  The coupling of two rotating spherical magnets is investigated
experimentally. For two specific angles between the input and output rotation
axes, a cogging-free coupling is observed, where the driven magnet is
phase-locked to the driving one. The striking difference between these two
modes of operation is the reversed sense of rotation of the driven magnet. For
other angles the experiments reveal a more complex dynamical behavior, which is
divided in three different classes. This is done by analysing the deviation
from a periodic motion of the driven magnet, and by measuring the total
harmonic distortion of this rotation. The experimental results can be
understood by a mathematical model based on pure dipole-dipole interaction,
with the addition of adequate friction terms.
