Introduction to ROS 2

AdvancedAdvanced45 minBefore this: Functions, Raspberry Pi and Pico

What you’ll learn

What ROS 2 is (and isn’t)
Nodes, topics, services and actions
What a tiny ROS 2 program looks like, and how to start

What is ROS 2?

ROS 2 (Robot Operating System 2) isn’t an operating system: it’s a free, open-source framework of tools and libraries that runs on Linux (and others), used by universities and companies to build complex robots. Its big idea is splitting a robot’s software into many small programs that talk to each other.

The building blocks

Concept	What it is	Example
Node	One small program with one job	`camera_node`, `motor_driver`, `planner`
Topic	A named channel; nodes publish messages to it and others subscribe	`/scan` (laser data), `/cmd_vel` (speed commands)
Message	A typed data structure	`Twist` = linear and angular speed
Service	A request with a reply	“Reset the map” → “done”
Action	A long task with progress updates	“Drive to the kitchen” → “50%… arrived”
Launch file	Starts many nodes together	Start the whole robot with one command

 [lidar node] --/scan--> [SLAM node] --/map--> [planner] --/cmd_vel--> [motor node]

Because every node uses the same message types, you can swap a real robot for a simulator, or one lidar for another, without rewriting everything.

Getting started

Install the current long-term support (LTS) release on Ubuntu Linux, following the official docs at docs.ros.org (a Raspberry Pi 4/5 can run it).
Try turtlesim (a 2D turtle robot) and the beginner tutorials.
Use the command-line tools: ros2 topic list, ros2 topic echo /topic, ros2 run.

A minimal Python publisher (rclpy)

import rclpy
from rclpy.node import Node
from geometry_msgs.msg import Twist

class Driver(Node):
    def __init__(self):
        super().__init__('driver')
        self.pub = self.create_publisher(Twist, '/cmd_vel', 10)
        self.create_timer(0.1, self.tick)       # 10 times a second

    def tick(self):
        msg = Twist()
        msg.linear.x = 0.2     # metres per second forward
        msg.angular.z = 0.5    # radians per second turning
        self.pub.publish(msg)

def main():
    rclpy.init()
    rclpy.spin(Driver())

if __name__ == '__main__':
    main()

With turtlesim running, publishing to /turtle1/cmd_vel instead makes the turtle drive in a circle.

Where Arduinos fit

A common design: ROS 2 runs on a Raspberry Pi or laptop, and a microcontroller handles motors and encoders, connected over USB (for example with micro-ROS or a simple serial bridge).

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