In short, it drives like a hamster wheel spins. The robot drives up the side of its own shell just like a hamster runs up the side of its wheel. Of course, the hamster never gets anywhere. No matter how hard it tries to climb, gravity pulls it down and the wheel falls away beneath it. Sphero works the same way – constantly climbing uphill, scrambling up the side of its own shell only to have the shell roll out from under it – which causes Sphero to roll. In a sense, Sphero runs on gravity.