper motor for sale in the UK.

http://www.arceurotrade.co.uk/Catalogue/Stepper-Motors/Stepper-Motors
Item Number: 160-010-00450

Specs are (for parallel): Current=4.2 A/Phase, Resistance=0.8 Ohm/Phase, Inductance 3.5 mH/Phase, Holding torque=3.5 Nm
Supply Voltage would be, using 20xVoltage= 20*(4.3*0.8)=69V or 32*Sqrt(3.5)=60V, so lets say 60V
Corner speed would be (0.191*60)/(0.0035*4.3)=761 rpm, geared 3:1=254 rpm, which compared to other motors mention here, seems ok.

It is pretty cheap at £35 (~60 $US) and i am thinking it should be ok with a 3:1 Belt drive.
It only has a 10mm shaft with no flats, but apart from that it seems pretty good for the price.

I would be very grateful if anyone would comment on it's suitability and/or check my calcs
Cheers, Greeny.

[Richards]

You used a different set of calculations than I use, but the end results were almost identical. I figured about 60V for the power supply and about 250 RPM when using a spur gear that had 1.25" pitch diameter and the speed set to 5" per second.

Most of the stepper motors that I've tested work very well up to about 1,000 RPM, so, assuming that your motor is typical, you would still be in the high torque range of the motor.

[Greeny]

Thanks Mike,

I used formulas that i'd gleaned from this and other threads, but really know very little about it!
I'm sure yours are more up to date.
I appreciate you taking the time to run the calcs, it's a big help.

Cheers
Greeny

[octobpra]

Hello Anybody, can you explained to me about motion king spec that i dont understand 580 N cm Min - 18 N cm Max ? is spec require min for MechMate ? that i heard min 4.51 N m ? i still dont understand that convertion unit which one i use for checking min tourqe min or max ? hope anybody reply me soon thanks.....

[jhiggins7]

Octobpra,

Your question is not clear. However, if you want to convert from Newton Centimeters to Newton Meters, you simply divide by 100. So, 580 N cm would equal 5.80 N m.

For any conversion you need, simply do a Google Search and you will find links to conversion calculators. For instance, Google: "convert Newton Cm to Newton Meters"

[Richards]

580 N-cm = 5.8 N-m = 821 oz*in

"Holding torque" is the value that I normally use when checking a motor's torque. Holding torque is the amount of torque that the motor produces when the motor is NOT turning and the stepper driver is giving full current to the motor. Holding torque is usually much higher than running torque. Running torque is the amount of torque that the motor produces at a specific speed.

When you look at a stepper motor's torque chart, you'll normally see a graph that shows the torque produced at specific speeds. As the speed goes higher, the torque goes lower. At a certain speed, the corner speed, torque drops dramatically. The larger the motor, the lower the corner speed. Most mid-sized 34-frame size stepper motors (at least the ones that I've tested) have a corner speed greater than 1,000 RPM. Even with a 7.2:1 transmission, and a 1.25-inch pitch diameter pinion gear, 1,000 RPM will move an axis at about 540 inches per minute.

With a 3:1 or a 3.6:1 belt-drive, I would like to have a motor that produces between 450 oz*in holding torque and 600 oz*in holding torque. (450 oz*in = 3.18 N-m = 318 N-cm, 600 oz*in = 4.24 N-m = 424 N-cm). That means that an Oriental Motor PK296-F4.5A, if connected bipolar parallel would work, or a PK299-F4.5A, wired half-coil, would work. Any other motor with similar torque curves would also work (PK299-03AA wired half-coil, PK299-02AA wired half-coil, PK296-03AA wired bipolar series).

Also, motors that have an Inductance rating between 1.5mH and 6mH are best suited for use with Gecko stepper drivers.

[toad]

Don'r mean to be buttin in, but I am presently using nema 23, which are too small. If I go with the geared motors will my existing 24V power supply and breakout board work, or will I needd to replace it all? I am presently coming directly off of the breakout board with 4- 280 OZ NEMA 23 motors.

[Richards]

Toad,

There are normally four components in the stepper chain:

1. A power supply

2. A break out board (i.e. PMDX-122)

3. A stepper driver (i.e. Gecko G203v)

4. A stepper motor (i.e. Oriental Motor PK296A2A-SG7.2)

The inductance of the stepper motor determines the voltage of the power supply, i.e. 32 X SQRT( Inductance ) = MAXIMUM voltage. When wired half-coil, the PK296A2A-SGxx motor is rated at 1.5mH, so it can be used with a power supply up to about 39VDC. When wired bipolar series, that motor is rated at 6mH inductance, so it can be used with a power supply up to about 78VDC.

The stepper driver has a minimum voltage and a maximum voltage. You must stay within the voltage limits of the power supply, even when the formula computes a voltage out of the range of the stepper driver.

[Gerald D]

Toad, you also need to consider the currents (Amps) and load capacity (VoltAmps) of your drives and power supply. There is a strong possibility that your existing drives and power supply are also too "lightweight".

[KenC]

Toad, what is your PSU type & rating?
From what I learn here, in theory, if its a 300VA unregulated 24Vdc, then you will need to find a motor with 0.5625mH (from V=32*Sqrt(mH)). I wouldn't guarantee much but at least you will be near.
If its a switching mode power supply, & its regulated, then you need a lot more meaty one.

