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Old Aug 25, 2011, 02:37 AM
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Originally Posted by Ron van Sommeren View Post
Christo, for the original LRK motors Lucas Retzbach found that dLRK gave 10% higher Kv for same number of winds (wires per slot).

Have you seen this new winding diagram 'calculator' for larger numbers of magnet/statorpoles?
http://www.rcgroups.com/forums/showt...ght=calculator
Thanks Ron, I saw the new calculator when you posted about it on LRK-Torquemax. It's quite impressive, although it doesn't show LRK winding schemes.

Christo
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Old Aug 25, 2011, 10:48 AM
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You can 'edit' out coils with the '-' character.

Regards, Ron
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Old Aug 25, 2011, 12:29 PM
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Originally Posted by Skylar View Post
I can't comment on how well it runs, because I haven't seen it run. All I'm saying is that I'm impressed that James persevered while everybody advised him not to try a wind different from ABC.

Yes, it's similar to 12N16P (which is also ABC), but if you look at 18N12P in Dr Okon's table, you'll notice that it can also be wound LRK.

BTW, I have a 12N16P motor and I just love the sound it makes.

Christo
for a 12N motor, best combination is 12N10P or 12N14P...12N16P doesnot get good efficiency, even though the magnet coverage maybe larger.

I personally prefer 12N8P, again, it is not a good combination with high efficiency, but the speed is much faster than 12N10P and 12N14P dLRKs...good for low-torque use, for example, ducted fans. Comparing with dLRKs, LRK also has good torque...but the speed is just too low, and teeth coverage can be quite low if you do not wire it properly, which is difficult and a little bit tricky
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Old Aug 25, 2011, 02:21 PM
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for a 12N motor, best combination is 12N10P or 12N14P...12N16P doesnot get good efficiency, even though the magnet coverage maybe larger.
I think it depends on the design of the motor. I have a 12N16P Torcman kit motor that I consider one of my best motors. When I tried a 16-magnet Scorpion conversion, it seemed to be a less successful combination.

Quote:
I personally prefer 12N8P, again, it is not a good combination with high efficiency, but the speed is much faster than 12N10P and 12N14P dLRKs...good for low-torque use, for example, ducted fans.
Efficiency is determined by the amount of copper loss and iron loss in a motor. The number of poles has little to do with efficiency. For example, I have wound a Scorpion HK3026 10-pole motor that spins 30,000RPM while maintaining 91% efficiency at 2000W output load.

Only if you do a full analysis on a motor are you qualified to comment on it's efficiency.

Quote:
Comparing with dLRKs, LRK also has good torque...but the speed is just too low...
You can change the number of windings to get higher speed. I have built some LRK-wound motors that really scream.

Christo
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Old Aug 25, 2011, 02:33 PM
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Originally Posted by Ron van Sommeren View Post
You can 'edit' out coils with the '-' character.
OK, now this is where it gets interesting. And for the record, this is what I've been doing. The trick is to know when it's allowed to edit out coils with '-' and when not to.

I suppose it's only allowed when the "LRK rules" are met? Please correct me if I'm wrong.

Christo
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Old Aug 25, 2011, 02:41 PM
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I have not played that much with it. The tool (advanced) gives some numbers, I don't understand all of them though. Maybe you can figure out their meaning?

Vriendelijke groeten Ron
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Old Aug 25, 2011, 03:43 PM
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Originally Posted by Skylar View Post
Efficiency is determined by the amount of copper loss and iron loss in a motor. The number of poles has little to do with efficiency. For example, I have wound a Scorpion HK3026 10-pole motor that spins 30,000RPM while maintaining 91% efficiency at 2000W output load.
Im not talking about efficiency and poles...

imagine in a fixed volume of space in a motor, what can you get out of it? Yes, what i am talking about is "coverage", to be more specific, magnet coverage, and teeth coverage. Magnet coverage is very obvious to see, it really matters. For teeth coverage, there is one example showing its value: the reason why so many manufacturers prefer "multiple thin wire" to "single thick wire", not because those little electrons tends to travel on the surface of copper, making the inner sheath of copper useless ( this effect is not that important for toys), but it's easier to achieve better teeth coverage. Though personally, I prefer single thick wire, looks pretty, but a bit hard to wind.
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Old Aug 25, 2011, 04:01 PM
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Antony (France)
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Quote:
Originally Posted by Skylar View Post
OK, now this is where it gets interesting. And for the record, this is what I've been doing. The trick is to know when it's allowed to edit out coils with '-' and when not to.

I suppose it's only allowed when the "LRK rules" are met? Please correct me if I'm wrong.

