New to ROS, and I need to use a pre-installed ros system
I am working on a robot project, and got a robot with ROS built inside its system. I was familiar with what ROS was, and trying to understand how this works.
The robot uses a nvidia jetson board with ubuntu 18.04 and ROS Melodic installed, set as master of the system. Using the board, I can look at its topics with the rostopic echo command in the promt, topics such as motor encoders or imu data.
What I am curious is that I have hooked another linux system with ROS installed(this case, a raspberry pi with Melodic) to the same network with the master, I made it available to look at the list of topics published by the jetson board. I can see the same list of topics as if I wrote the command in the jetson board.
The problem is that if I write
rostopic echo /oneofthelistedtopic/
in the raspi, I cannot get the topic.
I believe that since the raspi does not have any form of subscribing to the master code, it cannot read any topics. I am really new to the ROS system and linux altogether, and everything is very unclear to me. I have been looking at some turtlebot examples, but they were not actually helpful because the system I am trying to use is a custom system.
Is there anything I can read that can give me clear instructions on how to subscribe to a topic published by a master on a newly installed ROS system?
rostopic echo /topicstarts a subscriber. If it's not displaying anything, either there's nothing to display, or there's something wrong with the setup. The Understanding Topics tutorial gives an overview of topics. It's probably a good idea to go through all of the related ROS tutorials, too.