Motor focus for Sigma APO 70-300mm lens (Ardufocus, 28BYJ-48)

The motor is a 28BYJ-48, driven by a ULN2003 and Arduino Nano. I use the 5V version of the motor, which can be powered over USB - the mechanical load is minimal.

I use an inverted GT2 belt glued to the focuser of the Sigma lens. I recommend to use a metal pulley on the motor (although a printed one should work). The required travel range is minimal (2-3mm) so I use this rather bulky belt-coupler for the driving belt:

https://www.thingiverse.com/thing:40710

All screws and nuts are M3.

Some finishing touches are missing (like a top-cover for the lens assembly). I will add them in due time.