This article is from the Radio Control (R/C) Flying FAQ, by Shamim Mohamed shamim@math.isu.edu with numerous contributions by others.
Rare-earth magnets, of which the most common type is samarium cobalt, are
stronger for a given weight and volume than ferrite magnets. Perhaps an
even more important reason for getting a cobalt motor is that they also
have better brushes, bigger shafts, better bearings, are built more
carefully, and so on. For the serious electric flier, they are worth the
extra expense.
 
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