Robot floating after import


I have some problem when importing a Robot from URDF.
The problem is that the model is just floating in space and therefore not being able to move around.
The individual joints however can be moved relative to the robots base.

I have imported the URDF using the URDF Importer extension, with the fixed_base flag turned off and then configured most of the drives as appropriate.
A physics scene with set gravity is also present.

Does anyone have an idea on how to locate the issue here?