In this video, we are going to show how to create a launch file to spawn a URDF robot model in a given gazebo world.

Up to the end of the video, you will be able to spawn any robot model you may have described in URDF in Gazebo.

Step 1. Create a project in ROS Development Studio(ROSDS)

ROSDS helps you follow our tutorial in a fast pace without dealing without setting up an environment locally. If you haven’t had an account yet, you can create a free account here. Let’s create a new project and call it launch_urdf_model_in_gazebo.

Step 2. Create a package

Let’s create a ROS package for our code by using the following command.

cd ~/catkin_ws/src
catkin_create_pkg my_robot_urdf rospy

Then we create a m2wr.urdf file under the my_robot_urdf/urdf folder.

<?xml version="1.0"?>
<robot name="m2wr" xmlns:xacro="http://www.ros.org/wiki/xacro">
  <material name="black">
    <color rgba="0.0 0.0 0.0 1.0"/>
  </material>
  <material name="blue">
    <color rgba="0.203125 0.23828125 0.28515625 1.0"/>
  </material>
  <material name="green">
    <color rgba="0.0 0.8 0.0 1.0"/>
  </material>
  <material name="grey">
    <color rgba="0.2 0.2 0.2 1.0"/>
  </material>
  <material name="orange">
    <color rgba="1.0 0.423529411765 0.0392156862745 1.0"/>
  </material>
  <material name="brown">
    <color rgba="0.870588235294 0.811764705882 0.764705882353 1.0"/>
  </material>
  <material name="red">
    <color rgba="0.80078125 0.12890625 0.1328125 1.0"/>
  </material>
  <material name="white">
    <color rgba="1.0 1.0 1.0 1.0"/>
  </material>
  
    <gazebo reference="link_chassis">
    <material>Gazebo/Orange</material>
  </gazebo>
  <gazebo reference="link_left_wheel">
    <material>Gazebo/Blue</material>
  </gazebo>
  <gazebo reference="link_right_wheel">
    <material>Gazebo/Blue</material>
  </gazebo>
  
  <gazebo>
    <plugin filename="libgazebo_ros_diff_drive.so" name="differential_drive_controller">
      <alwaysOn>true</alwaysOn>
      <updateRate>20</updateRate>
      <leftJoint>joint_left_wheel</leftJoint>
      <rightJoint>joint_right_wheel</rightJoint>
      <wheelSeparation>0.4</wheelSeparation>
      <wheelDiameter>0.2</wheelDiameter>
      <torque>0.1</torque>
      <commandTopic>cmd_vel</commandTopic>
      <odometryTopic>odom</odometryTopic>
      <odometryFrame>odom</odometryFrame>
      <robotBaseFrame>link_chassis</robotBaseFrame>
    </plugin>
  </gazebo>
  
  <gazebo reference="sensor_laser">
    <sensor type="ray" name="head_hokuyo_sensor">
      <pose>0 0 0 0 0 0</pose>
      <visualize>false</visualize>
      <update_rate>20</update_rate>
      <ray>
        <scan>
          <horizontal>
            <samples>720</samples>
            <resolution>1</resolution>
            <min_angle>-1.570796</min_angle>
            <max_angle>1.570796</max_angle>
          </horizontal>
        </scan>
        <range>
          <min>0.10</min>
          <max>10.0</max>
          <resolution>0.01</resolution>
        </range>
        <noise>
          <type>gaussian</type>
          <mean>0.0</mean>
          <stddev>0.01</stddev>
        </noise>
      </ray>
      <plugin name="gazebo_ros_head_hokuyo_controller" filename="libgazebo_ros_laser.so">
        <topicName>/m2wr/laser/scan</topicName>
        <frameName>sensor_laser</frameName>
      </plugin>
    </sensor>
  </gazebo>
  
   <link name="link_chassis">
    <!-- pose and inertial -->
    <pose>0 0 0.1 0 0 0</pose>
    <inertial>
      <mass value="5"/>
      <origin rpy="0 0 0" xyz="0 0 0.1"/>
      <inertia ixx="0.0395416666667" ixy="0" ixz="0" iyy="0.106208333333" iyz="0" izz="0.106208333333"/>
    </inertial>
    <!-- body -->
    <collision name="collision_chassis">
      <geometry>
        <box size="0.5 0.3 0.07"/>
      </geometry>
    </collision>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <box size="0.5 0.3 0.07"/>
      </geometry>
      <material name="blue"/>
    </visual>
    <!-- caster front -->
    <collision name="caster_front_collision">
      <origin rpy=" 0 0 0" xyz="0.35 0 -0.05"/>
      <geometry>
        <sphere radius="0.05"/>
      </geometry>
      <surface>
        <friction>
          <ode>
            <mu>0</mu>
            <mu2>0</mu2>
            <slip1>1.0</slip1>
            <slip2>1.0</slip2>
          </ode>
        </friction>
      </surface>
    </collision>
    <visual name="caster_front_visual">
      <origin rpy=" 0 0 0" xyz="0.2 0 -0.05"/>
      <geometry>
        <sphere radius="0.05"/>
      </geometry>
    </visual>
  </link>
  
