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Controller

Example Topic
pid/PIDSim a PID controller driving a value to a setpoint

PID controller

A PID controller computes a correction from the error e = setpoint - measured value:

output = Kp * e                      proportional: reacts to the present error
       + Ki * sum(e * dt)            integral:     removes the steady-state offset (the past)
       + Kd * (e - e_previous) / dt  derivative:   damps overshoot (predicts the future)

The output is clamped to [min, max], for example a motor's maximum power.

Gain too high Effect
Kp fast, but oscillates
Ki removes offset, but overshoots and winds up
Kd damps, but amplifies measurement noise

pid.h/pid.cpp is based on the MIT-licensed implementation by Bradley J. Snyder. It uses the pimpl idiom: PID holds a std::unique_ptr<PIDImpl>, so the implementation can change without recompiling the code that uses it. The class is unit tested in tests/controller/PidTest.cpp.