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I am experimenting with using a stepper motor for a robotics project. I'd like to use microstepping to give a better resolution and smoother movement, but I have noticed that the finer the microsteps, the lower the torque from the motor. Why is this?

For reference I'm using the Allegro Micro A4988 motor driver, and a bipolar stepper motor.

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  • $\begingroup$ Do you have access to an oscilloscope? If so, check the step input of the A4988 for jitter (due for example to interrupt latency). Are you making your comparisons at the same motor speed (higher frequency on step input for microstepping)? $\endgroup$ – Tut May 27 '14 at 12:00
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    $\begingroup$ With full step, both phases are always on resulting in more torque for the same current setting. I posted the above comment (about jitter) because jitter in the step period can have a similar effect as reduced torque and can have a greater effect with microstepping if a higher frequency step pulse is used in order to achieve the same rotation rate. $\endgroup$ – Tut May 27 '14 at 13:09
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The reason for this is that when attempting to hold a position between positions, you are not only fighting the torque from your load but that generated by the magnets in your stepper more info here

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  • $\begingroup$ This is a comprehensive must read report for any stepper user. Usually only some of the factors are mentioned but this covers all the bases. Most important in case is the fact that the detent and holding torques may be opposing or adding your desired driving torque. So a tiny change in microstepping coil currents may not even move the rotor, in effect no useful torque generated. $\endgroup$ – KalleMP Mar 14 '15 at 6:30

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