bhargav-umd/beginner_tutorials

ROS Beginner Tutorials - Introduction to Publisher and Subscriber

Overview

This program is a basic introduction to a publisher and a subscriber in ROS. It creates two nodes, a talker (publisher) node and a listener (subscriber) nodes.

Dependencies

This program works on a device running Ubuntu 16.04 and ROS Kinetic Kame.

To install ROS Kinetic Kame in Ubuntu 16.04, follow the steps in this link.

To install ros, follow the installation steps in this link.

Build Instructions

To run this code in a ros workspace:

cd ~/ros_ws/
source devel/setup.bash
cd src/
git clone https://github.com/bhargav-umd/beginner_tutorials
cd ..
catkin_make

If you do not have a ros workspace:

mkdir -p ~/ros_ws/src
cd ~/ros_ws/
catkin_make
source devel/setup.bash
cd src/
git clone https://github.com/bhargav-umd/beginner_tutorials
cd ..
catkin_make

Run Instructions

After following the build instructions:

Run roscore in a new terminal:

source devel/setup.bash
roscore

Then run talker node in second terminal:

source devel/setup.bash
rosrun beginner_tutorials talker

Output will look like:

[ INFO] [1540934618.726572148]: GO TERPS GO 0

Finally run listener node in third terminal:

source devel/setup.bash
rosrun beginner_tutorials listener

Output will look like

[ INFO] [1540934620.527403735]: I heard: [GO TERPS GO 0]

To call the service

• Once both nodes are running in separate terminals as described above, check in another terminal that the service is being detected. rosservice list should output a few services and /update_string should be listed.

• Now run the following commands to call the service and change the string to be published (newString is the message to be published):

cd ros_ws
source devel/setup.bash
rosservice call /update_string newString

The talker and listener terminals should output now the new message containing newString

To run using launch file

• To run the package with a launch file, first close every terminal related to this package (including roscore).

• Now run the following commands in the terminal:

cd ros_ws
source devel/setup.bash
roslaunch beginner_tutorials beginner.launch frequency:=3

where frequency is the argument that changes the publisher frequency. The value 3 is just an example and it can be changed for whatever other integer value.

• Once the roslaunch command is executed, another terminal will be opened with the listener output. The first terminal outputs the talker node's output.