After few sessions with FSQ85 I have realized that the focusing precision is not adequate for critical focus and best star images over my APS size CCD chip. To get more precision with the existing Robofocus motor, I decided to design an adapter which allows me to use built-in microfocuser reduction. This adapter is affixed to the Robofocus motor shaft and has internal diameter just slightly larger than the microfocuser knob. After slipping the adapter over the knob, I hand tighten 3 nylon screws (to avoid marring the microfocuser knob). The Robofocus motor itself is attached by one large thumbscrew to a bracket mounded between the dovetail and tube rings (on the opposite side of the focuser, finder mounting holes provide an easy way to attach Robofocus to the OTA directly).

So far, this arrangement allows me to obtain 10x more focusing precision, which is readily visible on Focusmax V-curves.

One caveat - motor should be attached in such a way that no force is applied on the microfocuser shaft except the turning force - I.E. it must be coaxial with the motor. Otherwise, a thin axis of the planetary reduction can slightly bend and the microfocuser gear will slip.