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View Full Version : Selecting motors for the MechMate - some history


Gerald_D
Fri 27 October 2006, 03:34
Our first MechMate has 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, directly driving the pinion gears to the racks, without any gear reduction. This is a relative low-cost, low risk option - I know it well, it works.

However, because Mach3 can pulse at higher frequencies, you can use a geared motor for better cut quality. In this case, ShopBot did suggest the standard PK296A1A-SG3.6 (http://catalog.orientalmotor.com/item/stepping-motors--1068/pk-series-stepping-motors/pk296a1a-sg3-6?&plpver=11&origin=keyword&by=prod&filter=0) as being a close equivalent of the geared motors specially built for them. (reference (http://www.talkshopbot.com/forum/show.cgi?tpc=26&post=23651#POST23651)). Better cut quality, higher price, and the risk that I don't know what I'm talking about http://www.mechmate.com/Forum/clipart/happy.gif. But, I have designed the MechMate so that this geared motor *should* screw straight on. Most ShopBots use the similar motor & gearing, but they were handicapped by poor drivers - now that the Gecko-type drivers are freely available, folk are squeezing amazing performance from these motors. This could be my first choice today.....? (Edit on 2 Feb 2007: Instead of a 3.6 ratio gearbox, I would now lean towards a 7.2 ratio gearbox instead. It is becoming easier to supply the step frequency required by the 7.2 gearbox, and Doc Tanner says (http://www.mechmate.com/forums/showthread.php?p=2366&postcount=22) it works well. He is using the PK296A1A-SG7.2 motor (http://catalog.orientalmotor.com/item/stepping-motors-/pk-series-stepping-motors/pk296a1a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0)) (Edit on 9 Sept '07: The PK296A1A in series connection does not match to the G203V drive because the inductance is too high. If this motor/drive combination is used, it must be wired half-coil. The better motor choice for the G203V drive is the PK296A2A (http://catalog.orientalmotor.com/item/stepping-motors-/pk-series-stepping-motors/pk296a2a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0)motor with gearbox)

There are motors within the Oriental Motor range, with the same frame size, than can produce more torque at higher speeds, consuming bigger currents, but I am a bit concerned that the higher torque makes them run "rougher", the higher current makes them hotter and that cut quality will suffer. Art Fenerty made an interesting comment on his forum recently about maximum torque for a stepper motor for a CNC router. (link (http://www.machsupport.com/forum/index.php?topic=1488.msg8424#msg8424)). I had some 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) motors that I wanted to test sometime. (but Alan Conelly has them now)

Oriental Motor have worldwide representation. Their USA division has on-line shopping with public prices at these pages (page 1 (http://catalog.orientalmotor.com/viewitems/stepping-motors--1068/pk-series-stepping-motors?&plpver=11&forward=1&backtoname=&pane=), page 2 (http://catalog.orientalmotor.com/viewitems/stepping-motors--1068/pk-series-stepping-motors?&plpver=11&pagesize=200&pagenum=2&sortid=&sortorder=asc&backtoname=)). The ungeared PK299-01AA is $205, and the PK296A1A-SG3.6 is $257 on that list. (Some of the international offices of Oriental Motor have differences in their model ranges and numbers) The MechMate needs a quantity of 4 identical motors.

Having sung the praises of Oriental Motor, it must be recognised that stepper motors (not talking of gearboxes here) are not high-tech devices and many other manufacturers will probably offer comparable quality at a wide range of prices. (if the motor is with a gearbox, then I would probably stick to the OM brand) When looking for alternative motors to those suggested above, the following need to be taken into account:

The shafts need to be at least 12mm [0.5"] in diameter to carry the spring load and not bigger than 13mm 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. The motors must fit on the MechMate's mounting plates. They must be compatible to Gecko G202 drives (http://www.geckodrive.com/product.cfm?pid=10)

Added 22 March '07: The motor bodies should be of the modern square style (heavier, contains more iron, better for micro-stepping)

For the really forward-looking folk, consider motors with shaft extensions to the rear for encoders in the future, or consider that stepper motors may give way to servo motors. . . . .

Pretty good info on this topic. Check it out. http://www.cnczone.com/forums/showthread.php?t=52090

Donald W. Ross
Thu 09 November 2006, 10:17
I am building a 4X8 router along the same lines a MechMate. With the proper gear, would the PK296A1A-SG7.2 be a viable replacement for the PK296A1A-SG3.6?

Gerald_D
Thu 09 November 2006, 10:35
Apparently yes, but I am not so sure about its internal backlash. The 3.6:1 has only one pair of mating teeth (as far as I know) and this must have tiny backlash. The 7.2:1 might have 2 pairs of mating teeth with twice as much backlash?

Some people recently started using 7.2 gearboxes on ShopBots and they rave about them, but it is early days yet...

Dirk Hazeleger
Thu 09 November 2006, 11:30
According to Oriental, the 7.2 has less backlash. It is still a single stage gear reducer. The standard gearbox sold on orientals 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
Thu 09 November 2006, 12:16
Dirk, I wish I was within telephone distance of an Oriental Motor product specialist. The questions I would like to put to them are:

1. PK296A2A verus the PK296A1A. Are the motors in fact different? Isn't the 1 amp version just a labeled down 2 Amp motor? Who would be buying the 1 Amp? (presumably because of driver limitation - but surely the 2 Amp could be under-driven). Is the 1 Amp "smoother"? I can see the one has thinner wire in the stator coils (more resistance/inductance) what is the overall effect of this? (smoothness, detent, heating, etc.)

2. The "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
Thu 09 November 2006, 13:12
Gerald
Your questions are valid. I think the motors are different. Running the higher amp motors increases cost both on the driver and the power supply (If you mounted the 3 amp motors on your machine you would need a 600 VA transformer and 2 more caps because the max voltage would be around 35 volts).
Some applications don't need the high-speed torque. I would think under driving the higher amp motor would kill the low speed torque. So my opinion is they offer several motors so it will fit the application and not create unnecessary expense. If there?s more to it (or less) I don?t know.

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.

On a side note, I?m still curious as to Mike?s theory that torque has as much to do with smoothness of cut as resolution. I?m mounting my 1300oz motors on my PR direct drive to see how it will cut. May be interesting.
Dirk

Mike Richards
Fri 10 November 2006, 08:30
Be aware that the PK296A2A-SG motors are rated at 1.4V (unipolar) while the PK292-02AA motors are rated at 3V (unipolar). I didn't notice that difference until I touched a geared motor that I was running at about 70V. It was HOT! Reducing the voltage to about 30V works well and is within the 25X limit suggested by Gecko.

