Mahmoud Abas, Full-Stack Software Engineer & AI

ROS 2 Practical - How it works ?

In the print dialog, choose "Save as PDF" as the destination.

ROS 2 Practical - Lesson 1

How It Works

The ROS 2 workspace, package, and node model

The Big Picture

Workspace

Belongs to an organization or project

holds many

Package

Responsible for one specific task, e.g. robot controller or camera driver

contains one or more

Node

Talks to other nodes using pub-sub messaging

Install colcon

colcon is the CLI build tool for ROS 2
Uses the `ament` build system
Automates building, testing, and using multiple packages
Handles dependency ordering and environment setup

bash

sudo sh -c 'echo "deb [arch=amd64,arm64] http://repo.ros2.org/ubuntu/main `lsb_release -cs` main" > /etc/apt/sources.list.d/ros2-latest.list'
curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc | sudo apt-key add -
sudo apt update
sudo apt install python3-colcon-common-extensions
source /usr/share/colcon_argcomplete/hook/colcon-argcomplete.bash

Create Your Workspace

A workspace is just a folder with a src/ directory
colcon build compiles everything inside src/
install/setup.bash must be sourced to use built packages

bash

mkdir -p ros_ws/src
cd ros_ws
colcon build
source install/setup.bash

Create a Package

Two package types: C++ and Python
C++ packages use the default ros2 pkg create
Python packages need the --build-type ament_python flag and the rclpy dependency

bash

# C++ package
ros2 pkg create my_first_pkg

# Python package
ros2 pkg create my_first_py_pkg --build-type ament_python --dependencies rclpy

Rebuild the workspace after creating a package

Create Your First Node

A node is just an executable Python (or C++) file
Must be made executable with chmod +x

bash

touch ./my_first_py_pkg/my_first_py_pkg/my_first_node.py
chmod +x ./my_first_py_pkg/my_first_py_pkg/my_first_node.py

Write the Node Code

rclpy init

Node class

spin

shutdown

Register the Node as an Executable

Add an entry point in setup.py so ros2 run can find it

python

entry_points={
    'console_scripts': [
        "test_node = my_first_py_pkg.my_first_node:main"
    ],
},

Build and Run

Rebuild the workspace after editing setup.py, using --symlink-install to avoid rebuilding on every Python code change
Run the node via ros2 run

bash

colcon build --symlink-install
ros2 run my_first_py_pkg test_node

Inspect Running Nodes

rqt_graph visualizes running nodes and their pub/sub connections
ros2 node list lists all running nodes
ros2 node info shows details about a specific node

bash

rqt_graph
ros2 node list
ros2 node info /my_first_node

Key Takeaways

Workspace to package to node is the core ROS 2 project structure
colcon + ament is the standard build tool chain
--symlink-install speeds up the Python dev loop
Register executables via entry_points in setup.py
rqt_graph, ros2 node list, and ros2 node info are your first debugging tools

Open this lesson

Mahmoud AbasHow it works ?

sudo sh -c 'echo "deb [arch=amd64,arm64] http://repo.ros2.org/ubuntu/main `lsb_release -cs` main" > /etc/apt/sources.list.d/ros2-latest.list' curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc | sudo apt-key add - sudo apt update sudo apt install python3-colcon-common-extensions source /usr/share/colcon_argcomplete/hook/colcon-argcomplete.bash