The kobuki base alone isn't going to drift, so it is sensible that the tilted inertia triggers the drift. Not surprisingly I'm able to hack my URDF using a weightless superstructure, but I planned to deal with this in a far more practical way. I tried all I can think https://www.uk-exhibitionstands.co.uk/product/standard-square-blimp-tower-with-tapered-tube-blimp/