We define macros in this code to avoid repeatability and to make the code shorter. Here are the macros we have used in this code:

   <xacro:macro name="inertial_matrix" params="mass"> 
      <inertial> 
        <mass value="${mass}" /> 
        <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="0.5" iyz="0.0" izz="1.0" /> 
      </inertial> 
   </xacro:macro> 

This is the definition of the inertial matrix macro in which we can use mass as
its parameter:

   <xacro:macro name="transmission_block" params="joint_name"> 
    <transmission name="tran1"> 
      <type>transmission_interface/SimpleTransmission</type> 
      <joint name="${joint_name}"> 
        <hardwareInterface>PositionJointInterface</hardwareInterface> 
      </joint> 
      <actuator name="motor1"> 
        <hardwareInterface>PositionJointInterface</hardwareInterface> 
        <mechanicalReduction>1</mechanicalReduction> 
      </actuator> 
    </transmission> 
   </xacro:macro> 

In the section of the code, we can see the definition using the transmission tag.

The transmission tag relates a joint to an actuator. It defines the type of transmission that we are using in a particular joint and the type of motor and its parameters. It also defines the type of hardware interface we use when we interface with the ROS controllers.