Crash Course on Navigation to Stack with ROS 2

Introduction

• Target Audience: Beginners or those needing a refresher on the basics of Nav2.
• Content Overview: Install Nav2 stack, generate a map with SLAM, navigate using the map, and use TurtleBot 3 in simulation.
• Requirements: ROS 2 Humble installed on Ubuntu 22.04, preferably as a dual boot (not in VM). Basic knowledge of ROS 2.

Installing Nav2 Stack

• Ensure ROS 2 Humble is installed (source /opt/ros/humble/setup.bash in .bashrc).
• Update system: sudo apt update
• Install packages: sudo apt install ros-humble-navigation2 ros-humble-nav2-bringup sudo apt install ros-humble-turtlebot3*

Starting the TurtleBot 3 Simulation

• Source TurtleBot 3 model: export TURTLEBOT3_MODEL=waffle (add to .bashrc).
• Run Gazebo to simulate the environment: ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py
• Start teleoperation node: ros2 run turtlebot3_teleop teleop_keyboard

Generating a Map with SLAM

• Open three terminals:
  1. Launch TurtleBot 3 in Gazebo.
  2. Launch Cartographer for SLAM: ros2 launch turtlebot3_cartographer cartographer.launch.py use_sim_time:=true
  3. Start teleoperation node to move robot.
• Move the robot around to generate the map. Ensure full exploration of the space.
• Save the generated map: mkdir -p ~/maps ros2 run nav2_map_server map_saver_cli -f ~/maps/mymap

Understanding the Map Files

• .pgm file: Image of the map where white represents free space, black represents obstacles, and gray represents unknown regions.
• .yaml file: Metadata that includes image, resolution (meters per pixel), origin, negate, and occupied_thresh and free_thresh for defining occupied and free space probabilities.

Fixing Navigation 2 Issues

• Change DDS from Fast DDS to Cyclone DDS: sudo apt install ros-humble-rmw-cyclone-dds-cpp export RMW_IMPLEMENTATION=rmw_cyclone_dds_cpp (add `export RMW_IMPLEMENTATION=rmw_cyclone_dds_cpp` to `.bashrc`)
• Edit turtlebot3_navigation2 parameter file: sudo nano /opt/ros/humble/share/turtlebot3_navigation2/param/waffle.yaml # Modify 'robot_model_type' parameter robot_model_type: nav2_amcl::DifferentialMotionModel

Making the Robot Navigate Using the Map

• Start the simulation: ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py
• Launch navigation with the saved map: ros2 launch turtlebot3_navigation2 navigation2.launch.py use_sim_time:=true map:=~/maps/mymap.yaml
• In RViz, set the initial 2D pose estimate to align the robot with the map.
• Use the 2D Nav Goal tool in RViz to set a destination for the robot.

Waypoint Navigation

• Click on Waypoint Nav Tool in RViz.
• Set multiple waypoints on the map and start Waypoint following.
• Use Start Nav Through Poses for continuous navigation through waypoints (less stable).

Conclusion

• This crash course provides foundational knowledge to start with Nav2.
• For advanced understanding, including custom worlds, robots, and programming, refer to the extended course with over 6 hours of video content and practice activities.