Tracking position of juggling balls
Bluetooth accelerometer data from wii controllers embedded in juggling clubs. This didn't produce very interesting results because the acceleration hardly changed once the club was in the air.


Well, that's to be expected! You know, gravity's pull is rather constant on earth!

So the interesting thing here is the rotation (since basically, you could pretty well simulate how your cub flies as soon as you know how you've accelerated it with your hands). Alltogether, given a proper system model and a sufficiently fast accelerometer, that's a good approach.

You'd have to know the initial position (and assume initial zero speed) of the cub, but from that, a Kalman filter would usually be used to calculate the position of the cub.