PID control explained with a line-following robot

PID control runs an enormous share of the physical world: thermostats, cruise control, drones, 3D printers, and the steering of self-driving cars. It sounds technical, but a line-following robot makes every part of it intuitive. The robot's job is simple: stay on the line. PID is how it decides how hard to turn. The setup A line follower has a sensor that tells it how far off the line it is. Call that the error: zero means dead center, positive means it has drifted right, negative me...