I'm still thinking that torque of the motor, while in standby mode, is very important when running a multi-axis machine. Using a 3:1 gearbox on my Alpha greatly improved the cuts. Since the resolution of the machine without a gearbox should have been 3.14/1000 = 0.00314 inch per step, it should have been adequate for cutting wood with minimal chatter. (The offending chatter marks were certainly much larger than 0.00314 inches!) My theory is that 3X the standby torque keeps the non-moving axes from being pushed around by the active axis.

Gerald_D
Thu 23 November 2006, 21:48
The "taper hob gear" is actually a "taper gear". From their page (http://www.orientalmotor.com/in_motion/october_2004.htm):

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

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

Gerald_D
Thu 23 November 2006, 21:51
http://www.mechmate.com/Forum/messages/15/2041.gif

Kim Mortensen
Wed 06 December 2006, 09:06
Hey guys, I'm new here, and I'm a little puzzled. Are the Steppers connected directly to the Rack&Pinion drives, or should I use one with a gearbox on it.???

Gerald_D
Wed 06 December 2006, 10:00
Welcome Kim! The first post at the top of this thread is still applicable.

Kim Mortensen
Mon 29 January 2007, 21:10
Hi Gerald should this stepper here be just as good as the Oriental stepper...

www.motionking.com (http://www.motionking.com)

Motor Type
34HS5804

Gerald_D
Mon 29 January 2007, 22:54
Kim, that is a tricky question. It might be as good, but I have no experience of it. You have selected a much bigger size than what I use, and I am a bit concerned (http://www.mechmate.com/forums/showthread.php?t=255) that this may give problems such as rougher cuts.

Kim Mortensen
Mon 29 January 2007, 23:28
Gerald.. Could you direct me to the model that is closest to the Oriental stepper..???
The Steppers you use is also Nema34 right..???

KM

Gerald_D
Mon 29 January 2007, 23:52
From the first post on this thread, the motor that I am experienced with is the Oriental PK299-01AA. From the link, it is 85mm square, 96mm long, the mounting screw holes are 69.6mm square pattern, housing spigot 73mm diam by 2mm deep. (The spec does not say Nema34 exactly).

Physically, the MotionKing nearest this size is the 34HS980* group. The mechanical interface (Nema34?) is identical. (Nema is an American standard, not everyone uses it)

The holding torque is nearly identical at 430 to 450 N.cm.

Electrically, the nearest MotionKing is the 34HS9803 with 2.7A rated current, but after this point I have no idea how to pick an equivalent motor...http://www.mechmate.com/Forum/clipart/sad.gif

Kim Mortensen
Mon 29 January 2007, 23:56
ok. Maybe motionking can give me an answer if they compare them.. The bigger motor there I could get for only $57 a piece plus postage and packaging... But still very cheap for that big a motor...

Gerald_D
Tue 30 January 2007, 00:10
That is an excellent price!

The Chinese stepper motors seem to be okay in general. If they were bad, there would be a lot of people complaining, but I don't see complaints about their stepper motors. If you open a stepper motor (some people say you are crazy to do this) you can see that it is really a stupid/simple device. The magnets need to be a good quality, but China is doing good magnets....

Bob Cole
Tue 30 January 2007, 09:01
Gerald:
regarding these, (or any) motors for the MechMate. Do you recommend 4 wire or 8 wire motors? and why?
Do you think an 8 wire motor affords the user more flexibility in setting up his router?

Regards,
Bob C.

Gerald_D
Tue 30 January 2007, 10:43
Bob, 8 wire obviously gives more options than 4 or 6 wire, but I am still at a loss to understand whether we should be using unipolar, bipolar series or bipolar parallel wiring. Here is an exchange on the Gecko forum about 2 months ago....

Me:
Mariss, could you enlighten us why that Nanotec wiring diagram says:
8 lead wire parallel for high freqency > 1kHz, and
8 lead wire series for low freqency < 1kHz?
For CNC machines, the motor will spend most of its life in the low frequency range, no? I have difficulty deciding when to use series or parallel - the rule always seemed to me to use the parallel if the drive could cope, otherwise reduce current with series. Now there is another selection criteria....?
Thanks

Mariss:
You have "two motors in one" when you have an 8-wire motor.

1) "Both" motors have the same low-speed torque.

2) The series connection phase current is 1/2 the parallel connected
phase current and runs out of low-speed torque at 1/2 the speed of the
parallel connected motor for the same supply voltage.

3) The series connected motor runs cooler than a parallel connected
motor for the same supply voltage.

4) Use a series connection and/or a low power supply voltage for
low-speed applications. Use a parallel connection and/or a high power
supply voltage for high-speed applications.
Mariss

Me:
With a CNC router table, which can use the full speed range of the
stepper motor, what are the signs (or effects) that tell you it might
be wiser to use series rather than parallel? Only motor heating?
Roughness of cut? Etc. My impression is that parallel should be the
first choice if the driver can handle it, but then to drop to series
if the motor gets too hot. Is this simplistic logic faulty?

Another way of looking at it is to leave the motor parallel, but
change the resistor to limit the current at a lower value?
Thanks

Those questions are still in my mind...

DocTanner
Tue 30 January 2007, 10:48
Bob,
The GeckoDrive G202 - Step Motor drive that Gerald specs, doesn't care how many wire come with the motor. http://www.geckodrive.com/photos/Step_motor_basics.pdf
Ton's of good info there. I have had good luck using the http://catalog.orientalmotor.com/item/stepping-motors-/pk-series-stepping-motors /pk296a1a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0 (http://catalog.orientalmotor.com/item/stepping-motors-/pk-series-stepping-motors/pk296a1a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0)

Gerald_D
Tue 30 January 2007, 11:33
Doc, did you try the two different wiring options (unipolar & bipolar) and would you recommend one version over the other? My experimentation in this area didn't give me a conclusive result.

