I've seen many online plans at various times and places for so-called "barn door" mounts, simple sky tracking mounts to allow any camera with B or T shutter to be used for tracked sky photos -- tracked, so that stars, planets and nebula will appear as points (or at least small slightly fuzzy circles) instead of long trails, as would be the case with exposures over a few seconds using a fixed camera. What all seem to have in common is some combination of somewhat complicated geometry requiring considerable precision in fabrication, and tracking time limited to an hour or so before significant rate errors crop up (even discounting any errors in aiming the rotation axis at the celestial pole). It seems to me that a simpler mount could be built using a plain motor drive (shaded pole synchronous motors are common, have good torque, and hold rate very well if not asked to work against too much resistance), suitable belt reduction (belts can be readily slipped to move the mount between exposures and don't have periodic errors as gears can), and a counterbalanced platform to minimize torque requirements. Has anyone seen a plan for such a device, or had any experience in building one? Or would it be simpler to modify an old style telescope clock drive with a tripod ball head in place of the telescope tube?