I have noticed that some brands of large out runner motors when turned by hand feel as if you are turning past a magnet,and yet on another brand of the same physical size and kv rating does not have this resistance or a much lower resistance. Does anyone know why this is ????
08-22-2008, 04:43 AM
'Cogging', or the lack of it, is not a good indicator for quality, power, efficiency, torque, magnet strength, rpm.
Cogging depends on magnet strenght, stator geometry (hammerhead size), magnet size, statoriron, flux-ring iron, number of magnetpoles versus number of statorpoles, airgap between stator and magnet, gap between magnets, accuracy of magnetplacement (hight, distance, skewing). Magnet or statorskewing reduces cogging. The closer the mangetpole/statorpole ratio is to one, the less cogging. A ratio of one would give excessive cogging but that's not a problem, that kind of motor would not run anyway.
Cogging does not depend on number of winds (Kv), or amount of copper or windingresistance.
Apart from all this, a motor with shorted leads will always be difficult to crank because it will act as a generator
Vriendelijke groeten ;) Ron