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I am thinking to use Arduino to control a DC motor and apply a small torque to move the mirrors of my interferometer experiment. I have the components from the Arduino Starter Kit K000007, just to understand how it works because I am approaching it just now.

The mirror mount has a knob with a 2mm Hex hole and each revolution corresponds to a displacement of 50 microns: I would need a speed around 1/50 revolution/second, or even less. Is it possible to move the motor that slow? Moreover, I should use a coupler to interface the motor with the knob, basically some joint to connect the shaft to a 2mm Hex bar or something: could you suggest a way to do so?

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DC motors are made for spinning. Trying to spin it in sub full revolution steps is not really possible. But you can use a geared DC motor, where the rotor after the gear is slow enough for your purpose. Also this can give you enough torque for moving the knob (since small DC motors are often rather weak by their own). You can find geared DC motors with many different values (torque, voltage, speed, gear ratio, size...) at the typical online sellers. The small ones are rather cheap, so you might just buy some and test out, whats fitting for you. Otherwise you would need to set exact requirements for torque and speed (and maybe other parameters) and then search for a fitting one.

Also keep in mind, that you need something like a driver circuit for the motor. Since you will want to drive it in both directions, a H-bridge is needed. You can build those yourself with transistors, or buy a small chip, which incorporates the complete H-bridge (make sure to use one with MOSFETs in it, since they are more efficient). Also don't forget the flyback diode to avoid killing the electronics with the induction voltage from the motor.

I should use a coupler to interface the motor with the knob, basically some joint to connect the shaft to a 2mm Hex bar or something: could you suggest a way to do so?

Yes, you need some kind of coupler. But we cannot really suggest something here. It depends totally on your exact setup. This mechanical part will be something, that you have to design. There are different kinds of couplers available online, but I don't know, if they are good for your purpose.

Also maybe you should make sure to make the coupler flexible on the other axes than the rotation axis. That way the motor will not stall when a small disalignment happens, and the vibrations from the motor might not get transmitted to your mirror as much. I know this principle from my 3D printer, which uses a coupler like this one:

enter image description here

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  • Thank you! As I need a ratio of severlal thousands to one, I have to use a gearbox for sure. For the H bridge yes, I saw it in one of the projects contained in the starter kit, thus I should be covered for that.Regarding the coupler, I think that I could ask the university workshop to manufacture one similar to the one you suggested very easily.
    – Gianluca
    Commented Mar 17, 2021 at 8:17

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