[toad]

sounds like I need to start all over in the drive department. just hoping what I had would work, but apparently not. Thanks for the info.
Does Gecko sell a kit with 4 motors and all necessary components, or will I need to find each one individually.
Where is the most inexpensive place to find the rack and pinion?

Toad

[domino11]

Toad,
Best place for rack is Standard Steel. Gecko only sells drives. You can order the motors directly from orientalmotor.com.

[iclazion]

I am having a really hard time selecting a motor. REALLY
I want the most precise cutting mechmate possible to cut High Density Polyurethane, now the question I have is: What is needed for precise cutting? Does it have anything to do with the motor, and if it is geared or not? I have been looking at http://www.orientalmotor.com/products/ac-dc-step-motors/2-phase-step-motors-PK-PV.html#shgeared PK/PV Series 2-Phase stepping motor with SH Gear. Looking at the motors on my own is pointless, I have been looking at the criteria. But for me to know which motor is going to provide me with the most PRECISE cutting / working is really pointless. I have been going to-and-thro the forum, but really the only result is getting me more confused. Price also plays a role, but I want the pieces I am going to cut to be as clean as possible. Please I am a fish out of water here to be honest :)

[skypoke]

Iclazion,

Wanting the "best cut possible" from a Mechmate is a lofty goal. Your cut quality is only partly dependent on your motors, the workmanship quality in construction and alignment plays a factor also. Maybe if you would define what permissible error is then guys with existing machines can tell you if their setup would work for you.

What you might want to look at, though, is constructing belt drive reduction units in lieu of using the standard gear reduction unit. That will eliminate some backlash. High density poly though is among the least demanding materials to cut accurately, consistent density, soft and tools well, no knots etc. I suspect a standard Mech built with the geared drives will more than fill the bill.

Other things you can do to increase resolution (and sacrifice cut speed) are deep reductions on your motors and sizing pinions appropriately. Your tooling quality and feed speeds are another factor as is the quality of your programming.

Chuck

[domino11]

Also good to note, that as you push the gear reduction higher and reduce the pinion size, to get the same top speed, your computer now has to put out a lot more in terms of speed. Mach 3 also has a high limit on the rate at which it can ouput step and direction signals, so this could limit your top speed.

[iclazion]

Thank you Skypoke and domino11 for your quick response. I have been looking at the Nema 34 for a while now (that is the only descent motor available in South Africa) but that would mean I will have to add/build the belt reduction unit for each motor. But I would rather invest in a motor from orientalmotor. What is the verdict on the http://www.orientalmotor.com/products/ac-dc-step-motors/2-phase-step-motors-PK-PV.html#plgeared PL Geared Type? Max Holding Torque of 13.2 ~ 26 (lb-in). Will that sort our my reduction problems? Is this the investment I am looking for, for the Mechmate? :)

[Alan_c]

Iclazion

To re-iterate Chucks request, you need to give us mor info regarding what "accuracy" you need to achieve.

OM motors are rediculously expensive here so unless you have a willing partner in the states to send them to you, I suggest you get in touch with Greg at www.cncdirect.co.za He will also be able to help you out with belt reduction drive components, spindles, Geckos etc. He is just down the road from you in the big smoke (Jhb) and is very knowledgeable on these items.

As to whether your choice of OM moter is the investment you need to make on the MechMate, that is a question only you can answer! You need to read a lot more to fully understand what the MechMate is capable of and who has used what combination of motor or reduction or integral gearbox. The path to enlightenment is not a short one...:)

[iclazion]

:) Lol. Thanks alot Alan

I am starting on the initial design of my table at the moment and I will be documenting the progress as best I can to help those who might one day like to rather copy me. It's so much easier to follow a recipe, whoever I feel like I will be the guinea pig for the rest to come.

Quick question:
Do you think a Nema 34 would be able surpass even the most expensive Oriental Motor if the right belt reduction is fitted to the motors? My goal is to eventually cut/router 2” thick HDPE and to engrave aluminium or (praying) to have the ability to cut it.

I will be uploading my table specs, with 3D (lightwave) drawings and diagrams for people to follow. Because I am a masochist I might even upload the cost involved in the construction as I go along.

[KenC]

Hi iclazion,
The NEMA34 is the generic stepper motor size frame size used for MM, if I remember correctly, the OM are NEMA34, so are the motionking motors & keling motors.
NEMA stands for National Electric Manufacturers Association, more details read here (http://www.motorsanddrives.com/cowern/motorterms2.html)

What you should be more concern are the steps/rev, No. of phase, Torque, Inductance, Resistance & current rating.

You should read all the "sticky" threads in this section especially this particular thread if you wish to learn more about stepper motors.

Hope this helps.

Merry x'mas

[iclazion]

I have a question I would like to ask.

I am in the process of buying 4 X nema 34 motors with 10 micro step drivers. I have been looking at the “Gear Speed Step Freq Calculator” and would like to know the following. I am going to for the 24 teeth pinion on the motors, and I am a bit concerned about the “Belt/Gear reduction”. What is the advantage of a belt gear reduction ?

