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Module 1: The Robotic Nervous System (ROS 2)

1. Introduction: The Nervous System of Robotics​

Just as a biological nervous system transmits signals between the brain (planning) and the muscles (actuation), a robot needs a robust middleware to communicate between its software components. Robot Operating System 2 (ROS 2) is that nervous system.

In this module, we move away from monolithic codebases—where one error crashes the whole robot—and adopt a Distributed Node Architecture.

Why ROS 2? (vs. ROS 1)​

For the "Physical AI" era, we use ROS 2 because of three critical upgrades:

  1. DDS (Data Distribution Service): Unlike ROS 1, which relied on a central "Master" node (a single point of failure), ROS 2 uses industry-standard DDS for decentralized communication.
  2. Real-Time Capabilities: Essential for safety-critical tasks like humanoid balancing, where a millisecond delay can cause a fall.
  3. Python 3 First: Native support for modern AI libraries (PyTorch, TensorFlow) which we will need for our VLA modules.

2. Key Concepts: The Anatomy of Communication​

To build our "Butler Bot," you must master these four primitives:

  • Nodes: Independent executable processes. Think of them as individual neurons. One node reads the camera, another controls the wheels.
  • Topics: The "veins" of the system. Nodes publish data to topics (e.g., /camera/image_raw) or subscribe to them. This is asynchronous (Fire-and-forget).
  • Services: A synchronous two-way handshake. "I request X, you give me Y." (e.g., "Spawn a new object" or "Reset Simulation").
  • Actions: Designed for long-running tasks. "Go to the kitchen." This takes time, so the robot provides feedback ("I am 50% there") and allows cancellation ("Stop!").

3. Implementation: Setting Up Your Reflex Arc​

We will implement a basic "reflex arc" to demonstrate real-time interaction. This mimics a biological withdrawal reflex: Stimulus (Sensor) → Processing → Response (Motor).

Step 1: Environment Setup​

First, we verify our ROS 2 installation. Open your terminal and source the underlay:

source /opt/ros/jazzy/setup.bash
# Verify installation
printenv | grep ROS