RE: How does a brushless motor work?  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> Electric Aircraft Universe >> Brushed/Brushless motors, speed controls, gear drives >> RE: How does a brushless motor work?
Page: <<   < prev  1 2 [3] 4 5   next >   >>  

Login
Message << Older Topic   Newer Topic >>
RE: How does a brushless motor work? - 3/5/2005 9:04:28 PM   
adam_one


 

Posts: 399
Joined: 2/26/2003
From: Stockholm, SWEDEN
Status: offline
quote:

Say, your controller can handle a two pole motor at 140krpm. This means it can handle a four magnetpole motor up to 70krpm, a 8pole motor up to 35krpm, a 10pole motor up to 28krpm and a 14pole motor up to 20krpm.


Yes, and according to my formula, the 3-phase's frequency should be 2333.33Hz provided there's no slip between the stator and the rotor.

_____________________________

http://adamone.rchomepage.com

(in reply to Ron v. Sommeren)
       Post #: 51

RE: How does a brushless motor work? - 3/10/2005 8:20:02 PM   
Ron v. Sommeren



Posts: 92
Joined: 2/4/2002
From: near Nijmegen, NETHERLANDS
Status: offline 		Adam, since these motors, in combination with the ESC of course, are self-commutating, they have zero slippage.

(in reply to adam_one)
       Post #: 52

RE: How does a brushless motor work? - 3/11/2005 7:49:18 PM   
adam_one


 

Posts: 399
Joined: 2/26/2003
From: Stockholm, SWEDEN
Status: offline
quote:

Adam, since these motors, in combination with the ESC of course, are self-commutating, they have zero slippage.

Yes I agree Ron, the 3-phase ESC's actual output frequency depends on the motor's Kv and on actual load, since the ESC needs the back EMF signal before it sends the next pulse, while the pulse's duty cycle depends on the throttle position, right?

_____________________________

http://adamone.rchomepage.com

(in reply to Ron v. Sommeren)
       Post #: 53

RE: How does a brushless motor work? - 4/22/2005 5:13:02 AM   
warren52nz


 

Posts: 117
Joined: 6/20/2004
From: Auckland, NEW ZEALAND
Status: offline 		I think I'll jump in here. I've been trying to discover how a brushless motor can turn at any speed other than the speed that the ESC is "telling it" to. My helicopter can't keep up the same rpm when it's on full pitch than it does at 0 pitch. So it seemed to me that the rotor would be getting behind the rotating fields which would cause God knows what sort of problems.

But after reading this post, it sounds like the speed of the rotating fields reduces if the motor senses it is not keeping up. Is that right?

Kinda tricky.

Thanks
Warren

(in reply to Ron v. Sommeren)
       Post #: 54

RE: How does a brushless motor work? - 5/20/2005 7:31:16 AM   
Neomike


 

Posts: 1
Joined: 5/16/2005
From: , WA, USA
Status: offline 		It"s called slip. The difference between the speed of the rotating magnetic field and the rotor speed. More load more slip. The ability of the drive unit to keep up with the demand frequency, i.e. speed of the motor, is the torque avai;able or current response of the drive unit.
When the motor doesn"t keep up then CEMF starts to have an effect. You probably don"t want to go there, LOL.
The difference in speed between the rotating field and actual rotor speed ( slip) has an effect on CEMF and torque/curent in motor will increase bringing the rotor speed back to within the slip tolerence designed into the motor. Therefore, more load slower = more slip = more torque = back normal rotor frequency or speed.

Anyway I teach a motors and generators/drives class for the elevator industry and you would be surprised how simmilar the motor and drive unit concept is.
Hope this makes some sense it"s kinda late tonight.

mike

(in reply to warren52nz)
       Post #: 55

RE: How does a brushless motor work? - 5/23/2005 4:32:10 AM   
comptrguru


 

Posts: 1
Joined: 1/10/2003
From: San Diego, CA,
Status: offline 		Hey, Gang...
If I took the time to really study this topic, my ??'s were prolly answered. I couldn't 'get it', though. Bear with me, please.

Can I simply hook up twin brushless motors to one ESC? Series hook up? If not, how can I run twin brushless? Thanks mucho....

(in reply to Neomike)
       Post #: 56

RE: How does a brushless motor work? - 6/2/2005 3:04:30 PM   
Ron v. Sommeren



Posts: 92
Joined: 2/4/2002
From: near Nijmegen, NETHERLANDS
Status: offline
quote:

ORIGINAL: warren52nz
I've been trying to discover how a brushless motor can turn at any speed other than the speed that the ESC is "telling it" to. My helicopter can't keep up the same rpm when it's on full pitch than it does at 0 pitch. So it seemed to me that the rotor would be getting behind the rotating fields which would cause God knows what sort of problems.
It's the motor that tells the controller when to commutate. These brushless motors are the same as brushed motors, only here the reversing of the voltage/current is done by the ESC, based rotor position and speed information from the motor.

