Behold:

"The rolling element is a sphere a foot or so across, the upper part of which fits into a cage equipped with motors and drive-wheels.  The rider sits on a saddle projecting up from this framework.  Should he begin to topple, accelerometers detect the movement instantly, and the onboard microprocessor commands the motors to roll the sphere in the proper direction to frustrate the fall.  With fast enough electronics, the rider will feel absolutely safe, for the continual balancing tremors will be smaller than those which his own balancing reflexes would have to make were he simply standing up..."

"A really elegant, natural method of control and steering becomes possible.  The rider merely leans in the direction he wants to go; the unisphere obediently rolls in that direction to counter the fall, and continues to roll that way until he leans to one side to change direction, or leans back to stop.  With practice, this technique of balance-control -- which is merely a generalization of the art of steering a bicycle, itself a simple extension of our automatic balancing reflexes -- will become quite automatic.  The rider will navigate his unisphere forwards, backwards, and side-ways without even thinking about it."

New Scientist, 18 May 1978

Also re-printed in:
The Inventions of Daedalus: A Compendium of Plausible Schemes, David E. H. Jones (p. 28)

By all rights, there ought to be hundreds of competing self-balancing vehicles on the market right now.

Does anyone still believe that patents protect true inventors?