Starting the Gazebo simulator

Now that our workspace is compiled, let’s run a gazebo simulation and RViz using normal python launch files.

For that, run the following command in the terminal:

ros2 launch minimal_diff_drive_robot gazebo_and_rviz.launch.py

Again, you may see some error messages. As long as the simulation appears, you can just ignore those error messages.

Now, in a second terminal, let’s also launch the Robot State Publisher, so that we can properly see the robot in RViz (Robot Visualization tool).

 

ros2 run joint_state_publisher joint_state_publisher

Now you should be able to see both Gazebo simulator and RViz, similar to what we can see in the image below:

How to spawn a Gazebo robot using XML launch files – Gazebo and RViz launched

In case you want to know, the content of the file used to spawn the robot can be seen with:

cat ~/ros2_ws/src/minimal_diff_drive_robot/launch/gazebo_and_rviz.launch.py

Moving the robot around

To make sure everything is working as expected so far, you can also run a new command to move the robot around using the keyboard. For that, open a third terminal, and run the following command:

ros2 run teleop_twist_keyboard teleop_twist_keyboard

cat ~/ros2_ws/src/minimal_diff_drive_robot/launch/gazebo_and_rviz.launch.py

cat ~/ros2_ws/src/minimal_diff_drive_robot/launch/gazebo_and_rviz.launch.xml

<?xml version="1.0"?>

<launch>
  <arg name="model" default="$(find-pkg-share minimal_diff_drive_robot)/urdf/minimal_diff_drive_robot.urdf" />

  <arg name="start_gazebo" default="true" />
  <arg name="start_rviz" default="true" />

  <!-- Start Gazebo -->
  <group if="$(var start_gazebo)">
    <include file="$(find-pkg-share gazebo_ros)/launch/gazebo.launch.py">
      <!--arg name="paused" value="true"/>
      <arg name="use_sim_time" value="true"/>
      <arg name="gui" value="true"/>
      <arg name="recording" value="false"/>
      <arg name="debug" value="false"/>
      <arg name="verbose" value="true"/-->
    </include>

    <!-- Spawn robot in Gazebo -->
    <node name="spawn_robot_urdf" pkg="gazebo_ros" exec="spawn_entity.py"
      args="-file $(var model) -x 0.0 -y 0.0 -z 0.0 -entity my_robot" output="screen" />
  </group>

  <!-- TF description -->
  <node name="robot_state_publisher" pkg="robot_state_publisher" exec="robot_state_publisher" output="screen">
    <param name="robot_description" value="$(command 'cat $(var model)')"/>
    <param name="use_sim_time" value="true" />
  </node>

  <!-- Show in Rviz   -->
  <group if="$(var start_rviz)">
    <node name="rviz" pkg="rviz2" exec="rviz2" args="-d $(find-pkg-share minimal_diff_drive_robot)/config/robot.rviz">
      <param name="use_sim_time" value="true" />
    </node>
  </group>

</launch>

If we check carefully the output above, we can see that we start launching the Gazebo simulator, and in the same <group> we spawn the robot in Gazebo by calling spawn_entity.py

Then we launch the Robot State Publisher to be able to see the robot in RViz, and finally, we launch RViz itself.