Re: Gecko 2xx "Nema 42 modification"???

since you are direct coupling your motors to the lead screw, are you
using a helicoil type coupling or something a little more beefy...?

> 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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