Actuator PID Controller

The pid_command_controller runs at startup and writes PID gains into the actuator’s internal control loops. It supports four independent control modes — position, velocity, current, and force — and each actuator carries its own set of gains tuned for its mechanical characteristics.

Overview

Parameter	Value
Controller type	pid_command_controller/ActuatorPIDCommandController
ROS 2 node name	pid_command_controller
Trigger	Applied once at startup; gains persist until the hardware is power-cycled

Actuator List

The robot has different actuators across legs, pelvis, and arms based on the configuration type:

Group	Actuators
Left leg	leg_left_1 … leg_left_5, leg_left_length
Right leg	leg_right_1 … leg_right_5, leg_right_length
Pelvis	pelvis_1, pelvis_2
Left arm	arm_left_1 … arm_left_7
Right arm	arm_right_1 … arm_right_7

Each name in the parameter file carries the _actuator suffix (e.g. leg_left_1_actuator).

Control Modes

Position

Position control is used for precise joint-angle tracking. The controller closes the loop on the measured joint position and drives the error to zero, making it suitable for holding a target pose or following a slow trajectory.

Velocity

Velocity control is used during dynamic motions where the desired output is a joint angular rate rather than an absolute angle. It is the primary mode used by higher-level motion controllers that issue velocity commands.

Current

Current control sits at the innermost loop and determines torque output directly by regulating motor phase current. It is the fastest control mode and serves as the foundation on which position and velocity loops are built.

Force

Force control closes the loop on measured actuator force (or torque), allowing compliant interactions with the environment. It is used in tasks where limiting contact forces matters more than precise position tracking, such as during foot-contact phases of locomotion.

Impedance

Impedance control operates in “impedance-current mode”, where impedance control is implemented using the underlying current control. It utilizes “stiffness” and “dumping” components to regulate the actuator’s response, allowing for tractable behavior while controlling the current directly.

Configuration Reference

Below is an example pid_command_controller parameter block:

pid_command_controller:
  ros__parameters:
    type: pid_command_controller/ActuatorPIDCommandController
    actuator_names:
      - leg_left_1_actuator
      - leg_left_2_actuator

    position:
      leg_left_1_actuator:       {proportional: 0.0003,   integral: 0.000035, derivative: 1.0e-08}
      leg_left_2_actuator:       {proportional: 0.0003,   integral: 0.000035, derivative: 8.5e-08}

    velocity:
      leg_left_1_actuator:       {proportional: 1.1,  integral: 11.0,  derivative: 8.0e-04}
      leg_left_2_actuator:       {proportional: 1.1,  integral: 11.0,  derivative: 8.0e-04}

    current:
      leg_left_1_actuator:       {proportional: 1.47,  integral: 12000.0, derivative: 0.0}
      leg_left_2_actuator:       {proportional: 1.47,  integral: 12000.0, derivative: 0.0}

    force:
      leg_left_1_actuator:       {proportional: 0.000815,  integral: 0.7, derivative: 0.000475}
      leg_left_2_actuator:       {proportional: 0.000815,  integral: 0.7, derivative: 0.000475}

    impedance:
      leg_left_1_actuator:       {stiffness: 0.000815,  dumping: 0.000475}
      leg_left_2_actuator:       {stiffness: 0.000815,  dumping: 0.000475}