Random Explorer Bot - Autonomous Navigation with Nav2

Overview

An Autonomous Exploration System built with ROS2 and Nav2 that enables robots to continuously explore unknown environments. The system generates random navigation goals within specified boundaries, validates them against the current SLAM map, and handles unreachable goals gracefully with automatic timeout and retry mechanisms.

Key Features

• Dynamic Mapping: Real-time map generation using SLAM Toolbox
• Random Goal Generation: Smart goal selection with map validation and distance constraints
• Continuous Exploration: Autonomous navigation without human intervention
• Goal Timeout Handling: Automatic cancellation of unreachable goals
• Intelligent Obstacle Avoidance: Dynamic collision prevention using Nav2
• Visual Feedback: Colorful goal markers and progress tracking in RViz

System Architecture

graph TD
    A[Exploration Controller] --> B[Random Goal Generator]
    A --> C[Map Validator]
    A --> D[Nav2 Action Client]
    D --> E[Nav2 Stack]
    E --> F[Controller Server]
    E --> G[Planner Server]
    E --> H[Behavior Server]
    I[SLAM Toolbox] --> J[Dynamic Map]
    J --> C
    C --> B

Loading

Component Overview

Component	Responsibility
Exploration Controller	Main orchestration, state management, goal timeout handling
Random Goal Generator	Boundary-aware random points with min/max distance constraints
Map Validator	Collision-free goal validation with circular clearance check
Nav2 Stack	Path planning, obstacle avoidance
SLAM Toolbox	Real-time environment mapping

Prerequisites

System Requirements

• OS: Ubuntu 22.04 LTS
• ROS2: Humble Hawksbill
• RAM: 4GB minimum (8GB recommended)

Required Dependencies

sudo apt update
sudo apt install -y \
  ros-humble-desktop-full \
  ros-humble-navigation2 \
  ros-humble-nav2-bringup \
  ros-humble-slam-toolbox \
  ros-humble-turtlebot3* \
  ros-humble-gazebo-ros-pkgs \
  python3-colcon-common-extensions

Quick Start

Environment Setup

echo "export TURTLEBOT3_MODEL=burger" >> ~/.bashrc
source ~/.bashrc

Build

cd ~/nav2_explorer_ws
colcon build --packages-select random_explorer_bot
source install/setup.bash

Launch

Terminal 1 - Gazebo Simulation:

export TURTLEBOT3_MODEL=burger
ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py

Terminal 2 - Navigation & Exploration:

cd ~/nav2_explorer_ws
source install/setup.bash
ros2 launch random_explorer_bot explorer_nav.launch.py

Project Structure

random_explorer_bot/
├── config/
│   ├── nav2_params.yaml              # Navigation2 configuration
│   ├── exploration_params.yaml       # Exploration boundaries & timeouts
│   └── rviz_config.rviz             # Visualization settings
├── include/random_explorer_bot/
│   ├── random_goal_generator.hpp     # Goal generation logic
│   ├── exploration_controller.hpp    # Main controller
│   └── map_validator.hpp            # Map validation utilities
├── launch/
│   └── explorer_nav.launch.py        # Main launch file
├── src/
│   ├── exploration_controller.cpp    # Controller implementation
│   └── main.cpp                      # Node entry point
├── CMakeLists.txt
├── package.xml
└── README.md

Configuration

Exploration Parameters (config/exploration_params.yaml)

exploration_controller:
  ros__parameters:
    exploration_bounds:
      min_x: -4.5
      max_x: 4.5
      min_y: -4.5
      max_y: 4.5
    exploration_frequency: 0.5    # Hz
    goal_timeout_sec: 30.0        # Cancel unreachable goals after 30s
    min_goal_distance: 1.5        # Minimum distance from robot
    max_goal_attempts: 200

Key Nav2 Parameters (config/nav2_params.yaml)

bt_navigator:
  ros__parameters:
    default_server_timeout: 10    # Faster timeout for unreachable goals

planner_server:
  ros__parameters:
    GridBased:
      tolerance: 0.3              # Smaller tolerance = fails faster

controller_server:
  ros__parameters:
    max_vel_x: 0.26
    max_vel_theta: 1.0
    xy_goal_tolerance: 0.3
    yaw_goal_tolerance: 0.3

System Behavior

1. Initialize: Wait for map and Nav2 to be ready
2. Generate Goal: Create random valid goal within boundaries (min 1.5m from robot)
3. Navigate: Move to goal while avoiding obstacles
4. Handle Timeout: If goal unreachable for 30s, cancel and generate new goal
5. Repeat: Continue exploring indefinitely

Troubleshooting

Issue	Solution
"Failed to generate valid goal"	Increase exploration boundaries
Robot not moving	Wait 15-20 seconds for SLAM initialization
"worldToMap failed" errors	Normal - goal is outside mapped area, will auto-retry
Robot stuck on goal	Will timeout after 30s and try new goal

Debug Commands

# Check map
ros2 topic echo /map --once

# Verify Nav2
ros2 action list | grep navigate_to_pose

# Monitor goals
ros2 topic echo /exploration_goal_marker

Resources

• Nav2 Documentation
• SLAM Toolbox
• TurtleBot3 Manual
• ROS2 Humble Docs