How to move 4 wheeled robot

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I have created a URDF (in Xacro format) which has 4 wheels.

I added the skid-steer Gazebo plugin and amended the joints information etc. When I exeute my launch file /cmd_vel is in my topics list but my model does not move in either rviz nor gazebo when I publish commands to /cmd_vel.

Below is my xacro file:

<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="test_bot">

  <xacro:include filename="$(find sweep_bot)/urdf/sensors/camera.xacro"/>
  <xacro:include filename="$(find sweep_bot)/urdf/actuators/wheels.xacro"/>
  <xacro:include filename="$(find sweep_bot)/urdf/sensors/MultiCamera.xacro"/>

  <!-- body -->
  <xacro:property name="chasis_length" value="1.0"/>
  <xacro:property name="chasis_heigth" value="0.45"/>
  <xacro:property name="chasis_width" value="0.5"/>

  <link name="chasis">
    <inertial>
      <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
      <mass value="1.0"/>
      <inertia ixx="0.4" ixy="0.0" ixz="0.0" iyy="0.4" iyz="0.0" izz="0.2"/>
    </inertial>
    <visual name="">
      <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
      <geometry>
        <box size="${chasis_length} ${chasis_heigth} ${chasis_width}"/>
      </geometry>
      <material name="">
        <color rgba="0.0 1.0 0.0 1.0"/>
        <!-- <texture filename=""/> -->
      </material>
    </visual>
    <collision>
      <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
      <geometry>
        <box size="${chasis_length} ${chasis_heigth} ${chasis_width}"/>
      </geometry>
    </collision>
  </link>
  <gazebo reference='chasis'>
    <material>Gazebo/Orange</material>
  </gazebo>

  <!-- WHEELS -->
  <xacro:property name="wheel_radius" value="0.1"/>
  <xacro:property name="wheel_length" value="0.1"/>
  <xacro:property name="wheel_rpy" value="1.55 0.0 0.0"/>

  <xacro:macro name="wheel" params="side position flip alt">
    <xacro:property name="wheel_xyz" value="${alt * 0.3} ${flip * 0.2} -0.25"/>

    <link name="wheel_${side}_${position}">
      <inertial>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
        <mass value="1.0"/>
        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
      </inertial>
      <visual name="">
        <origin xyz="${wheel_xyz}" rpy="${wheel_rpy}"/>
        <geometry>
          <cylinder radius="${wheel_radius}" length="${wheel_length}"/>
        </geometry>
        <material name="">
          <color rgba="1.0 0.0 0.0 1.0"/>
          <texture filename=""/>
        </material>
      </visual>
      <collision>
        <origin xyz="${wheel_xyz}" rpy="${wheel_rpy}"/>
        <geometry>
          <cylinder radius="${wheel_radius}" length="${wheel_length}"/>
        </geometry>
      </collision>
    </link>

    <gazebo reference='"wheel_${side}_${position}'>
      <material>Gazebo/Red</material>
    </gazebo>

    <joint name="body_wheel_${side}_${position}_joint" type="revolute">
      <parent link="chasis"/>
      <child link="wheel_${side}_${position}"/>
      <limit lower="0.0" upper="0.0" effort="0.0" velocity="0.0"/>
    </joint>
  </xacro:macro>

  <xacro:wheel side="left" position="fore" flip='1' alt='1'/>
  <xacro ...