The problem of creating a self-balancing unicycle, a self-powered unicycle that balances itself in three dimensions, is an interesting problem in robotics and control theory.
The theoretical work on the unicycle problem is complemented by work on the construction of actual mechanically ridden unicycles.
Read more about Self-balancing Unicycle: Control Theory of The Self-balancing Unicycle, Early Work, Similar-looking Vehicles That Are Not True Unicycles, Fictional Self-balancing Unicycles