Background#
I've become an instructor at APTRG to teach about the Robot Operating System (ROS2). In this post, I want to share with you what we've learned together.
Chapter 1: Introduction#
- We use Ubuntu Noble 24.04 LTS as Operating System.
- Robot Operating System version is Jazzy EOL — support until 2029.
- Our goal is to implement drone control with PX4 firmware.
- We start from beginner to advance.
- ROS2 has ROS Client Layer (RCL) and ROS Middleware Layer (RMW).
- Robot implements Guidance, Navigation, and Control (GNC).
Jazzy Installation#
- Follow the official guide here.
- Make sure to source jazzy setup file to
.bashrc
Beginner: CLI Tools#
- Demo Turtlesim here.
- Use RQT to show topic and call service.
- Observe
/cmd_vel- Twist -> linear and angular (x, y, z).
- if linear: x++, turtle will go forward. otherwise
- if angular: z++, turtle will yaw counter clockwise, otherwise.
Understanding Nodes#
- Each node in ROS should be responsible for a single, modular purpose — e.g controlling the wheel motors, publishing sensor data.
- Each node can send and receive data from other nodes via topics, services, actions, or parameters.
Understanding Topics#
- ROS use topic to communicate between node.
- Publish and Subscribe — Asynchronous N:M communication ()
- Node can subscribe and publish many topics.
Understanding Services#
- a service is a request/response pattern where a client makes a request to a node providing the service and the service processes the request and generates a response
- Synchronous 1:1 communication.
- Not use a service for continuous calls; topics or even actions would be better suited.
Understanding Parameters#
- Nodes have parameters to define their default configuration values.
- Can get and set parameter values from the command line.
- Can also save the parameter settings to a file to reload them in a future session.