"Reaction wheel" stabilizes bicycles and inverted pendulums

From Hack a Day: http://hackaday.com/2012/06/29/self-balancer-does-it-differently-than-were-used-to-seeing/
and http://hackaday.com/2012/03/25/self-stabilizing-autonomous-bicycle/

These mechanisms use a "reaction wheel" that moves the object against any tipping action by rotating in the opposite direction. This is using the concept of conservation of angular momentum: wheel spins one way, object spins the other way to conserve angular momentum. So, the whole system moves against any tipping caused by external forces or inefficiencies.

The bikes have a reaction wheel mounted perpendicular to the main bike wheels. This first bike is from an Asian Youtube user and is a miniature bike. He also has a unicycle that moves forwards and backwards to stabilize in that direction, whereas a perpendicular reaction wheel stabilizes side to side motion.



The second video shows a full size bike and an inverted pendulum using this concept. (For a student's diploma thesis.)