The problem this month is to sort various colored marbles.  I was looking for classification methods as well as mechanical methods for handling marbles.

Classification

• Shine R, G, B light from LED on marble and measure reflected light using a photo resistor (or photo diode or transistor).
• OpenCV on Raspberry Pi w/ camera
• Measure capacitance difference (is there any?)
• Head absorption difference (perhaps flash the marble with xenon strobe light)
• Diameter difference (order different colors from different manufacturers).
• other offbeat methods like drone with camera, waiting for evolution to do something.

Mechanical Separation

• Solenoid to push one color off track
• Puff of air to push one color off the track
• Servo w/ arm to push marble in one (or two) directions