It is not clear to me what happens inside the stepper motor when it is manually and rapidly rotated in clockwise/counterclockwise, overcoming the torque of the motor.
As I understand, fly-back diodes are protecting the driver when the windings are not energized and the stepper is acting like a generator. So it seems to me that no additional protection is necessary if I manually rotate the shaft of the motor when it is fully powered. But I'm not 100% sure on this...
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I ordered this little bipolar NEMA 11 stepper, driven from this driver. The shaft of the stepper is linked to the axis of a knob with a 5-to-1 ratio spur gear. No half-stepping, no micro-stepping.
I plan to use an 8-diodes-array to protect the driver board: