Using the Gecko G540 drive a MechMate

[stefanv]

Did you guys follow the thread on cnc zone http://www.cnczone.com/forums/showthread.php?t=51083&page=21 ?
Somehow Mariss managed to design and build a new Gecko in about 2 weeks. 4 drives intergrated in 1 package for less than $300. Sort of small rack-mount, plug in your parallel port, plug in your drives, done! +power supply of course.

I think this would actually drive a Mechmate with 4 PK296A1A-SG7.2 's

The new G540 contains 4 heatsinked G250s (also new) each;
- 3A, 50VDC rated
- 10-microstep resolution
- mid-band resonance compensated
- smoothness adjust trimpot
- dual full-bridge heatsinkable all n-channel TO-251AA power MOSFETs
short-circuit, motor disconnect, over/under voltage, reversed polarity, thermal protect.
4 DB9 motor cable connectors
DB25 parallel port connector ported for Mach3
12 position 5mm removable terminal block misc I/O and power
Power and Fault indicator LEDs
anodized aluminum enclosure
internal socketed fuse
2.4" by 5.7" panel mount cut-out needed, 1" deep (61mm by 145mm by 26mm)
1.5" by 6" 4 mounting screw pattern, up to #6 screw size (38mm by 152mm)

Read the thread. Look at the picture! It makes you feel good about using Gecko's.
All respect to Mariss!

Stefan

[Gerald D]

992

[Richards]

That's a very nice looking unit, but I don't agree with Mariss that the DB-9 connector should be used with high-current stepper motors.

That type of connector was used by Bremson Data Systems in their replacement electronic drawers for Kodak S-type printers. That was always the point of first failure. When they redesigned their electronics to use heavier duty connectors, the problems disappeared.

[Gerald D]

Until I know the modularity of this thing a bit better, I would be nervous about the maintenance aspects. Right now we can burn a BOB costing $80 and replace it easily. We can see LED's on our BOB's for fault finding - this integrated unit looks a little bit too hands-off.

[cobra427mnsi]

But, it is the correct colour!!:D:D

[Gerald D]

. . . suddenly I have new respect for it! :D

[DIY-CDA]

Until I know the modularity of this thing a bit better, I would be nervous about the maintenance aspects. Right now we can burn a BOB costing $80 and replace it easily. We can see LED's on our BOB's for fault finding - this integrated unit looks a little bit too hands-off.

"BOB" sounds nice for being less expensive, sounds like a controller circuit. Where do we find information about this? (Then we can ask more newbie questions!) ;)

DIY-CDA "From newbie to 'dangerous' in 15 seconds flat!"

[Gerald D]

BOB has become an acronym for "break-out board", or more fully the parallel port break-out board. An example of a "BOB" is the PMDX-122 (http://www.mechmate.com/forums/showthread.php?t=346).

In the context of the G540 discussed on this thread, I mean the BOB to be that part which receives the parallel cable and divides it up to the four drives inside. The Gecko folk are calling it the motherboard.

[smreish]

If you haven't visited Gecko in a while. The new website is up and the G540 (http://www.geckodrive.com/product.aspx?c=3&i=14469) is now available. 299.00 USD

If your building a "smallish" mechmate, this might be an avenue for you!

[Gerald D]

Theoretically, it will be perfectly happy on a "full-sized" MechMate with unipolar/half-coil geared motors at 3Amp 40Volt. Could replace the PMDX-122 and 4x G203V's we typically use now. I would give it some time to iron out the potential bugs. The G203V had a buggy period in the beginning, and I suspect the same is possible for the G540. If you live near the Geckodrive company, you might only have a minor inconvenience if it needs to be re-called.

[Richards]

Gecko has a fairly strict requirement for full-performance that I've never noticed before. In the G540 manual it says:

"Choose a motor that has a rated current of 3.5A or less. Choose a motor that has a rated winding inductance of 2.5mH to 3mH if maximum power output (>100W mechanical) is a requirement. Never use a power supply voltage greater than 32 times the square-root of the motor inductance expressed in milli-Henries (mH)."

None of the Oriental Motor stepper motors perfectly match that inductance range, although the PK296-02AA comes pretty close at 3A and 3.5mH; however, that motor is not geared.

