ROS On Multiple Machines Manual

User Manual:

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ROS over Multiple Machines
This manual explains the process for connecting ROS Nodes on
multiple machines connected to the same network.
Example case for 2 Computers on same network:
Hostname comp1 comp2
IP 192.168.77.11 192.168.77.12
Case 1: Using On-board ROS :-
Configuring ROS master:
There should be only 1 master/ ROS core for handling the system.
In this example, let the comp1 be the master. Hence, roscore is run on this
computer.
comp1 : $ roscore
This should start the roscore displaying the master’s IP address and the port
number. 11311 is the default port of the master.
Configuring Slaves:
The slave machines need to know the masters’s as well as their own
IP address.
comp1 can act as a slave to itself along with being the master
Specify ROS master’s IP:
comp1 : $ export ROS_MASTER_URI=http://192.168.77.11:11311
Specify slave machine’s own IP:
comp1 : $ export ROS_IP=192.168.77.11
comp2 will only act as a slave machine.
SpecifyROS master’s IP:
comp2 : export ROS_MASTER_URI=http://192.168.77.11:11311
Specify slave machine’s own IP:
comp2 : $ export ROS_IP=192.168.77.12
Note: In case of more number of machines, one of them can solely act as the
master with the roscore running on it and all other nodes running on the slaves.
Resolve master’s name to IP (Optional):
Modify the “/etc/hosts” file in order to resolve master’s name to IP
in the slave machine.
In the slave machine, comp2, open the file as Root user:
comp2 : $ sudo nano /etc/hosts
Add the line to the “hosts” filein the format of:
<Master’s IP Address> <Master’s Name>
192.168.77.11 comp1
Save and close the file.
Note: The commands for specifying the IP address of ROS master and the
slave can also be added to a bash file and sourced when required instead of
typing it everytime.
Case 2: Using MATLAB-ROS :-
Robotics System Toolbox enables one to interface with ROS and use ROS
functionality in MATLAB and Simulink. One can connect to a ROS
network, collect data, send and receive one’s own messages, and deploy
code to a standalone system.
Configuring ROS Master:
To initialize ROS master using MATLAB-ROS, run the following
command in the Matlab Command Window.
For comp1,
>> rosinit
This should start the roscore and display the IP address of ROS master and the
port numbers of ROS Master and the global node on the command window.
Note: For running a ROS node in the master, the Matlab code just needs to be
run and no separate configurations are required.
Configuring Slaves:
Before running the slave nodes, MATLAB-ROS must be initialized
with a master in the network. To do so, the IP address of the ROS master must
be passed as an arguement to the “rosinit” function.
Eg: rosinit(‘<Master’s IP Address>’)
For comp2,
>> rosinit(‘192.168.77.11’)
Note: In case of one of the computer with MATLAB-ROS and
other with On-Board ROS, the nodes can communicate over the
network using the corresponding configurations.

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