Robot frames of reference in the URDF model

It is very important to understand how to place the different reference frames you will use for your robot. First, you have to decide where the <joint> elements are located in the space. In our case, we have two: one for the right wheel and one for the left wheel. Let's look at the one for the right wheel first:

  <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>

Now, let's look at the one for the left wheel:

 <joint name="joint_left_wheel" type="continuous">
   <parent link="base_link"/>
   <child link="left_wheel"/>
   ...