Building an articulated robot arm URDF using Xacro

In the next few sections, our rrbot URDF will be created and incrementally built to incorporate the advantages of each of the Xacro features we discussed for our robot.

Using the Xacro property tag

For the first iteration of our rrbot robot arm, we will build a URDF file that defines three links with the <visual>, <collision>, and <inertial> tags, and two joints with the <parent>, <child>, <origin>, and <axis> tags. This is a very similar format to the dd_robot URDF file that you are familiar with from Chapter 2, Creating Your First Two-Wheeled ROS Robot (in Simulation). The differences for the Xacro format are listed here and explained in more detail after the code is presented:

• Addition of the XML namespace declaration on the second line

• Use of the Xacro <property> tag to define constant values

• Addition of property names instead of values within the <box> and <origin> tags

• Simple math...