Mecanum mobile robot wheel friction direction

Hi all,
i am using gz sim to simulate a mecanum mobile robot.
Starting from the xacro file, I generate an urdf that I load into gazebo with “ros_gz_sim create” from a launcher.
Everything loads correctly but the robot won’t navigate correctly because I cant add the

<fdir1 ignition:expressed_in='chassis'>1 -1 0</fdir1> 

into the urdf, because xacro complains about the “ignition:” part.
Is there a way to embed this into the urdf, or I have to work only with the sdf ?
I also expect the keyword ignition to have changed in gz sim, is there a new keyword ?
The actual urdf/xacro code in which io specify the wheel link properties looks like this now:

      <gazebo reference="${prefix}front_left_wheel">
      <mu1 value="1.0"/>
      <mu2 value="0.0"/>
                <fdir1 ignition:expressed_in='base_link'>1 -1 0</fdir1>


The ignition:expressed_in attribute is a custom attribute and uses the xml namespace ignition, so you’ll need to add xmlns:ignition=" to your <robot> tag of your xacro file. So it would like like:

<robot name="my_robot" xmlns:xacro="" xmlns:ignition="">

See the sdformat documentation on custom elements and attributes. This example would also be helpful.

Starting in Gazebo Garden, you should use gz:expressed_in instead of ignition:expressed_in with the same change in the xmlns attribute. ignition:expressed_in is deprecated, but should still work, though you will get a warning about it.

Thank for the answer @azeey !
Importing "xmlns:ignition="">" resolves the problem in the XML/Xacro, but when I load the urdf model with “ros_gz_sim create” it loses the "ignition:expressed_in=‘base_link’ part.
I will have to investigate that package.