Today, flying vehicles are very popular. Even in their primary configuration, controlled by a radio controller, some flying vehicles can be considered robots that respond to their environment to stay in the air. Flying robots that have altitude sensors can hover in place. If they have Global Positioning System (GPS) sensors, they know where they are and can fly to a specific location. As more sensors are added, their capabilities increase.

As you will see in this chapter, there is some commonality between the mobile robots and flying robots in their command and control. ROS utilizes this commonality in the structure of the nodes, topics, messages, and services of these two categories of robots. The topic cmd_vel which was used for Turtlesim and TurtleBot earlier in this book is again used for the simulated and real quadrotors presented in this chapter. For sensors and devices that are common between mobile robots and flying robots, ROS takes advantage of this...