PID

PID, short for Proportional Integratal Derivative, is a very common way to control motors and systems that require specific and precise control over mainly its position and/or velocity. For a more in depth look at the basic concepts of PID, view [1].

Most of the time, any sort of PID control does not have to be perfect and can be tuned to be simply "good enough".

It is essentially just an equation that specifies an output given several different types of errors, mainly current error, change in error, and accumulation of error.

In terms of an equation, it takes the form of something like this (This isn't the "official" equation, it is formatted to be easier to understand as a function), where x, i, and v, are the current error, accumulation of error, and change in error respectively, and where kP, kI, kD are PID Gains (constants).

Error and gains can be in any unit desired, whether it be meters, cm, rotations, meters/sec, rpm, etc.

Note that for FRC, most of the time just kP is used and the other gains are left as 0.

$$u(x, i, v) = kP * x + kI * i + kD * v$$

[1] https://docs.wpilib.org/en/stable/docs/software/advanced-controls/introduction/introduction-to-pid.html