His is the specifications of the motor and driver:
Motor Specifications:
Frame Size: NEMA34
Step Angle: 1.8 degree
Voltage: 5.7V
Current: 3.0A/phase
Resistance: 1.9 Ohm/phase
Inductance: 22 mH/phase
Holding torque: 9.3N.m 1317oz-in
Rotor inertia: 3600g-cm2
Number of wire leads: 4
Weight: 5 kg
Length: 151mm

Driver Specifications:
Geckodrive Step Motor: G201
7A, 80VDC 10-microstep drive, Optoisolated step and direction inputs, Mid-band resonance damping, Silent 20kHz PWM switching, No low-speed vibration

[Claudiu]

The major advantage of a belt drive (belt gear reduction) is that you will have no backlash.
I use the OM with 7:1 gear reduction. I even had different backlashes in the drives so I had to take care to find two "matched" for the x. On my next MM I`ll go definetly with belt reductions.

[iclazion]

Hi Claudiu

I had a change of heart with the motors. I came on a topic that suggested I rather use a smaller motor, so I chose 873oz-in Nema 34 stepper motor instead of the 1317oz-in. In the end I want a CNC router that doesn’t tear or rip through my medium I will be cutting. I have payed for my motors and their driver, controllers, voltage regulators and breakout boards just a few hours ago. Very excited at the moment, and can’t wait for their arrival.

I am also going shopping tomorrow for my pinions and belt reduction gears/belts. There is a couple of questions I want to ask later on about setting up the belt reduction, and how you would mount yours.

PS: Do you think it is a good idea to use 2 motors on the X-axis? I ordered 4 motors. 2 for the x-axis, 1 for the y-axis and 1 for the z-axis.

[Claudiu]

Iclazion, if you are using underpowered motors there is a risk of loosing steps.
Ripping through medium is another discussion (http://www.mechmate.com/forums/forumdisplay.php?f=82) about feedrate, spindle speed and chipload.
Using two motors on the x is mandatory, as seen in Gerald`s plans.
Good luck with your build and post some pics.

[hennie]

Iclazion did you get your stuff from Greg in Edenvale?

[iclazion]

Hennie I ordered my motors from Hong Kong. The companies name is www.wantmotor.com they also supply me with the needed drivers, breakout boards and voltage regulators.

Claudiu I am a bit confused. I have been following this forum for a while now, and came upon http://www.mechmate.com/forums/showthread.php?t=255 where Gerald_D explains that a motor with High torque would be troublesome. Should I stop my order and rather get the 1317oz-in Nema 34 motor?

[hennie]

Iclazion, do you have gearboxes on the motors?

[iclazion]

Hennie it looks like I will have a look at a belt drive. At the moment there are no gearbox/gearhead on the nema 34 830 oz-in stepper motor. The company will custom any motor to your requirement ,the same with the voltage/drivers and breakout boards.

[iclazion]

PS they say their drivers are better and more advanced than that of gecko drives, but that remains to be seen. Will let you know if that is indeed the truth when my MM is finished and cutting.

[iclazion]

VARISPEED is an Oriental Motor Distributor in SOUTH AFRICA!

Got a quote for 4x PK296A2ASG7.2 motors, as described on the first page.
R7600 per motor. = R30400

[Kobus_Joubert]

Just bought 6 MotionKing stepper today... Total price delivered to my doorstep R 4120.63....will be here in less than 20 day's

[iclazion]

That's a good deal. :)

[Kobus_Joubert]

Sorry my mistake...worked on 5 steppers for my friend and that was R 4120.63. Six motors were R4944.75.......each stepper R 824.13.

Still a good deal

[gmcclure]

Kobus,

Is 34HS9801 still the most appropriate motor from Motionking,

want to use 203V drivers,

going to build 3:1 belt drive for all 4 motors

thanks

Graeme

[Kobus_Joubert]

34HS9801 is what I am using and the new one is the same. I use 202 drivers, but am sure the 203 will work as well.

[KenC]

If you look hard enough, you can see the similarity of the model codes, I can't work out the exact system, some use 34 to indicate Nema 34, other use the motor frange size, some has the length of the motor, but you always see the familiar 4-digit number which are very closely spec.

[gmcclure]

Thought others maybe interested in this, thanks to Matt for pointing to the MS Motor.


Graeme,



I would recommend the motor that requires 4.5A as you will most likely get better high speed torque from it. You can run that all the way up to 80VDC with no problem (83VDC is the motor’s maximum) and the G203V will perform just fine with it. We do not sell fuses but would be happy to send you some for free. If you email your mailing address to sales@geckodrive.com and say you need some fuses for the G203V we will send them out. Please let me know if you have any more questions. Thank you!



Marcus Freimanis

Geckodrive, Inc.

14662 Franklin Ave.

Suite E

Tustin, CA 92780

(714) 832-8874

[/I]From: Graeme McClure .
Sent: Wednesday, January 27, 2010 9:10 PM
To: support@geckodrive.com
Subject: Chice of two motors to go with 203V



Hello,



My intention is to use 203V drivers on a CNC router I am making at the moment (Mechmate)



I was looking at 2 motors and wonding if you would care to comment of suitablity of both and best choise (from and engineering view point)



MS Motor Motionking

34H280-45-4A 34HS9801



Torque 4.5 N.m 4.9 N.m

Rated I 4.5 amps 4 amps

ohm/phase 0.9 0.98

mH/phase 6.8 4.1

Rotor Inertia 1.6 1.55

kg 2.4 3

length 78mm 98mm

Wires 4 8



angel 1.8 1.8[/COLOR]

[Gerald D]

Graeme, I look at the weight and length for a start, and see you are comparing a single stack (light/short) to a double stack (heavy/long) motor. Single stack is okay with reduction (belt/gear) but it won't drive a MM if used direct drive like Kobus does.

