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Old 05-05-2014, 06:08 AM   #6
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Originally Posted by JetPlaneFlyer View Post
I'm no electronics expert but a few advantages of brushless would be:
  • No friction losses of in commutator.
  • No sparking and wear of the brushes and armature contacts.
  • No limitations on current and/or voltage caused by the commutator.
  • With brushless the timing of the motor can vary depending on load and RPM (making it more efficient) brushed timing is fixed for all conditions.

There is one advantage of the brushed motor over the typical sensorless brushless motor on RC models, and that's that the brushless can produce full torque right from stationary. A sensorless brushless has to initially spin up slowly at low torque until timing is established. This generally isn't a huge issue for airplanes but it's a problem for cars. the better cars have sensored brushless motors which gets around the problem.
Cogging is what you speak of. Essentially, on a sensorless motor, the esc sends to find the closest pole, but doesn't know without sensors, so what takes place is random bits of current that move the motor slightly. If not enough, it will actually keep cogging, as the motor is not turning enough to allow progression. Planes have this too. When you first start the throttle on very low, you will hear a ratchet sound. Sensored motors are used on on or offroad racing models, such as used in ROAR championships. Another way to solve this cogging is simply: add more poles. My buggy has a 6 pole motor, cogging is essentially non-existent. Also, the higher the kV, the more cogging will be present, along, to some degree, with gearing, although kV is the biggest factor. Because a higher kV motor has less torque, it takes more current to get that pole to "turn over", and thus, usually more throttle, a lighter vehicle, wheels with less rolling resistance, and 2wd rather than 4wd. On planes, well, there is simply much less going on really, there is no gears, contact friction of wheels, only resistance of trying to get the prop to spin.
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