We are using a double flywheel with 4 motors. When we initially fire the balls, the flywheel has maximum speed. The problem occurs when we stop the flywheel. When the flywheel is stopped, the motors have trouble starting again. We have a power expander attached and this doesn’t seem to be helping. Does anybody have any suggestions on how to fix this problem? It is really slowing down our shooting speed and our competition is a week away. Thank you!!!
Another motors per flywheel and managing the deceleration (see threads on ratchet on flywheel) to not make the motor and/or Cortex PTC unhappy.
What is your gear ratio? We’re seeing greater than 21:1 are needing more than 2 motors per flywheel.
Why are you stopping the flywheel and how soon after you stop it are you restarting it?
There is that end of autonomous period stoppage that will happen in an occasional match… 
Depending upon the feeder intake, you may not want the flywheel running all the time as it may fling out balls at inopportune times.
Pictures would be nice to see what you have going on. Close ups can help avoid revealing the entire robot.
Yes there are numerous reasons why one may stop and restart the flywheel motors. Depending on which of those myriad occurrences are associated with the problem may help lead to finding a solution.
We had the same issue arise during regular practice and we solved it by reducing the overall friction. We did this by switching to the vex turbo gear setting and this worked because those vex bearings are not the nicest bearings. Keeping as much of the gearing stuff as you can inside the motor where it is relatively lubricated can help.
Definitely make sure your shafts aren’t bent and that everything is aligned properly. As other people have said, lubricant can probably help.
When you are trying to get the flywheels spinning after stopping, what motor power level are you using? If it is too high, you might be drawing too much current, causing the PTCs to trip.
Make sure your deceleration from full speed to stopped is gradual, otherwise the motors will backspin and ruin the motors.