Problem with PID library to control motor speed

Projects Programming
1

I’ve use the PID_v1 library for motor speed control.
Lets say my setpoint is 50 and input is read from speed encoder in rpm
The question is
Do I need a feed foward PWM + Output from PID to drive a motor
Like analogWrite(50+Output) or I only need to Write only Output.
Because when I only use Output to drive a motor it will oscillate up and down
like it’s unstable. Is it because my Kp Ki or Kd is the value that unstable?
I see that if we concern only kp. It will be Error= setpoint-input and Output= Kp* Error
If the setpoint and input are both equal which mean no error then the output is zero.
Then there’s the problem.

Thanks

2

Use Output only.

If the speed oscillates, Kp is probably too high. Google "PID tuning" for tutorials on selecting the K values.