Multi-machine communication

4、Multi-machine communication

4、Multi-machine communication4.1、Login remotely4.1.1、SSH4.1.2、jupyter lab4.1.3、VNC4.2、ROS multi-machine communication4.2.1、Universal version4.2.2、Smiple version4.3、Webpage real-time monitoring

Note: You must know the IP of the robot before remote login. You can view the current IP address of the robot through an external display or OLED

4.1、Login remotely

4.1.1、SSH

Note: The system graphical interface cannot be displayed in this way.

PuTTY Login

Input IP address, then click【open】；

For Yahoom image, user name is pi password is yahboom

ubuntu system

1）Input following command in terminal


ssh pi@192.168.2.103

2）Then, input yes

3）Next, input yahboom

4.1.2、jupyter lab

Note: The system graphical interface cannot be displayed in this way.

Input following URL on browser, pree 【Enter】

Then, input password yahboom

Click【Log in】


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http://192.168.2.103:8888

After login, you can see following interface.

You can enter these folder, and modify content in file, click 【Terminal】 to enter command terminal.

4.1.3、VNC

Note: The system graphical interface can be displayed in this way.

4.2、ROS multi-machine communication

4.2.1、Universal version

All ros masters are under the same network; if multiple devices have similar processes, choose one as the master, and the others are all slaves; the following two devices are taken as an example.

Install the ssh server on two devices; install the chrony package for synchronization:


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sudo apt-get install chrony openssh-server

Input following command to view the IP information and host name of the two devices:


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Command: ifconfig 和 hostname

修改/etc文件夹下的hosts文件：


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sudo chmod a+w /etc/hosts
sudo vim /etc/hosts

将两台设备的IP和主机名分别添加到两台设备的hosts文件下，绑定用户；前面的IP，后面的是名字，尽量对齐 ;

After the modification, enter the following commands on both devices to restart the following network to realize the communication between the two devices:：


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sudo /etc/init.d/networking restart

After installation, input following command confirm whether the server has been started:


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ps -e|grep ssh

Input following command to check if the communication is normal:


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ping hostname of the device

Modify～/.bashrc file


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sudo vim ~/.bashrc

Add following content to ～/.bashrc file of master


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export ROS_MASTER_URI=http://Host username:11311

Add following content to ～/.bashrc file of slave


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export ROS_MASTER_URI=http://Host username:11311

For example, jetson nano as a master

After setting the IP, we need to refresh it, and then we can communicate.


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 source ~/.bashrc

Phenomenon show

Note: we need to start up ROS Master on ROS Master

ubuntu(virtual machine VM_Transbot)


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roscore
rosrun turtlesim turtle_teleop_key

Raspberry Pi (Transbot)


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rosrun turtlesim turtlesim_node

4.2.2、Smiple version

If jetson nano is the host and the IP address is known, you only need to modify the .bashrc file of the slave.


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sudo vim ~/.bashrc

Add following content file at the bottom.


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export ROS_MASTER_URI=http://主机IP:11311

The effect is the same as [4.2.1]

4.3、Webpage real-time monitoring

Environment setup


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sudo apt-get install ros-melodic-async-web-server-cpp ros-melodic-web-video-server ros-melodic-usb-cam

Ensure that the USB camera be insert correctly, input following command to check if the USB device exists ( it is video0)


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ll /dev

If the system prompts that the execution authority is not enough, you need to input the following command to add the execution authority.


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sudo chmod 777 /dev/video*

Modify usb_cam-test.launch file


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sudo vim /opt/ros/melodic/share/usb_cam/launch/usb_cam-test.launch


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<launch>
  <node name="usb_cam" pkg="usb_cam" type="usb_cam_node" output="screen" >
    <param name="video_device" value="/dev/video0" />
    <param name="image_width" value="640" />
    <param name="image_height" value="480" />
    <param name="pixel_format" value="yuyv" />
    <param name="camera_frame_id" value="usb_cam" />
    <param name="io_method" value="mmap"/>
  </node>
  <node name="image_view" pkg="image_view" type="image_view" respawn="false" output="screen">
    <remap from="image" to="/usb_cam/image_raw"/>
    <param name="autosize" value="true" />
  </node>
</launch>

change


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<launch>
    <arg name="open_view" default="false"/>
    <node name="usb_cam" pkg="usb_cam" type="usb_cam_node" output="screen">
        <param name="video_device" value="/dev/video0"/>
        <param name="image_width" value="640"/>
        <param name="image_height" value="480"/>
        <param name="pixel_format" value="yuyv"/>
        <param name="camera_frame_id" value="usb_cam"/>
        <param name="io_method" value="mmap"/>
    </node>
    <!-- 启动web_video_server -->
    <node pkg="web_video_server" type="web_video_server" name="web_video_server" output="screen"/>
    <!-- 是否启动image_view -->
    <group if="$(arg open_view)">
        <node name="image_view" pkg="image_view" type="image_view" respawn="false" output="screen">
            <remap from="image" to="/usb_cam/image_raw"/>
            <param name="autosize" value="true"/>
        </node>
    </group>
</launch>

Open terminal, input following command to start it.


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roslaunch usb_cam usb_cam-test.launch

View pictures


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View on local web browser 
http://localhost:8080/
If you want to view by other devices, you must ensure they at the same local area network
http://192.168.2.103:8080/
(192.168.2.103 is the IP address of the master)
Note: It is recommended to use Google browser, other browsers may not be able to open the image