Christo
Hi Christo
An other example
18S-18C-20P := (AaABbBCcC)x2 = AaABbBCcCAaABbBCcC
18S-9C-20P := A-A-b-C-C-a-B-B-c-
Louis
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Old Aug 25, 2011, 04:09 PM
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what really contribute to the efficiency of a motor, well, probably i should use the word "potential" which is more accurate to what i mean, are the following factors, not all but least:
1, To your respect, I'll put copper loss and iron loss in first place anyway: copper loss: try better wires with low resistance (silver? dream...superconductor? fancy wish), anyway, there are limits. copper can do a good job already
2, Iron loss: try thinner steel sheets to reduce the mag vortex. what i can find out of my favorite DC brushless fans are 0.33mm sheets. 0.2mm is hard to find. Sensor-less motor is an extreme example.
3, air-gap: smaller the better. still, there are limits, too small (less than 0.1mm) is also not so good. my experience is, 0.2-0.5mm, works good. air-gap is also related to volume of mag and volume of iron.
4, coverage: already stated above, mag and teeth coverage. one thing to add about mag coverage, good efficiency does not always mean 100% mag coverage. for LRKs, if i remember right, best efficiency is achieved when mag coverage is around 75%.
5, heat dispersion: related to rotor design, external cooling solutions, copper loss here again, air-gap (indirect heat transfer from stator to rotor), etc...actually "heat" is the shortest wood stick of a wooden barrel. it determines how far a motor can go.
6, besides above "hardware" factors, then the "softwares": wiring type, power input, etc...

Designing a motor is a very sophisticated work. Simply try wiring on commercially purchased, or "hardware" fixed models, is a good start anyway. Im not specialized in this area, actually, my profession is not even close to RC. But to me, motors are just like human body, a lot to explore and a lot to think, yet a lot to fix.
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Old Aug 25, 2011, 04:34 PM
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Originally Posted by Skylar View Post
I think it depends on the design of the motor. I have a 12N16P Torcman kit motor that I consider one of my best motors. When I tried a 16-magnet Scorpion conversion, it seemed to be a less successful combination.

Christo
about wiring and mag combination, well, N is multiple of 3, P is multiple of 2, N/P cannot be multiples of each other except that N/P can be multiples of 3 times each other,but exceptions exist.

best N/P combination? there is a simple way to remember, following above rules, try to keep P close to N. for example, for a 6N stator, 4P and 8P rotor are both good combination, 6N2P, 6N10P ....they also can rotate but not good. another example, for a 9N stator, 9N8P and 9N10P are both good combinations, again, 9N6P, 9N12P....they can run but not as good.

N/P = fraction, normally it means the motor can start more smoothly and less attraction between mag and stator, or simple less torque being felt when rotate the shaft by hand. Also, less noisy.

N/P = decimal, they normally have much stronger felt when rotating the shaft by hand, produce large and stunning sound when rotating. this kind of motors requires the shaft-rotor to be very stable, as they are comparatively easier to setoff due to significant attraction force between mag and stator steel. also, if it is used as ducted fan motor, the blades need to be extra strong, better metal blades. Or otherwise, the blade is easier to explode due to resonance effect when rotating speed is very high.

Back to 12N16P issue. I tried 12N16P conventional wiring, 12N14P dLRK / LRK wiring, 12N10P dLRK / LRK wiring, 12N8P conventional wiring. Though 12N8P is stated as not a very good combination, I find it best for a "ducted fan".
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Old Aug 26, 2011, 01:47 PM
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Generator

I want to steer the conversation in another direction for a while.

What makes a good generator (alternator)? If a certain design is a good motor, is it necessarily also a good generator? OK, for now, lets forget about steps taken to reduce cogging, etc. like stator skewing, air gap and shape of hammer heads.

IOW, if I take 2 BLDC motors, (a) is a very good one and (b) not so good, but it runs, with maybe lower efficiency due to less-than-desirable winding scheme, fill factor, etc. Will (a) be a better generator than (b)?

Christo
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Old Aug 26, 2011, 03:06 PM
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You started this thread, it's your party.

I lower efficiency motor will give a lower efficiency generator, that's all I can say. No news for you there I guess.


Prettig weekend Ron
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Old Aug 26, 2011, 03:17 PM
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I lower efficiency motor will give a lower efficiency generator, that's all I can say. No news for you there I guess.
I know it sounds like common sense that an efficient motor will make an efficient generator, but I just want to make sure. We've discussed optimising motors for years, but very little has been said about generators.

How about LRK vs dLRK? Does either of these winding methods favour generators in particular? We know that dLRK is more popular with motor manufacturers, despite more coils that have to be wound.

Christo
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Old Aug 26, 2011, 03:34 PM
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Hi Christo

I think that good efficiency is valuable both for motor or for generator, by principle.
(low ohmic resistance and low iron losses are good for both applications)
However
a) If the phase relation ship for 3 phases (120) is not perfect
It is a catastroph for a motor and the ESC standard algorithms
It is not (a catastroph) for a generator if you rectify sinusoidal outputs to use DC)

b) For a wind-mill a good motor with some Kv could be not matched, for a non optimum V/rpm as function of the wind speed and energy and the load (battery). A step-up or down converter is better for a ratio close to 1.

Louis
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Old Aug 26, 2011, 04:17 PM
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Hi Louis

You mentioned some valid points.

a) Phase relationship. So a poorly constructed/designed motor with varying stator teeth width or irregular magnet spacing could still work well as a generator. Very interesting.

b) Yes, the Kv of conventional RC motors is much too high and has to be rewound for a much lower Kv (or V/rpm). I saw some Chinese generators of approx. 1000W size with a speed limit of 30 rpm. The Kv must be very low. From a design point of view, long stators are better suited as they need less turns per coil.

Incidentally, there is a picture on the Scorpion System website that shows quite a "long" generator. It just says "under development", so hopefully we'll see some information soon.

Christo
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