PID Controllers

What are PID controllers good for?

PID controllers are a type of feedback controller which is commonly used in FTC and robotics. They are commonly used for controlling the position of a robot on a field, but they are also utilized for controlling things such as flywheels, arm mechanisms, and more. PID controllers are versatile, however they aren’t very honed or specialized for a specific use case.

Overview

A PID controller consists of three terms:

• Proportional: Multiplied by the current positional error in inches. This term is responsible for the majority of the robot’s movement.
• Integral: Multiplied by the sum of all previous errors. This term helps to reduce steady state error, which is the error that can occur when the robot is close to the target position, but it isn’t quite there yet.
• Derivative: Multiplied by the change in error since the last update. Helps to reduce oscillation.

Tuning a PID controller

When tuning a PID controller manually, it’s generally good advice to begin with the P term. Start at maybe 0.0001 and increase it very gradually until you are reaching just below your taget position. You don’t want to overshoot. If your robot is oscillating around the target position, you can try adding some D to reduce that oscillation. The D term is generally very small, and should be tuned very carefully, as too much of the D term can cause the response of the controller to be slow and it can also cause oscillation if you make it too big. Generally use very little of the D term. The I term is generally not used in path following, but in other cases, it can be used to increase the accuracy of your controller.