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From: rstevew@armory.com (Richard Steven Walz)
Subject: Re: Stepper driving question that's not in FAQ
Organization: The Armory
Date: Wed, 14 Sep 1994 08:30:24 GMT
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In article <3539fj$mtv@vixen.cso.uiuc.edu>,
Christopher J Burian <cburian@ux4.cso.uiuc.edu> wrote:
>I've got a unipolar stepper that I want to drive with extremely fine steps--
>like a synchro.  What phase differences to which wires do I use to send my
>digitally-generated sine waves to?  Is it possible to use PWM to generate the
>sine waves, if so what minimum frequency? or do I need to go analog/linear?
>The motor will be accelerating, go steady speed, or hold.
>
>Alternatively, where can I get a low-voltage (6-12V) 3-phase AC motor?  
>And with that, same question: can I generate the wave with PWM instead of
>linear circuit?
>
>Thanks,
>Chris
----------------------------------
Dear Chris,
If it's unipolar, I guess you are not going to use the whole sinewave???
If you meant a bipolar two coil job, then you would just use the sinewave
where an equivalent AC square wave would be applied as if it had its
corners waveshaped down to a sine. But if you mean unipolar as you wrote,
then all I would suppose is that you use only a digitally generated
positive half-sine with the negative phase appropriately missing or
sent with polarity reversed to the other bifilar winding input for each.

I can only surmise that this is what you mean, since you are
specifying a digitized sine wave. One wouldn't want to power both
directional coils on the same bifilar coil wrapped anti-pole to each
other! But if you could generate two fully bipolar sine waves, maybe you
would want to use the ends of the bifilar as a 2-phase!?

Then there's always the question that strikes me that sine-SQUARED for
unipolars MIGHT create higher torque, being all positive, but
I'd have to work that out to see!
-Steve Walz   rstevew@armory.com