DocTanner
Tue 30 January 2007, 12:35
I set mine up as 1 amp at 70volts and was so impressed by the power, speed and cut quality that I didn't even think of changing it!
Drives and motors produce no noticible heat. If the leds weren't lit up, you wouldn't know it was on.
When it gets back from the powdercoater tomorrow and I get it back together, I will give it a try.
I have an ncpod sitting on the desk, was thinking of giving it a try. But I'm not sure how it could be better! http://www.mechmate.com/Forum/clipart/happy.gif

Gerald_D
Tue 30 January 2007, 12:44
Very good to have a satisfied customer! http://www.mechmate.com/Forum/clipart/happy.gif

But, in the interest of science, it would be interesting to get a definitive answer on the best way wire the motors. Would appreciate you experimenting a bit. (Remember to change the current limit resistors accordingly).

Gerald_D
Thu 01 February 2007, 22:14
The Motionking discussion has been moved here (http://www.mechmate.com/forums/showthread.php?t=258).

Those who are actively pursuing this MotionKing option must consider the following:

1. Those motors have never been tested on a MechMate. They should work, but we don't know for sure.

2. Those motors are without gearboxes. They should work as well as my setup. But, the evidence is that my setup could work a lot better if I had gearboxes. Those geared motors mentioned at the start of this thread appear to be a much better (albeit more expensive) option.

3. If the Motionkings don't work, then please don't say you got bad advice from MechMate. I would love to be able to endorse a cheaper option, but I have to be cautious.

Kim Mortensen
Fri 02 February 2007, 05:00
Gerald...

Of course youo won't be held responsible. This is just a way for me to cut cost a little, and I'm wiolling to give it a try, even though I have been advised not to... One has to learn from ones mistakes right. But then again, I could get lucky and maybe end up with a motor that works fine at one quarter the cost of an Oriental motor...

Gerald_D
Fri 02 February 2007, 05:14
Kim, I would be very happy if you tested those motors and told us all about it. I am just a bit nervous about those folk already talking of bulk buying the experimental stuff.

Kim Mortensen
Fri 02 February 2007, 05:29
I would never bulk buy something I haven't tested. But I would however buy them for my self only. I'm also not keen on being the fall guy if everyone suddenly didn't get what they wanted from these motors.

Kim Mortensen
Fri 02 February 2007, 05:33
And on another note, if the motor seems to run a little uneven, the I'm going to build my own gearbox for it with belt pulleys and high tension belts.

Gerald_D
Fri 02 February 2007, 09:30
I have made an edit to the first post in this thread - see the bit in red.

To summarise the choices of motors....

1. Best cut quality (highest step frequency) will be obtained with the most expensive $257/motor option from Oriental Motor. (The backlash factor of these gearboxes is not discussed much - that is a bit of an unknown)

2. A commercially acceptable cut quality (smoothed with a few wipes of sandpaper if necessary) could be obtained with direct drive motors from about $50 to $110 each (Chinese) or $200 (Japanese). (Backlash is not a factor with this option. I have years of experience with this setup and 99% of our customers are happy with the cut quality)

A lots depends on where you live and what the shipping charges will be to your destination.

vadeem
Mon 12 February 2007, 18:38
Hey guys, I believe I'm reading the Motor specs right, and the PK296A1A-SG7.2 motor is 4.4 volts?

So I need to build a larger power supply than the example shown under power supply in order to have the recomended 25x voltage, right?

Gerald_D
Mon 12 February 2007, 20:17
Not quite right. The 25X is the absolute limit - it can be less. In this case the Gecko is limited at 80V, and this becomes your design voltage. The motor draws 1.5 Amp max. So the 75-80Volt / 300VA power supply illustrated there will do just fine.

vadeem
Tue 13 February 2007, 15:49
Thanks Gerald, I placed my order today.

I might remind everyone that the free UPS shipping ends March 31st 2007 at Orientalmotor, so you may want to pull the trigger now.

eric thomas
Sat 03 March 2007, 19:00
http://www.xylotex.com/4AxSysKit-425.htm
can you use this system for the mechmate?
why, why not

Gerald_D
Sat 03 March 2007, 20:37
Sorry, too small and underpowered.

Loren Gameros
Mon 05 March 2007, 10:31
Hi Gerald,

In a post on Fri. Feb 2 at 6:30 PM you had said the following:

"A commercially acceptable cut quality (smoothed with a few wipes of sandpaper if necessary) could be obtained with direct drive motors from about $50 to $110 each (Chinese)"

My question is which brand motor can be used for $50 to $110 dollars, and would you recomend them?

Gerald_D
Mon 05 March 2007, 11:15
Have a look at the posts above that one - I don't think I can say much more than that until I have actually tested the motors myself. (If shipping costs out here were not so darn expensive, I would have tested these economical options long ago) On the other hand, it will help if other guys tell us how the cheaper motors work in their MechMates, but nobody has gone this route yet. Want to be the first guineau pig?

Loren Gameros
Mon 05 March 2007, 13:12
Sure I'll be the g-pig, recomend some $50 range dollar motors and I'll try them out ASAP.

Gerald_D
Mon 05 March 2007, 22:12
Have a look at the MotionKing page (http://www.mechmate.com/Forum/messages/15/3326.html).

Thomas M. Rybczyk
Tue 06 March 2007, 05:25
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

bugmenot dillbert
Thu 08 March 2007, 13:12
I'm curious of the specs on those motors. They are rated 5.5amps at 2.4v which then require a 55-60V powersupply at 23-25x rated voltage but then with four motors in theory you need 22amps from the powersupply thus a 1200VAC powersupply for optimum performance? (but then you need to multiply this with that and so on and so forth and this is worst case, the motor may not be wired as bipolar(series/paralell?) which the rating is for, I'm totally at loss when it comes to figuring out this stuff, etc.) It also seems to have a little lower holding torque than the recommended vextra, but that may not matter.

What I wonder, if you can use a 300VAC powersupply with the vextras and the kelling motors may require four times as much power with possibly lower holding torque, where does all that energy go? Heat?

Gerald_D
Thu 08 March 2007, 23:19
Bugmenot, the guys who were recommending the 23-25x are now saying (http://finance.groups.yahoo.com/group/geckodrive/message/10931) 20x as the max voltage - you can use less.

But, to get to your main point, where does all this power go....? This is a question for which I would really also like an understandable answer. If I had money/time/space I would be buying all these motors and testing them against each other.

One group of guys have the logic that more power is always better. (Tim (http://en.wikipedia.org/wiki/Tim_Taylor_(fictional_character))). That's fine, but then we must have a reliable way of getting rid of the excess heat. A 300VA supply is easy to cool without blowing it full of dusty air. The big power supplies need breathing air and get choked on dust.

bugmenot dillbert
Fri 09 March 2007, 15:03
I tend to agree that more power is better than being short of power if optimum performance is needed, obviously considering cost.