(I am rather surprised that Geckodrive would venture an opinion when they were not informed of the application)

[gmcclure]

Gerald,

using 4:1 belt drive. Sorry cut that out of email paste

Graeme

[noel76]

Gerald.
I made a cnc router 3 years ago, 1200 oz-in on X axis, 640oz, on Y, both belt drive 3.75:1, and size 23, 230oz on Z, leadscrew drive, the machine has been working ok, but not fast enough, now i want to uprgade it to make it more ridgid and faster using the mechmate gantry plans, i have known that the most recommended motors are the PK296A2A-SG7.2, or PK296A2A-SG3.6, also i know that wired unipolar is the best choice for driving fast and slow speeds, my question is what kind of power supply is the most suitable for this motors, i would like to use the PK296A2A-SG3.6 and i need at least 350 ipm. of cutting, do you think can i achive that speed with that geared motor without getting too hot? Im using Deskcnc software and contoller, and gecko drives 203, my actual power supply is 36v, im not sure the amp. thank you in advance.

Noel.

[danilom]

Would these steppers be enough with belt reduction 3:1 ?

They are 3.5Nm , 4.2A per phase and 3.5mH , nema34 lenght 75mm

here is the data sheet :

http://www.arceurotrade.co.uk/projects/stepper/350Ncm%20Stepper%20Motor%20160-010-00450.pdf

As I am still in process of understanding plans and calculations, with modul 1 rack 30tooth pinion and belt 3:1 what would be the possible speed for cutting 19mm MDF? and would be these steppers be enough?

If someone is using similar motors any feedback would be nice.

Thank you

[Richards]

Those motors should work well with 3:1 reduction (even 2:1 should work). My rule of thumb is that you need at least 600 oz*in (4.25 Nm) to reliably drive an axis. The 34-size motors that I have are usually rated at about 300 oz*in or 600 oz*in (PK296 or PK299). The smaller motors would require a belt-drive but the larger motors can be used without a belt-drive (although resolution is about 0.0016 inch when driving direct).

You could probably use up to 60VDC for a power supply and still run the motor at 4.2A. At full voltage computed by Mariss' formula, the motor can heat up to about 80C when it's working hard. The motors that I've tested, when run at full voltage, all run faster than needed on a CNC machine, so by either limiting voltage or by limiting torque, you can keep the heat down to a point that you can touch the motor without getting burned. (Steppers are not resistors, so just plugging in different voltages in a formula won't give you the exact watts created, but it will be representative.)

[southernduckie]

hello,

Found these motors at a good price in Australia are they good for belt drive? torque looks low?:(


model #

34H280-45-8a

http://www.ms-motor.com/HB3418.htm

[PEU]

they look OK, are you planning on using a belt reduction?

[Richards]

The motor is rated at about 450 oz*in when wired half-coil. You would multiply that by the gear ratio of the belt drive, which would probably be at least 3:1 and possibly 4:1. At 3:1, you would have 1,350 oz*in, which is about 84 lb*in. That's the same torque that I have with the Oriental Motor Alpha 7.2:1 geared motors on my Shopbot. If you use Geckodrive stepper drivers that have 2,000 steps per revolution, a 3:1 belt-drive would give you a per-step resolution of 0.000654 inches if you used a 1.25-inch pitch diameter spur gear. Even at 25,000 steps per second, your jog speed would be faster than I would jog my machine.

A 35VDC to 45VDC power supply at 12A would give you plenty of power to drive four motors.

On paper, everything looks good to me.

[southernduckie]

Hi mike,

sounds good then :) i am thinking 3:1 if i could, how many (true holding) steps per inch could i expect? im not sure on full steps/half steps can u hold on a half step?:confused: or is it just smother cut?

Im looking for acurcy of 0.001mm or aproxmatly 0.00004" would that mean that i need more like 7.2:1? that would reduce my ipm to very low levels though?


Regards, Andrew

[David Bryant]

Hi all

I am about to order my motors and would like to know if anyone knows a reason why this should not work well on my MM.
Motion King 34HS9801 motors with 1/5 gear box reductions built on to the motor.
Motion King 2LA860 Drives.

Cheers
David

[shaper]

Hi David

do you have any specs on the driver? as I couldn't find any for it on their site or is this why you are asking, they can be a little cagey with specs from my experience.

Jed

[David Bryant]

Hi Jed
http://motionking.com/download/2LA860_Instruction_Rev.E.pdf

I am only unsure that the driver can be used in full step mode.

I do like the Gecko 203V spec, much nicer for the overloads but the Motion king are half the cost. I have a couple of Gecko's on order for work where I can do some testing :)
Cheers
David

[rotorzoomer]

Their is no buyers remorse (http://en.wikipedia.org/wiki/Buyer%27s_remorse) with the Gecko 203v and PMDX-125 combination...

