Tutorial for Establishing Communication

We will look into establishing communication between the robot and the computer. In ROS2, we need to configure the network settings for reliable communication. This allows the robot and the computer to communicate with each other. We will then proceed to ssh into the robot and launch the drivers on the robot

Network Configuration

Communication concepts of ROS to users by using existing middleware DDS. This DDS middleware has different implementations. To know more about this please refer to information on DDS and information on different implementations. Some of the common DDS implementations are Fast DDS, Connext DDS, RTI DDS etc.

Each of these implementations have different different logics to establish communication between the robot and the computer. Sometimes the network interface of the computer is not able to communicate with the network interface of the robot. So it is a good practice to configure the network settings to establish communication between the robot and the computer. Here we specify on which network interface the communication should happen. For example, in the below configuration, we specify wlp3s0 as the network interface name which is connected to the same network as the robot

Copy the content below and save it in a file. For example, the file can be named as ros2_network_config.xml and can be saved in the home directory or the ros2 workspace

<?xml version="1.0" encoding="UTF-8" ?>
<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
    <transport_descriptors>
        <transport_descriptor>
            <transport_id>CustomTcpTransport</transport_id>
            <type>TCPv4</type>
            <interfaceWhiteList>
                <address>wlp3s0</address>
            </interfaceWhiteList>
        </transport_descriptor>
    </transport_descriptors>

    <participant profile_name="CustomTcpTransportParticipant">
        <rtps>
            <useBuiltinTransports>false</useBuiltinTransports>
            <userTransports>
                <transport_id>CustomTcpTransport</transport_id>
            </userTransports>
        </rtps>
    </participant>
</profiles>

Once connecting to Robile5G network, run ip a command from your terminal. Replace the network interface name wlp3s0 in the above file with the network interface name from which your system is connected to Robile5G network. In your .bashrc file, add the following lines at the end of the file. Please make sure that the path to the ros2_network_config` file is correct. By setting RMW_IMPLEMENTATION as rmw_fastrtps_cpp, we are setting the DDS implementation to use as the Fast DDS

export FASTRTPS_DEFAULT_PROFILES_FILE=~/ros2_network_config.xml
export RMW_IMPLEMENTATION=rmw_fastrtps_cpp

SSH-ing into Robile (while using real-robot)

Make sure you have connected to the wifi network Robile5G. In one of terminals, ssh to the robot (please add these as aliases in ~/.bashrc for convenience)

ssh -x studentkelo@192.168.0.101   [**while connecting to Robile1**]
ssh -x studentkelo@192.168.0.102   [**while connecting to Robile2**]
ssh -x studentkelo@192.168.0.103   [**while connecting to Robile3**]
ssh -x studentkelo@192.168.0.104   [**while connecting to Robile4**]

Password while connecting to Robiles: area5142

For example, to add alias of the to connect to the terminal of Robile1, add the following line in your .bashrc file

alias robile1='ssh -x studentkelo@192.168.0.101'

Now, you can connect to the terminal of Robile1 by typing robile1 in the terminal, instead of typing the whole command

Note

In the bashrc of all robiles, the environmnet variable ROS_DOMAIN_ID is set to the respective robile number. For example, for Robile4, it is set to the number 4

To launch the robot in simulation, run the following command in a new terminal on your system (not the ssh-ed terminal of the robot)

ros2 launch robile_gazebo gazebo_4_wheel.launch.py

Launching the drivers (bringup) on the robot in a tmux session

One of the best practices to run the drivers on the robot is to use tmux. If the bringup launch file is directly run in the ssh-ed terminal, then the drivers will stop running when the communication is lost or the terminal is closed. To avoid this, we use tmux to run the bringup launch file in a new session. It allows you to run multiple terminals in a single terminal. Few important commands are listed in this github link

If not installed, install tmux by running the following command

sudo apt install tmux

Create a new session by running the following command in the terminal where the robot’s terminal is ssh-ed (replace session_name with any name of your choice)

tmux new -s session_name

Now run the desired commands in the session. For example, you can run the launch file to run the robot drivers

ros2 launch robile_bringup robot.launch.py

To detach the tmux session, press Ctrl+b and then press d. To attach the tmux session, run the following command (replace session_name with the name of the session you created)

tmux attach -t session_name [or] tmux a -t session_name

To list all the tmux sessions, run the following command

tmux list-sessions

To close the tmux session, run the following command

tmux kill-session -t session_name

Note

To verify the communication between the robot and the computer, run the following command in a new terminal. If you are using real-robot, make sure that the ROS_DOMAIN_ID is set to the respective robile number

ros2 topic list

If you get any error or if the entire list of topics is not printed, then run the following commands and try again to get the list of topics

ros2 daemon stop
ros2 daemon start

Visualizing Robile in Rviz2

To visualize the robot in Rviz2 while using real robot, run the following command in a new terminal. Make sure that the ROS_DOMAIN_ID is set to the respective robile number. For example, for Robile4, it is set to the number 4. Please don’t leave space between the equal sign and the number

export ROS_DOMAIN_ID=4
rviz2

To load the rviz2 config file, click on the Open Config button in the top left corner of the rviz2 window and select the file robile.rviz from folowing path

robile_gazebo/config/robile.rviz