I made the machine in the video below for no other reason than that I felt like making a vehicle that was propelled in a non-standard way. The idea arose when I wondered about setting my Product Design Engineering students the challenge of making a vehicle that wasn’t driven through its wheels. In the end we did a different project, but I still couldn’t resist having a go myself.
Originally there was going to be a separate weight that was shifted back and forth to make the vehicle tip. I was rather pleased when I realised that I could make the batteries, the Arduino, and one of the motors do double duty as the weight.
(I didn’t choose the carpet.)