ROS network

  • one ROS master in the entire network
  • all nodes must use the same ROS master (ROS_MASTER_URI)
  • two-way connection between devices
  • each device must present itself with a name that other devices recognize

http://wiki.ros.org/ROS/Tutorials/MultipleMachines

http://wiki.ros.org/ROS/NetworkSetup

Connection

ping the remote computer (hostname: IP or name) 

ping 192.168.65.60

Use ssh to connect to remote computer and ping your computer 

ssh student@192.168.65.60
ping 192.168.65.50

ROS_MASTER_URI

ROS master is set with variable ROS_MASTER_URI. It needs to be set withing each terminal. 

export ROS_MASTER_URI=http://[hostname]:11311
To check, use 
echo $ROS_MASTER_URI

Set parameter ROS_IP for IP or ROS_HOSTNAMEfor hostname if you have multiple addresses for a computer and need to force ROS to a particular one.

To do this automatically, add command to bashrc 

sudo nano ~/.bashrc
Add 
export ROS_MASTER_URI=http://[hostname]:11311

ATTENTION!

This can cause a problem, it you would like to run ROS master on the local computer.

Test connection

It is important to test connection in both ways:

  • master (publisher) >>> others (subscriber)
  • master (subscribers) <<< others (publisher)

Publisher: 

rostopic pub /test_connection std_msgs/Bool "data: True"

Subscriber: 

rostopic list

rostopic echo /test_connection

Exercise

Connect to master computer with Sick Nanoscan3 and connect to topic /sick_safetyscanners/scan.