My Robotic Manipulator #1: Basic URDF & RViz

Updated: 07 of August 2023

What we are going to learn

1. How to build a robot in a matter of minutes
2. How to see the robot in RViz
3. How to move the parts of the robot using Joint State Publisher

List of resources used in this post

1. Use the rosject: https://app.theconstructsim.com/l/5a5b6f9f/
2. The Construct: https://app.theconstructsim.com/
3. My Robot Manipulator repository: https://bitbucket.org/theconstructcore/my-robotic-manipulator
4. ROS Courses:
   1. URDF for Robot modeling: https://app.theconstructsim.com/Course/13
5. ROS2 Courses:
   1. URDF for Robot Modeling in ROS2 : https://app.theconstructsim.com/courses/83
   2. ROS2 Basics in 5 Days Humble (Python): https://app.theconstructsim.com/Course/132
   3. ROS2 Basics in 5 Days Humble (C++): https://app.theconstructsim.com/Course/133

Overview

From the URDF model, we’re going to define the first two links and visualize them in RViz. Up to the end of the video, we’ll have a basic model, a launch file to visualize it and a RViz configuration file for this specific project.

ROS Inside!

ROS Inside

Before anything else, if you want to use the logo above on your own robot or computer, feel free to download it and attach it to your robot. It is really free. Find it in the link below:

ROS Inside logo

In order to follow this tutorial, we need to have ROS installed in our system, and ideally a ROS Workspace (it can be named simulation_ws). To make your life easier, we have already prepared a rosject with a simulation for that: https://app.theconstructsim.com/l/5a5b6f9f/.

You can download the rosject on your own computer if you want to work locally, but just by copying the rosject (clicking the link), you will have a setup already prepared for you.

After the rosject has been successfully copied to your own area, you should see a Run button. Just click that button to launch the rosject (below you have a rosject example).

My Robotic Manipulator #1: Basic URDF & RViz – Run rosject (example of the RUN button)

After pressing the Run button, you should have the rosject loaded. Now, let’s head to the next section to get some real practice.

Compiling the workspace

As you may already know, instead of using a real robot, we are going to use a simulation. In order to see that simulated robot, we need to have our workspace compiled, and for that, we need a terminal.

Let’s open a terminal by clicking the Open a new terminal button.

 

Open a new Terminal

 

Once inside the first terminal, let’s run the commands below, to compile the workspace

cd ~/simulation_ws/

catkin_make

source devel/setup.bash

cd ~/simulation_ws/src

catkin_create_pkg mrm_description urdf

cd mrm_description/

mkdir urdf

cd urdf/

touch mrm.xacro

cd ~/simulation_ws/src/mrm_description/

mkdir launch

touch rviz.xacro

Open the IDE – Code Editor

<?xml version="1.0" ?>

<robot name="mrm" xmlns:xacro="http://www.ros.org/wiki/xacro">
    <link name="base_link">
        <visual>
          <origin rpy="0 0 0" xyz="0 0 0" />
          <geometry>
            <box size="1 1 1" />
          </geometry>
        </visual>
    </link>

    <joint name="base_link__link_01" type="revolute">
        <axis xyz="0 0 1"/>
        <limit effort="1000.0" lower="-3.14" upper="3.14" velocity="0.5"/>
        <origin rpy="0 0 0" xyz="0 0 0.5"/>
        <parent link="base_link"/>
        <child link="link_01"/>
      </joint>

    <link name="link_01">
        <visual>
          <origin rpy="0 0 0" xyz="0 0 0.2" />
          <geometry>
            <cylinder radius="0.35" length="0.4" />
          </geometry>
        </visual>
    </link>

</robot>

In the IDE (Code Editor), you can find it under the urdf folder:

<?xml version="1.0" ?>

<robot name="mrm" xmlns:xacro="http://www.ros.org/wiki/xacro">
  ...
</robot>

<link name="base_link">
  <visual>
    <origin rpy="0 0 0" xyz="0 0 0" />
    <geometry>
      <box size="1 1 1" />
    </geometry>
  </visual>
</link>

