The motor

I wanted the motor to be able to rotate the slide projector (which was sitting on a lazy Susan from Ikea) either clockwise or counter-clockwise. The advice I constantly got was to use an H-bridge, however, no-one could tell me where to get one. There were numerous Arduino shields available, but the form factor of the Android demo-kit (it has more pins than the standard ones) meant that it wouldn't fit. Eventually I found a place in Australia (in Perth) that had something appropriate, and I ended up using this one which arrived in two days.

It was tiny! Eventually I managed to solder on the legs and understand how to get it working. 

Unfortunately, I eventually turned off the motor feature for the demo at the GDD. I had planned to use the compass as feedback in order to turn the slide projector to face in the direction where the rainbow would be seen (directly opposite the sun). However, I think the magnetic field caused by the slide projector (probably a transformer) caused the compass to be inaccurate. I guess I will need to use another feedback method to know what the orientation of the lazy Susan is (suggestions welcome).