Magnet dimensions

[GriffinRU]

Well, I thought maybe that would be easy to explain by making it too simple. And when I was talking about magnet power, I was assuming that with segments you can easy pick up similar power magnets to achieve consistent magnetic field across wide selection. But that maybe not true, I haven’t measured magnetic field individually myself and haven’t compared one either.
When I was talking about magnet losing its power, I was thinking about high currents not high temperature. Magnet can be demagnetized with high current, especially when it is cool. While demagnetization with high temperature happens at relatively high temp, so before you reach one something will be smoking pretty well. But on other hand everything possible.

Usually, Eddy current losses in the magnets are ignored, due to the fact that magnet magnetic field and windings magnetic fields are synchronized. However completely cannot be ignored because of braking, accelerating and timing.

There are couple ways to reduce or eliminate Eddy current losses different motor manufactures use different approaches, based on their R&D data. It is known fact that Eddy current losses dependent on the magnetic thickness, air gap, magnet width etc. Eddy-current loss in the rotor can be reduced by either increasing the magnet thickness and air gap length simultaneously, or using segmented magnets for each pole. The increase in magnet thickness and air gap length effectively reduces the effect of armature reaction, while segmenting the magnets reduces the Eddy-current loop areas. Using a shielding cylinder around the magnets (aveox BL motors), segmenting and side-insulating the magnets are popular solutions as well.

Torque – more poles, big diameter, longer can, bigger magnets, smaller air gap
Speed – less poles, small diameter, shorter can, relaxed air gap

And building motor with small diameter but very long can not a good idea because of shaft flex.

Artur