The sterling gentlemen at our local cycle shop (Linden Cycle) donated 2 old bicycle wheels for our project. They also threw in a cog and a derailleur sprocket for a spiffy 3:1 gear ratio.
The idea is to weld the spoked aluminium wheel to the lazy susan turntable top, with the big cog in between. A bicycle chain to a stepper motor will then rotate it, giving up a pretty sweet azimuth system, controlled by a stepper driver and a microcontroller.
The altitude system will work similarly, just a touch worried about getting enogh holding torque for it to be useful!