cube_50.urdf

<robot name="cube_50">
  <!-- A cube of size 50mm -->
  <link name="base_link">
    <inertial>
      <mass value="0.1"/>
      <inertia ixx="0.0001" ixy="0.0" ixz="0.0"
               iyy="0.0001" iyz="0.0"
               izz="0.0001"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="0.05 0.05 0.05"/>
      </geometry>
      <material name="green">
        <color rgba="0 1 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="0.05 0.05 0.05"/>
      </geometry>
    </collision>
  </link>
</robot>