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Old Oct 14, 2012, 03:45 PM
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France, RA, Cormaranche-en-Bugey
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Raw kv is usually very close to the "true" kv, which is a bit higher because the applied voltage is higher than the bEMF.

I also use an eLogger.

I've just realized that I've made a mistake, your numbers are for APC 10x4.7, not 10x7, so the kv calculated from torque and amps is closer to 800 than what I've found first (I'll correct my previous post), and anyway it's not very accurate.

Always efficiency looks pretty bad, around 63% in 3S and 54% in 4S with the 10x4.7
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Old Oct 14, 2012, 04:54 PM
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flydiver's Avatar
United States, WA, Seattle
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I won't even pretend to dabble in the efficiency realm. I have been following the latest LRK discussion with interest as I have a bare stator looking for a wind and it seemed interesting....and easy.

But the efficiency discussion made me think of the beginning of this thread and how it was found a rewind by one of the better winders on the groups didn't make a whole lot of difference. Jack has done a lot of work on this motor since then and seems to have possibly found otherwise with some winds.
This is all very puzzling.
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Old Oct 14, 2012, 07:37 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by yomgui View Post
Raw kv is usually very close to the "true" kv, which is a bit higher because the applied voltage is higher than the bEMF.

I also use an eLogger.

I've just realized that I've made a mistake, your numbers are for APC 10x4.7, not 10x7, so the kv calculated from torque and amps is closer to 800 than what I've found first (I'll correct my previous post), and anyway it's not very accurate.

Always efficiency looks pretty bad, around 63% in 3S and 54% in 4S with the 10x4.7
I'm very confident that the kV is very close to 800. I did no load measurements at 2S, 3S, and 4S voltages and they calculated out to a raw Kv of 800 with a variation of only 10 or so.

Jack
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Old Oct 14, 2012, 08:16 PM
Jack
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Quote:
Originally Posted by flydiver View Post
I won't even pretend to dabble in the efficiency realm. I have been following the latest LRK discussion with interest as I have a bare stator looking for a wind and it seemed interesting....and easy.

But the efficiency discussion made me think of the beginning of this thread and how it was found a rewind by one of the better winders on the groups didn't make a whole lot of difference. Jack has done a lot of work on this motor since then and seems to have possibly found otherwise with some winds.
This is all very puzzling.
Yes it is!

I'm not sure that I am one of the better re-winders here, especially with regard to understanding motors and motor efficiency. Maybe I'm just good at getting wire on them and little else.

But when I look at the RPM I am getting out of the slow fly props I am getting those props well up into their useful RPM range.

The maximum safe RPM for APC slow fly props is 65,000 / diameter in inches. I use the same value for the Great Planes props because GP does not publish a limit and I have found the 65.000 limit to be safe in my testing and use. It is just my opinion that GP props are safe to that limit.

So if you look at the RPM I am getting from those props and the safe maximum RPM numbers, the motor looks like it is working well:

Great Planes SF 11 X 4.5 (65,000 / 11 = 5909 RPM max)
3S test RPM = 5245
4S test RPM = 5958

Great Planes SF 10 X 7 (65,000 / 10 = 6500 RPM max)
3S test RPM = 4543
4S test RPM = 5251

APC SF 10 X 4.7 (65,000 / 10 = 6500 RPM max)
3S test RPM = 5724
4S test RPM = 6563

So I get confused when I find this is what appears to be a useful motor but it is found to be inefficient by the efficiency numbers.

The testing with the APC Thin Electric 13 x 8 does not make it appear as useful. The RPM limit for the APC TE props is 145,000 / diameter in inches. So the tested RPM on that prop is:

APC TE 13 X 8 (145,000 / 13 = 11,154 RPM max)
3S test RPM = 4473 RPM
4S test RPM = 5022 RPM

The motor is attaining only 45% of the maximum allowable RPM with that prop. But then, when I look at the prop database at flybrushless.com and see that the APC TE 13 x 8 trust to RPM curve shows the prop to have a useful range that runs from 3900 to 6600 RPM I get confused again. The LRK wind on 4S is attaining 76% of the useful range now and, with a turn or two less on it, could probably attain all of it.

