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Old Aug 18, 2010, 10:20 PM
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ForeverFlying's Avatar
Christiansburg, VA
Joined Sep 2002
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Brush vs Brushless?

Dear Forum,
I am wondering if there is really any advantage to a brushless system vs a brush? Is the power to weight ratio much improved, or is it just a longevity issue?
Thanks for any insights!
Mike
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Old Aug 18, 2010, 10:31 PM
Air, Ground & Water
freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
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You cant compare the 2, brushless are lighter and mroe efficient then brushed, no burshes to replace. Once you go brushless you will never go back to brushed.
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Old Aug 18, 2010, 10:45 PM
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Joined Nov 2007
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This sounds like the start of a never ending discussion. I would estimate there may not be much difference between them. However it is possible to make a brushless motor that works very well but very difficult to hand make a brushed motor. Just about anyone can wind a good CDROM motor or build a kit. It is not that hard to hand build a 16", coreless motor for a wind generator. It is just about impossible to hand build a comparable DC generator.

Consider this case of an E-bike.
The designer has a design with a given motor (Kv=300), given battery and drive system. It all works very well and he is about to start production. At this point the motor manufacture submits a new motor (Kv=600) which is identical to the original but uses crappy magnets and costs half as much.
The new new motor runs twice the RPM and has half the torque (same HP). So the new E-bike design just uses a different gear ratio and has the same performance at less cost.

In this case the difference between the two motors is just the number of teeth on the motor sprocket. In many cases the only real difference between a cheap motor and an expensive motor is gear ratio.

The motor is just a converter between the battery and load, if the battery is kept constant the only thing the motor contributes is weight and efficiency.
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Old Aug 18, 2010, 10:46 PM
Way to many airplanes!
Canada, QC
Joined Oct 2009
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Quote:
Originally Posted by freechip View Post
You cant compare the 2, brushless are lighter and mroe efficient then brushed, no burshes to replace. Once you go brushless you will never go back to brushed.
Brushless lighter and more efficient than brushed??? Care to explain why all the ultra-micro airplanes (where 1gr saving is great) have brushed motor then? Ooops, maybe because brushed motor can be coreless, and are much lighter while being relatively power efficient. Yes, you're right, brushless are great because they last much longer since you don't have brushes to replace, but basically both type of motors have their plus and minus. Sure enough, on 2S to 6S, nothing is better than brushless, but on 1S, brushed motor still have their place and one of the main reason is weight.
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Old Aug 18, 2010, 10:58 PM
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freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
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I was thinking about lipos when the lighter part came out.
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Old Aug 18, 2010, 11:03 PM
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freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
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Brushless Motor
PROS

•Electronic commutation based on Hall position sensors
•Speed/Torque - flat, enables operation at all speeds with rated load
•High efficiency, no voltage drop across brushes
•High output power/frame size.
•Reduced size due to superior thermal characteristics.
•Has the windings on the stator, which is connected to the case, the heat disipation is better
•Higher speed range - no mechanical limitation imposed by brushes/commutator
•Low electric noise generation
CONS
•Higher cost of construction
•Control is complex and expensive
•Electric Controller is required to keep the motor running. It offers double the price of the motor.

Brushed Motor
Pros
•Two wire control
•Replaceable brushes for extended life
•Low cost of construction
•Simple and inexpensive control
•No controller is required for fixed speeds
•Operates in extreme environments due to lack of electronics
Cons
•Periodic maintenance is required
•Speed/torque is moderately flat. At higher speeds, brush friction increases, thus reducing useful torque
•Poor heat dissipation due to internal rotor contsruction
•Higher rotor inertia which limits the dynamic characteristics
•Lower speed range due to mechanical limitations on the brushes
•Brush Arcing will generate noise causing EMI

There is more POSTIVE and less Negatives for the BRUSHLESS motor then there is for the brushed.
But like in everything else, there is always an application for each specific motor in the case of the micro stuff mention earlier.
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Old Aug 19, 2010, 04:20 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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I can add one more 'con' against brushless, (though brushless still has it over brushed for me, and I still use both).