(I've posted a question on the geckodrive forum about using the PK296A2A-SGxx motors. )

[Marc Shlaes]

Copied from elsewhere:

. . . what motors did you find that are powerful enough for the MM and still fit the parameters of the G540??? . . . .

[javeria]

. . . . .like Marc, even I am surprised the G540 can pull a mechmate - interested to know more of your electronics.

[bradm]

. . . . the Oriental Motors PK296A2A-SG7.2 ( http://catalog.orientalmotor.com/item/stepping-motors/pk-series-stepping-motors/pk296a2a-sg7-2?&seo=110# )

Wired unipolar, you get 3A at 3VDC 1ohm 3.5mH (I actually wired half phase, but close enough). Coupled with a 24V toroid based power supply, I'm running at about 37 VDC (measured).

The G540 ( http://geckodrive.com/upload/G540%20REV3%20MANUAL.pdf ) wants 2.5 to 3.5mH for "maximum wattage output", but remember that the limiting factor on this motor is the gearbox, anyway, and I'm awfully close to that spec on the half phase wiring.

The other G540 specs are up to 3.5A (almost perfect match), and up to 18-50VDC. I'm comfortably in the middle of the range.

I did spend a bunch of time reading and rereading those specs, because it seemed too good to be true. It's part of why getting that big gantry to dance at almost a foot a second was a big test for me.

[Gerald D]

Marc, Irfan & Brad's posts copied to this thread.

[PEU]

See above, the Oriental Motors PK296A2A-SG7.2 ( http://catalog.orientalmotor.com/item/stepping-motors/pk-series-stepping-motors/pk296a2a-sg7-2?&seo=110# )

Wired unipolar, you get 3A at 3VDC 1ohm 3.5mH (I actually wired half phase, but close enough). Coupled with a 24V toroid based power supply, I'm running at about 37 VDC (measured).

The G540 ( http://geckodrive.com/upload/G540%20REV3%20MANUAL.pdf ) wants 2.5 to 3.5mH for "maximum wattage output", but remember that the limiting factor on this motor is the gearbox, anyway, and I'm awfully close to that spec on the half phase wiring.

The other G540 specs are up to 3.5A (almost perfect match), and up to 18-50VDC. I'm comfortably in the middle of the range.

I did spend a bunch of time reading and rereading those specs, because it seemed too good to be true. It's part of why getting that big gantry to dance at almost a foot a second was a big test for me.


Please correct me if Im wrong, if you wire the motors bipolar but half coil you lose 1.414 times the torque at low speeds compared to bipolar series, you compensate this with the motors reduction head I guess, but my question is, whats the point of using a geared motor if you lose around half the torque on the motor side?

Wouldn't be better to find a motor that can be wired bipolar series and meet the inductance requirements of the 540?

Check the comparative curves here: http://www.probotix.com/stepper_motors/unipolar_bipolar/


Pablo

[Gerald D]

Pablo, when you are cutting wood, you need more torque to cut the wood at high speed. For low speed cutting, you need very little torque.

[vishnu]

Pablo, when you are cutting wood, you need more torque to cut the wood at high speed. For low speed cutting, you need very little torque.


I think Gerald is right just consider the cut quality as the primary objective, it would work fine with MDF and soft material but not with thick plywood and wood. G540 will be good alternative with a small scale machine or plasma cutting machine where you have low resistance. I think we can wait a little bit to know about the relaibility. But if the units are bug free then it would be the best low cost alternative for all machine builders.

Vishnu

[PEU]

But if the units are bug free then it would be the best low cost alternative for all machine builders.

Vishnu

But if cost is not the main decision point, I mean a 540 is about a half of 4x203+BBox not a lot of money for a mechmate machine, you would still go for half coil bipolar for its torque characteristics?

I would love to be able to cut 18mm plywood or 5mm MDF with the same quality.


Pablo

[bradm]

A lot depends on which motors you're going to drive. I think that the G540 provides more torque than you need on the gearboxes of my motors, so larger drivers would just be wasteful.

The entire system is balanced around the capabilities of the gearboxes, which are the "weakest link". One of their strengths, however, is that I need much less holding force from the motors.

If I were using direct drive motors, or belt-reduction, I'd then want to optimize my motor output, possibly.

