I don't feel I can properly answer all of those questions, but here is my take on it.
1. The outrunner principle moves the force application point significantly away from the rotating axis. While I haven't calculated the relative effect of this against the increased pole-count, I suspect this is just as strong a contributing factor.
2. These motors have 12 stator poles and 14 rotor poles. 540-size car motors generally have 2 rotor poles and 3 stator poles. The average spacing of a live stator pole to a permanent magnet is FAR closer in the outrunner design.
3. In order to make an inrunner with the same pole count, it would have to be physically much larger than an outrunner of the same power, so I don't think they are really directly comparable.
4. Every sensorless ESC I have tried with outrunner motors runs them. Currently I am using a Hobbywing Extreme Stock and the starting smoothness and speed control is just as good as any sensor-based system I have used on normal car motors. There is likely to be a stronger back-EMF signal at low rotating speeds than you get from a conventional system, leading to improved sensorless performance.
As an idea of the starting performance, I can grip one of these motrors quite tightly in my fist and smoothly throttle up, and it just starts rotating without any trouble.
5. Switching frequency does need to be higher for outrunner motors, but it is still way within the capability of all modern ESCs.
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08-12-2013
Mardave
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