[Gerald D]

That "Motionking" drive is just a re-labelled Leadshine drive - the word Leadshine still appears in 2 places in their text. And Leadshine are quite acceptable drives.

(Mark, I have some buyer's remorse over the G203V drives. They are not killproof and we have a couple as evidence of that. The hype about their fantastic support doesn't help when you are far away from them. The G201X would have served us as well as the G203V, at a much better price.)

[Richards]

Andrew,

A resolution of 0.00004-inch per step would require about 50:1 reduction. Did you mean 0.0004-inch (0.0003937)?

With a 4:1 belt-drive and a 1-inch diameter spur gear, you would get about 0.000397-inches per step.

The bigger question is whether you should expect to have repeatable performance of 0.0004-inches per step. You're looking at moves that are about 1/10th the thickness of a piece of common copy paper. I think that you're expecting too much from a mechanical machine that uses a rack/pinion system and V-rollers.

To get that kind of resolution, your rails would have to be at least that accurate. Your mounting of the rails would have to perfect with no variation at any point. Your V-rollers would have to ride those rails perfectly and the V-rollers would have to be perfectly round and mounted perfectly centered. You could not have any debris on the rails that was thicker than 0.0004". The tension on the rack/pinion would have to be perfect with no slop or backlash. Temperature would have to be controlled so that the metal did not expand or contract during the cut. The material that you cut would have to be 100% stable, without any tendency to shrink or expand because of temperature or humidity.

On my Shopbot, on a good day, when I'm really watching what I'm doing and I'm cutting slow (less than 60-inches per minute), I can sometimes hold resolution to 0.002-inches, which is 5X worse than you're hoping to get. That 0.002" is the difference in sizes when I cut parts for inlays. Sometimes the parts fit and sometimes I have to do a little sanding to get the inlay to slip into place.

I have a good friend who is a machinist who operates machines that cost well over $100,000. He described the difficulty and expense of holding 0.0005" tolerances in mild steel. His machine had a resolution of 0.00025", 2X better than the tolerance that he was expected to hold. He had to make several finishing passes, each one progressively finer. Even then, he said that most of the parts ended up in the trash. What upset him the most was that he knew than there was no reason for that specification on those parts. He said that the completed piece would have functioned flawlessly if it was specified to have a tolerance of 0.0015". The customer was the Government. The company was paid on a cost plus basis, meaning that they charged for the time and materials required to make the part, plus a percentage for overhead. There was no incentive for the company to talk to the engineer that specified the tolerances. The company was more than happy to see most of the parts end up in the trash; it meant more money in its pocket.

When I was much younger, I had a fascination with rifles. I found a gunsmith in Murray, Utah, who had been trained by the famous P.O. Ackley. That gunsmith prided himself on assembling rifles that had a tolerance of 0.002", and those rifles were expensive. He told me that even with that amount of looseness, his customers complained. At the range, as temperatures inside the rifle changed, the shooter had to use more and more pressure to close the bolt. They had to use cartridges that had been previously fired in that particular rifle and then reloaded with minimal neck sizing only during the reloading process. The barrel floated in the stock, with no point of contact with the wood. He said that their was no known way to keep a wooden stock from changing dimensions, so the only solution was to not let the wood touch the barrel.

What I'm really trying to say is that in the world of cutting wood on a CNC machine, there is a very practical limit on the repeatable resolution that you can expect from a machine AND from the material that you're cutting. A good operator who keeps his machine in good repair can expect to hold that practical tolerance, but I'm guessing that the real world resolution, even on a well built and well maintained MechMate is much, much coarser than 0.0004".

[southernduckie]

Hello Mike,

Thanks for your reply

by coincidence some of the parts are for firearms (i shoot center fire bench rest 500-1000m), but a tollerance of 0.001mm is not that tight ;)in an engineering perspective, i worked in a toolmaking shop for several years, 30 year old mills can do it (although the scrap bin is heavy). you are right very light cuts are required with razor sharp tools.
the minimum specifications i am looking for are,

resolution of at least 0.005mm to gain the following
repeatability to 0.01mm (allowing for hand lapping due to accuracy issues)
x,y 90' acuracy of +-0.01`
x,y/z 90' acuracy of +-0.05`

looks though i might need to revise designs/use:(

cheers Andrew

[Richards]

Andrew,

I don't want to discourage you because I've never built or used a MechMate. When my Shopbot bites the dust, I'll most likely get busy and build a MechMate.

You might ask Gerald about what to expect IF you build carefully and adjust everything to its optimum point.

The machine that I own is a PRT-Alpha 120 X 60 Shopbot, which has a lot of design compromises that Gerald addressed in the MechMate design. The 'ripples' on the rails on my machine are still a major factor in "chatter marks". The general flexibility of my machine contributes to unexplained errors.

However, even with Gerald's improved design, when I look at your requirements, I'm concerned.

My expertise, if I can claim any expertise, is in the electronics portion, particularly stepper motors. I've never had enough money to buy a gearbox that had zero backlash. The Alpha motors on my machine have a list price of $1,800 each (with stepper driver) and they have a perceptible amount of backlash, probably much more than 0.0004". A belt-drive is virtually backlash free, but, depending on the belt material, it may have a little elasticity. The belts that I used on my machine, before I bought the 7.2:1 geared motors, were tight, but I'm sure that they had some elasticity.

