The Kobuki base alone will not drift, so it makes sense which the tilted inertia causes the drift. Naturally I can hack my URDF having a weightless superstructure, but I planned to deal with this in a far more sensible way. I tried all I can contemplate, and all failed: https://www.uk-exhibitionstands.co.uk/product/casonara-seg-light-box-counter-100m/