Turtle Controller - ROS 2 Humble Tutorial Package

A comprehensive beginner-friendly ROS 2 package demonstrating fundamental concepts using the turtlesim simulator. This package includes examples of publishers, subscribers, services, clients, and launch files.

Overview

This package is designed as a complete learning resource for ROS 2 beginners. It demonstrates:

• Topic Publishers - Sending velocity commands to control turtle movement
• Topic Subscribers - Receiving and displaying turtle pose information
• Service Servers - Providing rotation services
• Service Clients - Calling rotation services
• Launch Files - Starting multiple nodes simultaneously

Learning Objectives

By working through this package, you will learn:

• How to create and structure a ROS 2 workspace
• How to create a Python-based ROS 2 package
• How to implement publishers and subscribers
• How to create and use services
• How to write launch files for complex systems
• ROS 2 best practices and conventions

Prerequisites

• Ubuntu 22.04 (Jammy Jellyfish)
• ROS 2 Humble installed and configured
• Python 3.10+
• Basic understanding of Python programming
• Terminal/command line familiarity

Installation Check

Verify your ROS 2 installation:

ros2 --version

You should see output similar to: ros2 cli version: 0.18.x

Learning Outcomes

After completing these exercises, you should be able to:

• Create ROS 2 workspaces and packages
• Write publisher nodes that send messages
• Write subscriber nodes that receive messages
• Create service servers that handle requests
• Create service clients that call services
• Write launch files to manage multiple nodes
• Use ROS 2 command-line tools for debugging
• Understand the publish-subscribe pattern
• Understand the request-response pattern

Exercises

1. Exercise 1: Setting Up Your Workspace
2. Exercise 2: Creating a Topic Publisher
3. Exercise 3: Creating a Topic Subscriber
4. Exercise 4: Creating a Service Server
5. Exercise 5: Creating a Service Client
6. Exercise 6: Creating Launch Files

Verification Checklist

Use this checklist to verify you've completed everything:

• Workspace created and built successfully
• Package created with correct dependencies
• Velocity publisher moves turtle in a circle
• Pose subscriber prints turtle position
• Rotate service can be called manually
• Rotate client works from command line
• Basic launch file starts all nodes
• All nodes appear in ros2 node list
• All topics appear in ros2 topic list

Next Steps

Once you've completed all exercises:

1. Experiment: Modify the velocity values to create different movement patterns
2. Extend: Add new features (e.g., move to specific coordinates)
3. Optimize: Can you reduce code duplication?
4. Document: Add detailed comments explaining your code
5. Share: Help others who are stuck!

Final Package Structure

turtle_controller/
├── launch/
│   ├── turtle_system_launch.py          # Basic launch file
│   └── turtle_complete_launch.py        # Comprehensive launch file
├── turtle_controller/
│   ├── __init__.py
│   ├── velocity_publisher.py            # Publishes velocity commands
│   ├── pose_subscriber.py               # Subscribes to turtle pose
│   ├── rotate_service.py                # Service server for rotation
│   └── rotate_client.py                 # Service client for rotation
├── package.xml                          # Package metadata
├── setup.py                             # Python package setup
├── setup.cfg                            # Package configuration
└── README.md                            # This file

Useful Commands

Inspect Running System

# List all nodes
ros2 node list

# List all topics
ros2 topic list

# See topic info
ros2 topic info /turtle1/cmd_vel

# Echo topic messages
ros2 topic echo /turtle1/pose

# List services
ros2 service list

# See service type
ros2 service type /rotate_turtle

# View computational graph
rqt_graph

Additional Resources

Official Documentation

• ROS 2 Documentation
• ROS 2 Tutorials
• Turtlesim Documentation

Learning Materials

• Understanding ROS 2 Nodes
• Understanding Topics
• Understanding Services
• Creating Launch Files