Doesn't more current mean more heat, thus the vextras should run cooler? I would really like to know if there is a rule of thumb where more current is better for high speed or vise versa or better for low speed torque, but I guess that is a question for the people at geckodrive.

Mike Richards
Fri 09 March 2007, 20:52
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.

Gerald_D
Thu 22 March 2007, 12:23
First post edited to prefer the modern square body motors.

glenn Crawford
Thu 29 March 2007, 05:25
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
Thu 29 March 2007, 06:18
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
Thu 29 March 2007, 08:33
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
Sun 13 May 2007, 08:25
I have been turning over the stepper vs. servo motor option all week. I was wondering if anybody new of a N. American source for servo motors that will work with the gecko 320/340 drives. Most of the Motors i am finding are designed to use their respective manufacturer controllers (I'm finding some that have bus voltages of 325vdc-560vdc!). Any idea would be great. The conclusion is if i can afford a servo setup, that the way i will go, if not, then geared stepper like the $260 ones from oriental. looking to build the controls by june 30, then start in on the steel.

Frank D
Sun 13 May 2007, 10:04
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
Mon 14 May 2007, 09:32
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
Mon 14 May 2007, 10:06
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
Mon 14 May 2007, 10:29
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
Mon 14 May 2007, 15:54
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
Mon 14 May 2007, 16:51
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
Mon 14 May 2007, 19:56
Thanks doc,
It?s what I was hopping to get!! http://www.mechmate.com/Forum/clipart/happy.gif
Later, Robert

IN-WondeR
Tue 22 May 2007, 08:21
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
Tue 22 May 2007, 09:12
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
Tue 22 May 2007, 10:21
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
Tue 22 May 2007, 10:37
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
Sun 27 May 2007, 13:09
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
Mon 20 August 2007, 08:59
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
Mon 20 August 2007, 09:39
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 an obvious reason why a 2 amp motor would be "better".

domino11
Mon 20 August 2007, 10:31
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
Mon 20 August 2007, 11:09
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
Mon 20 August 2007, 12:20
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.

Gerald D
Mon 20 August 2007, 12:22
Mike, Art 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
Mon 20 August 2007, 16:24
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
Tue 21 August 2007, 05:25
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
Wed 05 September 2007, 10:40
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
Wed 05 September 2007, 23:01
Suggest you first find the Vexta price before you decide which company is the better supplier. On paper, the motors are very similar.

javeria
Thu 06 September 2007, 04:33
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
Thu 06 September 2007, 09:14
Have you considered importing from Motionking, China? They might even tell you they have a stockist/agent in India.

thesaent14
Tue 11 September 2007, 21:07
Sorry, too small and underpowered.

i guesst you just answer my first Q?

is funy geral i just read this hall and you send me back here lol

well a bit about my motors i have a set of super vexta 5-phase motors with there drivers here is a picture of them in my small machine

this are the drives
http://i15.photobucket.com/albums/a388/thesaent14/mics/cncdrives002.jpg
and this are the motors
http://i15.photobucket.com/albums/a388/thesaent14/mics/cncdrives004.jpg

can any one tell me if any of this is good to install in my machine

Richards
Tue 11 September 2007, 22:55
Here's a link to an Oriental Motor document that shows the why there are 2-phase motors and 5-phase motors:

http://www.orientalmotor.com/MotionControl101/2phase-v-5phase-intro.htm

Read it carefully, and it will answer most of your questions.

My own opinion on the matter is that I would NOT use 5-phase motors. Using 5-phase motors means that I would NOT be able to use Gecko G20x stepper drivers. To me, the 5-phase motors are like the Oriental Motor Alpha drivers/steppers that I have on my Shopbot PRT-Alpha machine. The motors and the drivers are a package - a very expensive package. Just one motor/driver costs about $1,100 retail. Gecko stepper drives cost less than $150 each and the motors cost about $200 each. So for about $1,400 plus another $100 for a power supply, I can buy four motors and four drivers and a power supply that has much better resolution that the Oriental Motor Alpha driver/stepper.

Right now, I have two of the 23 frame size 5-phase stepper motors and drivers and one of the 34-frame size 5-phase stepper motors and driver. None of them have ever been used. Very possibly, none of them will ever be used. Why? Because, if I build them into a machine, I will have to support them and replace them in the event that one fails. That costs too much to make it practical. So, unless I find a way to use them in one of my own projects, I probably won't use them at all. (Please don't ask me to sell them at 10 cents on the dollar. Deep down, I am a business man and as a business man, I don't give away expensive parts and pieces. Sorry, but there is a line between giving advice freely and giving away parts and pieces that cost a lot of money to buy. Even though those motors and drivers may have very little value to anyone else, they still cost more than $3,000 to buy. As far as that goes, I also have about $15,000 worth of Ziatech STD-32 controllers on hand. I bought those shortly before Ziatech was bought by Intel. Those boards are all factory new - but will never see life in a new machine for the same reason - it's simply much cheaper to buy a Z-World processor and design a process control computer around the Z-World processor than it is to use the Ziatech parts that are sitting on my shelf. Just so I don't sound too mercenary, how would you feel if I sold you a process control computer that had all new parts but when the machine broke I told you that the manufacturer had gone out of business; therefore, I couldn't service your brand-new machine? Sometimes we get a little bitter when suppliers that we trust suddenly close their doors without warning us. That happened to me with Ampro computers and their Little Board Z80, with Ziatech with their STD-32 line and with Oriental Motors with their 5-phase Vexta line. In the case of Oriental Motors, they still make other fine 5-phase motors and drivers, but I've decided to use their 2-phase motors with Gecko drivers to get the best value for my money.)

Gerald D
Tue 11 September 2007, 23:13
Manny, have you tested those motors and drives? Do they work smoothly for you?

What is the diameter and length of the output shafts? (Notice that all three motors are different). We are looking for a 1/2" shaft more than 1.25" long.

There is a chance you might be able to use a motor for the z-axis . . . .