[domino11]

Until I know the modularity of this thing a bit better, I would be nervous about the maintenance aspects. Right now we can burn a BOB costing $80 and replace it easily. We can see LED's on our BOB's for fault finding - this integrated unit looks a little bit too hands-off.

Gerald,
This post was from Mariss today at CncZone. http://www.cnczone.com/forums/showpost.php?p=510717&postcount=3

The G540 motor outputs are protected against short-circuits (winding to winding, winding to ground, etc.), reversed power supply polarity, over-voltage and under-voltage. The protection is pretty much the same as what's in a G203V except for over-temperature protection.

The G540 contains four individual G250 drives. Each are held in place with a pair of 2-56 socket head screws. Replacing the drives requires only an Allen wrench. The cover unsnaps and the motherboard unplugs to reveal the four drives. There are no wires inside at all. Simply unscrew the bad drive, replace it, plug in the motherboard and snap the cover back on.

Reversed supply polarity or over-voltage (>68VDC) will blow an internal ultra-fast fuse. The fuse is socketed on the motherboard. Unsnap the cover, unplug the motherboard and replace the fuse. Plug the motherboard back in, snap on the cover and it's good to go.

We have yet to see a blown drive but then there aren't that many G540s out there yet, less than 1,000 have shipped to date. I have dealt with a few support calls where the G540 wouldn't come out of fault (red LED) where the cause was traced to a shorted or miswired motor. Clearing that resulted in the G540 running (green LED) with no damage to the drives.

Mariss

[Gerald D]

Heath, I have always been comfortable that the G250 drives are easy to replace, but how easy it to replace the motherboard? If we blow a traditional BOB today, we can replace it with any generic version from a couple of sources. If I blow a G203 today, I could also replace that with a couple of options.

Similar to the laptop vs desktop PC scenario: desktops are repairable with lots of generic options, but I steer clear of laptops :)

[Gerald D]

And if you want a 5th drive for an indexer?

Further, the DB9 connectors for the motors do not appeal to me at all. My experience with DB connectors hasn't always been 100%, and then it has been with much lower currents. Would have to figure out what to do with the screen of the motor cable when it gets to that connector. Can a DB connector accept the thickish wire cores we use for our motors?

[domino11]

Gerald,
I am not saying the G540 is perfect for every applicaton, but just thought Mariss' post might help some in their decision. :) The screen termination is no problem when using metallic backshells. The fifth axis does seem to be a problem. DB9 style connectors can easily fit a 20AWG wire which might be ok for some applications (more expensive connectors with replaceable pins can go up to 18 AWG).

[Richards]

It looks like a two-wire proximity sensor could be directly connected to the G540 without needing to add an auxiliary power supply or other electronic components. You can buy two-wire proximity sensors from AutomationDirect (www.automationdirect.com) for $18.50 each and another $10 or $15 for the cable, depending on the cable length.

I've tested the two-wire sensors with a circuit very similar to the one Mariss uses on the G540's "motherboard", and it works perfectly; however, I still haven't purchased a G540. The DB9 connectors just aren't the kind of connectors that I would like to see on a high current, moderate voltage device.3237

[bradm]

I can confirm that three wire prox sensors from automation direct work just fine on my G540 / mechmate. I love watching the machine auto zero.

I hadn't realized that two wire prox existed. However, I still need my 12v aux supply to drive the spindle (er, router) SSR, so it wasn't much trouble.

Note that Z-Zeroing works as well, simply by grounding the appropriate input pin on the G540 using an aluminum plate and the bit.

[sailfl]

Brad,

I agree. There is comfort in watching the machine find 0,0. It is well behaved. It knows how to go home. If it only could remember where home is when you wake it up......

[bradm]

Let me stir this pot a little. I bought a $99 harbor freight lathe with the intention of eventually ripping the motor out, grafting on a stepper motor I've got laying around, and slapping the whole thing onto one of the ends of my MM. It'll fit nicely along one of the short ends of my spoilboard with a bit of bracket fabrication, and allow me to work pieces up to about 38" on my 50" wide table capacity.

As I envision it, when I use the indexer, I'll just "park" the gantry at the end of the table above the lathe / indexer, disconnect one of the X motors and patch in the indexer motor (*). Load a new config into EMC that uses the one X motor for indexing, and the Y and Z motors, and I'm ready to go.

