Inertia Element Conversion Issues in URDF to SDF in ROS2 Iron (Worked in Galactic)

Question

I am encountering an issue in ROS2 Iron that wasn't present in ROS2 Galactic, related to the conversion of a URDF file (generated from XACRO) to SDF, specifically regarding the inertia elements. I am using ROS2 Iron on Ubuntu 22.04

Problem Description:

In ROS2 Galactic, the conversion of my URDF file (generated from a XACRO file with inertia calculations) to SDF was successful. However, after upgrading to ROS2 Iron, the same URDF to SDF conversion process leads to errors.

Steps Taken:

1- I created a simple XACRO file with basic inertia calculations and successfully converted it to a URDF file using the command:

xacro simple_wheel.xacro > simple_wheel.urdf

2 - When converting the generated URDF file to SDF using the following command:

gz sdf -p simple_wheel.urdf > simple_wheel.sdf

3- I received errors related to the inertia elements:

Error: Inertial: inertia element ixx is not a valid double
       at line 334 in ./urdf_parser/src/link.cpp
Error: Could not parse inertial element for Link [simple_wheel]
       at line 435 in ./urdf_parser/src/link.cpp

The URDF file includes correctly formatted inertia elements, but they seem to be misinterpreted during the SDF conversion.

Specific Questions:

1. Are there known issues or changes in ROS2 Iron affecting the URDF to SDF conversion process, especially regarding inertia elements?
2. Do I need to follow a different procedure or use specific tools in ROS2 Iron for accurate SDF conversion?
3. Is there a recommended workaround or solution to ensure that inertia elements are correctly processed during the URDF to SDF conversion in ROS2 Iron?

XACRO File Snippet for Reference:

<?xml version="1.0"?>
<robot name="simple_robot" xmlns:xacro="http://www.ros.org/wiki/xacro">
    <xacro:property name="wheel_mass" value="74"/>
    <xacro:property name="wheel_radius" value="0.536"/>
    <xacro:property name="ixx_iyy_inertia" value="0.5 * ${wheel_mass} * ${wheel_radius} * ${wheel_radius}"/>
    <xacro:property name="izz_inertia" value="${wheel_mass} * ${wheel_radius} * ${wheel_radius}"/>
    <!-- link definitions -->
</robot>

I appreciate any insights or suggestions

Answer 1

I needed to put the calculated value directly instead sum the xacros variables....did not find another way to fix it.

The fix is below:

  <!-- calculate moments of inertia -->
  <xacro:property name="wheel_mass" value="74"/>
  <xacro:property name="wheel_radius" value="0.536"/>
  <!-- <xacro:property name="ixx_iyy_inertia" value="0.5 * ${wheel_mass} * ${wheel_radius} * ${wheel_radius}"/>
  <xacro:property name="izz_inertia" value="${wheel_mass} * ${wheel_radius} * ${wheel_radius}"/> -->
  <xacro:property name="ixx_iyy_inertia" value="10.629952"/>
  <xacro:property name="izz_inertia" value="21.259904"/>