Re: Gecko Drives

>Is anyone on the list using the Gecko Stepper drive on a machine yet?
>Comments?

Bill,

Yes, I have retrofitted a MaxNC 10 mill. Here is some information I
send to someone else:

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I saw your message about trying some goldmine 400 count servos and a
Sherline. Here is a conversion (temporary one) I did on my MaxNC.

First off, the top speed went from ~15ipm to >120ipm! Matter of fact,
it goes so fast that it heats (melts?) the BS&A antibacklash nuts I
retrofitted (the active cam ones).

Anyways, the screw couplers, motor "mounts" (nema 23 to SKC servo)
were all self fabricated quickly to try out the servo units (I was
mainly interested in the performace of the servo drivers, not the
goldmine motors. PS was an Alton 28V 25amp supply, front end was
DeskNC for dos (and I tried CNC-Pro). Both worked ok, but on the
MaxNC 1/20" pitch screw and the 400 count encoders, each inch was
32,000 steps, so to go 120ipm, the computer had to generate 64,000
pps. The computer ended up being the limiting factor (AMD K6-266).

I tested them with the default (as suggested on the servo sheet that
came with the motors). At this setting, they ran "warm" but not too
hot. When I tried uping the gain, they got very hot (mainly the X
axis). Since I don't have an O-scope and could not tell any performance
difference, I just set them back to the defaults.

As for running them, I did a couple of sample files, mainly some
engraving in engraver's plastic (lettering with a V-bit and then a
1/16" endmill to cut out). These were all very quick files (~5 to 10
minutes each peice), so no long term testing was done. I did do some
"dry runs" of some Millwizard type files (3D contouring) and the
motion was very smooth and the motors just got warm, but the biggest
problem was the antibacklash nuts. They (well, the X axis, as that one
did most of the moving) over heated and would melt?/seize up causing
the driver to go into "fault" mode.

Now, I did not do any official "testing" of the torque of these motors,
but a simple grab the spindle nut and hold the end of the table and
try to "prevent" the table from moving proved unsuccessful. It was
stronger than my hand could hold. Like I said, very scientific. :)
I figured that if I could not make it stop, there was plenty of torque
to spare. Plus the BS&A nuts are only rated to 25lbs of force.

Lastly, unfortunately, this is not going to be permanent. I am planning
on using these drives for a CNC Router. I found some really nice
Hitachi DC servos with MAGNETIC encoders (no contact and no worry of
dust contamination).

I have the DXF files of the motor mounts, but they may not work for
a Sherline. I have 4 pictures of the MaxNC and the Gecko drives with
the Goldmine servos. If there is enough interest, I will eithe email
them directly or upload them to CAD_CAM_DRO file area.

Bruce