If a field derotator is a 1 rpd drive couldn't one be built with a pivot and counterweights? Axis of pivot would be parallel to optical axis, counterweights would hang down to drive rotation at 1 rpd by gravity. Wouldn't want to use it in a wind, but would it work? Bill B Chuck Hards wrote:
Basically, it's a drawtube that rotates, driven by a stepper motor via belts or gears. Whatever's locked in the drawtube is rotated with it. They don't need active control, since they are basically just a clockwork mechanism, 1 rpd., but it wouldn't surprise me if they existed with programmable rates or scripting capability. There are commercially-made units; I think even Meade offers one for their 16" SCT when it's mounted in alt-az. mode. But I don't have the details for any off-the-shelf units.
C.