The transfer function of the PID compensator GC(s) is (KP + KI/s) or KI*(KP/KI*s + 1)/s The transfer function G(s) of the motor is 1/(tau_m*s + 1). KP multiplies the noise so to keep the noise below 5% then the max KP would be 5. Typically after filtering this can get down to 1% of the RPM. The main factor limiting the value of KP is the magnitude of the noise on the RPM feedback signal. The shooter has a w_max = 5614 rpm so if the feedbacks are not normalized then KP and KI must be divided by w_max. During autonomous this would be the delay before we can shoot.įor WPILIB we want KI_WPILIB = T*KI =. 33 sec which means the error should be around 5% of the target by 1 second (three time constants). The 599 shooter wheel has an open loop time constant tau_m =. If you are feeding back RPM then the gains must be divided by w_max. KI_WPILIB = T/tau_d where T is the PID period. If the integral computation used in the PID loop doesn’t contain a dt factor (i.e it is just an error accumulation) as is typical of the WPILIB PIDcontroller then the KI must be multiplied by the PID update period. w_max = 12v/ke*60/2pi rpm which is approx w_free of the motor.ĭ) The desired motor response time constant, tau_d, is smaller than the motor tau_m by a factor of r. I wanted to post some formula’s for deriving P and I gains for a velocity PID control loop such as a shooter used in the 2012 Rebound Rumble game.Ī) motor L/R time constant is small relative to motor control frequencies.ī) The system ( motor , gearbox and wheel) first order time constant tau_m is known.Ĭ) The input speeds are normalized to the maximum motor speed, w_max.

Robotc pid control