Controller Yaml File

The final thing to do is to specify which controller is required for your application.

A ros2_control_node in the controller_manager package is given a controller.yaml file which specifies the controllers that you will be using. For the drivetrain, a joint_state_broadcaster as well as a differential_drivetrain_controller (diff_drive_controller — ROS2_Control: Rolling Nov 2024 documentation ) are desired.

Thus, the config yaml file passed to the ros2_control_node looks as follows (differential_drive_train explained below).

controller_manager:
  ros__parameters:
    update_rate: 100 # Hz

    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster

    differential_drivetrain_controller:
      type: diff_drive_controller/DiffDriveController

differential_drivetrain_controller:
  ros__parameters:
    left_wheel_names: [ "left_front_wheel_joint", "left_middle_wheel_joint", "left_back_wheel_joint" ]
    right_wheel_names: [ "right_front_wheel_joint", "right_middle_wheel_joint", "right_back_wheel_joint" ]

    # Should match values defined in uwrt_mars_rover_drivetrain_description's generated urdf
    wheel_separation: 0.997 # wheelbase_length = chassis_width + wheel_width
    wheels_per_side: 3
    wheel_radius: 0.15

    wheel_separation_multiplier: 1.0
    left_wheel_radius_multiplier: 1.0
    right_wheel_radius_multiplier: 1.0

    odom_frame_id: odom
    base_frame_id: base_link
    pose_covariance_diagonal: [ 0.001, 0.001, 0.001, 0.001, 0.001, 0.01 ]
    twist_covariance_diagonal: [ 0.001, 0.001, 0.001, 0.001, 0.001, 0.01 ]

    publish_rate: 50.0
    enable_odom_tf: true
    open_loop: false # If true, integrates vel_cmd to estimate odom, else uses wheel feedback to compute odom
    position_feedback: true # If true, uses position state_interface for odom calculations, else use velocity state interface
    # TODO: this setting doesnt really make sense to me to tie both odom pose and twist calculations to either use position or
    #       velocity. It makes most sense to optimally use position for the pose calculation and velocity for the twist calculation...
    #       as done in https://github.com/clearpathrobotics/ros_controllers/pull/18
    #       Relevant Discussion: https://github.com/ros-controls/ros2_controllers/pull/260/files/a45fd434abe90c1a377d57a54da86c6d1650240d#r776837336

    cmd_vel_timeout: 0.2 # seconds. min cmd_vel publish rate is 5Hz
    publish_limited_velocity: true
    use_stamped_vel: false # FIXME (npalmar): chaneg back to true
    velocity_rolling_window_size: 10

    # Velocity and acceleration limits
    # Whenever a min_* is unspecified, default to -max_*
    linear:
      x:
        has_velocity_limits: false
        has_acceleration_limits: false
        has_jerk_limits: false
    #        max_velocity: 1.0
    #        max_acceleration: 1.0
    #        max_jerk: 0.0

    angular:
      z:
        has_velocity_limits: false
        has_acceleration_limits: false
        has_jerk_limits: false
#        max_velocity: 1.0
#        max_acceleration: 1.0
#        max_jerk: 0.0

The differential drive train controller config specifies the names of the joints that are required by the controller, the actual size of the drivetrain (wheel radius, wheel separation, etc). A more detailed explanation on params can be found here: https://github.com/ros-controls/ros2_controllers/blob/master/diff_drive_controller/src/diff_drive_controller_parameter.yaml .