Your first robot design has been a simple two-wheeled differential drive model defined in URDF. There are many other properties that can be defined in the URDF file, and you are free to extend the dd_robot model. This introductory exercise was provided so that the elements of simulation can be understood by the reader. In Chapter 3, Driving Around with TurtleBot, we will use a simulated and a real TurtleBot to explore a variety of ROS control methods for mobile robot navigation. The rqt toolset will be introduced and used to monitor and control the TurtleBot's movements.

In Chapter 5, Creating Your First Robot Arm (in Simulation), we will extend our understanding of URDF by learning more about Xacro. We will build a Xacro file to define a robot model for a robot arm.