I would like to know if anyone has found an encoder that fits onto the shaft of the CIM Motor. The shaft is 5/16" in diameter.
It’s actually 8mm, which is very close to 5/16.
US Digital sells several encoders that can be configured for 8mm. The [E2](http://usdigital.com/products/encoders/incremental/rotary/kit/E2(http://usdigital.com/products/encoders/incremental/rotary/kit/E6) has bore options from 2mm to 1 inch.
If you’re looking for something to measure the speed of a shooter, an optical or magnetic sensor may be a better choice.
Assuming your goal is to measure the rpm of a wheel, one thing you may want to consider is using a hall effect sensor. My team used one this year on our shooter wheel and have had no problems at all, whereas we have burned out two encoders elsewhere on the robot.