URDF link mass inertia properties

edit

The origin of the inertial element of the URDF must be taken from the center of mass of the link. So the XYZ of the inertial origin is the offset from the link's origin to the center of mass. Currently, the orientation of the inertial element is assumed to match the orientation of link's origin and RPY for the inertial origin is not supported. Therefore if you were pulling values from SolidWorks mass properties, you should probably use the moment of inertia taken at the center of mass and aligned with the output coordinate system (Lxx).

However, a few caveats. Make sure the 'output coordinate system' you choose aligns with the coordinate system in the URDF. Many times in SW, the default coordinate system has Y pointing upward, but in URDF and Gazebo, Z is assumed to be pointing upward. Place your 'output coordinate system' by inserting a reference coordinate system in SolidWorks at either the origin location of the joint connecting this link with its parent link, or in the case of the base_link, place the output coordinate system at the collision/visual origin (typically the default origin for the model).

I'm going to toot my own horn here and plug the SolidWorks to URDF exporter for exactly this. Though, I realize answering this question four months after you asked it is of little help.