Location: Outside U.S.
Country: South Africa
Date: March 2009
You can also see that the next logical step after "step 4" is to go
back to the current flow shown in step 1. When this happens, the motor
once again rotates ahead one step (it does NOT rotate backwards 3
steps!). If you continue to go through the 1-4 step sequence again and
again, the motor will continue to rotate in steps, until you stop. The
big advantage of a stepper motor, is that you can rotate it an EXACT
number of rotations, simply by sending it the correct number of step
sequences. So, for example, if you had a motor that rotates in 36°
increments, and you wanted it to turn exactly 1.6 revolutions (16
steps), you simply send 16 of the above step sequences (that is,
repeat steps 1 to 4, 4 times), then stop. The motor will then rotate
one full revolution, then another 216° (0.6 of a revolution), then it
will stop in this exact position.
The simplest stepper motors drive the hands in wrist watches. These
motors have only one coil and each step is 180°, so the motor rotates
180° almost instantly, then stops for one second, then rotates another
180°, and so on. The motor is connected via gears to drive the hands.
More complex stepper motors have as many as 5 coils and very fine
steps (1000 or more per revolution).
Click here to return to the Engineering Archives
Update: June 2012