[KenWittlief]

what your mentor is describing is a closed loop feedback system

yes it will work, the caveat is your max wheel speed will have to be something less than the full speed of the motor.

When the battery is fully charged the PWM values might be 200. Then as the battery gets lower the PWM values will go up, 210, 220...to 254, whatever it takes to keep the wheel spinning at the 'right' speed.

At that point you feedback system will be 'railed' and wont be able to keep up.

Its a great idea: it will hold the wheel speed constant as long as the battery is able to supply the power needed.

BTW, a bonus of this system, when you launch a ball the sensor will see that the wheel has slowed down, and it will increase the PWM output to get it back up to launch speed. This means you will be able to fire sequential shots faster.

Feedback is one of the most powerful tools an engineer has at his disposal!

EDIT: and the spell check is the 2nd most powerful tool (edited for speeling :^)