  <link name="link_right_wheel">
    <inertial>
      <mass value="0.2"/>
      <origin rpy="0 1.5707 1.5707" xyz="0 0 0"/>
      <inertia ixx="0.000526666666667" ixy="0" ixz="0" iyy="0.000526666666667" iyz="0" izz="0.001"/>
    </inertial>
    <collision name="link_right_wheel_collision">
      <origin rpy="0 1.5707 1.5707" xyz="0 0 0"/>
      <geometry>
        <cylinder length="0.04" radius="0.1"/>
      </geometry>
    </collision>
    <visual name="link_right_wheel_visual">
      <origin rpy="0 1.5707 1.5707" xyz="0 0 0"/>
      <geometry>
        <cylinder length="0.04" radius="0.1"/>
      </geometry>
    </visual>
  </link>
  
  <joint name="joint_right_wheel" type="continuous">
    <origin rpy="0 0 0" xyz="-0.05 0.15 0"/>
    <child link="link_right_wheel"/>
    <parent link="link_chassis"/>
    <axis rpy="0 0 0" xyz="0 1 0"/>
    <limit effort="10000" velocity="1000"/>
    <joint_properties damping="1.0" friction="1.0"/>
  </joint>
  
  <link name="link_left_wheel">
    <inertial>
      <mass value="0.2"/>
      <origin rpy="0 1.5707 1.5707" xyz="0 0 0"/>
      <inertia ixx="0.000526666666667" ixy="0" ixz="0" iyy="0.000526666666667" iyz="0" izz="0.001"/>
    </inertial>
    <collision name="link_left_wheel_collision">
      <origin rpy="0 1.5707 1.5707" xyz="0 0 0"/>
      <geometry>
        <cylinder length="0.04" radius="0.1"/>
      </geometry>
    </collision>
    <visual name="link_left_wheel_visual">
      <origin rpy="0 1.5707 1.5707" xyz="0 0 0"/>
      <geometry>
        <cylinder length="0.04" radius="0.1"/>
      </geometry>
    </visual>
  </link>
  
  <joint name="joint_left_wheel" type="continuous">
    <origin rpy="0 0 0" xyz="-0.05 -0.15 0"/>
    <child link="link_left_wheel"/>
    <parent link="link_chassis"/>
    <axis rpy="0 0 0" xyz="0 1 0"/>
    <limit effort="10000" velocity="1000"/>
    <joint_properties damping="1.0" friction="1.0"/>
  </joint>
  
  
</robot>

This file defines the physical parameters of our robot and the type of controller that we want to use.

We’ll create a launch file to launch this description. We name it spawn_urdf.launch and put it under the launch folder.

<?xml version="1.0" encoding="UTF-8"?>
<launch>
    <param name="robot_description" command="cat '$(find my_robot_urdf)/urdf/m2wr.urdf'" />
    
    <node name="mybot_spawn" pkg="gazebo_ros" type="spawn_model" output="screen"
          args="-urdf -param robot_description -model m2wr" />
          
</launch>

You can see that the launch file try to find the description file from the my_robot_urdf package.

Now we have to compile it with the following command

cd ~/catkin_ws
catkin_make
source devel/setup.bash

Now you can launch an empty world simulation from Simulations->Empty, then use the command roslaunch my_robot_urdf spawn_urdf.launch  to spawn the robot!

If you are interested in this topic and want to learn more about URDF, please check our Robot Creation with URDF course.

Edit by: Tony Huang

Related resources and links:

• Robot Ignite Academy
• ROS Development Studio
• My 2 wheeled robot model repository:https://bitbucket.org/theconstructcore/two-wheeled-robot-simulation
• Original question: http://answers.gazebosim.org/question/19959/how-to-create-launch-file-for-my-urdf-file-and-open-it-in-gazebo/