Re: Stepper Motor Basics

On Sat, 12 Apr 2008 19:02:05 -0700 (PDT), Bill Bowden
<wrongaddress@xxxxxxx> wrote:

I have a stepper motor from Airpax, modle C82710 that has 6 wires
connected to 2 windings with a center tap. It's rated at 12 volts, 36
ohms from center tap to the end of the winding, and 7.5 degrees per
step.

I'm not too familiar with stepper motors, but understand the shaft can
be moved in either direction one step at a time. I read some articles
on Google but couldn't find any that showed the necessary signals and
timing to rotate the motor continously in one direction.

I played around with it, and found I could move the motor shaft one
step at a time by just alternating the connection to either side of
one of the windings with the center tap common. But it only goes so
far and stops, and the second winding was not being used.

So, the question is, what is a proper polarity and timing sequence on
the various connections to continuously move the motor in the same
direction?

Sounds like you have a uni-polar stepper there. The simplest way to
drive it is just to use four transistors. Apply your 12 V to the
common and setup the transistors to turn on to provide a ground path
for the desired winding. Sequence them in the order A, B, ~A, ~B.

Once you have that part working, you can look into half-stepping (two
phases on at once) and beefier drive circuits (choppers) that control
the current through the windings for higher torque and speed.

Wikipedia has a pretty good article with additional links.
http://en.wikipedia.org/wiki/Stepper_motor

--
Rich Webb Norfolk, VA
.

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