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Courses/ROS 2 Practical

TurtleBot3 Lab 07 - Autonomous Navigation with Nav2

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TurtleBot3 Lab 07: Autonomous Navigation with Nav2

From a saved map to autonomous goal-reaching

This lab introduces autonomous navigation using the Nav2 stack. Building on SLAM from Lab 06, students learn to use pre-built maps for robot localization and path planning.

Learning Objectives

  • Understand the Nav2 navigation stack architecture
  • Learn about AMCL (Adaptive Monte Carlo Localization)
  • Experience autonomous path planning and execution
  • Practice setting navigation goals using RViz

Prerequisites

  • Completion of Lab 06 (SLAM fundamentals)
  • Nav2 packages installed: 
    sudo apt install ros-jazzy-navigation2 ros-jazzy-nav2-bringup

Quick Start - Lab07 Package

Step 1: Build the Package

cd ~/Desktop/ROS-2-Practical-Course-Roadmap-2025/ros_ws
colcon build --packages-select turtlebot3_lab07
source install/setup.bash

Step 2: Launch Navigation

export TURTLEBOT3_MODEL=waffle_pi
ros2 launch turtlebot3_lab07 lab07.launch.py

This launches Gazebo, Nav2, and RViz in a single command.

  • Example with a map saved in ~/maps:
cd ~/Desktop/ROS-2-Practical-Course-Roadmap-2025/ros_ws
source /opt/ros/jazzy/setup.bash
source install/setup.bash
export TURTLEBOT3_MODEL=waffle_pi
ros2 launch turtlebot3_lab07 lab07.launch.py map:=$HOME/maps/my_map.yaml

Step 3: Set Initial Pose (REQUIRED)

IMPORTANT: You MUST set the initial pose before the robot can navigate.

  source /opt/ros/jazzy/setup.bash
  ros2 topic pub /initialpose geometry_msgs/msg/PoseWithCovarianceStamped "{header: {frame_id: 
  'map'}, pose: {pose: {position: {x: -2.0, y: -0.5, z: 0.0}, orientation: {w: 1.0}}}}" --once

Step 4: Send Navigation Goals

  1. Click "2D Goal Pose" button in RViz toolbar
  2. Click and drag on the map where you want the robot to go
  3. Watch the robot autonomously plan a path and navigate!

Alternative: Set initial pose via command line:

ros2 topic pub /initialpose geometry_msgs/msg/PoseWithCovarianceStamped \
  "{header: {frame_id: 'map'}, pose: {pose: {position: {x: -2.0, y: -0.5, z: 0.0}, orientation: {w: 1.0}}}}" --once

Optional: Use Your Own Map from Lab 06

export TURTLEBOT3_MODEL=waffle_pi
ros2 launch turtlebot3_lab07 lab07.launch.py map:=$HOME/maps/my_map.yaml

Package Structure

ros_ws/turtlebot3_lab07/
├── package.xml                 # Package dependencies
├── setup.py                    # Build configuration
├── resource/turtlebot3_lab07   # Package marker
├── launch/lab07.launch.py      # All-in-one launch file
└── turtlebot3_lab07/__init__.py

The launch file starts:

  • Gazebo simulation (TurtleBot3 World)
  • Nav2 stack (AMCL, planners, controllers, costmaps)
  • RViz with navigation visualization

Nav2 Components

ComponentDescription
AMCLEstimates robot pose on a known map
Map ServerLoads and serves the occupancy grid map
Planner ServerComputes global paths from start to goal
Controller ServerExecutes path with local obstacle avoidance
BT NavigatorBehavior Tree-based navigation orchestration

Key Topics

TopicDescription
/mapStatic map from map server
/scanLIDAR data for localization
/cmd_velVelocity commands to robot
/goal_poseNavigation goal from RViz
/planComputed global path

Using RViz for Navigation

Setting Initial Pose

The robot doesn't know where it is on the map initially. You must tell it:

  1. Click "2D Pose Estimate" button
  2. Click on the map where the robot is located
  3. Drag to set the orientation (direction robot is facing)
  4. Watch the particle cloud (red arrows) converge

Sending Navigation Goals

  1. Click "2D Goal Pose" button
  2. Click on the map destination
  3. Drag to set desired final orientation
  4. Watch the robot plan and execute the path

Troubleshooting

Gazebo/RViz Frozen or Static

  • Ensure you sourced the workspace: source install/setup.bash
  • Wait at least 30 seconds for full initialization
  • Check if simulation clock is advancing: ros2 topic echo /clock --once
  • Kill any leftover processes: pkill -f "ros2|gazebo|rviz" and retry

Robot Not Localizing

  • Ensure initial pose is set correctly (Step 3)
  • The robot spawns at (-2, -0.5) in TurtleBot3 World
  • Drive slowly to help AMCL converge

Navigation Fails to Plan

  • Check goal is in free space (white area on map)
  • Try a closer goal first
  • Verify TF: ros2 run tf2_tools view_frames

"Waiting for Transform" Errors

  • Wait longer for initialization (~30 seconds)
  • Ensure all nodes started: ros2 node list

Useful Commands

# Check Nav2 nodes are running
ros2 node list | grep -E "amcl|planner|controller|bt_navigator"
 
# Monitor navigation status
ros2 topic echo /navigate_to_pose/_action/status
 
# View TF tree
ros2 run tf2_tools view_frames
 
# Send navigation goal via command line
ros2 action send_goal /navigate_to_pose nav2_msgs/action/NavigateToPose \
  "{pose: {header: {frame_id: 'map'}, pose: {position: {x: 0.5, y: 0.5}, orientation: {w: 1.0}}}}"

Nav2 Architecture

                    ┌─────────────────┐
                    │   RViz Goal     │
                    │  (2D Goal Pose) │
                    └────────┬────────┘
                             │
                             ▼
                    ┌─────────────────┐
                    │  BT Navigator   │
                    └────────┬────────┘
                             │
              ┌──────────────┼──────────────┐
              ▼              ▼              ▼
     ┌────────────┐  ┌────────────┐  ┌────────────┐
     │  Planner   │  │ Controller │  │  Behavior  │
     │ (Global)   │  │  (Local)   │  │ (Recovery) │
     └─────┬──────┘  └─────┬──────┘  └────────────┘
           │               │
           ▼               ▼
     ┌────────────┐  ┌────────────┐
     │  Global    │  │   Local    │
     │  Costmap   │  │  Costmap   │
     └────────────┘  └────────────┘
                   │
            ┌──────┴──────┐
            │    AMCL     │
            │ (Localize)  │
            └─────────────┘

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