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

Peter,

Interesting you're running 1870oz-in NEMA42's with stock(?) 210's. Maybe you
just got lucky and the direct connection (no belts) damps any instability
for you. I've got the original CNC conversion articles in HSM's "Projects
Seven", and am eagerly reading the new series in HSM.

In response to my query to Geckodrives, I got a couple of speedy (but
non-technical) replies:

---
Dear Mr. Hvidston,

The G210 drive can be modified at the factory to run a size 42 motor. After
the modification, it would be unsuitable for small size 23 steppers.

Dear Mr. Hvidston,

The size 42 modification is not considered reversible, unless you have
surface mount technology available.

To purchase the G210's with this modification, you need only specify "42
modification". There is no charge.
---

The Gecko folks seem very responsive, and the products sound great. I'll be
ordering some 210's to run these motors. I was hoping to get a little more
technical info out of them on the mod since I might want to un-modify them
down the road, and I do have SMT rework capability.

I got the big motors to use in various test-beds. First use may be on an
RF-31 "play-pen", then use them on a 3-axis wood carver using a 3HP router.
Ultimately, the RF-31 will use servos and ball-screws, but for now it's
play-time.

Thanks for the input.

Paul R. Hvidston, N6MGN
ACKSYS Engineering
Upland, CA

----- Original Message -----
From: "Peter" <prenolds@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, February 27, 2002 8:31 AM
Subject: 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