Maybe the main reason that I'm concerned is that I simply expected my Shopbot to give me cut quality equal to the cut quality of most other CNC machines. Boy, was I surprised! After I had the machine long enough to verify that the chatter marks were not operator error, that "surprise" turned to anger, particularly because the sales literature advertised +/- 0.003" accuracy. The "chatter" marks were easily 0.06", or about 10X worse than their advertised +/- accuracy.

I've learned to live with the "accuracy" that my machine produces. When a customer wants high precision, I usually run a test to show him what I can do. Sometimes that means that he takes his work to another shop.

[Gerald D]

Quite simply, the MechMate concept & design is meant for processing wood and holding tolerances measureable with the tools found in the typical woodworking workshop.....ie. tape measure, steel rule and sometimes, in our wildest dreams, a vernier caliper. Our inconsistencies we would blame on the wood. :)

[southernduckie]

Thank you for your time Mike and Gerald,
I can see where you are both comming from:) im going to continue to build a MM to learn if nothing else:cool: i will put the machine to very good use, It can build the next monster of accuracy which can be 1' x 2' this will be hopefully cheaper to get prefect results on.

Regards Andrew

[Mojo]

I am looking for suggestions for motors and drivers from people with what's available in todays market (looking at last post date being 2008 and the link for first choice is broken) thanks all.

[Richards]

Mojo,

If you read Gerald's first post (27 October 2006), you'll find that his information is just a good today as it was when he wrote it. (I tried most of the links in that post and they still worked for me.)

[Mojo]

I did read his post but the link for first motor doesn't bring me to that motor type and researching the part number comes up with a blank currently I am going to contact the company and try to find out what they suggest as a replacement motor or what the new part number may be thanks

[MetalHead]

Mojo

OM Motor info is here.
http://catalog.orientalmotor.com/item/all-categories/pk-series-stepping-motors/pk296a2a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0

Let me know if you are wanting these motors.

I saw the links were broken a few says back and have not had a chance to fix the links yet.

[Mojo]

I plan on buying these motors in a week or so. thanks again for the quick response

[Richards]

Mojo,

Let's review the basic requirements. The PK296A2A-SG7.2 motor from Oriental Motor is limited to 3A by Oriental Motor. That means that the Geckodrive G201, G201x, G202, G203v, G250, G251 and G540 could all be used. The G250 would require a special header or a customer "mother board" to be of any practical use. The G540 at $250 or $300, depending on your supplier, is perfect IF you don't need more than two output lines and four input lines, otherwise you should consider a Break-Out-Board, such as the PMDX-122.

That motor has an inductance of 1.5mH when wired half-coil. Because that motor is actually under driven at 3A, you could probably use a power supply voltage up to 50V @ 3A per motor and still stay within the 80C temperature rating of the insulation on the motor. Personally, I use a 35VDC power supply with those motors. They still run at full usable speed and at full usable torque.

Although most of us use a linear power supply, i.e., a toroidal transformer, a bridge diode and one or more capacitors, you could use a switching power supply as long as you add a large capacitor (10,000 to 30,000 uF) on the output of the switching power supply. Some people also add a high wattage diode in series with the output of a switching power supply. I don't. To me, that diode just drops the voltage by about 0.7 volts without offering significant protection. I could possibly see the use of a reversed biased diode in parallel with the capacitor that would act as a steering diode to handle voltage spikes when the power was turned off, but even that shouldn't be necessary with a properly designed switching power supply.

I have tested those motors extensively using the Geckodrive G202 stepper drivers, a 35VDC power supply and a PMDX-122 BOB. I've also done extensive testing with G203v stepper drivers, a 35VDC power supply and a PMFX-122 BOB. My favorite is still the G540 with a 35VDC power supply. No BOB is necessary. All three test setups worked flawlessly. I would only use the G20x stepper drivers and the PMDX-122 IF I needed additional I/O.

Keep in mind that SOME SG geared motors have a little backlash. The motors that I own have no detectable backlash.

For those people who live in a part of the world where the Oriental Motor products are hard to get or are too expensive, the second option would be to buy a good quality 34-size motor that has about 300 oz*in to 450 oz*in of torque (similar to the PK296-02A, PK296-03A, PK296-F4.5A) and that has inductance of 3.5 mH or less. Using that size motor with a 3:1 to 4:1 belt-drive and a power supply sized to the inductance of the motor, would give excellent resolution and excellent torque. The belt drive is more bulky than the SG gearbox and it usually must be custom made, so it isn't the ideal solution for everyone. I've made several belt-drives using material ranging from polycarbonate to aluminum to Delrin. I prefer those made from 1/2-inch thick Delrin. They were light weight and easy to machine on my Shopbot.

[Mountaincraft]

I have heard someone say elsewhere, that when using 2 motors on the X axis, an encoder should be used on each motor for 'feedback'.. Is this true? What exactly does the encoder do, and do the gecko drivers listed work with encoders?...

