video (6 megs)To start the demo, press the button once. The motors will then begin their "dance" which lasts just under two minutes.
Stepping motors have two sets of electromagnets (the field) which are made to "flip" their magnetic polarity from North to South and South to North in a particular sequence. The armature (the part that turns) has permanent-magnetic teeth which are attracted and repelled by the changing of the field. If the changing of field is sequenced properly, the armature will "step" a specific amount for each change in field polarity. In many motors, including the ones shown here, one step is 1.8 degrees. Stepping motors have more wires than other kinds of motors because each field magnet is supplied by two, or three wires, depending on the style. These motors have six leads.
The stepping action comes from controlling current through the field as a series of pulses. Each of the two motors is run by a PIC 16F688 microcontroller. The PIC chip turns on the field windings by switching transistors on and off. Each transistor has an LED for you to see the pattern.
The motors in this display perform better than most hobbiest-built motor drivers because this setup ramps the motor speed up and down. Also, this motor driver uses resistors to limit the large current stepping motors draw at low speed. Using the resistors allow a higher top speed.
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