Re: [CAD_CAM_EDM_DRO] Gecko 2xx "Nema 42 modification"???

I'd be interested if Mariss can answer this one on-list. My experience
with G210's running 1870oz-in NEMA42's has been extremely positive. My
motors are direct coupled (no belts) to the three axes of a BP-clone and
I have not experienced any motor growl. Only problem I had was that I
was losing position accuracy due to a bug in the step rate multiplier
PCB when set to 5 step/microstep i.e. X2. Once the step mult. board was
replaced n/c under warranty, they have performed flawlessly.

You do have to be careful about your acceleration rates - if you try to
accelerate too fast, the stepper will "spit the dummy" (an Aussie
expression - U.S. translation: "spit the pacifier"... anyone who's had a
baby will know what I mean) and just sit there buzzing. I have my big
machine (runs a Flashcut controller) set at 7500 steps per second per
second acceleration. I have set top speed rapid at 2.2 meters per
minute (U.S. translation: 86 IPM) I can go faster (110 IPM) but the
motor has very little torque at such high speed.

Your motors should be fine for the RF31 . I also have a Busy Bee Mill
Drill with ~500oz-in servo motors direct driven and get acceptable
performance although things get a little tight at the ends of the table
travel. This (busy bee) machine still has the original acme leadscrew
threads rather than ball screws (on the big machine) which I do
recommend you consider fitting. The last two issues of HSM discuss this.

Cheers, Peter


Paul R. Hvidston wrote:

> Question for the group:
>
> I Fired off a question to Geckodrives, but users on the list might also have
> had experience with this one and I could use all the input I can get.
>
> I purchased three large steppers on eBay recently (SIGMA 20-4247TD200-F1.3,
> and hopefully I didn't make a real bad purchase) so I could start playing
> around CNC-ing my RF31. The seller said that a previous customer used Geckos
> with a NEMA 42 modification. The explanation I received was:
>
> "These steppers work FLAWLESSLY with gecko stepperdrivers with the nema 42
> modification.
> I had a lot of trouble with intermitent stalling with drivers purchased
> without the nema 42 modification."
>
> "as it was "explained" to me, the nema 42 motor's are designed to run in a
> different RPM / torque range. the Mid band stabilization circuit on
> standard gecko drivers can get "saturated" causing that annoying motor growl
> (phase lock) and subsequent positioning error. since replacing the standard
> gecko driver with the modified drivers all my axis (especially the Y axis
> which carries the beam) run perfectly. the Modified drivers cost the same
> as the standard, but they do have a distinct label engraved on them. The
> guy who developed the gecko driver is the guy I spoke with, and he was very
> helpful"
>
> The published ratings for the motors are:
>
> 200 step
> 540 oz-in @ 50 sps
> 635 oz-in holding
> 22.6 oz-in detent torque
> 5.0 Amp phase current
> 1.29 ohms phase resistance
> 2.2 mH phase inductance
> 17.4 oz-in^2 rotor inertia
> 10 lbs. weight, 30 watts dissipation, 8-wire
>
> Anybody know about this?
>
> Thanks all,
>
> Paul R. Hvidston, N6MGN
> ACKSYS Engineering
> Upland, CA
>
>
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