Using the Gecko G540 drive a MechMate
 

Did you guys follow the thread on cnc zone http://www.cnczone.com/forums/showth...=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

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.

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.

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

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

What is "BOB" unit? Where may I learn?
 

"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!"

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.

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.

Gecko 540 now available
 

If you haven't visited Gecko in a while. The new website is up and the G540 is now available. 299.00 USD

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

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.

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. )

Copied from elsewhere:

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

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

. . . . the Oriental Motors PK296A2A-SG7.2 ( http://catalog.orientalmotor.com/ite...g7-2?&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.

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

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_moto...polar_bipolar/


Pablo

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

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

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.

Gerald,
This post was from Mariss today at CncZone. http://www.cnczone.com/forums/showpo...17&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

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 :)

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?

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).

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.Attachment 3237

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.

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......

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!

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.

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).