Hands-On ROS for Robotics Programming

The URDF model's left and right wheels

Given that you already know the basic URDF tags, it is straightforward to read the definition for the right wheel, as shown in the following code snippet:

  <!-- Right Wheel -->  <link name="right_wheel">    <visual>      <origin xyz="0 0 0" rpy="1.570795 0 0" />      <geometry>          <cylinder length="0.1" radius="0.2" />      </geometry>      <material name="black">        <color rgba="0.05 0.05 0.05 1"/>      </material>    </visual>  </link>  <joint name="joint_right_wheel" type="continuous">    <parent link="base_link"/>    <child link="right_wheel"/>    <origin xyz="0 -0.30 0" rpy="0 0 0" />     <axis xyz="0 1 0" />  </joint>

Inside the <origin> tag, the first component of the rpy attribute (rotation around the X axis), 1.570795 = π/2, is what sets the wheel ...