[spycatcher]

Two wheels gives it a turning radius of zero which is one of the breakthroughs.

[sam_paine]

Two wheels gives it a turning radius of zero which is one of the breakthroughs.

Ever heard of a caster? (And not a fly fisher.)

[Lx]

Imagine a tricycle in reverse, where the big wheels are at the back and the small wheel is in the front. If you rotated one of the big wheels in a clockwise direction and the other in a counter clockwise direction, voila, you have a device that can turn completely around with a zero turning radius. Just don't put the small balance wheel ten feet out or you'd need that much room to rotate even though you have a zero turning radius. In other words, not exactly a breakthrough.