Hi Rob , have you had a look at Mel Bartels web pages .
If you don't know who he is , he is sort of the Grand Master of telscope making and computer controll scopes namely DOBs in the amature world.
His site and links are full of info for the dob converter to get ideas.
if it's not there it's not worth it.
There is also a forum for the builder as well.
http://www.bbastrodesigns.com/cot/cot.html
http://groups.yahoo.com/group/scope-drive/
You will notice that he has controllers in various stages of construction for purchase as well that are for stepper and the new servo systems. The later I have just recieved and included a quick pic of.
I am in the middle of building a large EQ friction roller fork mount.
The systems will work on vertually any mount especially DOBs and conversion is not that dificult.
There is an explanation on the difference between stepper and dc servo systems and what each requires to function and track properly .
Mark