This project was a spin-off of my earlier Ball-and-Plate experiments.
The details of the build can be found here on Instructables.
My main interest was to see how effective it would be to control the tilt of the board using body movements. Ultrasonic proximity sensors were used to detect forward/back and left/right movements. It worked pretty well in a controlled environment, but as soon as I got it out at the school fair it was too difficult to keep other people out of the sonar detection range. So it wasn't very effective other than as a novelty.
Fortunately I also made a hand-held controller that was basically a wired remote control. The Arduino reads the tilt of an accelerometer in the hand-controller, and drives the gearmotors until the tilt of the accelerometer attached to the board matches the hand-controller.
I later added a bluetooth module, and got it working with Android phones
At the school fair - 2011