Re: [APML] AC Synchronous Stepper Motor

[Tim Cole <pegmind@igs.net>]

At 02-06-00 21:51, you wrote:
>
>>The motor sounds like a reversable 110v synchronous motor and not
>>a stepper. Steppers typically have more leads and would run from
>>DC stepping drivers. Not sure what you are driving it with but if it
>>is ac, the motor may need a starter capacitor to function properly.
>
>    The motor is clearly labeled, Slo-Syn Motor, Synchronous/Stepping, 120 
>AC .1 amps, 72 RPM @60 Hertz.  When one turns the shaft, it has that 
>stuttering feel of a DC stepping motor.

My memory is fuzzy on this area. The last time I took an engineering course
on AC motors was --- well, a long time ago. However, I believe
"synchronous/stepping" is a bit of a misnomer. For a given frequency, the
speed of an AC motor is dependent on the number of poles. (More poles ->
less speed).  Beyond a certain number of poles, the motor will start
"cogging" (the "stuttering" action you describe).

My old textbooks never indicated that cogging was a desireable thing, but
it seems to me you could use that behavior for rotor motion control. For
instance, I think it would be easier to stop a cogging motor at a specified
shaft position than a freely rotating synchronous motor.

If my supposition is correct, the three wires would be for two phases and a
common. One way to create a second phase from non-industrial 1-phase power
would be to include a capacitor (and an inductor, but perhaps there's
enough inductance in wires and windings). The capacitor would *not* do the
same function as the starting capacitor of a small 1-phase induction motor.


Clear Skies!
Tim Cole, RASC Ottawa Center
pegmind@igs.net

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