Any good sites on how brushless dc motors work?

or just grab a cheap 12 VDC muffin fan and look at it. Windings in the center, a Hall effect switch to flip polarity, and a "refigerator magnet" strip inside the rotating hub.

OK, I have a spare cpu fan, so I took that, and looked at it. I guess the tiny resistor-looking thing is something to do with the hall effect unit. It's that hall thing I want to learn more about, as I want to build a much larger version of one of these motors.

I believe now, having seen this small example, that the seam in the rotor magnet is what triggers the sensor. If so, that's pretty cool.

Sensors are old hat. Modern speed controllers (eg for Permanant magnet brushless DC model aircraft motors) don't need them anymore. If you have a motor with say three windings then at any one time only two are powered. The third winding is used to sense rotor position (the controller looks for the zero crossing). The tricky problem is how to get the motor to start in the right direction and all the speed controller manufacturers have their own tricks for that. Essentially it involves pulling the rotor to a known position then applying a rotating field (but it's much more complex than that).

So in other words, this is all to make the electric motor both brushless, and at the same time, to make the motor start rotating, when the switch is flicked, and not let the electric motor stall in the field, and consequently burn out? It makes sense that each manufacturer has their own cicuit wizardry to initially position the motor.

My little project will be a little brushless generator driven via pulley attached to small engine, or human power. So, can my generator be brushless? I suspect it can, and would like the simplest example a diagram for such a brushless circuit. It doesn't really have to be b/less, but I'd rather do it that way, if it's 'simple enough'.

thanks for the knowledge

The sensors have been a source of problem to model flyers (particularly on high power competition systems operating at 1400W+). The sensor has to be in the right place w.r.t the coils and any error in the sensor detecting the position of the rotor results in a timing error. At high powers there is a lot of noise about and if the sensor triggers at the wrong time it's possible to blow up all the FETs in the controller. Sensorless systems have proven more reliable.

Try contacting the author of this site...

See under "Brushless DC PM Servo Motors"

Colin

OK, I have seen the otherpower.com site, and plan to peruse in much more depth, as it's one of several where I've learned an incredible amount lately.

Still, I need to throw this question out here, for a quick reply: When I tore the little muffin motor apart, I see that the armature is stacked layers of metal, and the fine copper coil wound around that. Why the stacked metal plates, and not a single solid core?

Thanks, George

Thats to improve efficiency by reducing eddy currents in the core (see also transformers).