ROS Basics

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In order to learn ROS, you need to know in advance how to program in C++ or Python. Also, you need to be comfortable using the Linux shell.

In order to run ROS nodes, you need to type roscore into one of the terminals. Prior to that, you should make sure that you sourced these two directories in ~/.bashrc in order to make sure you can use your code with ROS functionalities:

If you want to develop such nodes, ROS works on a subscriber/publisher basis ros_architecture. Everything takes place in the catkin_ws directory.

catkin_ws directory

In order to create a ROS package, we need to call in catkins_ws/src:

catkin_create_pkg package_name rospy[or roscpp] ros_packages

for example: catkin_create_pkg my_robot_controller rospy turtlesim which will return:

If we want to add other packages later, we can simply add them in package.xml. To run, we would need to type in another terminal rosrun my_robot_controller script.py

In order to build the new ROS package we just created, we call

catkin_make inside /catkin_ws Also, in order to run the node through rosrun, you need to make the script executable with chmod +x script.py Also, for the script to work, it needs to have #!/usr/bin/env python3 as first line in order to know the interpreter

ROS useful commands

Question

• rosnode list shows all active nodes
• rosnode kill node_name kills any active node
• rqt_graph opens up a GUI that shows the relationships between active nodes.
• rostopic info /node_name gives details about the type, publishers and subscribers.

• rosmsg show

• rostopic echo gives real-time data of a topic