(PS. I spent nearly an hour looking for specs on those Vexta motors in the photo. At $150/hr (my day job rate), you owe me about ?? beers ;))

thesaent14
Wed 12 September 2007, 16:12
geral D my motors are 1/2" shaft and 1.25" long and i am working with them in my machine now they do work really good and smoth

btw

i have a 24 pack:D:cool:

this is my machine now the pictures are old i do have 3 of the motors and the drivers are the same.
http://i15.photobucket.com/albums/a388/thesaent14/mics/cnc006.jpg

Gerald D
Wed 12 September 2007, 20:22
There is a *possibility* that these motors could work for the y and z-axis. I am afraid that you will have to experiment.

thesaent14
Wed 12 September 2007, 20:44
how about if i get the new motors and use the drivers i have now if you see the in the pictures those are the vexta drives the model number is UDX5128NA

i was reading on the page about the 5 and 2 phase i probably will be able to get away with it

Gerald D
Wed 12 September 2007, 20:55
5-phase steppers are basically obsolete, a museum might be interested in that driver and motor. :( (I seriously spent a long time looking at your drivers and there was just no info, which means they probably went off the market before the internet existed)

thesaent14
Wed 12 September 2007, 21:04
i guest i least words lol don't use them i will have to go with the ones you recomend well ebay will have some new items now i am looking to start this machine really soon

Richards
Thu 13 September 2007, 05:32
Manny,
If the drives and motors run, they can be used. The 596 motor will have torque similar to a PK296 motor (about 300 oz*in). You may have to build a belt-drive gear box to get enough torque to use it. The 5913 motor will have torque similar to a PK2913 (about 900 oz*in). That motor has would work without a gear box. The 566 motor is probably too small to be useful on a CNC router. It is similar to a PK266 motor (about 125 oz*in). Because it has a 0.25-inch shaft, it is probably too light, even with 7.2:1 gearing (10-tooth to 72-tooth timing belt pulleys).

Because Mach 3 has excellent ability to handle motor tuning, almost any motor can be used.

My main concern is that you may have to do a lot of extra work just to make the motors useful (belt drive transmission). You will end up with a motor that has 1/4th the resolution of a Gecko driven motor. With the addition of a belt-driven transmission, your cost will actually be equal to or more than buying a new PK296A2A-SG3.6 or PK296A2A-SG7.2 motor (at least in the USA).

No matter what you decide to do, always remember that a Mechmate, with all of its excellent features, will only work as well as its motors. Using strong, smooth motors will let the machine do all that it is capable of doing.

thesaent14
Thu 13 September 2007, 16:04
can i use all my drives and buy the motors if is not that bad if i can't them i will go with the geckos and the motors Gerald recommend

Richards
Thu 13 September 2007, 16:08
Sorry, Manny, but I misunderstood. Each motor must be matched to its own driver. A driver for a 566 motor with not work with a 596 motor, etc. Unless you have matched drivers and stepper motors, then I would suggest that you buy the Geckos and the motors that Gerald recommends.

thesaent14
Thu 13 September 2007, 16:17
i think i will go with those on least the is any other working choist if not i will get them i just don't want to spend the money if i got the posibility of use them you know i guest i am stuck with all this motors and drives

btw

you can use the diprent drivers and motors as long they have they both have the same wire colors

joepardy
Wed 31 October 2007, 14:50
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
Wed 31 October 2007, 17:34
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
Thu 01 November 2007, 00:44
Joe, I got stuck at "BC head" - what is that? :confused:

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

Richards
Thu 01 November 2007, 02:28
'BC' would normally be 'tilt' and 'swivel' capability for the Z-axis. So, the machine would be able to have six-axes of movement. Most machines have three axes of movement, X, Y, and Z. Some include an A-axis, which is normally the Indexer to enable the machine to cut around a cylinder. The 'BC' movements could probably be thought of as the ability to dish out a bowl, cutting both the inside of the bowl and the outside of the bowl without re-fixturing the bowl.

While controlling all six axes is possible with the Gecko G100 controller, I can't even start to imagine using software to design and to toolpath all six axes.

Gerald D
Thu 01 November 2007, 04:10
Venturing into A territory was bad enough - I'll watch this B and C from the sidelines. :)

joepardy
Thu 01 November 2007, 04:44
Mike,

THANKS for the recommendation. I will put the PS-8N54 on my parts list.

Gerald,

The BC head is similar to what Rainnea and/or Colin have on their systems.

Thanks again for the help! :)

driller
Thu 01 November 2007, 05:44
Joe,
<snip>

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.

<snip>


Isn't that only true if you use the same voltage ?

when using half coil you have one set of parameters, when using series, you have a whole different set.

If you select a power supply for half coil, your voltage will be low and your current will be high.

if you wire the motor for series and use that power supply, it will draw half the amps, but because it is using the voltage for the half winding, it is not getting the full performance at hight speeds.

Both style motors will get the same torque up to the corner speed of the way they are powered.

(in real simple terms, corner speed is that point where any more voltage is wasted and the motor just gets hot.)

Mariss has a white paper in the files section of the geckodrives group that discusses this and how wire and select amps and voltage.

- - - - - -

to add to Joe's origional questions about power supply.

There are actually two main power supplies. one is your wall power. 220 AC volts or 110 AC volts. that powers all your tools. router and such. it also powers your DC voltage power supply.

Since the comment about using larger spindles, vacuum motors and such was mentioned, that falls to your AC or main power, not your DC power.

Since you can easily add a Solid State Relay (SSR) to power 220VAC devices there is no need to worry about that part of the power supply.

the AC needs to be able to handle the total watts. And if you use a secondary panel for all your high power AC stuff, you would need to make sure you have a circuit breaker in your main panel for those things.

The stepper motor panel does not use that much power, usually less than 1,500 watts or 15 amps at 110 VAC. your router probably uses that much, and should not be on the same breaker.

As note about steppers.....

Interestingly, a large table router will have two axes that need fast motion. the X and Y need to be able to move at high speed, with power.

The Z, and in your case the BC axes are also slow axes so could be used with a series power supply.


I agree with Mike that half coil is the way to go, and add that you do not lose torque by going that way, you do gain power at high speed.

Dave

Richards
Thu 01 November 2007, 08:25
Joe,
The PS-8N54 should work perfectly if the motors are wired Bipolar Series. It will be about 2X too much voltage if the motors are wired half-coil.

joepardy
Thu 01 November 2007, 09:11
Mike,

If I wire the motors half-coil as both you and Dave have recommended, then based on your last comment "It (PS-8N54) will be about 2X too much voltage", are you suggesting that maybe I should use a different power supply?

