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Old 03-13-2008, 07:50 AM   #19 (permalink)
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Join Date: Sep 2006

HFG and I have been having an ongoing PM conversation.

The diagram of the motor in the Brushed Motor section is actually a Brushless Motor. In a brushed motor, the brushes are need since the coils are rotating and yuo need to get the power to them. So the coils are on the shaft that turns, and the brushes work like the next diagram (red and blue rotating commutator).

Brushed Motor:

The concept of the motors are pretty much the same, changing the energized coils to push/pull the permanent magnets around. The difference is that a brushless motor needs the siwtching of the coils to be controlled outside the motor. Brushed motors control their own switching.

On 3 phase AC motors, like many large pieces of machine equipment, they use the 3 phases to energize the coils in sequence. Works well, but only a single speed that is a steady as the power line frequency (which in the US is very stable).

About the only place I have seen outrunner motors is model aircraft and computer disk drives. In disk drives they are used because they can produce enough torque in a very thin package. In models they are also used for the higher torque allowing direct drive of larger props or more reasonable gearing for things like helis.

In GENERAL, an outrunner will produce more torque and less Kv (RPM per volt) than inrunners. But there is now a significant amount of overlap for lower Kv inrunners and high Kv outrunners.
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