Hello,
I am having some difficulty using PID on my flywheel motors. The wheels start up smoothly but then they significantly decrease speed. When I launch a ball through, they increase speed a lot but then go back down.
I would greatly appreciate some help.
PID is one area where it is very difficult to give advise without a complete understanding of the robot design. I suggest you start by reading some of the existing threads that are discussing PID, here are two good ones if you are using your own PID control loop.
https://vexforum.com/t/pid-theory-question/32289/1
https://vexforum.com/t/physics-of-the-flywheel-launcher/29357/1
This one discusses using the internal PID that ROBOTC V4 contains.
https://vexforum.com/t/robotc-has-pid-to-control-your-flywheel/31108/1
If you then have specific questions about implementation details feel free to start another thread.