Or will the PS-8N54 work for both applications? :confused:

domino11
Thu 01 November 2007, 09:15
Venturing into A territory was bad enough - I'll watch this B and C from the sidelines. :)

Gerald,
Have you done any work in the A axis? I dont remember seeing any evidence of A axis type work at the Camcraft site. If you do any A Axis stuff maybe you could show us a video? :cool:

A six axis mechmate would be awesome though

Gerald D
Thu 01 November 2007, 09:32
My venture into A axis was allowing it to be discussed at this forum and offering suggestions to Art.

A six axis MechMate will not be a MechMate - it will be experimental and not production.

driller
Thu 01 November 2007, 10:24
I can see how it is exciting to try to use the basic MachMate design as the base and then do things like make a 24 inch Z axis. That is a lot of rise for the unit.

An articulating head on the end of the Z would require more height between the bottom of the car and the top of the table.

Deffinitely experimenal territory.

Dave

joepardy
Thu 01 November 2007, 10:28
Agreed - but the most exciting place to live - is on the edge! :eek:

Richards
Thu 01 November 2007, 11:05
Joe,
The PS-5N30 power supply would be the best match when motors are wired half-coil. The 5 in the part number means 500W. The 30 in the part number means 30VDC. That power supply puts out more than 15A, or about 35% more than your motors will draw, so you won't have to worry about either excessive heat or voltage droop caused by too much current being drawn through the power supply. If AnTek offers a PS-6N30 or a PS-8N30 at or near the same price, the larger power supplies would be even better. (Most power supply manufacturers would just substiture a 600VA or an 800VA toroidal transformer in place of the 500VA toroidal transformer, so the cost increase would be minimal.)

domino11
Thu 01 November 2007, 11:06
Gerald,
I did not intend to infer that you include 6 ,5 or 4 axis details into your plans. I just meant it would be an incredible machine. :)

joepardy
Thu 01 November 2007, 11:37
Richard,

It appears that the largest 30VDC unit is the 500W. They do go up to 1000W on the 35VDC units.

Is that an option? Or should I stay with the 30VDC.

If I need to, I will ask if they can custom build an 800W unit.

Richards
Thu 01 November 2007, 12:06
Joe,
The PS-5N30 should work perfectly. I use a toroidal transformer that outputs 50% of the current of the PS-5N30 with four PK296B2A-SG3.6 motors without any problems. I would ask AnTek if they can/will substitute a 600VA or an 800VA toroidal transformer, but if they can't (because of physical size limitations, etc.), then the PS-5N30 will still work just fine. (I'm very conservative when it comes to power supplies, so I tend to over-specify the power supply whenever I have a choice. Going larger is not always good. It costs more and it is bulkier. If the smaller power supply works, then nothing would be gained from going larger. Even if all your motors were just creeping along at minimal speed, where they draw the most current, the PS-5N30 is rated to handle 100% of the combined amp requirements .)

Gerald D
Thu 01 November 2007, 12:08
Gerald,
I did not intend to infer that you include 6 ,5 or 4 axis details into your plans. I just meant it would be an incredible machine. :)

. . . checks dictionary for "incredible" . . . . beyond belief or understanding . . . . that's sounds right :D

joepardy
Thu 01 November 2007, 12:23
Mike,

I just sent them an email and asked. Awaiting a reply. I would like to go a little over - in the event that I need to change the motors on the BC axis - or if at sometime I want to add an A axis. You just never know the future.

Again, THANKS for the recommendation!

driller
Thu 01 November 2007, 20:52
I would like to point out Mikes post of earlier today

quote : 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.
end quote


As you may or may not know, it is not possible to use any more power than the motors can take. Using his calculations 350VA is the limit. getting anything larger is like putting an extra 20 gallon gas tank in the trunk of your car. not connecting it to anything, just dragging it around wherever you go.

using 30 volts and a 500 watt transformer is already 43% over sized.

It's not magic, it's math.

Dave

Richards
Thu 01 November 2007, 23:53
Dave,
The point of concern for me is the 0.66 multiplier. I believe that that multiplier 'computes' the average current draw of a stepper motor, not the worse case current draw. Because stepper motors used in CNC routers are expected to perform flawlessly over a wide range of speeds, I like to assume that every CNC router will spend a good deal of its time with all motors creeping along at less than 50 RPM (V-Carving, 3D, etc), so I always make sure that the power supply can handle 100% current draw from all the motors at the same time. I also assume that every shop is like mine - without air conditioning - and that every power company lets the power droop 10% when everybody else is running their air conditioners. That means that I have to plan for real world conditions where stepper motors might draw 100% of their rated current and the power company might only give me 90% of the power that I need. Bottom line - oversized power supplies.

On the other hand, in my other life as a process control computer designer, just the opposite was true. Those computers were designed to ramp the steppers up to 1,000 RPM as fast as possible, run a certain number of steps and then ramp down as fast as possible. The Kodak-S series photo printers were housed in comfortable air conditioned rooms - because photo paper is very sensitive to heat. Voltage regulation had to be within 0.5% otherwise the color temperature of the printing lamp would change. Because of the controlled conditions and the specific function required of the stepper motors, I could get away with a much smaller power supply.

This last summer there was a rash of heat related problems on another forum where an upgrade kit was offered allowing the owners of older model machines an easy upgrade path to Gecko controlled stepper motors. The idea to move to Gecko stepper drivers was good, but the implementation of that idea caused some grief. The Gecko G202 stepper drivers were mounted to a PCB board instead of mounting them to a substantial heat sink. The 'reduced current mode' was jumpered OFF, causing the stepper drivers to furnish full current when in standby. The power supply was a switcher without a large filter capacitor. In addition, the power supply was set to deliver about 50% of the voltage that the motors could handle. After the initial kinks were worked out, the upgrade worked pretty good - until summertime temperatures hit 100 F. The usual 'fix' for that problem was to open the controller case and then to use the biggest fan possible to circulate air past those stepper drivers. Although I disagreed with their design philosophy from the beginning, I'm NOT pointing fingers at them. Their upgrade helped a lot of people get a remarkable increase in speed and cut quality at a reasonable cost. In my opinion, the problem was that they read the documents, did the math and then built the controller - without being aware of some of the 'gotchas'. The motors used in those machines are the same as the PK296A1A-SG3.6, which draw 1A when wired Bipolar Series. The Gecko G202 documentation states that heat sinks MUST be used with motors drawing 6A or more. Almost anyone reading that documentation would assume that the G202 would never need a heat sink when used with a 1A motor, so a heat sink was not used. Well, the problem is, the controller has provisions for up to six G202 stepper drivers, all mounted very close together. In addition, when a G202 is jumpered to turn 'reduced current mode' OFF, those stepper drivers run A LOT hotter than normal. Put all of that in a closed case and you end up with a lot of heat - and stepper drivers that shut down until they cool off.