The 'con' ?, they are so much lighter that converting some brushed model to brushless can mean adding lead to the nose or moving the battery forward, (if possible), to get the CG right.
The worst scenario for a conversion is where the brushed motor also used a gearbox, (usually because the are very poor at turning big props in direct drive), there is that extra weight to compensate for as well.
So to some degree it can depend on the model, short nosed models could benefit form those old heavy brushed motors.

Here's the other side of the coin though -
My B-17 originally ran brushed motors with belt drives, (times 4 remember), also Nimh batteries. She now runs brushless direct drive, Lipos, weighs almost 2lbs less, (actually 1lb 15oz), flies better and draw much less current, so longer flights possible. And luckily, with a little bit of battery movement I got the CG back in place without any lead.

So that's one big 'pro' for brushless.
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Old Aug 19, 2010, 05:57 AM
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East Anglia, UK
Joined Sep 2002
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Quote:
Originally Posted by freechip View Post
Brushless Motor
PROS

•Electronic commutation based on Hall position sensors
Incorrect. For most sensorless designs.
Quote:
•Speed/Torque - flat, enables operation at all speeds with rated load
Incorrect, with most sensorless designs.
Quote:
•High efficiency, no voltage drop across brushes
Brush losses are not major in most designs. Up to 95%+ efficiency is possible with brushed motors.
Quote:
•High output power/frame size.
Incorrect by and large. Apart from the physical size of the brush gear, the same amount of material needs to be in a motor for the same power.
Quote:
•Reduced size due to superior thermal characteristics.
Almost true. But not really significant.
Quote:
•Has the windings on the stator, which is connected to the case, the heat dissipation is better
Arguable, since spinning windings are in the breeze.
Quote:
•Higher speed range - no mechanical limitation imposed by brushes/commutator
True, but electrical limits still imposed by FET switching times.
Quote:
•Low electric noise generation
True. But ESC switching still generates noise.
CONS
Quote:
•Higher cost of construction
False. Outrunners are way cheaper to make than a brushed motor. No brush gear for a start.
Quote:
•Control is complex and expensive
True, but not that expensive, as you can see.
Quote:
•Electric Controller is required to keep the motor running. It offers double the price of the motor.
The cost of a commutator versus the cost of circuit board is in many cases not that different these days.
Brushed Motor
Pros
Quote:
•Two wire control
Correct.
Quote:
•Replaceable brushes for extended life
That's a con. Brushless don't need new brushes
Quote:
•Low cost of construction
#
Incorrect. Outrunner is cheaper to make.
Quote:
•Simple and inexpensive control
Correct.
Quote:
•No controller is required for fixed speeds
Correct.
Quote:
•Operates in extreme environments due to lack of electronics
Sort of. Magnets still heat sensitive.
Cons
Quote:
•Periodic maintenance is required
Correct. But run sanely we are talking thousands of hours.
Quote:
•Speed/torque is moderately flat. At higher speeds, brush friction increases, thus reducing useful torque
Correct that its flat, incorrect that the friction changes with speed.
Quote:
•Poor heat dissipation due to internal rotor contsruction
Not really relevant. Or only partly so.
Quote:
•Higher rotor inertia which limits the dynamic characteristics
Incorrect in most cases. Certainly outrunners of equivalent size have just as much inertia.
Quote:
•Lower speed range due to mechanical limitations on the brushes
Correct.
Quote:
•Brush Arcing will generate noise causing EMI
Correct.
Quote:
There is more POSTIVE and less Negatives for the BRUSHLESS motor then there is for the brushed.
But like in everything else, there is always an application for each specific motor in the case of the micro stuff mention earlier.
What is more true, is that the single thing that makes most brushless motors better is that they don't use ferrite magnets. And that they lend themselves to hand winding by very cheap labour.

Quality inrunners are very expensive to make.
You really need a winding machine for an inrunner or a brushed motor:
The real leap forward though, was in abandoning mass machine produced brushed motors of highly dubious quality and poor magnets and going to exceptionally good magnets on cheap hand wound stators - the outrunner. Still of dubious quality, but generally smaller and lighter (though barely more efficient) than a brushed motor. Mainly due to the magnets. The multipole design also helps to get better performance at lower RPM where props work better, thus reducing need for gearboxes.
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Old Aug 19, 2010, 09:36 AM
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Canada, ON, Rockland
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Thanks Vintage1 for the clarification, you can email google and wikipedia to correct them also. I just cut and past google search. There is always both side to everything.

