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

Weyland wrote:

>On Monday 13 October 2003 06:54 pm, Robert Campbell spake:
>
>
>
>>Weyland,
>>
>>What stepper motors are you currently using? Size 23 or 34 and what is the
>>oz/in and voltage and current listed on the motors. What voltage is your
>>power supply?
>>
>>Bob Campbell
>>
>>
>
>Hey Bob,
>
>These are size 42's; 635oz/in holding torque, 540oz/in @ 50steps/sec.
>Power supply voltage is variable up to 81.6VDC,
>via a Variac controlling a 1KVA 2:1 transformer.
>
>

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

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.

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. 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. 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.

How are you driving the leadscrews? With a toothed belt? That is probably
the best way. Unless you use a coupling with some flex, direct coaxial
shaft drive can cause binding due to the unavoidable shaft misalignment.

Jon