Bouncing a ping-pong ball on a paddle isn't terribly challenging for someone with even a modicum of hand-eye coordination, but what if you were blindfolded and had to only rely on your ears? That makes the challenge almost impossible, but unexpectedly it turned out to be an effective approach for this ball-juggling contraption.
Building a machine like this to sit on my desk and bounce a ping-pong ball all day would utterly destroy my productivity, but for Tobias Kuhn, it presented a unique challenge of trying to find the best way to stop the ball from bouncing off the tiny platform.
Kuhn's initial approach was to emulate how a human would keep the ball bouncing, by surrounding the platform with a series of LED phototransistors that worked like eyes, visually tracking the movement of the ball so that the platform could make timing and angle adjustments to keep it bouncing.
It worked, but it wasn't exactly elegant. So Kuhn went back to the drawing board and came up with a radically different approach for the latest version of his machine. Beneath the moving platform are now four tiny microphones that are constantly listening for the sound of the ball bouncing off the platform.
The intensity of the sound picked up by the four mics can be compared and used to extrapolate where the bounce occurred and additional processing can then calculate necessary adjustments to the moving platform to keep the ball as centred as possible.