I'm not trying to argue with motor experts, just come to where I can understand it all...

Jack
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Old Oct 14, 2012, 08:26 PM
What goes up must come down..
Canada, QC, Saint-Laurent
Joined Jan 2002
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I believe you have a good motor on your hand, actually it sounds very good for my type of flying / plane.
If I want to do the same but with more Kv how many turns of 21 AWG should I do?
9 turns LRK Wye for 957 kv? # AWG?
Is this correct?
Roger
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Last edited by rodair; Oct 14, 2012 at 08:53 PM.
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Old Oct 14, 2012, 08:46 PM
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France, RA, Cormaranche-en-Bugey
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I don't know what's strange with that motor, even if it's really strange or not... and if it does the job... who cares ??

Just a guess but doesn't it might looks like you don't reach WOT or something ??

Amps and rpm not sticking to kv, low efficiency... looks like that IMO
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Old Oct 14, 2012, 08:56 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Here: http://www.rcgroups.com/forums/showp...&postcount=266

There are three, TC6 is the latest and best, the simple one is useful too. They are all free! Thanks to manuel_v!

You can run them with the free openoffice.org Calc application. Or Excel.

That one you have the screen shot from there is set for generating winds for a motor that has a 957 kV. The attached one is better if you are starting with a stock DAT-750.

I don't use the wire length thing and have it set to zero. I do know that a stripped single phase from a stock motor is about 78" long. And that it takes a 48" or so piece of 21 AWG to do the 19 turn LRK wind.

Jack
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Old Oct 15, 2012, 04:38 PM
Jack
USA, ME, Ellsworth
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Quote:
Originally Posted by yomgui View Post
I don't know what's strange with that motor, even if it's really strange or not... and if it does the job... who cares ??

Just a guess but doesn't it might looks like you don't reach WOT or something ??

Amps and rpm not sticking to kv, low efficiency... looks like that IMO
I am using a servo tester for a throttle and a Phoenix 80 ESC. When I power up I have the servo tester knob in the center position. When I turn the servo tester up (CW) when it sees full throttle it sends a tune, then I turn it down (CCW) and when the P80 sees a throttle closed value it sends another tune and arms arms itself.

That mid throttle start up then to full and then to closed is the standard way to calibrate the throttle on a P80 and I do it on every start up.

Then when I turn the servo tester up the motor runs and a ways before I have it rotated fully CW the red "full throttle" LED on the P80 lights up. So it is seeing valid no throttle and full throttle signals from the servo tester.

I just did all the same things using a TX (mid throttle at start, close it to arm, etc.) all the same things happen.

So I did two more no load tests, one using the transmitter and the other using the servo tester and both get me the same no load RPM:

Transmitter = 13039 RPM 16.32V 2.29A = 799 kV

Servo tester = 13038 RPM 16.27V 2.25A = 801 kV

Jack
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Last edited by jackerbes; Oct 15, 2012 at 04:44 PM.
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Old Oct 15, 2012, 10:44 PM
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Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
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I'm still puzzled by the apparently lousy performance of this motor....I know that g/W is not the ultimate arbiter but just for fun I tried to compare your DT750 figures with some other motors I have tested [matching RPM as well as I can]. I don't have the GP SF props but I found that in my Spreadsheet I had comparable data for both the APC 13x8E and the 10x4.7 APC SF. I think the thrust estimates from flybrushless are not too far off.. so, for your motor, I'm using those which you posted for your re-wound DT750. The thrust figures for the JGF and AXI motors are my own measured data.