<joint name="base_link__link_01" type="revolute">
  <axis xyz="0 0 1"/>
  <limit effort="1000.0" lower="-3.14" upper="3.14" velocity="0.5"/>
  <origin rpy="0 0 0" xyz="0 0 0.5"/>
  <parent link="base_link"/>
  <child link="link_01"/>
</joint>

<link name="link_01">
  <visual>
  <origin rpy="0 0 0" xyz="0 0 0.2" />
  <geometry>
    <cylinder radius="0.35" length="0.4" />
  </geometry>
  </visual>
</link>

cat ~/simulation_ws/src/mrm_description/launch/rviz.launch

<launch>
  <param name="robot_description" command="$(find xacro)/xacro --inorder '$(find mrm_description)/urdf/mrm.xacro'"/>
  
  <!-- Combine joint values -->
  <node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher"/>
  
  <!-- Show in Rviz   -->
  <node name="rviz" pkg="rviz" type="rviz" args="-d $(find mrm_description)/launch/config.rviz" />
  
  <!-- send joint values -->
  <node name="joint_state_publisher_gui" pkg="joint_state_publisher_gui" type="joint_state_publisher_gui">
    <param name="use_gui" value="true"/>
  </node>

</launch>

 <node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher"/>

<!-- send joint values -->
<node name="joint_state_publisher_gui" pkg="joint_state_publisher_gui" type="joint_state_publisher_gui">
    <param name="use_gui" value="True"/>
</node>

cd ~/simulation_ws/

catkin_make

...
-- catkin 0.8.10
-- BUILD_SHARED_LIBS is on
-- BUILD_SHARED_LIBS is on
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- ~~  traversing 1 packages in topological order:
-- ~~  - mrm_description
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- +++ processing catkin package: 'mrm_description'
-- ==> add_subdirectory(mrm_description)
-- Configuring done
-- Generating done
-- Build files have been written to: /home/user/simulation_ws/build
####
#### Running command: "make -j8 -l8" in "/home/user/simulation_ws/build"
####

Lauching RViz to see our robot model

In the previous sections we already learned how to open a terminal.

Now, in order to launch RViz, let’s run the following commands in the first terminal:

source ~/simulation_ws/devel/setup.bash


roslaunch mrm_description rviz.launch

In the RViz window, we should have everything in place. We shouldn’t have the red errors like in the image above, because in the rosject we already provided the config.rviz in the launch file, if you remember well.

What we did for creating that config.rviz file was the following, in RViz:

• Changed Fixed Frame to base_link
• Added an Axis element
• Added a RobotModel element

The images below show the operations described above:

Congratulations. Now you know how to create a basic robot with two links and a joint using Xacro files.

We hope this post was really helpful to you. If you want a live version of this post with more details, please check the video in the next section. Although the video was recorded in a previous version of The Construct platform, it still adds a lot of value:

Youtube video

So this is the post for today. Remember that we have the live version of this post on YouTube. If you liked the content, please consider subscribing to our youtube channel. We are publishing new content ~every day.

Keep pushing your ROS Learning.

Related Courses & Training

If you want to learn more about ROS and ROS2, we recommend the following courses:

1. ROS Courses:
   1. URDF for Robot modeling (ROS 1): https://app.theconstructsim.com/Course/13
2. ROS2 Courses:
   1. URDF for Robot Modeling in ROS2 : https://app.theconstructsim.com/courses/83

• • ROS2 Basics in 5 Days Humble (Python): https://app.theconstructsim.com/Course/132
  • ROS2 Basics in 5 Days Humble (C++): https://app.theconstructsim.com/Course/133
  • Open-RMF / Fleet Management Training: https://www.theconstruct.ai/robot-fleet-management-ros2-open-rmf-training/