Writing Your First Script

We can write a program and robot will do these instructions. In this lesson you will learn how to launch, create and modify a script. We will launch python script but it does not matter if you know this language or not.

Open a new terminal. Launch the empty world:

roslaunch turtlebot_gazebo turtlebot_world.launch world_file:=/opt/ros/indigo/share/turtlebot_gazebo/worlds/empty.world

Launching a Script

You should do these instructions step by step:

1. Create a new directory.

mkdir ~/helloworld

2. Change directory.

cd ~/helloworld/

3. Download sources.

git clone https://github.com/markwsilliman/turtlebot/

NOTE: You need to have Github account to do this step.

4. Change directory.

cd turtlebot

5. Launch script.

python goforward.py

6. The TurtleBot is going forward in Gazebo.

7. Press Ctrl+C in the terminal to stop TurtleBot.

Creating and Modifying a Script

Now you will modify the existing script. TurtleBot will revolve on its axis.

1. Change directory.

cd ~/helloworld/turtlebot/

2. Create a copy of goforward.py.

cp goforward.py goincircles.py

3. Edit goincircles.py.

emacs -nw goincircles.py

NOTE: You can use editor which you prefer.

4. Modify linear.x from 0.2 to 0 and angular.z from 0 to 0.5.

NOTE: TurtleBot uses only linear.x and angular.z values because it works in a planar (2D) world and it has a differential drive system which cannot move laterally.

5. Press Ctrl+X, then Ctrl+S to save the changes. After saving is finished, you will see a message like this: Wrote /home/<user_name>/helloworld/turtlebot/goincircles.py.

6. Press Ctrl+X, then Ctrl+C to exit Emacs.

7. Launch script.

python goincircles.py

8. TurtleBot is revolving on its axis.

9. Press Ctrl+C in the terminal to stop TurtleBot.

Launching another Script

1. Change directory.

cd ~/helloworld/turtlebot/

2. Launch script.

python draw_a_square.py

3. TurtleBot is drawing a square.

4. Press Ctrl+C in the terminal to stop TurtleBot.

You can watch these steps in this video:

Open files goforward.py and draw_a_square.py and try to understand the meaning of the commands reading the comments.

You can learn more about Python in this book or find basic online tutorial.