Small whiteboard vehicle (used by my wife for traffic management).
It uses a 10x3mm neodym magnet with countersunk hole for a small screw 2.5x6mm.
OpenSCAD source provided. Should be fairly easy to modify.
The wheels have a small recess that should be oriented outwards when mounting.
Print with support as layed out in the stl file.

Velleman

K8200

No

Yes

0.21