How to Remap

Explanation of the exercise

This is a simple example of how to remap correctly. In this case, we are going to edit the fake_turtlebot.launch file to move the robot from RBX1 package with our keyboard.

Download and install RBX1 repository

First, go to a workspace folder.

cd ~/<yourWorkspace>/src

Now, copy the follow line in the terminal:

git clone https://github.com/pirobot/rbx1.git

Install a needed repository:

sudo apt-get install python-rosinstall

Now we have a copy of the RBX1 repository in our workspace, it's time to compile it

cd <yourWorkspace>
catkin_make

In case of presenting any issue, try install the next ROS dependencies:

sudo apt-get install ros-kinetic-arbotix-python

How to know which topics remap?

First, run ROS in the terminal

roscore

Then, run the launch file:

roslaunch rbx1_bringup fake_turtlebot.launch

Now, in other terminal, we will observe the active topics with the command:

rostopic list

The answer must be something like this:

julianroa18@julianroa18-Aspire-E5-575G:~$ rostopic list
/cmd_vel
/diagnostics
/joint_states
/odom
/rosout
/rosout_agg
/tf
/tf_static

Note the topic "/cmd_vel", we will need it later. That is our first topic to remap. To know which is the second topic we need, run the turtle_teleop_key node in another terminal:

rosrun turtlesim turtle_teleop_key

Displays the list of active topics again:

rostopic list

Now the list is similar to:

julianroa18@julianroa18-Aspire-E5-575G:~$ rostopic list
/cmd_vel
/diagnostics
/joint_states
/odom
/rosout
/rosout_agg
/tf
/tf_static
/turtle1/cmd_vel

The last one, "/turtle1/cmd_vel" is the second topic that we will remap. Save that topics for the next step

REMAP

Remap is a way of "cheating" a ROS node, so when it thinks it is subscribing to or publishing to "/topic1" it really does it to "/topic2"

Remap works like this

<remap from="/different_topic" to="/needed_topic"/>

For our example, the correct way is:

<remap from="/cmd_vel" to="/turtle1/cmd_vel"/>

Now add this line in the fake_turtlebot.launch file and the new file should look like this:

<launch>
  <param name="/use_sim_time" value="false" />

  <!-- Load the URDF/Xacro model of our robot -->
  <arg name="urdf_file" default="$(find xacro)/xacro.py '$(find rbx1_description)/urdf/turtlebot.urdf.xacro'" />
   
  <param name="robot_description" command="$(arg urdf_file)" />
    
  <node name="arbotix" pkg="arbotix_python" type="arbotix_driver" output="screen" clear_params="true">
      <rosparam file="$(find rbx1_bringup)/config/fake_turtlebot_arbotix.yaml" command="load" />
      <param name="sim" value="true"/>
      <remap from="/cmd_vel" to="/turtle1/cmd_vel"/>
  </node>
  
  <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher">
      <param name="publish_frequency" type="double" value="20.0" />
  </node>
  
</launch>

How to show the result

Save the changes in the .launch file and kill all the procces in the terminal, except roscore. Run the .launch and the turtle_teleop_key node again, and then copy the next command in another terminal

rqt_graph

Finally, execute the next line to do the control

rosrun rviz rviz -d `rospack find rbx1_nav`/sim.rviz

Move the robot with you keyboard, if you want to change the velocity of the robot, execute the next line in the terminal:

rosparam set teleop_turtle/scale_linear 0.5

Where 0.5 is the new velocity. Execute again and enjoy :)

Collaborators

• Kevin Parra
• Julián Roa

Tutor

• Hernán Hernandez