What are oscillations in PID?

I’m learning how to tune the k constants for PID. They mention about oscillations in the article “An Introduction to PID Controllers, Written by George Gillard”. I’m just confused when they start talking about oscillations (in the k constant mathematics estimation part towards the end). This PID control is for my chassis to have precise movements. When they talk about oscillations, are they referring to the chassis oscillating around the setPoint, going back and forth, or something else? Thank you in advance.

Yup. You can see here P bouncing around.

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Oscillations are what will happen when you go too far and the control loop is compensating for you. So going past where you want and recovering results in a back and forth oscillating motion as you settle into the target state. Even when you are pretty darn tuned you get some movement as the integral ramps up to set you back to the desired hold point.

If you don’t go past the desired point, you will be too low and never reach where you want. So oscillations let you know it is working harder than it should and you can tune additional variables.

The reasons the oscillations also matter is to get the tuning formulas to work out well. You want to get to the critical frequency where it thrashes about and does not settle down.

You can actually do some additional math and use algebra instead of differential equations to get your constants set. But that is for another day.

What is the y axis? The distance around the set point?

EDIT: No it is position. The goal was a position of 1.

Oh okay gotcha