  The coupling of two rotating spherical magnets is investigated
experimentally, with particular emphasis on those motions where the driven
magnet follows the driving one with a uniform angular speed, which is a feature
of the so called cogging free couplings. The experiment makes use of standard
equipment and digital image processing. The theory for these couplings is based
on fundamental dipole-dipole interactions with analytically accessible
solutions. Technical applications of this kind of coupling are foreseeable
particularly for small machines, an advantage which also comes handy for
classroom demonstrations of this feature of the fundamental concept of
dipole-dipole coupling.