Also, I'd like to learn why using two motors is preferable to one motor and a drive shaft to connect both sides of the X drive on the gantry?... (just curious on this as to the general design considerations of one style over the other)

I have also seen elsewhere that it is a good idea to use motors with the second shaft on the back of the motor, as then a 'damper' (ie harmonic balancer) can be attached.. Any comment on this as well?

Because of those two factors, I'm thinking it is a good idea to plan on the 'B' model motors, but I'm not sure if it is something that is necessary or justifies the extra few dollars per motor..

Anyways, as interesting as reading this whole thread has been, and somewhat overwhelming, I didn't really see anyone address these topics, so I thought I'd toss them out there for comment from the gurus of all things mechmate and CNC.. :)

Thanks,
Mark

[danilom]

Encoder could be used with stepper motors but is primary used with servo motors, ,it tells relative or apsolute position of motors shaft while it rotates it, so a driver starts the motor and waits until it gets the needed position from encoder and then it stops it (its servo motor principle of work)
Stepper motor gets command to move one step and it moves, no need to monitor its shaft with encoder, unless you need a system that does not miss steps becouse of some other reasons (use more powerfull stepper or gear/belt reduction then) and then the driver would "notice" that the encoder did not emit enough pulses so he would order a steper motor to move one or the number of missed steps.
stepper drives from geckodrive are not designed for use with encoder. Only their servo drivers.

I dont know much about dampers but they might be used I read somewhere but have not seen a lot talk about them.

sorry for somewhat crude english

[Mojo]

Mike, thanks for the in-depth reply. I was thinking i would use the PK296A2A-SG7.2 motor from Oriental Motor (geared) with the G540 drivers. I plan on using 3 motors for X,Y,Z and 1 for A which will be for the indexer. any thoughts on this would be much appreciated. This part of the build will be the toughest for me i think as it is all new territory.

Keep in mind that SOME SG geared motors have a little backlash. The motors that I own have no detectable backlash. I am assuming you own the motors listed above?

[bradm]

Mark,

The problem is that real world shafts aren't as stiff as you might think. They twist.

Mike,

You need two motors for the X. If you're thinking shaft, you need to (A) figure out where it would go in the mechmate design, and (B) determine if the motor needs to be upgraded. I think you'll discover that a suitable shaft and associated hardware will cost out to be more than another motor, and that you can't drive a large enough motor with the G540.

So now you're probably wondering how to make an indexer work. Here's an idea: get a G251 as well. How to drive it? Depends on how comfortable you are with electronics. One way would be to tap into the X step and direction inside your G540 and bring them out. Another is a second bob on a second parallel port. Another is using signals from a serial port if you have one, possibly inserting your own optocouplers. Ask if you start thinking about going this route.

As Danilo says, a well designed stepper system does not need encoders.

[Mountaincraft]

I wasn't really considering using a shaft on the mechmate.. but was just curious as to why when it was being designed, the decision was made to use two motors vs one motor and a shaft..

It's going to be a while before I get to the 'dedicated' mechmate router table, but I will probably consider adding an indexer when I do... The plasma gets built first, and it will double as a part time router (lighter duty) until the router can be built..

I will be sticking pretty close to 'recommended' components, so I feel pretty confident that mine will be a 'well designed' stepper system.... I'm building a temp cheapo table to use while the mechmates get built, but I want to buy as much of the hardware and electronics as possible sized and purposed for eventual use in the mechmate tables...

Gracias,
Mark

[Mojo]

Mike, thanks for the in-depth reply. I was thinking i would use the PK296A2A-SG7.2 motor from Oriental Motor (geared) with the G540 drivers. I plan on using 3 motors for X,Y,Z and 1 for A which will be for the indexer. any thoughts on this would be much appreciated. This part of the build will be the toughest for me i think as it is all new territory.

Keep in mind that SOME SG geared motors have a little backlash. The motors that I own have no detectable backlash. I am assuming you own the motors listed above?

Oops forgot one motor for the Y car so i will be using 5 motors total

[smreish]

Mojo.
Okay - (Brad you can chime in here if you can help - Theatrical Brains think alike)

I would most likely use the G540 for the x y and z format of the machine and then add a PMDX board and single G203v driver for the indexer. Thus, utilzing two (2) LPT ports for communication.

My thoughts on this is experience - when adding the indexer on MM #5, I wished like heck I had some extra I/O ports on the machine to do duty purpose index switches or edge finders for really complex part work. Or that single contact closure to turn on the webcam viewer in Mach when the G-code hit a fault - to record the event.

Nevertheless, that option of having a separate, HIGH Current driver will allow you have much more freedom on picking a stepper motor sized appropriately for your indexer axis.

...Makes me think of the PK 296-F4.5A (which draws 6.3 Amps bipolar) which I used on my indexer. Lot's of torque required to turn large diameter (heavy) projects. It got hot and would draw every bit of that current load on the 4' x 4' x 8' blocks of foam (even thru the 40:1 double reduction gearbox it was attached to)

My thoughts.

[Mojo]

I would assume a separate power supply for this driver and stepper would be in order? thank again

[smreish]

Nope,
Depending on your choice (remember, the Mh determines the proper voltage) so, a choice would be find a Stepper motor with a similar inductance (to maintain similar voltage requirement) and high current. It's a math game. Lucky for us in the US, it's easy to get almost any flavor of stepper from Oriental Motor - same day service on the west coast.