My advice to Joe may be a little too conservative, but I can guarantee that if he uses the recommended power supply, that his stepper drivers and his stepper motors will work, even on the hottest summer days. Bottom line - I'm an old white haired guy who really gets tired of fixing things that spending an extra $10 or $20 could have prevented. Over the last thirty years, I've driven more than 1,800,000 miles (60,000 miles per year - or more), installing process control computers and fixing competitors' machines. Many of those miles were driven to fix a competitor's machine - mostly because the designer went by the book and assumed that the machine would live in a perfect environment and that the power company could be trusted. I'm really not bragging about my machines; I just had an excellent mentor. George, my mentor, before opening his own business, designed electronics for the military. He often said that, as a designer of military electronics, he knew that if and when the devices he designed ever had to be used, that many lives would depend on his ability to design things better than the average engineer. That philosophy worked for him, and, so far, it is working for me.

Things are really no different in our CNC router world when we try to determine how fast we can spin a cutter and how fast we can push it through the wood. We start with the math (chip load calculator) and then add a large dose of seat-of-the-pants experience. Before long, each of us becomes one of the go-to-guys that the newbies seek out when they can't figure out why their cuts look and feel terrible when compared to ours. Usually, that's when we start enjoying our work because we know that there will be few surprises. That's really my goal when I suggest electrical components. Most of the time I have the recommended components right in front of me. And most of the time, I've run those components harder than they would ever be run in the field. That gives me peace of mind - knowing that there will be few surprises.

Gerald D
Thu 01 November 2007, 23:57
Edit to add: I cross-posted with Mike above - havn't read his whole post yet, but the first sentence tells me we are on the same wave-length.

Dave, it is not that simple. The 0.66 is not a mathematical number, it is a general rule of thumb for 3-axis routers. Nobody has ventured to give the rule of thumb for 5-axis. Even the 4-axis (indexer) blokes who don't current reduce on the one axis are pushing it. (The 0.66 seems to be for the current reducers on all 3 or 4 motors).

joepardy
Fri 02 November 2007, 03:27
Again, THANKS to Dave, Mike & Gerald for information. I contacted Antek and they informed me that they can produce a PS-6N32 and a PS-8N32. I have not received a price yet - but I am sure that they will be reasonable. With regards to the potential for problems when "heat" is an issue, I would like to ultimately install it in a factory environment - without air conditioning. Summertime temperaturs in this facility routinely reach 100 degrees.

driller
Fri 02 November 2007, 05:04
Dave,
The point of concern for me is the 0.66 multiplier. I believe that that multiplier 'computes' the average current draw of a stepper motor, not the worse case current draw. Because stepper motors used in CNC routers are expected to perform flawlessly over a wide range of speeds, I like to assume that every CNC router will spend a good deal of its time with all motors creeping along at less than 50 RPM (V-Carving, 3D, etc), so I always make sure that the power supply can handle 100% current draw from all the motors at the same time. I also assume that every shop is like mine - without air conditioning - and that every power company lets the power droop 10% when everybody else is running their air conditioners. That means that I have to plan for real world conditions where stepper motors might draw 100% of their rated current and the power company might only give me 90% of the power that I need. Bottom line - oversized power supplies.

<snip>


I can see where you are coming from. the Gecko is a PWM chopper style driver. most of us think linear and not digital. Mariss has been designing stepper drivers for over 30 years and has a failure rate of less than 1% He has been making the Gecko no for over 6 years, so when he says 66% is enough, it means not just worst case, but WORST CASE. Mariss is very conservative in his numbers. his failure rate and success show he is pretty good about such things.

Joe listed his motors as :
(4) PK296A2A-SG (3 amps x 4 motors = 12 amps)
(2) PK264A2A-SG (2 amps x 2 motors = 4 amps)

for the 16 amps listed, and using 30 volts, we can calculate 16x30 = 480 watts. That is full amps as if the motors could all run at full amps all the time.

Although it is not possible for that to happen due to the nature of PWM and choppers and motor inductance, one would be fully covered with a 500 watt power supply.

Taking into account that Mariss is quite conservative in all his calculations, you can use much less that the 66% is recommends. His 66% is already well over sized for his drivers.

Just as a note, Mariss has said he uses a rule of thumb of taking the full design and cutting the voltage back to 80% and the amperage back to 70%. If you look at the components, the Geckos use components rated for 100 volts and 10 amps. He lists 80 volts and 70 amps following the 80/70 rule of thumb.

So, the 66% is not some out of the air number, nor is it the result of an over optimistic engineers adding up all the specs. it is a real world, worst case number. If you have the opportunity to actually test a power supply on a bunch of steppers to find out the real power number, you will not believe how low it really is.

I think the bottom line is to address Joe's question. I think Mike nailed it with the recomendation to use single coil wiring, and I think that when Mariss, the manufacturer, offers a calculation, you are extreemly safe with it. We use all of his other calculations for his product, why change what he recommends ?

Dave

ps: As for your comments about heat in a sealed enclosure, I cannot agree more, but at the current levels of the Gecko's the heat generated is in low single digit watts per driver. Makes me concerned, but since others have not had a problem, I remain (mostly) silent on that topic.

Richards
Fri 02 November 2007, 07:33
Dave,
I see that you've asked Mariss for a definitive answer on the Geckdrive forum. I was going to do the same thing. Somewhere I remember reading that the 0.66 multiplier was for the older round motors and that the newer square motors, being a better design, could pull more current. That post, if it even exists, might have been made by someone other than Mariss. At any rate, let's hope that Mariss helps us out on this.

driller
Fri 02 November 2007, 08:08
I did a search on Geckodrives for the exact reason. I really like to get Mariss to answer such questions. he does the whole 9 yards and actual testing and such. That way, there is no question.

But, this industry is so dynamic that if someone were to have problems, we would all hear about it pretty quickly. (look at the rabbit problems)

My first unit was a HUGE transformer, something like 35 amps. the next was 20 amps, then the last one was 7 amps, and on 4 steppers of 3.5 amps, I have never encountered a problem.

