The torque of the radial magnetic coupling between perpendicular magne
tic gears with different magnetic poles has been investigated experime
ntally. The torque of magnetic coupling decreases with increasing the
distance between the magnetic gears. For different multipole magnetic
couplings with the same magnetic field strength, the torque of magneti
c coupling increases as the number of magnetic poles increases for dis
tances smaller than a critical separation distance d(c), but it is rev
ersed as the separation distance becomes larger. This critical separat
ion distance for our sintered NdFeB magnet system with an iron yoke of
2 mm thickness is roughly between 9 and 11 mm. This phenomenon is exp
lained by analyzing the magnetic coupling strength of different poles
of magnets on the perpendicular magnetic gears.