multi-robot-infrastructure.md

How to namespace multiple robots and have them on the same roscore

To have multiple robots on the same ROS core and each of them listen to a separate node, namespacing would be an easy and efficient way to help.

Set namespace on robots' onboard computers with environment variable

• Boot up the robot and ssh into it

• On the robot's onboard computer, open the terminal and type in

nano ~/.bashrc

Then add the following line to the end of the file, using the robots name as the namespace

export ROS_NAMESPACE={namespace_you_choose}

Also make the following other changes:

alias bu='roslaunch turtlebot3_bringup turtlebot3_robot.launch'
export IP="$(ifconfig | sed -En 's/127.0.0.1//;s/.*inet (addr:)?(([0-9]*\.){3}[0-9]*).*/\2/p')"
export ROS_IP=$IP
export ROS_MASTER_URI=http://roscore1.cs.brandeis.edu:11311
export ROS_NAMESPACE=roba
export TB3_MODEL=burger
export TURTLEBOT3_MODEL=burger

• Save the file and don't forget to do source ~/.bashrc

Set namespace on your laptop with environment variable

• Now that the robot is configured properly with its own unique name space, how do we talk to it?

• There are three ways:

  1. Configure your laptop to be permanently associated with the same name space

  2. Set a temporary environment variable that specifies the name space

  3. Add the namespace to a launch file

  4. Use the __ns parameter for roslaunch or rosrun (not recommended)

Permanently associate your laptop with the name space

• Use the same steps above. Make sure your namespace is exactly the same as the namespace of the robot you want to control.

• From now on, whenever you do, e.g. a cmd_vel, it will be directed just to your robot.

Use an environment variable

• Set namespace for a termimal with temporary environment variable.

• To set a namespace temporarily for a terminal, which will be gone when you close the termial, just type in export ROS_NAMESPACE={namespace_you_choose} directly in your terminal window.

• You can use echo $ROS_NAMESPACE to check it.

Use the .launch file

• To set namespace for a node in launch file, Use the attribute ns, for example:

<node name="listener1" pkg="rospy_tutorials" type="listener.py" ns="{namespace_you_choose}" />

Not recommended: add __ns to the run or launch command

1. Launch/Run a file/node with namespace in terminal. Add a special key __ns (double underscore here!) to your command, for example: roslaunch turtlebot3_teleop turtlebot3_teleop_key.launch __ns:={namespace_you_choose} However,

2. Use of this keyword is generally not encouraged as it is provided for special cases where environment variables cannot be set. (http://wiki.ros.org/Nodes)

Publishing/Subsribing topics in other namespace

Do a rostopic list, you will find out topics under a namespace will be listed as /{namespace}/{topic_name}

Make changes to turtlebot3_navigation package on your laptop

• Type roscd turtlebot3_navigation to go to the package directory.

• Type cd launch to go to the folder that stores .launch files.

• Open the turtlebot3_navigation.launch file with nano or your favorite code editor.

• You will see the scripts for launching move base and rviz:

  <!-- move_base -->
  <include file="$(find turtlebot3_navigation)/launch/move_base.launch">
    <arg name="model" value="$(arg model)" />
    <arg name="move_forward_only" value="$(arg move_forward_only)"/>
  </include>

  <!-- rviz -->
  <group if="$(arg open_rviz)">
    <node pkg="rviz" type="rviz" name="rviz" required="true"
          args="-d $(find turtlebot3_navigation)/rviz/turtlebot3_navigation.rviz"/>
  </group>

Change move base arguments

• Add another argument cmd_vel_topic to the four arguments in the <!-- Arguments --> section:

    <!-- Arguments -->
    <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
    <arg name="map_file" default="$(find turtlebot3_navigation)/maps/map.yaml"/>
    <arg name="open_rviz" default="true"/>
    <arg name="move_forward_only" default="false"/>
    <arg name="cmd_vel_topic" default="/{namespace_you_choose}/cmd_vel"/>

  • Pass the new argument to move base launch file:

    <!-- move_base -->
    <include file="$(find turtlebot3_navigation)/launch/move_base.launch">
     <arg name="model" value="$(arg model)" />
     <arg name="move_forward_only" value="$(arg move_forward_only)"/>
     <arg name="cmd_vel_topic" value="$(arg cmd_vel_topic)"/>
    </include>

• These changes will make move base publish to /{namespace_you_choose}/cmd_vel instead of /cmd_vel. Open the move_base.launch file in the launch folder, you will see why it worked.

Change rviz arguments

• Type roscd turtlebot3_navigation to go to the package directory.

• Type cd rviz to go to the folder that has turtlebot3_navigation.rviz. It stores all the arguments for rviz.

• Open turtlebot3_navigation.rviz with VSCode or other realiable code editors, since this file is long and a bit messy.

• In the .rviz file, search for all the lines that has the part Topic:

• Add your namespace to the topics you found. For example, change

    Topic: /move_base/local_costmap/footprint
    `

  to

    Topic: /roba/move_base/local_costmap/footprint

• These changes will make rviz subsribe to topics in your namespace.