Waypoint Follower Robot

The following repository tries to build a robot from scratch, put a lidar on it and then navigate through 4 waypoints. It also tries to dockerize the entire application so that it can work on any computer.

This repository was made by following this tutorial - (https://automaticaddison.com/the-ultimate-guide-to-the-ros-2-navigation-stack).

URDF and SDF Files

In the models folder, there is a URDF file. This URDF file describes the entire robot structure with joint and sensor information. This robot, named basic_mobile_bot, features a main chassis with two rear drive wheels and a front caster wheel for mobility. It includes a LIDAR sensor, mounted on a fixed base. It is said that URDFs don’t always work that well with Gazebo. It is recommended to use an SDF file for Gazebo stuff and a URDF file for ROS stuff. Thus there is also a SDF file present.

Creating the world

The map of the world is given in maps. The actual world is in the worlds folder. It is imperative that the robot_model_type in nav2_params.yam is set to "nav2_amcl::DifferentialMotionModel". Otherwise RViz does not import the map correctly. Also it is imperative to allow publishment of odom by keeping <publish_odom_tf>true</publish_odom_tf>. This allows for the system to callculate transformations between odom and other frames in the robot.

The launch folder has the launch file. It loads all the appropriate data files and then launches nodes like robot_state_publisher,'rviz2 etc. We are not using the robot_localisation package and the only sensor on board is the lidar and thus the robot's localisation wouldn't be that good.

I have set the initial_pose of the robot already in the nav2_params.yaml.

Waypoint following node

There were 4 waypoints given to the environment once it loaded. The script for this is given in src/waypoint_follower.py. This script is adopted from Samsung Research. This script accepts 4 poses and continually sends signals to the robot to go to the required waypoint. It also has a feedback where it stops when it has reached a waypoint.

Running the Code

Prerequisites

• Ubuntu 22
• ROS 2 Humble
• Nav2 packages

Instructions

0. Install Nav2

   sudo apt install ros-humble-navigation2
   sudo apt install ros-humble-nav2-bringup
   

1. Build the package

   colcon build
   source install/setup.bash
   

2. Set Environment Variables:

   • Add the following lines to your .bashrc file:

     source /opt/ros/humble/setup.bash  
     export GAZEBO_MODEL_PATH=$GAZEBO_MODEL_PATH:/home/shounak/dev_ws/src/basic_mobile_robot/models/
     

     Into the terminal,

     source install/setup.bash

3. Launch Nav2 and the Entire Simulations:

   ros2 launch basic_mobile_robot basic_mobile_bot.launch.py
   

   This will load the world along with all the nodes like nav2.

4. Launch the WayPoint Follower Node:

   • Open a new terminal and run:

     source install/setup.bash
     ros2 run basic_mobile_robot waypoint_follower.py
     

   • The robot should follow to the waypoints and then stop after the 4 waypoints.

Visualization

Here's a video demonstrating the robot following 4 waypoints:

video.mp4