PID Loops

[Chris27]

read this starting at page 23

http://www.cs.cmu.edu/afs/cs/academi...y_friction.pdf


Basically, PID is a function that takes an input a target (set point) you want to achieve and your current error to this target and outputs the motor speed to get there.

P refers to a term that is proportional to the error. It is used to achieve the desired rise time to get to the set point. However having a high P will cause
the system to oscillate around the set point.

D refers to a term that is proportional to he derivative of the error. It is used to dampen the system to reduced the oscillations. If you overly dampen the system, you may rob it of the power it needs to actually reach the set point. This is called steady state error.

I refers to a term that is proportional to the integral of the error. It is used to address steady state error. Basically, as long as error persists, the system will try harder and harder to reduce the error. This may become dangerous because of wind up. E.g. say that you disable power to a motor
for a moment. The I term will cause the speed output to rise as the error is
not going away (the motor is disabled). When the motor is finally re enabled, it will go flying.

Sometimes you can get away with just using P especially if there is a lot of
friction in the system which would make it hard to shoot past the set point.

Hope that helps.