#Robotc pid control code#

#pragma config(Motor, port10, myMotor, tmotorNormal, openLoop) #pragma config(Sensor, dgtl1, myEncoder, sensorQuadEncoder)

#Robotc pid control code#

The code has a bunch of definitions at the beginning used to set motor direction, encoder scaling (for example you could scale so the units were inches rather than raw counts), the maximum motor speeds and the limit for integrating the error. As the derivative and integral terms are being calculated at a constant interval this delta time becomes irrelevant and is folded into the Kd and Ki constants. This gives us a constant delta time when comparing to the theoretical equations. The PID control runs as a task with a fixed wait time at the end of each pass through the loop. The code allows joystick channel2 (right analog vertical) to change pidRequestedValue therefore causing the motor to run until the encoder count again matches. A variable called РІР‚СљpidRequestedValueРІР‚Сњ can be set and the motor will run until the encoder count matches this value. The following code controls one motor and uses one encoder as feedback. Commercial motor controllers would typically run at a higher frequency than this but thatРІР‚в„ўs not an option for us. There are some problems in implementing PID control on the cortex as the motor speed can only be updated at around 60Hz at best (ports 1 & 10) and in practice somewhat slower than that if using the other ports needing the motor controller.

I donРІР‚в„ўt claim to be an expert in this area, the math and implementation are pretty simple but tuning can be tricky and depends on the physical aspects of the system being controlled and itРІР‚в„ўs desired response.

There have been a couple of questions lately about PID control, in particular there is an open thread in the RobotC technical discussion but only Jesse can post answers there, so I thought it was time to show some code doing a simple implementation.