Running ROS on multiple machines

You can run this tutorial on:

Introduction

In this manual you will learn how to configure ROS to work on multiple computers.You will use this configuration to set up system consisting of robot and computer or two computers (gazebo version), which perform task of searching an object.

In this manual you will need computer and robot with the same equipment as in the previous manual.

In case you are working on Gazebo simulator, it is possible to setup system to work on multiple computers, to do it you can have two computers with ROS.

Network setup

To run ROS on multiple machines, all of them must be in the same local network. If you want to use separated networks use Husarnet

While working on multiple machines, you need only one roscore running. Choose one device for it- we will call it master. Options for configuration are:

  1. Husarnet :

    ROSbots are coming preconfigured with Husarnet support, which provide low-latency, secure connection between robots. Husarnet is a P2P Virtual LAN network, so from your ROSbots point of view, they are in the same LAN network even if they are not physically in the same network. Husarnet setup is covered in Connecting through Husarnet section.

  2. .Bashrc

    On the master device open the .bashrc file:

    nano ~/.bashrc

    To disable husarnet entries, find lines:

    export ROS_MASTER_URI=http://master:11311
export ROS_IPV6=on

    and comment them with #:

    #export ROS_MASTER_URI=http://master:11311
#export ROS_IPV6=on

    Then add two lines at file ending, replacing X.X.X.X and Y.Y.Y.Y with IP address of master device.

    export ROS_MASTER_URI=http://X.X.X.X:11311
export ROS_IP=Y.Y.Y.Y

    On second robot also open the .bashrc file, comment Husarnet entries and add two lines at file ending. This time replace X.X.X.X with IP address of master device and Y.Y.Y.Y with IP address of second robot.

  3. Hostname + .bashrc

    Last option is to use hostname, which is more convenient than using physical addresses. To do it instead of using physical address in .bashrc use:

    export ROS_MASTER_URI=http://computer-master:11311
export ROS_IP=robot

    Now we have to tell what this hostname means. To do it edit file /etc/hostnames with sudo privileges:

    127.0.0.1    localhost
X.X.X.X     computer-master 
X.X.X.X     robot

One benefit of using Husarnet is that it manages hostnames so you don't have to worry about it.

TIP! If you do changes in .bashrc file always source it with . ~/.bashrc or reopen terminal

TIP 2! Remember that roscore must be running on the device indicated as ROS master!!!

Task 1

As a remember:

  • astra.launch - roslaunch astra_launch astra.launch
  • rqt_graph - rosrun rqt_graph rqt_graph
  • image_view - rosrun image_view image_view image:=/camera/rgb/image_raw

  1. Set configuration for working on multiple machines on two devices. On the device named master launch roscore. First check if connection works simple with rostopic list command on second device - if you are unable to see topics then reconfigure your network communication. On the second device run astra.launch and image_view nodes. Now run rqt_graph on both of them, you should see the same graph.

  2. Next run image_view node on machine with roscore. You should see the image from camera mounted on the device with astra.launch running. Again use rqt_graph to examine what changed in the system.

In case of using gazebo:

  1. Configure connection the same way as with Husarnet or manually by yourself. Next launch roscore on the device named master, launch gazebo simulation roslaunch tutorial_pkg tutorial_4.launch use_gazebo:=true teach:=true recognize:=false and image_view nodes. Examine connection with rqt_graph.
  1. Now let's use second machine. First check if connection works simple with rostopic list command on second device - if you are unable to see topics then reconfigure your network communication. Next run image_view node on the second machine. You should see the image from camera running inside gazebo. Again use rqt_graph to examine what changed in the system.

Performing a task with multiple machines

Task 2

In this section we will program robot and computer to outsource computer power. To do that we will need one node for image processing - it will run on computer and we will need a node that publishes camera stream - it will run on ROSbot. For recognizing objects we will use find_object_2d node.

Running task

We will follow the pattern form previous tutorial but this time we do it using two machines. As a remember anything could be an object to recognize, but remember, that the more edges and contrast colours it has, the easier it will be recognized. A piece of paper with something drawn on it would be enough for this tutorial.

  1. Start roscore, open terminal on your computer (master) and type roscore

  2. On ROSbot you should run astra.launch image transport and bridge to CORE2.

    For connection to CORE2 we will use package rosbot_ekf

    To launch rosserial communication and Kalman filter for mbed firmware run:

    roslaunch rosbot_ekf all.launch

    For PRO version add parameter:

    roslaunch rosbot_ekf all.launch rosbot_pro:=true

  3. On computer (master) we will launch also image transport and find_object_2d node.

Image transport node provides compressed image delivery from one device to another, on sending machine you have to run this node for compression and on receiving machine you have to decompress image. Before we used image view without any compression which is enough just for see if it's working, but if only you want to implement some real time image processing it's necessary to compress image.