As it turns out, those much maligned DB-9s should be quite convenient for this. I'll report back if they ever start giving me trouble.

Can somebody explain to me why I need more than 3 drives (and certainly not 5) for an indexer on a 3 axis table with a non-tiltable cutting head? Why would I want to move the X once it's in position?

(*) I'm thinking of fabricating "shorting" plugs for the two gantry motors that short the motor windings together to make them really resistant to moving when in this configuration. If it turns out to be insufficient, there's always clamps!

[Richards]

Brad,

If you want to switch motors and still use the same stepper driver, why not just put in a multi-position switch? Plugging and unplugging a DB-9 connector will expand the already-fragile contacts, but shutting off the power, and then turning the switch's handle would do the job without the worry of creating loose contacts.

[Gerald D]

Can somebody explain to me why I need more than 3 drives (and certainly not 5) for an indexer on a 3 axis table with a non-tiltable cutting head? Why would I want to move the X once it's in position?

Sometimes you want to cut with the tip of an end mill (for sharp corners), other times cut with the side of the end mill (smoother cut).

[Nikonauts]

I can confirm that three wire prox sensors from automation direct work just fine on my G540 / mechmate. I love watching the machine auto zero.

I hadn't realized that two wire prox existed. However, I still need my 12v aux supply to drive the spindle (er, router) SSR, so it wasn't much trouble.

Note that Z-Zeroing works as well, simply by grounding the appropriate input pin on the G540 using an aluminum plate and the bit.

Nice to hear someone got G540 working with MechMate. :D
Now that's one less to worry about for me.

[Richards]

My G540 arrived yesterday and I had time today to start running it through its paces. I started out with some PK268-02AA motors (because I have a drawer full of them and I wouldn't be too upset if I fried one). However, I was pleasantly surprised. The G540 handled the 2A motors at 48V without any problems. When I get time, I'll hook up some PK296B2A-SG3.6 motors and see what happens.

I'm still concerned with the DB-9 motor connectors. In a perfect world, they would handle the current, but . . . It looks to me, that if you screwed the DB-9 connectors firmly in place and didn't make habit of removing the connectors, that the G540 would be a viable alternative to the G203v stepper drivers.

The I/O on the G540 is limited with two outputs, four inputs (plus the disable input), and a VFD speed control built in, but that would be enough for most CNC routers. The unit is well built. I pulled the cover off to take a look inside and saw that Mariss had done a great job - as usual.

After more testing, I'll be able to form a more accurate opinion, but on first look, the G540 is impressive. It certainly is simple to hook-up and because of its limitations, the control box could be much smaller than a box built for the G20x stepper drivers.

[Gerald D]

That DB9 connector also means that some soldering needs to be done. That is another potential can of worms, because it is not the easiest soldering for a beginner. It needs some practice and practicing on those connectors can get expensive. Maybe get some old/spare connectors to practice on first. The tip of the soldering iron should be shaped nearer to a blunt pencil, rather than a screwdriver.

The posts relating to the soldering of the connectors were moved to their own thread:
http://www.mechmate.com/forums/showthread.php?t=1486 (http://www.mechmate.com/forums/showthread.php?t=1486)

[PEU]

BTW, there is a special for the 540 running at the cnczone, here are the details: http://www.cnczone.com/forums/showthread.php?p=560304#post560304

[Richards]

The G540 drives four PK296B2A-SG3.6 motors very well.

I've got the test bench configured with a 35VDC power supply, four PK296B2A-SG3.6 motors, the G540 and cables with 3.2K resistors. The 1K + 2.2K resistor combination is the closest match I had on hand to 3K. The G540's current limit resistors require 1K per amp of motor current. The PK296B2A-SG3.6 steppers are rated at 3A, but the PK296-F4.5 is rated at 4.5A. All other electrical specs for those two motors are identical, so I'm assuming that Oriental Motor has de-rated the PK296B2A-SGxx motors because of the gearbox. In any case, I thought that driving the steppers as close as I could to the G540's 3.5A current limit would be a good exercise.

For those who are wondering what the difference is between the PK296B2A-SGxx motor and the PK296A2A-SGxx motor, the PK296B2A-SGxx motor is the PK296A2A-SGxx motor with a dual-ended shaft.

