There are all manner of ways of motorise a telescopes focus.  Being a big of a bodger I have taken the motor and gears out of a scanner and coupled to the LX200 focus knob.  Ideally the focus needs to be easy for the motor to turn and have little backlash.  Difficult to achieve with the standard plastic thrust washers so I swap for a bearing set.  At the scope there is a hand pad with in and out controls and a lead for computer control.