# stepper motor

a stepper motor is microstepped. when pulsed, the shaft moves by a small step and then returns to its original position, ultimately
producing no revolution at all. this happens for the entire duration of
the pulse. what could the reason be ?
the reply i got is :I presume you are using a small microstep size. The magnetic pole at the full step position you started from pulls the rotor back to that full step position because there is not enough energy in the coils to overcome the strong magnetic attraction at full step positions. Microstepping at small resolutions is not a guarantee that the motor will move a full "microstep" for each pulse issued by the controller. Microstepping mearly provides smooth motion. You may need to issue a few pulses before the rotor actually moves off a pole position. Between the poles, you are more likely to see a single pulse result in rotor movement because the energy from the pole magnets is equalized and the stator currents are stronger. (Sine Cosine relationship is about equal). Use larger microsteps if you want to guarantee rotor position without an encoder. You will need to experiment on your system to find the smallest step that will "hold" position. It may be only in the order of 1/16 or 1/8. To hold position you need a closed loop controller with encoder feedback. Using an encoder will also show you how much the shaft actually moves for 1 microstep. For lower resolutions, the step size will vary depending on how far you are from a pole. Hope this helps. (If you really need to position very precisely and in fine increments, you will need to use a servo or a high mechanical ratio, which will severely cut down on your top speed.)
My response :
Thanks a lot for the detailed reply.. my application is actually microstepping a stepper to 128 micro steps and then converting it into linear motion, in the order of microns. The prob i actually experienced
was : while using a stepper of 0.65 peak current and 5V dc, 1.8 degree step angle, i could feel a jerk when pulsed for one microstep. But when
i went in for a motor of .16 peak current and 5V same 1.8 step angle, there was an oscillation as i mentioned in my earlier query.

stepper to 128 steps or may be not above 16 microsteps ????? As my entire application revolves around this microstepping by a very small step, its of great concern. please help me out.
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You need to fit a gear reduction head to the motor, so that you can do full steps, yet get the fine resolution you need.
For instance with a 100 to 1 gear motor you can get 1/50th of a degree stable micro steps that will hold stable between pulses. that would be 17,000 steps within a 360 degree circle.. great leverage via the gear box for both the drive and resistance to forces that would drive the motor backwards.
Phil Scott

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On 7 Mar 2006 01:20:56 -0800, suchi snipped-for-privacy@yahoo.com wrote: