[sjtrny]

Proportional-integral-derivative (PID) controller is a feedback loop algorithm for control. You give some desired goal (in this case is to reach a position) and it moves to that goal by iteratively attempting to minimise the error (in this case distance).

A real life example is the stabilisation of quadcopters ("drones" eugh I hate that word). Where instead of attempting to reach a location the target is to maintain a specific angle relative to the ground.

As always wikipedia is your friend http://en.wikipedia.org/wiki/PID_controller.

[sz4kerto]

In short, you're pushing the ball around, and the force you use depends on three things:

- how far the ball is from the target (P, proportional)

- how far the ball has been from the target over time (I, integrator), so if you are very far even after a long time you try to push harder

- how quickly is the ball approaching the target (D, derivator), i.e. if you're approaching quickly then you decrease the force, if you're approaching too slow then you increase the force

[watmough]

The article links the Wikipedia page: https://en.wikipedia.org/wiki/PID_controller

If the goal is to teach about PID controllers, then the demo could use a graph showing the parameters through time.