Thanks to careful engineering, this blind juggler robot is able to keep a ball bouncing on it’s surface without any feedback about where the ball may or may not be. At first glance, it might seem like this is an open-loop control system, however the trick is that the clever design of the bouncing surface and actuation rate actually provide a built-in form of feedback. The curvature of the surface is set up so that a ball with a known springiness (coefficient of restitution) will receive just enough force in the sideways direction to nudge it back towards the center. Additionally, the height of the ball’s bounce is kept in check by accelerating the actuator unevenly, so that if the ball hits the plate too early, it receives extra force so that it bounces higher and takes longer to come down next time.

Besides just being a fun experiment, adding this kind of built-in mechanical feedback can make it easier to develop traditional feedback control systems. [via boingboing]