Babot is a beautiful DIY balancing robot that uses computer vision and a Raspberry Pi to balance a ball on its surface.
A camera placed under the transparent surface detects the position of the ball. Then a raspberry pi runs a PID algorithm to tilt the plate in the right position using three servo motors.
Babot will be delivered as a kit, all you will need is a Raspberry Pi. The Python code will be completely open source so you can modify it to make Babot do exactly what you want.