Running the nodes on ROSbots

Create launch file under tutorial_pkg/launch and name it as tutorial_5_rosbot.launch:

<launch>

    <arg name="rosbot_pro" default="false" />

    <arg name="teach" default="true"/>
    <arg name="recognize" default="false"/>

    <include file="$(find rosbot_ekf)/launch/all.launch">
        <arg name="rosbot_pro" value="$(arg rosbot_pro)" />
    </include>
    <include file="$(find astra_launch)/launch/astra.launch"/>

    <node pkg="tf" type="static_transform_publisher" name="camera_publisher" args="-0.03 0 0.18 0 0 0 base_link camera_link 100" />

    <node pkg="image_transport" type="republish" name="rgb_compress" args=" raw in:=/camera/rgb/image_raw compressed out:=/rgb_republish"/>

</launch>

And launch file for PC computer, name it `tutorial_5_pc.launch:

<launch>

    <arg name="teach" default="true"/>
    <arg name="recognize" default="false"/>

    <node name="teleop_twist_keyboard" pkg="teleop_twist_keyboard" type="teleop_twist_keyboard.py" output="screen"/>

    <node pkg="image_transport" type="republish" name="rgb_decompress" args=" compressed in:=/rgb_republish raw out:=/rgb_raw" >
        <param name="compressed/mode" value="color"/>
    </node>

    <node pkg="find_object_2d" type="find_object_2d" name="find_object_2d">
        <remap from="image" to="/rgb_raw"/>
        <param name="gui" value="$(arg teach)"/>
        <param if="$(arg recognize)" name="objects_path" value="$(find tutorial_pkg)/image_rec/"/>
    </node>

</launch>

Use rqt_graph to see how the system is working now.

That's all you don't have to worry about nothing more than properly configuration of .bashrc rest stays the same. If you have more than 2 devices the pattern is the same. ROS takes care of all data exchange. That is really simple, isn't it?

Running the nodes in Gazebo

Gazebo node will be running on one machine. Second machine will be responsible for image processing.

At one machine use following launch file and save it as tutorial_5_gazebo_1.launch:

<launch>

    <arg name="teach" default="false"/>
    <arg name="recognize" default="true"/>

    <arg if="$(arg teach)" name="chosen_world" value="rosbot_world_teaching"/>
    <arg if="$(arg recognize)" name="chosen_world" value="rosbot_world_recognition"/>

    <include file="$(find rosbot_gazebo)/launch/$(arg chosen_world).launch"/>

    <include file="$(find rosbot_description)/launch/rosbot_gazebo.launch"/>

    <node pkg="image_transport" type="republish" name="rgb_compress" args=" raw in:=/camera/rgb/image_raw compressed out:=/rgb_republish"/>

</launch>

At the other machine use this launch file and save it as tutorial_5_gazebo_2.launch:


<launch>
    <arg name="teach" default="true"/>
    <arg name="recognize" default="false"/>

    <node name="teleop_twist_keyboard" pkg="teleop_twist_keyboard" type="teleop_twist_keyboard.py" output="screen"/>

    <node pkg="image_transport" type="republish" name="rgb_decompress" args=" compressed in:=/rgb_republish raw out:=/rgb_raw" >
        <param name="compressed/mode" value="color"/>
    </node>

    <node pkg="find_object_2d" type="find_object_2d" name="find_object_2d">
        <remap from="image" to="/rgb_raw"/>
        <param name="gui" value="$(arg teach)"/>
        <param if="$(arg recognize)" name="objects_path" value="$(find tutorial_pkg)/image_rec/"/>
    </node>

</launch>

Use rqt_graph to see how the system is working now.

Connecting through Husarnet

In the case when more sophisticated network setup is required, e.g. robots will be connected to internet using LTE modem or different WiFi networks. For easy connecting robots in advanced network configurations, you can use Husarnet - the global LAN network for secure P2P connection between robots and IoT devices.

Connection setup

Log in to Husarnet Dashboard or create an account if you don't have it yet.

You should see Husarnet Dashboard with no networks nor elements:

husarnet-dashboard-empty

Push button "Create network" and in dialog type desired network name into field Network name:

husarnet-add-network-dialog

After pushing button "Create", you will be redirected to network view:

husarnet-empty-network

You can use button "Add element" to add to your network cloud elements or mobile app, but now we will use terminal method.

Adding ROS device to network

Before you add device to network, it is required to setup the environment.

Open .bashrc file and find lines that you added at the beginning of this tutorial:

export ROS_MASTER_URI=http://X.X.X.X:11311
export ROS_IP=Y.Y.Y.Y

and replace them with:

export ROS_MASTER_URI=http://master:11311
export ROS_IPV6=on

ROS_IPV6 makes ROS enable IPv6 mode - Husarnet is a IPv6 network. Setting ROS_MASTER_URI to http://master:11311 ensures ROS will always connect to host called master - which exactly machine it is depends on the setting on the Husarnet Dashboard.

Execute command:

sudo husarnet websetup

You will get response similar to:

Go to https://app.husarnet.com/husarnet/fc94cd22622bf708b9bb22d5589275fa8832943ffdb0175bff7e16ce to manage your network from web browser.

Open the provide link in web browser, you will see device configuration dialog:

husarnet-add-device

Type desired name of the device into field Name for this device, you will use this name to distinguish your devices in dashboard. From Add to network dropdown menu choose name of network that you created in previous step.

Repeat procedure of adding device with second robot.

Setting the master

After adding both robots, your network should look like below:

husarnet-two-elements

You can set device to be master in its settings. Choose device you want to be master and open configuration dialog by clicking its name, status or address:

husarnet-set-master

Check ROS master checkbox and push button "Update".

When you will start roscore on master, message ROS master (roscore) is not running on robot-2. will be gone.

Your first Husarnet network is configured and ready:

husarnet-network-ready

Running the nodes with Husarnet

Husarnet provide encrypted and direct virtual network for your devices, but it does not modify the ROS workflow. Just go back to section "Running the nodes on ROSbots", start required nodes and observe as your robots perform the task.

Summary

After completing this tutorial you should be able to configure your CORE2 devices to work together and exchange data with each other. You should also know how to program robots for performing tasks in cooperation.

by Łukasz Mitka and Adam Krawczyk, Husarion

Do you need any support with completing this tutorial or have any difficulties with software or hardware? Feel free to describe your thoughts on our community forum: https://community.husarion.com/ or to contact with our support: support@husarion.com

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