[Robotgroup] Stepper Motor Help..?

[Vern Graner]

Ok, so by now many (if not all) of you should be familiar with The
RoboSpinArt machine :)

http://www.robospinart.com

As you may know, a key component is a rotating platter what holds a
paper card. In the prototype machine, we used a DC motor and found that,
though it spins quite fast enough, it is hard to control the speed
precisely. I would prefer to have fine control of it in order to
facilitate printing on the rotating paper using one of the Parallax ink
jet printer kits:

http://www.parallax.com/detail.asp?product_id=27949

So, I read up on a bit on stepper motors and controllers, and bought
this controller for testing:

http://www.parallax.com/detail.asp?product_id=27938

Based on the specs, in THEORY, we should be able to get a maximum of
1500 RPM out of this controller. Here's how we came to this conclusion
(in case there's something we missed):

-The stepper motor is 1.8 degrees per step

-1.8 degrees per step divided by 360 degrees per
  revolution = 200 steps per revolution

-The controller max is 5000 steps per second

-5000 steps per second divided by 200 steps
  per revolution = 25 revolutions per second

-25 revolutions per second * 60 seconds = 1500 RPM

Ok, so 1500 RPM is acceptable as the DC motor we were using was spinning
at ~1800 RPM. So, Paul built up a test jig with a BSII and a surplus
stepper motor:

http://www.notepad.org/step/

With the demo code loaded, we tried to ramp up the speed to 1500 RPM...
And then the trouble begins..  :)

The stepper motor spins up to about (visual observation guess) ~130 RPM
and then stops spinning and just "buzzes".  :(  Some googling revealed
that in order to keep the stator from "slipping", you can juice up the
voltage. So I replaced the 12v 1000ma wall wart with a bench top supply
that could deliver 35v at 3 amps. On testing again, I think it got up to
about 300 rpm, but still no where *near* the theoretical maximum of 1500
RPM.  :(

So, thinking maybe I had a bad stepper I tried a couple of other motors
I had laying about. All performed substantially the same.  :(

So, anyone with some stepper motor experience have any idea as to what I
can do to get a stepper to spin at 1500 RPM with this little controller?

ADVthanksANCE!  :)

Vern

-- 
Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
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