As for the geckodrives yahoo site...

the last post was in Oct 2005, from some guy named Dave

Mariss's resonse, post # 6893

Re: Power supply selection ??

Square motors deliver more power than a round motor of the same
dimensions. Consequently they draw more from the supply. My anectodal
experience is the supply current should equal the motor's unipolar or
parallel nameplate rating. I will be running tests when time allows
to nail down the multiplier and back it up with actual data.

Mariss

larry1larry
Mon 10 December 2007, 20:49
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
Tue 11 December 2007, 03:47
Larry,
Keep reading, just keep reading.

smreish
Tue 11 December 2007, 04:25
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
Tue 11 December 2007, 13:47
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
Tue 11 December 2007, 16:12
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
Tue 11 December 2007, 21:48
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. ;)

Richards
Fri 28 December 2007, 08:19
I've received several emails over the last few weeks from CNC builders (not those who've built a MechMate - as far as I know) who are getting really slow cut speeds with the PK296A1A-SGxx motors. The main complaint is that the motors start to lose steps at around 2 to 2-1/2 inches per second.

We've got to realize that the PK296 motor is basically a 300 oz*in motor. It was never designed to push a gantry that weighs hundreds of pounds. With proper ramping, it can do much more than would be expected, but it is a small motor. However, to be fair, it is the only practical motor that is affordable. The Oriental Motor AS-alpha series motors cost about five times as much. The PK299 motors with a belt-drive added to them are big and bulky and expensive.

Sometimes we concentrate on the wrong numbers when we select a particular motor. For instance, the PK296A2A-SG7.2 motor, with a 30-tooth spur gear, could move an axis about 14.7 inches per second if we only looked at a pulse rate of 45,000 pulses per second and multiplied the per-step resolution of .000327 by 45,000. What we sometimes ignore is that full torque for that motor is a little less than 6 inches per second. If we're using the PK296A1A-SG7.2 motor, then full torque is about 4 inches per second.

What I'm trying to say is that the emails I'm receiving make me think that too many people are expecting too much from those little motors. I normally run my Shopbot PRT-Alpha, which has 600 oz*in motors with a 3:1 belt-drive, which gives me 1,800 oz*in, at 6-ips when I cut MDF and plywood at a depth of 1/4-inch to 3/8-inch per pass. That's with a 3-hp spindle. If I put those same motors on a MechMate, I'm sure that I could run faster per pass without deflection, but my experience makes me think that I would never achieve the speeds that the math would make me assume were possible.

Expect less than the raw numbers would indicated. With proper ramping, proper cutting methods, and sharp cutters, you will learn to get the most from your machine - including reasonable speeds.

Charlie
Fri 28 December 2007, 13:28
600oz*in X 3.1beltdrive = 1800oz*in.
Then
300oz*in X 7.2 = 2160oz*in ?
I think you said that the max load on the gearbox is 400oz*in, is that true? I couldnt find it anywhere yet. So is that why your not calculating the same?
I cant yet figure out why those people are looseing steps. Isnt the motor on easy street behind reduction gears? Sure I understand looseing speed with reduction but looseing torque too?? Unless your saying it is a bad rampping setting. Meaning not the motors fault. Im confused. Could you help a guy out?
:)

Richards
Fri 28 December 2007, 16:26
Charlie,
The gearbox used with the Oriental Motor's PK296AxA-SGxx motor is rated at very low torque - compared to the mechanical multiplication that you would expect the drive and gearbox to have. I don't know of anyone who has actually broken a gearbox by trying to push too hard; but, I have received many e-mails from users who have had the motor lose steps. From that, I assume that something inside the gearbox might be binding to the point that the gearbox starts to seize - and the motor loses steps.

I had a long telephone conversation with tech support at Oriental Motor, about 1-1/2 years ago, when we discussed this very issue. The end result of that telephone call was that the maximum torqure for the PK296AxA-SG7.2 motor is about 45 lb*in, or about 720 oz*in. The maximum torque for the PK296AxA-SG3.6 motor is about 20 lb*in, or about 320 oz*in.

Those torque ratings, combined with the maximum allowable speed from those gearboxes place limits on how hard and how fast those gearboxes can be driven.

(Oriental Motor publishes torque charts for all of its products, including the PK296AxA-SGxx motors. Just go to the motor's specifications and then click on "More Specificatons" to get the torque charts.)

revved_up
Tue 22 January 2008, 12:33
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
Tue 13 May 2008, 03:58
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
Tue 13 May 2008, 07:03
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
Tue 13 May 2008, 16:40
Andy,

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

Marc Shlaes
Tue 13 May 2008, 16:52
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
Tue 13 May 2008, 19:23
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
Tue 13 May 2008, 19:41
...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
Tue 13 May 2008, 21:11
I think you will need a lot more than 3:1 reduction for a servo motor to work on a MechMate...

Kevin

Marc Shlaes
Tue 13 May 2008, 21:46
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
Tue 13 May 2008, 22:43
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
Tue 13 May 2008, 23:19
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
Wed 14 May 2008, 19:28
Sean,

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

smreish
Wed 14 May 2008, 20:02
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
Thu 15 May 2008, 09:04
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
Thu 15 May 2008, 20:47
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
Fri 16 May 2008, 05:49
Marc, thank you for sharing this valuable link.
Robert

PEU
Fri 22 August 2008, 13:08
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
Sat 23 August 2008, 05:18
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
Sat 23 August 2008, 16:54
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
Sun 24 August 2008, 08:13
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
Sun 24 August 2008, 09:33
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
Tue 26 August 2008, 23:11
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
Tue 26 August 2008, 23:21
5 N.m = 5 Newton.meter = 0.5 kilogram.meter = 500 kilogram.millimeter

which is 20 kilogram at 25mm

sprayhead
Wed 27 August 2008, 00:17
20.41Kg :p

Recalculated using G accel.

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

Thanks
Francis

Gerald D
Wed 27 August 2008, 00:31
Sounds like you are starting to believe us :)

sprayhead
Fri 10 October 2008, 06:58
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
Fri 10 October 2008, 07:39
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
Fri 10 October 2008, 08:30
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
Fri 10 October 2008, 08:41
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
Fri 10 October 2008, 08:50
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
Fri 10 October 2008, 21:52
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
Fri 10 October 2008, 22:00
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
Fri 10 October 2008, 23:12
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)