ROS-Noetic-2H30

ROS Tutorial (ROS1) - ROS Noetic 2H30 Crash Course on YouTube

Directory structure of the catkin workspace

This repository resides inside the src directory of the catkin workspace named as yt_ros_ws.

user@host:~/ros/yt_ros_ws
└── src
    ├── figures
    │   ├── course-end.png
    │   ├── rosgraph-closedloop-pub-sub.png
    │   ├── rosgraph-publisher.png
    │   └── rosgraph-subscriber.png
    ├── my_robot_controller         # package name
    │   ├── CMakeLists.txt
    │   ├── package.xml
    │   ├── scripts                 # directory containing the python scripts (nodes)
    │   │   ├── draw_circle.py
    │   │   ├── my_first_node.py
    │   │   ├── pose_subscriber.py
    │   │   └── turtle_controller.py
    │   └── src
    └── README.md

Running a Node

Note : ROS version must be sourced before anything source /opt/ros/noetic/setup.bash

1. Give execution permission to the python script $ chmod +x script.py
2. Change directory to the catkin workspace and do $ catkin build
3. source the setup basch script in devel directory $ source ~/ros/yt_ros_ws/devel/setup.bash
4. Initialize ros master $ roscore
5. Run the node $ rosrun <package name> <script.py>

Realizing Publisher-Subscriber Architecture

Subsciber Program

In this program the custom node will subscribe to an existing turtlesim/Pose topic and prints the pose (x, y) coordinates.

bimalka98@LAP-BIMALKA98:~$ rostopic info /turtle1/pose 
Type: turtlesim/Pose

Publishers: 
 * /turtlesim (http://LAP-BIMALKA98:36309/)

Subscribers: 
 * /turtle_pose_subscriber (http://LAP-BIMALKA98:43567/)

Publisher Program

In this program the custom node will publish to an existing /turtle1/cmd_vel topic, to draw a circle.

bimalka98@LAP-BIMALKA98:~$ rostopic info /turtle1/cmd_vel 
Type: geometry_msgs/Twist

Publishers: 
 * /draw_circle (http://LAP-BIMALKA98:46635/)

Subscribers: 
 * /turtlesim (http://LAP-BIMALKA98:44519/)

Pub-Sub Closed Loop Program

This program combines above two pub-sub mechanisms to control the turtle bot intelligently.