Maurits sent us his unicycle balancing robot which actually has one wheel for moving.
Now meet another balancing robot. This one balances on one wheel and apparently uses two RCX bricks and four sensors along with three tires to maintain balance on the axis perpendicular to its unicycle. The robot balances on the main axis by directly powering the wheel. The axis perpendicular to its unicycle is balanced by the set of rotating tires. Check out the video!