Assumption: Connection to and Teleoperation of the Turtlebot are functional.

This first step in learning how to control a robot is to learn how to get its actuators to work. The vanilla turtlebot only really has two of them, a left wheel and a right wheel. This would be the simplest instantiation of a (non-trivial) mobile robot. The Learn Turtlebot github repository has been cloned to the TurtleBot Adventures repository as “turtlebot.” It provides some simple python-based ROS scripts for controlling the robot. The code is quite primitive, so you can see how well this work by using open-loop commands and some form of dead-reckoning.

The particular python code of interest is:

1. goforward.py
2. draw_a_square.py

which both command the robot to move via velocity commands.

The commands are organized into a twist vector, which encodes the forward, sideways/lateral, and rotational velocity commands to the robot. Due to the nature of the robot, it cannot move siwdeways, so the “y” component of the twist should always be zero (I believe that it gets ignored deeper in the code, so it might not matter. Just know that it is most likely not going to do anything). The robot can move forward (or backward) as well as turn in place, plus any reasonable combination of the two. In mechanics, a velocity given with the body as the reference frame (as opposed to some static world coordinate) is called a twist. Hence the use of that variable in the code.

Connect to the turtlebot and run the code on it (of course, you'll first have to clone it).

Adventure Contents