(I'm getting 'Access Denied' replies on the idlers+mount.scad and picture, might be an escaping issue. ).

This thing is for motorization of an Azimuth/Altitude mounted 300mm Dobsonian telescope.

The idea is to have a belt running over large (>40cm) quarter circle pulley bolted to the scope and on a small (less than 1cm radius) pulley direct on a stepper motor.
This should give zero-backlash, high-speed driving, with an accuracy of (assuming perfect 16 step microstepping) 11 arcseconds.
With some more gearing down, better resolution is possible, but achieving zero backlash will be harder.

Animation:
http://youtu.be/Y1-zTE1iXZs

Update: got the design returned from weight watchers

Todo: printing, testing, resolution/accuracy tests.

Longer term:

• Make manual control for constant rate
• Make Arduino sketch that does hour angle/declination to az/alt conversions and that can follow an object across the sky
• finish Stellarium plugin to allow slew (goto) commands from within Stellarium, possibly with gcode?