Project2

Project #2 - Go Chase It!

Summary of Tasks

In this project, you should create two ROS packages inside your catkin_ws/src: the drive_bot and the ball_chaser. Here are the steps to design the robot, house it inside your world, and program it to chase white-colored balls:

1. drive_bot:

   • Create a my_robot ROS package to hold your robot, the white ball, and the world.
   • Design a differential drive robot with the Unified Robot Description Format. Add two sensors to your robot: a lidar and a camera. Add Gazebo plugins for your robot’s differential drive, lidar, and camera. The robot you design should be significantly different from the one presented in the project lesson. Minimum required changes are adjusting the color, wheel radius, and chassis dimensions. You can also completely redesign the robot model!
   • Create a new world, which is different from the world you built in the Build My World project and house your robot inside that world.
   • Add a white-colored ball to your Gazebo world and save a new copy of this world.
   • The world.launch file should launch your world with the white-colored ball and your robot.

2. ball_chaser:

   • Create a ball_chaser ROS package to hold your C++ nodes.
   • Write a drive_bot C++ node that will provide a ball_chaser/command_robot service to drive the robot by controlling its linear x and angular z velocities. The service should publish to the wheel joints and return back the requested velocities.
   • Write a process_image C++ node that reads your robot’s camera image, analyzes it to determine the presence and position of a white ball. If a white ball exists in the image, your node should request a service via a client to drive the robot towards it.
   • The ball_chaser.launch should run both the drive_bot and the process_image nodes.

Directory Structure

.Project2
├── ball_chaser                         # ball_chaser package
│   ├── CMakeLists.txt                  # compiler instructions
│   ├── launch                          # launch folder for launch files
│   │   └── ball_chaser.launch
│   ├── package.xml                     # package info
│   ├── src                             # source folder for C++ scripts
│   │   ├── drive_bot.cpp
│   │   └── process_image.cpp
│   └── srv                             # service folder for ROS services
│       └── DriveToTarget.srv
├── images                              # output results
│   ├── demo.gif
│   ├── gazebo1.png
│   ├── gazebo2.png
│   └── rviz.png
├── my_robot                            # my_robot package
│   ├── CMakeLists.txt                  # compiler instructions
│   ├── launch                          # launch folder for launch files
│   │   ├── robot_description.launch
│   │   └── world.launch
│   ├── meshes                          # meshes folder for sensors
│   │   └── hokuyo.dae
│   ├── package.xml                     # package info
│   ├── urdf                            # urdf folder for xarco files
│   │   ├── my_robot.gazebo
│   │   └── my_robot.xacro
│   └── worlds                          # world folder for world files
│       ├── empty.world
│       └── UdacityOffice.world
└── README.md

Build Instructions

1. Open Terminal/CLI by using Ctrl + Alt + T shortcut.
2. Create and initialize a catkin_ws

mkdir -p /<your_dir>/catkin_ws/src
cd /<your_dir>/catkin_ws/src
catkin_init_workspace

3. Clone this repo inside /<your_dir>/catkin_ws/src
4. Ensure src directory has my_robot and ball_chaser directory inside it
5. Switch to catkin_ws

cd /<your_dir>/catkin_ws

7. Build the code and ensure there are no build errors reported

catkin_make

8. Launch RViz and Gazebo. This may take a while upon initial loading.

source devel/setup.bash
roslaunch my_robot world.launch

9. Setup RViz (ROS Visualization) to visualize sensor readings. On the left side of RViz, under Displays:
   • Select odom for fixed frame
   • Click the Add button and
     • add RobotModel and your robot model should load up in RViz.
     • add Camera and select the rgb/image_raw topic that was defined in the camera Gazebo plugin
     • add LaserScan and select the /scan topic that was defined in the Hokuyo Gazebo plugin
10. Open another Terminal/CLI by using Ctrl + Alt + T shortcut. Switch to catkin_ws

cd /<your_dir>/catkin_ws

11. Run drive_bot and process_image, which can be done by executing ball_chaser.launch

source devel/setup.bash
roslaunch ball_chaser ball_chaser.launch

12. In Gazebo, move the white ball around so its in the robot's cameras field of view. The robot will move right if the white ball is found on the right side, left for left and forward if its in the center region. The robot will not move if there is no white ball detected in the camera.