13x8 APC E: DT750: 4473rpm, 124W, 769g = 6.20g/W
13x8 APC E: Justgofly 550XT: 4530rpm, 106W, 790g = 7.45g/W

13x8 APC E: DT750: 5022rpm, 221W, 979g = 4.43g/W
13x8 APC E: Justgofly 550XT: 5055rpm, 158W, 994g = 6.30g/W

10x4.7 APC SF: DT750: 5724rpm, 93W, 584g = 6.28g/W
10x4.7 APC SF: AXI 2212/26: 5790rpm, 80W, 576g = 7.20g/W

10x4.7 APC SF: DT 750: 6563rpm, 164W, 787g = 4.80g/W
10x4.7 APC SF: AXI 2212/26: 6660rpm, 137W, 795g = 5.80g/W
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Old Oct 16, 2012, 12:41 AM
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manuel v's Avatar
Mexico, BC, Mexicali
Joined Aug 2004
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The big problem with this motor is the amount off cooper.

One 18T 22awg DLRK Delta termination has 36wires for slot.
785Kv.
APC 11x4.7sf TP 1320 3S:
6666 rpm @ 10.6v/17.4a 1227 grams 43.3 oz/thrust 81.0% Efficient
(data post no.8)

and this motor 19t 21AWG LRK Star termination has 19wire for slot.

Fore same cooper fill is necesary 36 tuns 22AWG delta termination, o 18 turns 19AWG star termination.

But this is not possible motor
Because the bell has very little clarity in the front.
This is not a motor for this LRK winding.

Manuel V.
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Old Oct 16, 2012, 07:10 AM
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yomgui's Avatar
France, RA, Cormaranche-en-Bugey
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Quote:
Originally Posted by jackerbes View Post
APC TE 13 X 8
3S = 4473 RPM, 10.42V, 11.90A, 124W, temp 66F 73F
4S = 5022 RPM, 14.95V, 14.75A, 221W, temp 74F to 86F

3S thrust estimate = 769g
4S thrust estimate = 979g
My 835 kv - 80 g motor shows (not exactly same prop):
4585 rpm, 10.42V, 11.65A, 745 g at 90% throttle,
5038 rpm, 14.95V, 12.74, 899 g at 82% throttle,

Quote:
Originally Posted by jackerbes View Post
GP SF 11 X 4.5
3S = 5245 RPM, 10.53V, 10.38A, 109W, temp 72F to 78F (115F post run peak)
4S = 5958 RPM, 15.19V, 12.44A, 189W, temp 76F to 92F (105F post run peak)

3S thrust estimate = 707g
4S thrust estimate = 933g
I have (APC 11x4.7SF):
5271 rpm, 10.53V, 10,76A, 712g at 93% throttle
6004 rpm, 15.19V, 12.73A, 924g at 86% throttle

Quote:
Originally Posted by jackerbes View Post
GP SF 10 X 7
3S = 4543 RPM, 10.22V, 12.07A, 123W, temp 69F to 80F (89F post run peak)
4S = 5251 RPM, 14.99V, 14.16A, 212W, temp 73F to 95F (111F post run peak)

3S thrust estimate = 472g
4S thrust estimate = 635g
I have (APC 11x7SF):
4520 rpm, 10.22V, 12.21A, 673 g at 91% throttle,
5198 rpm, 14.99V, 14.89A, 890g at 85% throttle,
1 inch more in diameter to reach same load on motor !??


Quote:
Originally Posted by jackerbes View Post
APC SF 10 X 4.7
3S = 5724 RPM, 10.56V, 8.77A, 93W, temp 71F to 73F (83F post run peak)
4S = 6563 RPM, 15.37V, 10.69A, 164W, temp 71F to 77F (89F post run peak)

3S thrust estimate = 584g
4S thrust estimate = 787g
I have (APC 10x4.7SF):
5736 rpm, 10.56V, 8.08A, 560g at 92% throttle,
6554 rpm, 15.37V, 9.45A, 732g at 84% throttle.

I really think it looks like your setup don't reach full throttle under load, might be due to the ESC ?!

Quite puzzling for sure !
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Old Oct 16, 2012, 08:02 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by Dr Kiwi View Post
I'm still puzzled by the apparently lousy performance of this motor....I know that g/W is not the ultimate arbiter but just for fun I tried to compare your DT750 figures with some other motors I have tested [matching RPM as well as I can]. I don't have the GP SF props but..<snip>...
Is it lousy performance or just lousy numbers when you compare the efficiency to other motor?