I would plan for that extra driver in the total CURRENT of the transformer. Same voltage, just bigger capacity on the wattage (current size)

I'll do some math later if you want.....but there are far more experts here on the forum than me.

(Mike, Gerald, Brad, Mike.....thoughts on this?)

Sean

[Mojo]

ok thanks very much will do more research on my end then.

[bradm]

As I kind of hinted at up in #232, I'm with Sean on this. As long as the indexer motor can be kept in close spec to the others, think in terms of adding one more driver, and a BOB. Since you gain from extra I/O pins anyway, it makes sense.

[Mojo]

thanks Brad

[Richards]

The Oriental Motor PK296A2A-SGxx geared motors are rated at 1.5mH when wired half-coil. The PK296-03AA motor and the PK296-F4.5A motor are also rated 1.5mH when wired half-coil. I regularly run the PK296B2A-SG3.6 motors and a PK296-F4.5A motor from a 35VDC power supply with excellent results. If you need more torque, the PK299-F4.5A motor can be used, wired either half-coil or bipolar parallel. It can use a power supply up to 50VDC, but I use it with the same 35VDC power supply that I use with the smaller motors. It still gives excellent results.

As a general rule, voltage affects top speed and current affects torque. 35VDC allows any of the motors that I've listed to run at 1,500 RPM, which is past the "knee portion" of the torque curve. Going faster is possible, but torque falls off rapidly as speed increases.

You COULD design a microprocessor controlled feedback circuit using an encoder on a stepper motor, but for most purposes it is not necessary. As long as you don't drive the motor too hard to the point that you miss steps, you can always count on the fact that it will move exactly as expected. Every time I've started to design an encoder circuit, I've ended up stopping the project because it would take a very sophisticated circuit to "make up" lost steps (ramping would be involved) while accumulating on-going steps. It would be even more difficult to synchronize several axes. It's much easier to NOT drive the motors past their ability to move reliably.

[Sacramento]

Hi
Can anyone inform me if I can I use MotionKing 34HS9801 with Geckdrives 540?
If not which Gekdrive shoul I use with this motor?
Thanks for your help

[Richards]

The 34HS9801 motor is rated 4A and 4.1 mH. The 4.1mH means that it can use up to 64VDC.

The Geckodrive G540 is rated at 3.5A and 50VDC. If you underrated the motors to 3.5A and 50VDC, then you could use the G540. You might loose a little torque and a little speed.

The G201x stepper driver or the G203v stepper driver would let you use the motors at their full potential, but the G201x costs about $115 each and the G203v costs about $150 each. With either the G201x or the G203v you would also need a break-out-board. The PMDX-122 costs about $90.

I have used large motors with the G540 by changing the current limiting resistor to permit only 3.5A or less current to flow through the motors. I have also used motors rated for more than 50VDC with a 50VDC power supply. Those motors still performed very well.

In most cases, we will be more than satisfied with a motor that has a maximum speed of 750 to 1,000 RPM (depending on how much the motor is geared down). Those big motors easily ran at 1,000 RPM on the G540's 50VDC maximum. (As a point of comparison, those same motors ran at 2,500 RPM to 3,000 RPM when run at full voltage on a G203v stepper driver. Those high speeds would not be practical on a CNC router.)

[giz]

Good to know. I'm looking into using the Deitech equivalent of the MK 34HS9801 paired with the G540. It seems like a very cost-effective route to take.

[KenC]

I use matching M860 (~US50) suggested by Deitech, maybe they will recommand a later matching driver model if you ask nicely ;)

[J.R. Hatcher]

I have purchased 5 9802 motors from Deitech. I'm satisfied with them except they don't have flats on the shafts ... they have keys. Has anyone removed the keys so flats could be ground? If yes ..... how did you do it?

[Kenrbass]

JR,

Gears with a keyway can be purchased. I have them on my machine (shopbot) and bought them through them. They were about 15 dollars each. I think the shaft size on my motors is 14mm. I'm sure they could be purchased elsewhere though.

I had a machine with flats for the gears before and I like the keyed version much better. No slippage at all.

Ken

[Gerald D]

I would have much preferred keyways in the motor shafts, the flat spot shafts are way inferior.

If you are set up for cutting the mating keyway in the pinion, with a keyway broach, bushing (& shim), then the process is ridiculously easy.

See http://homemetalshopclub.org/news/10/broaching.pdf

The broach/bushing/shim can be purchased ready-made from a number of suppliers. Example. (http://www.dumont.com/prodc.html)

[KevinP]

Do I understand the specs correctly: The PK296A2A-SG7.2 geared motor is 704 in-oz output at the gearbox output shaft?

If so, the stepper itself appears to supply 98 in-oz plus whatever the gearbox eats up in losses. The output seems really small unless it's a NEMA 23 motor on a NEMA 34 gearbox. That looks possible based on the pictures. The outputs and ratios from the 3.6 to 10 ratio gearbox versions seem to support this. It looks like the 18:1 has been de-rated slightly, or the gearbox has higher losses like it went two-stage.

[danilom]

704 in-oz output is only limitation of the gearbox, motor has more power