ROS On Multiple Machines 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
IP

comp1
192.168.77.11

comp2
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:
 
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(‘’)
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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