Try this ascom project:
https://sourceforge.net/projects/ard...?source=navbar
I did this about 2 years ago and it works brilliantly. Bought a 400 steps/cycle stepper motor from a local supplier and it's sufficient to get critical focus on my scope with half stepping. Having said that, I would suggest getting a geared motor for the extra torque and resolution. They are a little more expensive but worth it if you have a fast scope and/or small pixels to achieve critical focus.
You'll have to make a bracket for your focuser. I just made mine out of some aluminium L brackets and bolts from the local alu supplier. Also, you'll have to work out a way to attach the stepper motor to the craford. I used a 5mm axle connector to directly drive the craford mechanism from the motor - it seems to be the most secure and backlash free option.