# outrunner induction motrs



## hydragon (Oct 12, 2015)

Are there any outrunner induction motors?


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## riba2233 (Apr 29, 2015)

Yeah, used for industrial fans. 

Also, this:

https://endless-sphere.com/forums/viewtopic.php?f=30&t=73164


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## dougingraham (Jul 26, 2011)

hydragon said:


> Are there any outrunner induction motors?


Outrunners are not as good as the alternative from an efficiency standpoint. The reason they are so prevalent in the RC hobby world is they are cheap to make because the stator can be easily machine wound. The loss in efficiency comes partly from the slots being near the center of the motor and this makes it difficult to get adequate copper fill. When the slots are near the outside of the motor it is much easier to fill them with copper. The rotating outside of the motor is more massive than an inner rotor and an increase in mass here also costs in efficiency. Outrunners are also more difficult to cool. With an inrunner the heat is generated mainly in the windings which are on the outside of the case. So cooling the case does a good job of cooling the motor. In the case of an induction motor this is less of an issue because you don't have permanent magnets that would be ruined by heat.

The advantage of an outrunner for RC planes is that you can usually get away without using a gearbox so you gain back that 5% loss in the gears but since they are probably around 10 to 15% less efficient you still have a net loss in efficiency of at least 5% in addition to the fact that they weigh more for a given output. Since you pretty much have to have some sort of gearbox in an EV you don't get even this small advantage. Wheel motors are outrunners so if you could make one of these work long term that would be a small advantage.

I used to tell people that we (RC modelers) would never have adopted out runners if lipo batteries had not come out about the same time. The advantages of the LiPo batteries completely masked the disadvantages of the outrunner motors.

Is there some particular reason you want an outrunner in an EV?


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