(in reply to warren52nz)
       Post #: 57

RE: How does a brushless motor work? - 6/2/2005 3:07:30 PM   
Ron v. Sommeren



Posts: 92
Joined: 2/4/2002
From: near Nijmegen, NETHERLANDS
Status: offline 		@Neomike
There is no slip in these motors.

(in reply to comptrguru)
       Post #: 58

RE: How does a brushless motor work? - 7/13/2005 4:53:19 PM   
Seed of Chucky


 

Posts: 2
Joined: 6/23/2005
From: , CA, USA
Status: offline 		I am fairly new to brushless, converted from brushed, but these little motors are powerful! Because they make a lot less noise when spinning the props, I have almost accidentally bumped into the prop on my workbench while testing! Wouldn't have been pretty.

Because brushed motors are so much louder than the brushless, I just feel they are more dangerous.

But on the other hand, I love brushless! My motor has already lasted longer than any of my brushed ones and I'm sure there is a ton more life to it. Maybe you guys would know just how long a typical BL motor can last for without crashes??

(in reply to Ron v. Sommeren)
       Post #: 59

RE: How does a brushless motor work? - 8/12/2005 8:04:27 PM   
A TRAIN


 

Posts: 3
Joined: 8/2/2005
From: Saute, GA, USA
Status: offline 		I have a posted thread somewhere on this site but.---would 2 outruners hooked up in parallel to a esc of sufficient size run EXACTLY at the same speed? I want to do this to a Vought V173 (flying flapjack) which has props on the extreme outboard position.

(in reply to Matt Kirsch)
       Post #: 60

RE: How does a brushless motor work? - 8/12/2005 9:34:46 PM   
ron_van_sommeren



Posts: 226
Joined: 9/24/2002
From: Nijmegen/the NetherlandsNetherlands, NETHERLANDS
Status: offline 		Two brushless motors, whether in- or out-runner, in parallel will always be in perfect sync, if they start.

(in reply to A TRAIN)
       Post #: 61

RE: How does a brushless motor work? - 8/13/2005 2:41:03 AM   
A TRAIN


 

Posts: 3
Joined: 8/2/2005
From: Saute, GA, USA
Status: offline 		Many thanks Ron. Now comes the hard part ----building the "thing".

(in reply to ron_van_sommeren)
       Post #: 62

RE: How does a brushless motor work? - 9/9/2005 5:14:50 PM   
rodparsons


 

Posts: 1
Joined: 5/19/2004
From: , AUSTRALIA
Status: offline 		A question Ron. I'm using a brushless helicoptor motor for a cutting spindle on a milling machine.
So what you are saying is that if it is running at 30,000RPM and I start cutting through some material.
The speed will slow down but the ESC will automaticly adjust the timing output to the motor to get it back up to that speed. So in other words the ESC uses the back EMF from the motor as a feedback loop to keep the speed constant.

Is this right????

Thanks
Rod

(in reply to A TRAIN)
       Post #: 63

RE: How does a brushless motor work? - 9/9/2005 6:07:06 PM   
MatC


 

Posts: 1
Joined: 9/9/2005
From: , UNITED KINGDOM
Status: offline 		To clarify a few points here:

Running two brushless motors from the same esc: you can't, it will not work. They might start and run together, but they won't work right for long. As soon as one slows down, the other may well get out of sync, lose power, run backwards, etc. Not good. If it worked for a short time, they would run at exactly the same speed though.

As regards the ESC and motor working together, it's something like this:
The ESC senses the motor position, and gives the output accordingly. There isn't any one set speed, the ESC just applies power using the motor's position to know which windings to activate. It's like an old clock with a pendulum: the clock senses the position, and adds a little power to make it go more in that direction. Starting is somewhat different, but that's another topic

So it's not that the esc "reduces speed if the motor falls behind", more like "the esc always knows where the motor is, and powers accordingly".

(in reply to rodparsons)
       Post #: 64

RE: How does a brushless motor work? - 9/9/2005 7:35:17 PM   
A TRAIN


 

Posts: 3
Joined: 8/2/2005
From: Saute, GA, USA
Status: offline 		I assume then that to use two brushless motors on my Vought V-173 (Flying Pancake), I will have to use two brushless esc's. Another great idea goes down in flames! ! mike

(in reply to MatC)
       Post #: 65

RE: How does a brushless motor work? - 9/10/2005 2:36:57 AM   
sky9flyer