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Weeks 3-5: ROS 2 Fundamentals

Learning Objectives​

During these three weeks, students will master the core concepts and tools of ROS 2, the middleware framework that enables communication between different components of a robotic system.

Topics Covered​

  • ROS 2 architecture and core concepts

    • Understanding the distributed computing model
    • Nodes, topics, services, and actions
    • The DDS (Data Distribution Service) communication layer

  • Nodes, topics, services, and actions

    • Creating and managing ROS 2 nodes
    • Publisher-subscriber pattern with topics
    • Request-response pattern with services
    • Long-running tasks with actions

  • Building ROS 2 packages with Python

    • Package structure and organization
    • Creating nodes in Python using rclpy
    • Managing dependencies and build configurations

  • Launch files and parameter management

    • Organizing complex systems with launch files
    • Managing system parameters
    • Configuration management for different environments

Key Concepts​

ROS 2 Architecture​

ROS 2 uses a distributed computing architecture based on the Data Distribution Service (DDS) standard. This provides:

  • Decentralized communication: No single point of failure
  • Language independence: Nodes can be written in different programming languages
  • Transport flexibility: Multiple transport mechanisms (TCP, UDP, shared memory)
  • Quality of Service (QoS): Configurable communication behavior for different use cases

Communication Patterns​

ROS 2 provides four main communication patterns:

  1. Topics (Publish/Subscribe): Asynchronous, many-to-many communication
  2. Services (Request/Response): Synchronous, one-to-one communication
  3. Actions: Asynchronous, long-running tasks with feedback
  4. Parameters: Configuration values shared across nodes

rclpy​

rclpy is the Python client library for ROS 2. It provides:

  • Node creation and management
  • Publisher and subscriber interfaces
  • Service and action clients/servers
  • Parameter handling
  • Time and logging utilities

Practical Exercises​

  1. Create a simple publisher and subscriber
  2. Implement a service server and client
  3. Build a ROS 2 package with multiple nodes
  4. Use launch files to start complex systems
  5. Manage parameters for different robot configurations

Assignments​

  1. ROS 2 package development project
  2. Implement a simple robot controller using ROS 2
  3. Create a launch file for a multi-node system