After an hour of running all four motors at speeds ranging from 50 RPM to 1300 RPM (motor shaft speed, the gear box's output shaft is turning 3.6X slower), the motors are at 90F and the G540 is 100F. The G540 is just sitting on a wooden bench without heat-sinking of any kind.

Wiring time, compared to connecting the PMDX-122 and four G20x stepper drives is minimal. It took just over 1/2-hour to build four new cables this morning, including the time it took to install shrink-tubing on the cables and the time it took to install ferrules on each wire.

It looks to me like the G540 would be a good stepper driver for a MINIMAL system (assuming that the DB-9 connectors continue to carry the required Amps).

Edited: My G540 is one of the "custom" units that Pablo referred to. I has a non-standard nut on the DB-9 female connectors to suit a particular customer's special needs. If I use this G540 in production, I will have to use a non-standard length screw and some spacers between the DB-9 female and DB-9 male connectors.

[inventall]

Hi all,
This my first post. Found out about this site last Monday and can’t stop reading!! Must Build MechMate!! :D I have done nothing all week, because I have been up every night till 5am!

Thinking of using the g540 on my MM for 3 reasons
1) It’s almost $400 cheaper (vs. 4-203v's and bob)
2) I am in CA with Gecko (so shipping is cheap if it has to be sent back a couple of times)
3) It’s almost $400 cheaper, I could buy 2 and still be ahead

I am planning on building MM with the PK299A2A7.2 as per recommended, anyone foresee any other reason for not using the g540? as yet, other than the DB9 connectors.

Also had a thought on the DB9 could you buy 2-DB9 patch cords cut them in half Splice in shielded cables and resistors inside you’re your control box? Much easier to splice than solder ends, I think.
Thanks Gerald and all for this grate site and all your hard work. I don’t think I can sleep till I finish this thing

The posts relating to the soldering of the connectors were moved to their own thread:
http://www.mechmate.com/forums/showthread.php?t=1486 (http://www.mechmate.com/forums/showthread.php?t=1486)

[inventall]

Gerald,
Thanks for the pics I understand what a DB9 connector is and as far as soldering goes it is a easy job, but will not be as durable as the factory molded connectors. Just not sure about the gauge of the simple DB9 patch cord. I can’t believe I must have had 10 of them around and threw them all out. Anyway my g540 will be here tomorrow.

[danmauch]

I have sold over 30 of the G540's systems. I too was worried about the DB9 connectors. I talked with Mariss about that . He stated that the db9 were easily rated for the currrent that the G540's put out. In my own tests I have not had a problem with the connectors. I have run into problems with some chines 10ft cables getting hot. With 22 AWG cable there isn't a problem.
I have a crimping tool so I buy the db9 crimp type pins for uses with the connectors. The regular low cost crimping tools that they sell for that job doesn't do a good job. I have a expensive tool that does a great job. I bought it on ebay for a fraction of the cost.

Dan Mauch

Advertising section of this post moved here (http://www.mechmate.com/forums/showthread.php?t=1959).

[MAC2009]

Mike,
You mentioned early in this thread The G540 can be used with the two wire prox switches. Can they be used in series?

I have done some looking around but have not come across a circuit diagram
for the G540 any body have a line on one.

MAC

[smreish]

http://www.geckodrive.com/images/fck_uploads/G540%20REV3%20MANUAL.pdf

[MAC2009]

Thank you for your reply. I do have the manual. It shows limit switches each
with it's own Pin. Can they be wired in series to one pin leaving more in put free?

The diagram I was wondering about, for the BOB in side.


Thanks
MAC

[smreish]

Mac,
The G540 inputs are not form c (dry contacts) thus, I would suggest you need to add a simple relay to the prox sensor and wire those in series.

I have a detailed explanation of this in the following threads:



http://www.mechmate.com/forums/showthread.php?t=584&highlight=prox&page=4

Certain Proximity sensors will allow you to wire in series, but I found that a certain small level of BAD EMF is picked up by the proximity sensor and the addition of relay's on all my machines elimitated/isolated that.

The relays I used are the DIN mounted and located in this thread

http://www.mechmate.com/forums/showthread.php?t=584&highlight=prox&page=10

[MAC2009]

I feel this is the best way also, question was over an early post.

I think I m on the right track using relay in series



MAC