Manually rotating a powered stepper?

Thread Starter


Joined Jan 27, 2016
Hi to all,

I've just ordered a Nema 11 bipolar Stepper motor and a Big Easy Driver from Sparkfun to drive it.
My plan is to use this very small stepper (yes, I have space problems) to rotate a knob by using a spur-gear with around a 5-to-1 ratio.

My intention is to allow the "user" to manually rotate the knob (dia = 35mm) when the windings are not energized.
Since even a rapid rotation of just 90° of the knob will cause around 1.25 fast turns of the stepper shaft, then it is obvious to me that I need some protection when the stepper is acting as a generator.

But, here comes the additional requirement: I would also like to allow the user to overcome the stepper torque and rotate the knob in "emergency" situations, even if the windings are energized.

It is not clear to me what is the behavior of the stepper is such situation. It is still acting as a generator when rapidly rotated? I think it is not.
More important: will the fly-back diodes still protect my driver circuit?

For now I plan to use an array of Schottky-diodes like in the image below. But I'm not sure if this is enough...:(