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View Full Version : Brushless Motor = Three Phase Motor?


Lieutenant Loughead
11-20-2008, 02:53 PM
Hey guys,

Later this morning, I've got a job interview with a company which uses three phase motors for winches... I started thinking of my electric airplanes, and how I can try to use that "brushless motor" knowledge to relate to their "three phase" winch motors... After all, there are three wires coming out of the brushless motor! :o

So, is there any relationship between a "brushless motor" and a "three phase motor"?

thanks for your help!

aviatordave
11-20-2008, 11:13 PM
There are alot of similiarities, look around this website....dont get caught up in the math calcs.

http://www.aerodesign.de/peter/2001/LRK350/Warum_dreht_er_so_eng.html

Murocflyer
11-21-2008, 12:14 AM
I hope your interview went well! Is this going to effect your RC store opening?

Frank

TDisaster
11-21-2008, 12:57 AM
I was thinking the same thing today in electrical. We were doing job sheets and I found a few books on motors. Interesting stuff for sure :).

ron_van_sommeren
11-21-2008, 02:14 AM
'Our' brushless DC (BLDC) motors are brushed motors with the mechanical commutator replaced by an electronic one, the ESC. In combinations with the ESC it's operates iso-synchronous, not synchronous and not a-synchronous: the motor 'tells' the ESC when to do the switching. Having said this, the motors can operate synchronous on 3-phase mains, if the voltage were not much too high and too dangerous.

Vriendelijke groeten ;) Ron

Larry3215
11-21-2008, 06:29 AM
Like Ron said, there are similarities but its kind of an apples and oranges thing. Both are fruit, but still very different :)

kaindub
11-21-2008, 06:43 AM
An electric motor connected to three phase mains supply is generally of a type called an induction motor.
Its called an induction motor because there is no magnetic field wilst the motor is unpowered.
Note .All motors need a magnetic field to operate - that is basic physics.

The induction motor generates a magnetic field in the rotor when the power is switched on. I know how but the ewxplanation is too boring ofr this forum.

The motors we use in planes already have the magnetic field. That's the magnets in either the inner part (for an inrunner or on the outer part for an outrunner. The magnets are attached to the rotor.
They are a form of synchronous motor.

All motors operate on the same principle.
Magnetic filed , wire carrying current going into the field causing rotation.
Differences are where the magnets and the wire are located - rotor or stator, and the principle of how the current carryimg wire is 'moved' from magnet to magnet.

Lieutenant Loughead
11-21-2008, 02:20 PM
Thanks for the explanation, guys -- I appreciate it.

I hope your interview went well!Thanks Frank. I think the interview went very well -- however (just like every other company right now), that company is in a "hiring freeze" until January 1, 2009. Even then, they're not sure they'll be hiring... ...and if they do, they're going to be offering a fraction of the salary they normally do... :(

Is this going to effect your RC store opening?No -- actually, it's quite the opposite... You see, the RC store was a "backup plan", in case I got laid off (which happened to me 15 days ago). So, I called up my father and my aunt, and told them if we hurry, we could open the store in time for Christmas (one year early)...

...both said the money they had put aside for me was in the stock market, and is currently worth about 40% of what it was this time last year. Therefore, I must look for another full time job... :(

Nobody knows when the market will turn around -- and I simply can not open the store until the market bounces back... :o

Larry3215
11-21-2008, 05:55 PM
Thats a serious bummer.

I am just waiting for the shoe to drop at my work too. Its no fun at all in my position and yours is much worse.

Hope things turn around for you soon!

Good luck!

pilotpete2
11-21-2008, 07:48 PM
Hi Ron,
I'm not so sure that a permanent magnet BLDC motor will self start with 50 or 60Hz AC current. I'm under the impression that the rotor must spin up to speed in one cycle of the AC current. A typical 12 stator pole outrunner (4 pole per phase) will run at 1500 RPM on 50Hz, not likely to be able to start on its own.
Anyone who has played a classic Hammond B3 (blues organ) will remember that you had to hold a spring loaded starter switch for about 10 sec. until the tone wheel shaft was brought up to speed by an asynchronous induction motor, at that point the synchronous motor could maintain correct RPM and pitch.
Regards,
Pete

Murocflyer
11-22-2008, 01:38 AM
Sorry to hear that Guy! I hope things get better for you real soon.

Frank

dbcisco
11-26-2008, 09:39 PM
The industrial motors (BL and brushed) are usually designed to run at a single speed which is frequency dependent. To get speed changes requires a much more complex controlling system. Some industrial BL's have a brushed "starter" motor to bring them up to synchronous speed.