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Old Oct 02, 2006, 07:33 AM
gnofliwr is offline
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aka: A.Roger Wilfong
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Novi, Michigan, United States
Joined Jan 2001
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Quote:
Originally Posted by Drunkskunk
to add some more confusion here. A brushed motor is around 40% efficent, while a brushless is around 80% efficent, so the brushed does twice as much work per watt as the brushed. but then you have inrunner's on gears fighting against direct drive out runners, so Watts become meaningless as a power rating.
I respectfully disagree.

Generally, brushless motors are more efficient than brushed motors and cobalt motors are more efficient than ferrite motors, but any statistician will tell you that what is true for the whole is not necessarily true for the part.

Also, the 40% efficiency rating for brushed motors is low. Even the lowly speed 400 can easily do 60-65%. A properly loaded Astro cobalt motor can easily do 75-80% efficiency. Some cheap outrunner brushless motors have a hard time reaching 70% efficiency. And, if you improperly load any motor you can get really low numbers.

The traditional watts/pound rule of thumb is from Keith Shaw. Since power is easy to measure at the battery, Keith used input watts as the measure. Keith is a big user and strong advocate of Astro cobalt motors so he used their efficiency (~75%) as the basis for the rule of thumb.

- Roger
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