Would you consider the difference in those numbers to make this motor lousy? I think I could adjust the kV up (thereby, with fewer turns, increase the wire size too) and get the RPMs matched up better.

Did you return the GP props I sent to you for testing to me? That might explain why they were only tested one time. They are the ones with right angled tiplets and are marked "GP dia. x pitch S" in Imperial and metric. If you don't have them and I send them to you again, will you test them along with similar props?

Jack
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Old Oct 16, 2012, 08:45 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by yomgui View Post
My 835 kv - 80 g motor shows (not exactly same prop):
4585 rpm, 10.42V, 11.65A, 745 g at 90% throttle,
5038 rpm, 14.95V, 12.74, 899 g at 82% throttle,

I have (APC 11x4.7SF):
5271 rpm, 10.53V, 10,76A, 712g at 93% throttle
6004 rpm, 15.19V, 12.73A, 924g at 86% throttle

I have (APC 11x7SF):
4520 rpm, 10.22V, 12.21A, 673 g at 91% throttle,
5198 rpm, 14.99V, 14.89A, 890g at 85% throttle,
1 inch more in diameter to reach same load on motor !??

I have (APC 10x4.7SF):
5736 rpm, 10.56V, 8.08A, 560g at 92% throttle,
6554 rpm, 15.37V, 9.45A, 732g at 84% throttle.

I really think it looks like your setup don't reach full throttle under load, might be due to the ESC ?!

Quite puzzling for sure !
I think I tested that (see my 04:38 post) and found that the ESC is working fine, and changing from a servo tester to a transmitter does not change anything. I'll try it again with a different ESC too I guess...

Jack
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Old Oct 16, 2012, 08:49 AM
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Chattanooga, Tennessee, United States
Joined May 2003
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Yes, Jack... I do have those GP props, thank you... it was just that I hadn't used them with any motors at RPM comparable to your DT750.
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Old Oct 16, 2012, 09:27 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by manuel v View Post
The big problem with this motor is the amount off cooper.

One 18T 22awg DLRK Delta termination has 36wires for slot.
785Kv.
APC 11x4.7sf TP 1320 3S:
6666 rpm @ 10.6v/17.4a 1227 grams 43.3 oz/thrust 81.0% Efficient
(data post no.8)

and this motor 19t 21AWG LRK Star termination has 19wire for slot.

Fore same cooper fill is necesary 36 tuns 22AWG delta termination, o 18 turns 19AWG star termination.

But this is not possible motor
Because the bell has very little clarity in the front.
This is not a motor for this LRK winding.

Manuel V.
You are right of course, I'm not arguing about that. But we can still talk about the confusion as to why it seems to work pretty well for a lousy motor, right? I think I am going to learn something. But you have inspred me to look at the details a little more:

Volume of copper:

Original wind (0.7239mm3) has 96% more copper than the LRK wind (0.3676mm3).

Surface area

LRK wind (0.410 mm2) has a 12% more surface area than the original wind (0.3619 mm2).

Length of wire

LRK wind length (1168mm) is 58% of the length of the original wind (2000mm).

There is still good clearance (3mm +) between the top of the bell and the LRK winding now. When I run out of room on this motor it is on the sides of the arms or in the slots when I wind all 12 arms.

If I did this same 19 turn LRK wind with a 1168mm long piece of 19 AWG wire I would have a copper volume of 0.763mm3 and that is close to the original wind's volume of 0.7239mm3.

And then I would also have a better basis for comparing the LRK wind to the dLRK wind at the same kV. And that is the comparison I started out trying to do here...

That is what I will do next, a 19 turn LRK wind with 19 AWG wire. The image shows the 13 turn 18 AWG test wind, I think I can get 19 turns of 19 AWG in there. I'm waiting for the wire to arrive, it will be here soon.

Jack
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Last edited by jackerbes; Oct 16, 2012 at 10:49 AM. Reason: change cubic centimeters to cubic millimeters
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