Building an articulated robot arm URDF using Xacro

Our simple robot arm model rrbot consists of three link elements of various heights and two joint elements that join the links together. The joint elements each connect two of the links and enable the links to rotate around one of its axes.

In the next few sections, the rrbot URDF will be created and incrementally built to incorporate the advantages of each of the Xacro features we discussed in the last section. If you have not created the ros_robotics package, refer to the Creating and building a ROS package section in Chapter 2, Creating Your First Two-Wheeled ROS Robot (in Simulation).

Specifying a namespace

In order to create the URDF file from Xacro files, the Xacro file must contain an XML namespace declaration using the xmlns attribute with the xacro tag and corresponding URI. Here is the XML namespace (xmlns) attribute for our rrbot robot arm:

<robot name="rrbot" xmlns:xacro="http://www.ros.org/wiki/xacro">

This declaration is vital...