The kobuki base by yourself will not drift, so it makes sense that the tilted inertia leads to the drift. Needless to say I can hack my URDF with a weightless superstructure, but I planned to deal with this in a far more sensible way. I attempted all I'm able https://www.uk-exhibitionstands.co.uk/product-category/hanging-towers-seating/blimp-towers/