PID

Generic PID class

Constructors

PID();
PID(float kp, float ki, float kd);
PID(float kp, float ki, float kd, float starti);
PID(float kp, float ki, float kd, float starti,
    float settle_error, float settle_time, float exit_error,
    float timeout, float stall_timeout = 0);

starti keeps the integral term at 0 until error drops below it, which prevents integral windup on large errors.

The settling constructor adds exit conditions. The controller is settled when error stays below settle_error for settle_time, or once the motion has run longer than timeout.

Parameter	Description
kp	Proportional constant.
ki	Integral constant.
kd	Derivative constant.
starti	Maximum error at which the integral term starts accumulating.
settle_error	Maximum error to be considered settled.
settle_time	Minimum time (ms) under settle_error to be considered settled.
exit_error	Error at which the motion is considered finished.
timeout	Time (ms) after which to give up and move on. 0 disables it.
stall_timeout	Time (ms) to give up when the robot is near 0 velocity. 0 disables it.

Methods

compute

float compute(float error);

Computes the output power from the current error. Includes two optimizations: the integral term resets to 0 whenever the robot crosses error == 0, and integral only accumulates while error is below starti.

• Returns — the output power.

is_settled

bool is_settled();

Returns whether the movement has settled, per the settling rules described above.

• Returns — true if the movement is settled.

Public members

These are readable at any time (e.g. for graphing or debugging):

Member	Description
error	Current error.
kp, ki, kd	Active PID gains.
starti	Integral gating threshold.
settle_error, settle_time	Active settle conditions.
exit_error	Active exit error.
timeout, stall_timeout	Active timeouts.
accumulated_error	Running integral sum.
previous_error	Error from the previous compute() call.
output	Last computed output.
time_spent_settled	Time (ms) the controller has been within settle_error.
time_spent_running	Total time (ms) the controller has been running.
time_spent_stalled	Time (ms) the controller has been near 0 velocity.
exiting	true once an exit condition has been met.