Unit 2, the RobotModel is not loaded

Course Support Mastering Gazebo Simulator
1

In Unit 2 the RobotModel is not loaded and not found in when searching the add buton. Additional when starting the launch file I get the following erroer
[ WARN] [1693983715.118299266]: The root link link_chassis has an inertia specified in the URDF, but KDL does not support a root link with an inertia. As a workaround, you can add an extra dummy link to your URDF.

I think that the two isues are related and would greatly appriciate some help

L.

2

Hi,

Its always better in gazebo models to add innertias to the links. TRy that first.

Also I recommend that first start with a very basic urdf, with ONle link, see if it appears in gazebo, the physics are right.

If all went well then add a second link with a joint, try again and so on. This way is safer and yo detect errors very easily

Also for future posts, try to add some code, git or better a Rosject with instructions on how to reproduce your error, that way can can help you better an faster :wink:

3

Thanks for the quick replay, but I feel that my point was missed.

I am specifically talking about the start of the second unit. In the urdf there is only one link with inertia. As the warning mentions
[ WARN] [1694002328.545464278]: The root link link_chassis has an inertia specified in the URDF, but KDL does not support a root link with an inertia. As a workaround, you can add an extra dummy link to your URDF.

The existance of the inertia might be the problem.

Thanks for the help

4

Added a “dummy link”

<?xml version="1.0" ?>

<robot name="robot"> 

  <link name="world" />

  <joint name="world_to_base_link=" type="fixed">
    <parent link="world"/>
    <child link="base_link"/>
  </joint>

  <link name="base_link" />

  <joint name="base_link_to_chassis" type="fixed">
    <parent link="base_link"/>
    <child link="link_chassis"/>
  </joint>

  <link name="link_chassis">
    <inertial>
            <mass value="10" />
            <origin xyz="0 0 0.3" rpy="0 0 0" />
            <inertia ixx="1.5417" ixy="0" ixz="0" iyy="3.467" iyz="0" izz="4.742" />
        </inertial>

        <collision>
            <geometry>
                <box size="2 1.3 0.4" />
            </geometry>
        </collision>

        <visual>
            <geometry>
                <box size="2 1.3 0.4" />
            </geometry>
            <material name="Red">
                <color rgba="1 0 0 1" />
            </material>
        </visual>
        </link>
</robot>```
5

This topic was automatically closed 5 days after the last reply. New replies are no longer allowed.

6

Hi,

What error appears exactly please? The urdf you state here , its convenient that to set the inertias in the base link that connects to the world, that’s it test that. If that doesn’t work, nothing will and its related to how you are spawing the robot , maybe missing the robot state publisher or something like that. Pleas share the rosject or full package that maybe that way we can debug a bit better