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Am currently getting the following warning which I think is the cause of UWSim crashing if challenged by anything more than loading:

The root link base_link 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've gone looking through the .xml files and I've looked around on the internet, and though a lot of people seem to talk about this warning I have found no solutions. I am working from the default cirs.xml for UWSim inside ROS Indigo.

Does anyone have suggestions to fix this problem? Is it ROS or UWSim?

Thanks if anyone does have a solution.


Originally posted by jhoban on ROS Answers with karma: 5 on 2016-03-01

Post score: 0

Original comments

Comment by gokarna_baskota on 2021-12-13:
Here I am getting same warning:

[ WARN] [1639396403.511927089]: 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.

and error in rviz as shown in picture:

how to solve this problem

How to solve this?

Comment by jarvisschultz on 2021-12-13:
@gokarna_baskota please do not post answers that are not actually answers. This is a Q&A site not a discussion forum. I've reposted your answer as a question comment. Additionally, the image you posted seems to mostly contain text, which is not ideal. It's always preferable to add actual text instead of screenshots so that it can be searched. Finally, I can't really read the image anyway because it's so small. Read more guidelines here: https://wiki.ros.org/Support

The warning in this question is really just a warning. I'm guessing you have an actual issue. Perhaps it would be best to open a new question for your issue specifically. Best of luck!


1 Answer 1


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Hi Janet,

This warning is only saying KDL does not support root links with inertia. But UWSim only uses KDL to publish the TF tree using the URDF provided to build the robot. The robot is NOT simulated through KDL so that is the reason the warning can safely ignored. I tried to find a way to hide it, but I didn't find it. In the case of UWSim is used for simulated force sensor that, obviously, need a mass to produce a simulated force, if there are no force sensors can be safely removed from URDF.

If you are experimenting a crash it should have another cause. If you provide us more information about the crash maybe we can help you ;).

Originally posted by Javier Perez with karma: 486 on 2016-03-02

This answer was ACCEPTED on the original site

Post score: 1

Original comments

Comment by jhoban on 2016-03-02:
Crash info...well it's booting up any of the scenes without problem and the C++ program for the joystick interface compiles with no errors, but any movement of the joystick after booting has completed results in the simulator crashing and closing down.


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