PID control loops - closed loop feedback

[kevinw]

Originally Posted by mightywombat

pid = request;

error = request - actual; //find the difference of the two values

pid = pid + (error/PID_PROP); //add the proportional part of the error

pid = pid + ((actual - lastactual)/PID_DER); // add the derivative part of the error

pid = pid + (sumerror/PID_INT); //integral part of the pid

pid = pid + 127;

return(pid);
}

What is the reason for adding the requested position to the PID control output? Is there a need for a feed-forward term in the control loop? Are you scaling the output after pid is returned?

Also, you might want to add overflow checking, just in case.