rpat

OK all of you electrical engineers, I would like to know the theory behind the brushless motor. I know how a brushed motor works, but I do not understand the workings of a brushed motor. Why three leads, and how is the power to the motor work?
I did a search and did not come up with anything on the workings of the brushless motor. Any input would be appreciated.
Rich

Jonathan Ott

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The simplest way I can explain it, after being told in a more technical manner is this:

There are a number of stators in the motor, the number is divisible by 3, hence 3 wires. Now, when energized by the specialized speed control, the stators are energized in sequence and that makes the bell (on a CD-Rom type) spin. You have to have the special speed control, or it will not work.

You know that like poles on magnets repell, well, think that each stator is "+" when energized and nothing is happening when not energized. If each magnet has the "-" pole facing the stator, then when it comes around to an energized stator it will push away from it., do this in sequence faster than you can think and it will cause it all to spin 'round & 'round

That is a very simplistic approch to it. I'm sure someone will come in here and give us a headache full of information on how it all works...Bring it on boys!!!

wreck_em_all

I know you understand brushed motors, but the following leads to an answer to your question. In a brushed motor the commutation process keeps the magnetic field moving ahead of the rotating part of the motor. This of course is done by mechanical means. As the motor rotates, the mechanical motion of the commutator allows the coil of wire ahead of the rotor position to be energized. This causes magnetic attraction to "pull" the rotor around. This is exactly what is happening in a brushless motor except the commutation process is done electronically. The windings and magnets are arranged so that the wire coils are electronically energized ahead of the rotor position. A computer in the ESC keeps track of rotor position and figures out what coil to energize and when. The ESC's computer knows rotor position info from a set of Hall effect sensors (sensored motor) or by measuring back electro-motive force voltage (BEMF - sensorless motor). Brushless EP motors are 3 phase thus 3 wires. This makes for smooth operation and control.

rpat

Thanks guys,
I had a feeling that it was some sort of three phase process. I am under the impression that the brushless set up inside of the motor is exactly the opposite set up of the brushed set up mechanically. The thing that I learned here is that the ESC actually controlls the process where as the brushaed set up is left on it's own to spin the armature. So I guess that the brushless set up is controlled by the computer and the brushed set up is just a mechanical set up. Am I right on that assumption ?
Rich

wreck_em_all

I am not sure I would say the brushed and brushless setups are opposite. They definately are different. Your assumption is essentially correct.

big tree

Since a brushless motor is three phase do you reverse rotation by changing two of the three wires? What I am getting at is I want to make a brushless motor into a pusher.


Thanks

HairyYeti

[img]brushed.jpg[/img]armature.jpg[img][/img][img]magnets.jpg[/img]
Bare with me i have never posted pictures on forums before, but i have pictures of a "brushed" motor(thanks to howstuffworks.com) that have been essentially taken apart. i hope that they have loaded properly.
[img]brushless.jpg[/img]
I also have a picture of a brushless motor(I forget where its from). The only thing that should be different(i believe) from the RC brushless you can buy is the Printed circuit board in the picture provided is basically a polarity controller(speed controller). From the brushless picture, you can see that the magnets and wire of a brushed motor have been "switched" The magnets are mounted and balanced on the armature and the wire is wound into a sleeve in a design that can allow for current to pass through a section of the sleeve to "pull/push" the magnets.

The brushless motor design does a few things different from a brushed:
1) Eliminates Brushes(commutators). Brushes create friction which produces heat, noise, and hinders the max rpm.(bad for efficiency)

2) Gets rid of the "core"(Thing the wire gets wrapped around in a brushed to increase the magnetic field).Eliminating weight that has to be forced to move also increasing efficiency.

Brushless motors overall are much better than brushed, the only downside to them is that they cost more to make and the motor in most cases will outlive the application.(blenders, mixers, ect.)

I hope this helps. Also if i have left anything out, or something needs correction please feel free to. I gathered all this information for a speech on electric motors for my technical writing class. Although i wish i could have found a better brushless picture.

wreck_em_all

Yes, reversing any 2 wires wil reverse rotation. I have done a number of brushless pushers no problem.

wreck_em_all

RC BL motors usually do not have an internal PCB. The PCB shown in your illustration holds the Hall Effect sensors (item #3) and not speed control. It does not appear the illustrated PCB is of adequate size to contain the power transistors needed to control a motor of that type.

Inrunner BL motors have a magnetized rotor with wire coils on the inside of the motor can. The rotor is inside the coiled wire. Outrunner BL motors have coiled wire rotors with magnets on the inside of the motor can. The wire coils are inside the magnets. It is possible to have a BL motor with magnets and coils configured the same as brushed motors.

You are confusing coreless and brushless. Wire wrapped around iron acts like a lense for magnetism. It concentrates and increases the strength of the magnetic field. BL motors have iron, coreless motors do not.

Ron v. Sommeren

See the brushless motor FAQ:
http://www.rcuniverse.com/forum/How_...1558046/tm.htm

rpat

Thanks guys,
I have a better understanding of what is going on inside the motor now. The piece about the inside brushless and the outrunner types made me think for a second but you guys are right that everthing is reversed on an outrunner.
Rich

Ron v. Sommeren

About the advantages of outrunners:
http://www.yahoogroups.com/group/lrk-torquemax/

Ron v. Sommeren

Weight in itself does not effect efficiency. It also has little effect on inertia since the inertia of the prop is much larger/greater/bigger (whatever )

rpat

Thanks guys for all of the insight into the brushless motor. I have a much better understanding of the motor. I liked the site that actually showed a complete cycle of the motor. The third wire acting as a timing device kind of made it all fall together for me.
I am going to start another thread on how a speed controller works so get your fingertips warmed up.
Rich