Re: [CAD_CAM_EDM_DRO] Need help and motors, and quickly...

On Tuesday 14 October 2003 02:01 am, Jon Elson spake:

> I don't understand the problem. What is the voltage/current rating on
> these motors? (If you don't have that, what is the winding resistance?)

From the data sheet -
Toque @ 50 sps = 540oz/in
Holding torque = 635oz/in
Detent torque = 22.6oz/in
Phase current = Unipolar = 3.5;Bipolar = 5.0
Phase resistance = 1.29 Ohms
Phase inductance = 3.3 Ohms
Rotor inertia = 17.4oz/in
Power disapation = 30 Watts
These are eight wire motors.

> What current do you have the Gecko drives set to?

I've tried both 3.5 and 5.0 Amps.

> Making a few guesses here, I think you must have high inductance
> motors, which were probably really designed as Slo-Syn motors to
> be run at 50 or 60 Hz with a phase shift capacitor. In other words,
> they really are NOT stepper motors, they are low-speed synchronous
> AC motors. Some early CNC mills were set up with these motors,
> and they did not perform too well, as you see.

...hence Mariss's explanation that these are possibly
the worst motors I could have bought for my situation...

> What you want is a size 34 motor, I think, with good torque specs.
> Also, you want to be sure the voltage rating is low, as this is somewhat
> an indication of winding inductance. There are probably size 42 motors
> around that will work, too, but you need to make sure the inductance is
> low. I have some 200 Oz-In size 34 motors on my mini-mill, and I get
> 1400 RPM on a Gecko 201A drive, using a 48 V DC supply.

Yes, this is what I need to know... what people have found to work well...

> I was
> very impressed with what the Gecko 201 could make these motors do.
> (By the way, they are 20+ years old, and didn't perform anywhere near
> that well on the original L-R driver in the printer they came in.)
> When I say low voltage, you want a size 34 motor with a winding
> voltage at rated current under about 2.0 V, if possible.

Ah. Okay.
Mariss recommended a PK268-03A for me,
so I was looking for something I could fly in...

> If you go for
> a size 42 motor, you may have to settle for a voltage somewhat higher.
> Even going to motors rated at 4.5 V, for instance, will cause noticable
> reduction in speed.

No, no... I've also been edjumakated on
why I really don't want a bigger motor now...

> How are you driving the leadscrews? With a toothed belt? That is probably
> the best way.

Yes.

Now - anyone got any of yours or Mariss's
recommended motors and is able to overnight them to me?

Thanks,

Weyland