GeckoDrive 201 and Bridgeport Stepper Motors -was- Re: [CAD_CAM_EDM_DRO] Hello!

Tim Goldstein wrote:
<snipped>
I would not be the only one on the list that has bought a 4 ton machine
on e-bay!
<snipped>

Howdy All! This is one of the few places where this does not make you
the "Lone Ranger". <G> But alas, mine only weighed 3000+ pounds, a mere
1 1/2 tons. Hard to imagine this is a "lightweight" mill. Now the
obligatory [CAD_CAM_EDM_DRO] content. I got some GeckoDrives #201 to
drive the 3 stack NEMA 42 motors (known as Big Mutha' or BM) on my
Bridgeport Series I CNC, and have some observations after running a
drive on my workbench. For those of you considering these modules, here
are a few things I discovered. The test routine is a simple basic
program which outputs step and direction to the parallel port (PP) on a
66MHz 486.

1. Mariss is GREAT to deal with. After someone in the Post Office
purloined the the 1st set of GeckoDrives he sent, he very graciously
sent a second set at no charge. I may be biased as a result, but that's
life.

1a. He also really knows some stuff! And he told me before I bought the
drives about the ins and outs of these units. So any problems or
difficulties arise from my own ignorance or silliness.

2. The modules are very easy to setup and run. (My electronics
background is fairly limited, basic AC/DC, soldering etc.) 2 wires for
the power, 3 wires for the step/dir/+5, 4 wires for the stepper coils.
He has 2 terminals so you can set current limiting, but I didn't bother
with that. Physically they about 2 1/2" square and 3/4" high. The screw
terminals won't allow any wire larger than 14AWG, which is no problem
for the step/dir but might be a concern when running the drive at 80vdc
and 7 amps. (I always over-engineer everything I build, so may just be
my mania for "more".)

3. These are micro-stepping drives. Period. They take 2000 step pulses
from the PP to get 1 rev from a 200 step motor. This is not a problem if
you can work with that. I don't know if CNC Pro or the other front-ends
will allow me to scale the output to take care of this.

3a. The printed instructions point out that the module supply is
24-80vdc and the supply should be in the range of 4 to 10 times the
nominal stepper voltage to get good micro-stepping. The BMs operate at a
nominal 56 volts which doesn't leave much headroom for the microstepping
to happen. I ran the drive at 74vdc and found the performance on this
Big Mutha' less than stellar. The actual test showed that the stepper
was energized and would vaguely run. It didn't seem to have any real
"sense of commitment to the effort".

4. I have run several smaller steppers on this drive and have been
amazed with how well it worked. The best one was a Matshusita NEMA 34
5.5v 4.4ohm/coil running off 24vdc. Good solid feel, nice micro step,
some "hunting" when it settled on one spot. I expect the hunting will be
eliminated when there is a mechanical load on the stepper.

Next Steps

1. Swap both motor and drive module to determine where the problem
really lays. I will post more later on what I find.

2. I'm going to look at the output pulses of one of my Geckos and will
consider using the output to drive some 200v 10amp MOSFETs.

3. If that isn't the answer, I'll use them to CAM my lathe. <G>

Summary

On balance, I found that these GeckoDrive 201 units are solid and work
very well when you can get the required headroom between the motor
voltage and the drive voltage. As I said at the beginning, any mistakes
or errors I have made on this project are of my own doing and cannot be
laid at anybody else's door.

Rick Dulas





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