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ROS 2 Lyrical lab 08 · 2–3 hours

ros2_control and diagnostics

Connect a simulated arm to controller_manager, command a trajectory and record evidence.

Practice this lab in your browser: Controller lifecycle

Understand before building

How this part of ROS 2 works

ros2_control separates application commands, controllers, and hardware interfaces. controller_manager coordinates lifecycle and update execution.

A controller must be configured, active, and connected to the correct claimed interfaces before a trajectory can affect simulated state.

Before you start

  • Lab 07 complete
  • Industrial Robots access for model-specific work

Files you will touch

  • src/training_arm_description/urdf/training_arm.ros2_control.xacro
  • src/training_arm_bringup/config/controllers.yaml

Step 1

Set up

sudo apt install ros-lyrical-ros2-control ros-lyrical-ros2-controllers
ros2 control list_hardware_interfaces
ros2 control list_controllers

Step 2

Create the file

<!-- Include this block inside the robot description. -->
<ros2_control name="TrainingArm" type="system">
  <hardware><plugin>mock_components/GenericSystem</plugin></hardware>
  <joint name="joint_1">
    <command_interface name="position"/>
    <state_interface name="position"/>
    <state_interface name="velocity"/>
  </joint>
</ros2_control>

# controllers.yaml
controller_manager:
  ros__parameters:
    update_rate: 100
    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster
    arm_controller:
      type: joint_trajectory_controller/JointTrajectoryController
arm_controller:
  ros__parameters:
    joints: [joint_1]
    command_interfaces: [position]
    state_interfaces: [position, velocity]

What each part does

  1. 1.controller_manager runs at the configured update rate and loads two controller plugins.
  2. 2.The broadcaster publishes state; the trajectory controller claims command interfaces for motion.

Step 3

Build, run and inspect

ros2 run controller_manager spawner joint_state_broadcaster
ros2 run controller_manager spawner arm_controller
ros2 control list_controllers
ros2 bag record /joint_states /arm_controller/controller_state

Proof that it works

  • Both controllers report active
  • Command and state interfaces are claimed correctly
  • The bag records joint state and controller state topics

Recovery notes

  • Use mock hardware until stop, limit and recovery behavior are proven.
  • A robot_description change requires restarting controller_manager; live URDF reload is not supported.
ros2_control controller manager