wow you guys are hardcore. if i can get you guys the measurement around the cameras focus ring and some measurements of the base of the camera and all do you think you could CAD something like this? i have a few more facts to help you guys out.
the saddle bracket clamps on to two 15mm diameter rods that stick out of an aluminum base that mounts onto the camera. these parts would also need to be built to mount the follow focus system, however they are relatively simple to design.
its ok if the black knob turns infinitely in either direction, there is no stopper on the cameras focus ring. the ring is connected to a sensor which controls the cameras lenses. basically, the focus ring on the camera can be spun in either direction without causing any harm to the camera or lenses. the focus though is electronically limited.
there are two ways to approach the gear that interfaces with the cameras focus ring. you can either bore out a large aluminum gear and slide it onto the cameras focus ring, then use a gear on the follow focus to interface with it. or, you can design a more custom gear that would fit in the not so gearlike grooves of the cameras focus ring. heres a detailed picture
http://www.frimu.nl/AG-DVX100.jpg the focus ring is the one to the left of the numbered ring. has little grooves in it. THERE ARE 30 "PEAKS" and 30 "VALLEYS" on the cameras focus ring. the distance around the focus ring is about 28.8mm.. not exactly sure though cause i took it with a crap tailors measure.