🐢 ROS2 Turtlesim Controller & Monitor

A ROS2 package that implements a multi-node control system for turtlesim. This project demonstrates process management, custom service calls, subscriber/publisher patterns, and safety monitoring within the ROS2 ecosystem.

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📑 Table of Contents

• Overview
• Project Architecture
• Installation & Build
• Usage
• Nodes Description
• Safety Features

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📖 Overview

This package allows users to interactively control two turtles in a simulation while a background monitoring process ensures safety. It features:

• ✅ Automatic Setup: Spawns a second turtle immediately upon launch.
• ✅ Interactive UI: A dedicated terminal interface for sending velocity commands.
• ✅ Safety Monitor: A high-priority node that overrides user commands to prevent collisions or boundary breaches.

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📂 Project Architecture

assignment1_rt/
├── launch/
│   └── assignment1.launch.py      # Main launch file (Orchestrator)
├── assignment1_rt/
│   ├── __init__.py
│   ├── ui_node.py                 # User Interface (Input)
│   ├── distance_monitor.py        # Safety Controller (Logic)
│   ├── distance_checks.py         # Helper Class (Calculations)
│   └── turtle_spawn.py            # Service Client (Setup)
├── package.xml
├── setup.py
└── setup.cfg

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⚙️ Installation & Build

Assuming ROS2 Humble and its dependencies are already installed:

1. Navigate to your ROS2 workspace src folder:

   cd ~/ros2_ws/src

2. Clone the repository from GitHub:

   git clone https://github.com/Belal-Elmikkawy/Assignment1_RT1.git

3. Go back to the workspace root and install dependencies:

   cd ~/ros2_ws
   rosdep install --from-paths src --ignore-src -r -y

4. Build the package:

   colcon build --packages-select assignment1_rt

5. Source the setup file:

   source install/setup.bash

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🚀 Usage

Run the entire project with:

ros2 launch assignment1_rt assignment1.launch.py

The Interface

A new terminal window titled ui_node will appear. Use it to control the robots:

• Select Robot: turtle1 or turtle2
• Linear X: Speed forward (+) or backward (-)
• Angular Z: Rotation speed (Clockwise/Counter-Clockwise)

Note: The turtle moves for 1.0 second and then stops automatically.

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📦 Nodes Description

1. ui_node.py – User Interface Node

• Purpose: Provides an interactive terminal interface for the user.
• Functionality:
  • Captures user input for selecting the turtle (turtle1 or turtle2).
  • Accepts velocity commands: Linear X and Angular Z.
  • Publishes geometry_msgs/Twist messages to the corresponding topic (/turtleX/cmd_vel).
• Interaction:
  • Works independently but sends commands that can be overridden by the safety monitor.

2. distance_monitor.py – Safety Controller Node

• Purpose: Ensures safe operation of both turtles.
• Functionality:
  • Subscribes to /turtle1/pose and /turtle2/pose topics.
  • Calculates the Euclidean distance between turtles using helper functions.
  • Checks for collisions and boundary violations.
  • Publishes zero velocity to turtles if safety conditions are breached.
• Interaction:
  • Overrides commands from ui_node when safety limits are exceeded.

3. distance_checks.py – Helper Class

• Purpose: Provides reusable functions for distance and boundary calculations.
• Functionality:
  • Computes Euclidean distance between two points.
  • Validates if a turtle is within safe boundaries.
• Interaction:
  • Used internally by distance_monitor.py for logic processing.

4. turtle_spawn.py – Service Client Node

• Purpose: Spawns the second turtle in the simulation.
• Functionality:
  • Calls the /spawn service provided by turtlesim.
  • Places turtle2 at coordinates (7.0, 7.0) with a default orientation.
• Interaction:
  • Runs once at launch to set up the environment.

5. turtlesim_node – Simulator Node

• Purpose: The standard ROS2 turtlesim node.
• Functionality:
  • Provides the simulation environment for the turtles.
  • Offers topics like /turtleX/cmd_vel and /turtleX/pose for control and monitoring.
• Interaction:
  • Acts as the base system that other nodes interact with.

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🛡 Safety Features

The distance_monitor node runs at 10Hz and performs:

• Collision Detection:
  • Condition: Distance between turtle1 and turtle2 < 2.0.
  • Action: Publishes 0.0 velocity to both turtles immediately.
• Boundary Constraints:
  • Condition: Any turtle gets closer than 1.0 unit to the wall (0 or 11).
  • Action: Stops the specific turtle approaching the wall.

When a safety breach occurs, a warning is logged:

[WARN] [distance_monitor]: Turtles too close! Dist: 1.45

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