AN UNCONTROLLED WALKING TOY THAT CANNOT STAND STILL

We built a simple two-leg toy that can walk stably with no control sys tem. It walks downhill powered only by gravity. It seems to be the fir st McGreer-like passive-dynamic walker that is statically unstable in all standing positions, yet is stable in motion. It is one of a few kn own mechanical devices that are stable near a statically unstable conf iguration but do not depend on spinning parts. Its design is loosely b ased on simulations which do not predict its observed stability. Its m otion highlights the possible role of uncontrolled nonholonomic mechan ics in balance.