ROS2 TurtleSim Goal-Seeking with PID Control

An autonomous navigation implementation for the ROS2 turtlesim environment. This project demonstrates a decoupled control strategy where a robot first rotates toward a waypoint and then translates toward it using tuned PID (Proportional-Integral-Derivative) controllers.

Overview

This repository contains a ROS2 package that enables a robot to follow a series of waypoints defined in a configuration file. The project is split into two phases:

1. Part 1: Basic Goal Seeker – Implements the core logic to parse waypoints and navigate using a simple proportional controller and state-based movement (rotate-then-translate).
2. Part 2: Full PID Controller – Enhances the movement profile by implementing full PID logic for both linear and angular velocities, ensuring smooth acceleration and deceleration while minimizing overshoot.

Installation

Prerequisites

• ROS2 Humble (or compatible version)
• tf_transformations:

sudo apt install ros-humble-tf-transformations

Build

1. Clone this repository into your colcon workspace src folder.
2. Navigate to the workspace root and build:

colcon build --packages-select goal_seek
source install/setup.bash

Usage

Running the PID Controller (Part 2)

To launch the full PID-controlled navigation along with the simulator:

ros2 launch goal_seek goal_seek_part_2.launch.py

Configuration

Waypoints are managed via a text file located at goal_seek/config/goals.txt. The format is simple space-separated x y coordinates:

4.5 6.4
7.6 2.4
8.7 2.3

Control Logic

The robot follows a state-machine approach within the Odometry callback:

1. Heading Correction: If the angular error exceeds the threshold, the robot stops linear movement and rotates.
2. Translation: Once facing the goal, the robot moves forward, using the PID controller to ramp down velocity as it approaches the coordinate.
3. Wait State: Upon reaching a goal (within a defined distance threshold), the robot pauses for 5 seconds before fetching the next waypoint.

PID Implementation

The control output is calculated as:

Where:

• Proportional (): Corrects based on current error.
• Integral (): Eliminates steady-state error.
• Derivative (): Dampens oscillations and prevents overshoot.

Project Structure

• goal_seek_part_2.py: The primary node featuring the PID controller.
• publish_odom.py: A utility node that converts turtlesim/Pose data into standard nav_msgs/Odometry.
• launch/: Contains Python launch files to bring up the simulation and controllers simultaneously.

Resources

• https://pidexplained.com/pid-controller-explained/
• https://docs.ros.org/en/humble/p/nav_msgs/msg/Odometry.html
• Getting current time in ros2 : self.get_clock().now()
• TF Transformations