Using the gazebo_ros2_control Plugin to Connect ROS 2 Control with Gazebo Harmonic

When you try to move a simulated robot in Gazebo using ROS 2 commands, the joint states may not update or the robot may drift unexpectedly.

Problem

Many tutorials show how to spawn a robot model in Gazebo and then drive it with a ROS 2 twist message, but the connection between the physics engine and the ROS 2 control loop is often missing. Without the proper plugin, the controller manager cannot read joint states or send commands, leaving the robot unresponsive.

Thesis

The gazebo_ros2_control plugin bridges Gazebo Harmonic (or later) and the ros2_control framework, letting you reuse standard ROS 2 controllers while Gazebo handles the physics.

Preparing the robot description

Add a gazebo block to your URDF or SDF that loads the plugin and exposes the hardware interfaces.

<gazebo>
    <plugin filename='libgazebo_ros2_control.so' name='gazebo_ros2_control'>
        <robotNamespace>/</robotNamespace>
    </plugin>
</gazebo>

Make sure the URDF also contains <transmission> tags or <joint> definitions that ros2_control can interpret, and that each joint declares the command interface you plan to use (position, velocity, or effort).

Worked example: launching a differential‑drive robot

1. Source your ROS 2 workspace:
2. source ~/ros2_ws/install/setup.bash
3. Launch Gazebo with the world that contains your model:
4. ros2 launch my_robot_gazebo world.launch.py world:=my_world.sdf
5. In another terminal, start the controller manager and spawn the standard controllers:
6. ros2 run controller_manager spawner joint_state_broadcaster --controller-manager /controller_manager
7. ros2 run controller_manager spawner diff_drive_controller --controller-manager /controller_manager
8. Verify that the plugin is active by checking the Gazebo console for a line similar to:
9. [gazebo_ros2_control] Loaded plugin for robot my_robot
10. Send a velocity command:
11. ros2 topic pub /diff_drive_controller/cmd_vel geometry_msgs/msg/Twist '{linear: {x: 0.5}, angular: {z: 0.2}}' -r 10
12. Monitor the joint states:
13. ros2 topic echo /joint_states
14. Watch the real‑time factor in Gazebo’s GUI; a value close to 1.0 indicates the control loop is keeping pace with physics.

Limitations and practical checks

• The plugin is only available in Gazebo Harmonic (2023.04) and later; older Gazebo Classic releases require the deprecated gazebo_ros_pkgs stack, which does not support the full ros2_control API.
• If the Gazebo solver timestep (set in the world SDF <physics> tag) differs significantly from the ROS 2 control loop period, you may see jitter or instability. Reduce the max step size or use a fixed‑step update rate for the controller manager to mitigate this.
• Joint limits, damping, and friction must be mirrored in both the URDF/SDF and the controller YAML configuration; mismatches can cause the simulator to apply forces the controller does not expect.
• Practical way to check the result: after sending a command, confirm that the joint positions in /joint_states change proportionally and that the odometry topic (e.g., /odom) reflects the expected motion. Additionally, run ros2 topic hz /joint_states to verify a steady publish rate.

Actionable closing

Start with a simple differential‑drive model, add the gazebo_ros2_control plugin tag, launch the simulation, and spawn the joint_state_broadcaster and your chosen controller. Verify the joint states and real‑time factor, then iterate on more complex robots or custom controllers. This approach gives you a reproducible pipeline where Gazebo handles the physics and ROS 2 handles the control logic, without modifying the simulator source.