Mecanum mobile robot wheel friction direction

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,
1

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"/>
        <collision>
          <surface>
            <friction>
              <ode>
                <mu>1.0</mu>
                <mu2>0.0</mu2>
                <fdir1 ignition:expressed_in='base_link'>1 -1 0</fdir1>
              </ode>
            </friction>
          </surface>
        </collision>
      </gazebo>

Thanks

2

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

<robot name="my_robot" xmlns:xacro="http://www.ros.org/wiki/xacro" xmlns:ignition="http://gazebosim.org/schema">

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.

3

Thank for the answer @azeey !
Importing "xmlns:ignition="http://gazebosim.org/schema">" 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.
Thanks

4

Hey @Stefano_Mutti, I am having a similar problem as you mentioned here, in that my xacro has the "ignition:expressed_in=‘base_link’ portion but it does not seem to be taking effect in the final sdf. Any chance you were able to find a solution?

5

hi @spelletier1996 .
I don’t remember what the problem was but now is working correctly.
Take a look at this file where I am using it: