The robot we are working with is a differential robot with two wheels, and two caster wheels. The complete characteristics of the robot should model as the Gazebo-ROS plugin for the simulation. Luckily, the plugin for a basic differential drive is already implemented.

In order to move the robot in Gazebo, we should add a Gazebo ROS plugin file called libgazebo_ros_diff_drive.so to get the differential drive behavior in this robot.

Here is the complete code snippet of the definition of this plugin and its parameters:

  <!-- Differential drive controller  --> 
  <gazebo> 
    <plugin name="differential_drive_controller" filename="libgazebo_ros_diff_drive.so"> 
 
      <rosDebugLevel>Debug</rosDebugLevel> 
      <publishWheelTF>false</publishWheelTF> 
      <robotNamespace>/</robotNamespace> 
      <publishTf>1</publishTf> 
      <publishWheelJointState>false</publishWheelJointState> 
      <alwaysOn>true</alwaysOn> 
      <updateRate>100.0</updateRate> 
 
      <leftJoint>front_left_wheel_joint</leftJoint> 
      <rightJoint>front_right_wheel_joint</rightJoint> 
 
      <wheelSeparation>${2*base_radius}</wheelSeparation> 
      <wheelDiameter>${2*wheel_radius}</wheelDiameter> 
      <broadcastTF>1</broadcastTF> 
      <wheelTorque>30</wheelTorque> 
      <wheelAcceleration>1.8</wheelAcceleration> 
      <commandTopic>cmd_vel</commandTopic> 
      <odometryFrame>odom</odometryFrame>  
      <odometryTopic>odom</odometryTopic>  
      <robotBaseFrame>base_footprint</robotBaseFrame> 
 
 
    </plugin> 
  </gazebo> 

We can provide the parameters such as wheel joints of the robot (joints should be of a continuous type), wheel separation, wheel diameters, odometry topic, and so on in this plugin.

An important parameter that we need to move the robot is

<commandTopic>cmd_vel</commandTopic> 

This parameter is the command velocity topic to the plugin, which is basically a Twist message in ROS (sensor_msgs/Twist). We can publish the Twist message into the /cmd_vel topic and we can see the robot start moving from its position.