Brushless is the new thing and is here to stay, if you still want to run with yesterdays tech. no problem its your HOBBY.

The OP want to know if there is an advantage running brushless over brushed and for most application brushless is better.
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Old Aug 19, 2010, 10:15 AM
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East Anglia, UK
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Quote:
Originally Posted by freechip View Post
Thanks Vintage1 for the clarification, you can email google and wikipedia to correct them also. I just cut and past google search. There is always both side to everything.

I gave up correcting wikipedia. You have to have a big ego to write for wiki, and big egos dont like being told they are wrong.

What you posted is possibly;y true of industrial large motors, but its totally wrong for crappy Chinese out runners.

Quote:
Brushless is the new thing and is here to stay, if you still want to run with yesterdays tech. no problem its your HOBBY.
It merely reflects the fact that electronics is cheap and reliable, and old fashioned technology is expensive and wears out.

Bruished-> brushless is analogous to having cars with fuel injection and electronic ignition rather than contact breakers and carburettors. It doesn't actually make the car cheaper, but there is less to service, and efficiency can be a bit better.
Quote:
The OP want to know if there is an advantage running brushless over brushed and for most application brushless is better.
Mostly, prices are so similar and for $5 you can make a slightly better brushless than brushed. I run whatever tickles my fancy,. I can get similar efficiencies. The only difference is weight really. But with LIPO batteries weight is seldom a problem, except how to get enough into the nose...
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Old Aug 19, 2010, 04:33 PM
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Joined Sep 2006
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Brush is still the way to go for very light Indoor flyers (less than 20 grams total) and much more easier to implement for multi engines projects. Up to Speed-400 size brush is still competeitive, but motors and esc are getting hard to come by! For larger motors the brushless get actually cheaper(remember the price of these big Astroflight motors?)and lighters. A good source for cheap brush motors:
http://www.allelectronics.com/make-a...-Motors/1.html
And many other surplus places.
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Old Aug 19, 2010, 04:38 PM
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There is another detail about brushed motor that keep them alive. They can give full power even you make it almost jamed. This is why many people use it in crawlers. If you try that with a brushless motor, the result is the esc is trying to pulse the motor to make it rotating and it will burn in 5 seconds. So.. I think the brushed motor win a point here, otherwise the brushless win far away.
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Old Aug 20, 2010, 03:38 AM
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United States, UT, Salina
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Quote:
Originally Posted by vintage1 View Post
Incorrect.
I just knew you would quickly set this straight.

It's actually getting difficult to find large selections of brushed controllers anymore though.

Lately I'm using them for light control on my night flying planes.
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Old Aug 20, 2010, 09:55 AM
Motors beat engines!
Milwaukee Wisconsin, United States
Joined Feb 2001
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Quote:
Originally Posted by Bilbobaker View Post
It's actually getting difficult to find large selections of brushed controllers anymore though.


Plenty of choices here :http://www.bphobbies.com/view.asp?id=A0780190
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Old Aug 20, 2010, 11:04 AM
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Quote:
Originally Posted by RealGambler View Post
Brushless lighter and more efficient than brushed??? Care to explain why all the ultra-micro airplanes (where 1gr saving is great) have brushed motor then? Ooops, maybe because brushed motor can be coreless, and are much lighter while being relatively power efficient. Yes, you're right, brushless are great because they last much longer since you don't have brushes to replace, but basically both type of motors have their plus and minus. Sure enough, on 2S to 6S, nothing is better than brushless, but on 1S, brushed motor still have their place and one of the main reason is weight.
Micro motors, whether brushed or brushless are more difficult and hence more expensive to manufacture than larger scale motors. The reason that small brushed motors are popular with "ultra-micro airplane" manufacturers has nothing to do with performance, it is due to the ready supply of cheap brushed motors for the cell phone market.
If you are prepared to spend the money then you can get a micro brushless motor over twice as powerful than a similar weight phone vibrator motor.
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