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Old Apr 03, 2015, 02:44 PM
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Rewinding Scorpion S-2215-18

Original KV 1127 9 Turns per leg .21mm wire @ 6 Strands
Current KV 1224 9 Turns per leg 29 AWG Wire @ 3 Strands

Yes thats right. I don't know why but the KV is now higher since I checked it right after I rewound it. I always do a check at least 4 or 5 times too.

OK The RPM check with a GWS 9X5 was 9086 compared to Scorpion
Scorpion and GB Test data says it should turn 9300.

Topping off the battery to test with a new can with new magnets.
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Old Apr 03, 2015, 03:29 PM
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Same results with the new can from the S-2215 kit.

RPM = 9094
Thrust was 24.4 oz
3 Cell battery fully charged.

That Tech-Fixx is awesome. They already shipped the wire
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Old Apr 03, 2015, 05:33 PM
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Well, I couldn't resist. I put the original can back on and remounted the motor on the 450 cub and maddened it. 24 oz static thrust is certainly plenty of power for that plane. Once it gets going, it really gets going. The motor hardly gets warm. Once the wire arrives, I'm going to wind the kit and check the results.
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Old Apr 03, 2015, 07:51 PM
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Did you get the 200⠁C grade insulation? I used it and the insulation didn't burn with a soldering gun, pretty impressive.
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Old Apr 03, 2015, 08:05 PM
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Yes I did. I think 200C wire is more than enough. Most magnets begin to break down at 175C and my goal is to make motors that are built in a way where they don't have to get hot to work.

The Micro Dan wire I have hear needs a butane torch to get the coating off. the leads for soldering. They say has to get to 300C before it comes off but I think it's rated at 200C as well.
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Old Apr 03, 2015, 09:19 PM
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I have received new motors that had Kv ratings that were off by as much as 10 or 15 percent from their "sold as" Kv.

And when we do Kv's we are doing it slightly different than they would do it in a laboratory. We do a "raw Kv" by going to full throttle and measuring the RPM and voltage at the same moment in time. Then we divide the RPM by the voltage. That will produce a Kv that is slightly different than a Kv determined by the other method. But it is quick, easy, and close enough for our purposes.

The other method for determining Kv's is best called the "drill press method" and it is a little more time consuming and complicated to do. You can read how to do it here:

http://www.bavaria-direct.co.za/constants/#Kv

And we are always going to find variations in the RPM based who reads it and what they use to read it and even how that was used. I use an eLogger and that records the RPM and voltage. The voltage value will be quite steady, the RPM will show variations in the readings so I take a 3 to 5 second sample and use the average value for that period of time.

So a good thing to do is to just accept what you get for a Kv rating as long as it is reasonably close to what it was sold as or what you expected to get.

The most accurate readings will be when you take a new motor and measure the raw Kv using the full throttle RPM and voltage values. And entering that raw Kv value in the spreadsheet instead of the "sold as" Kv will give you more accurate Kv predictions for other windings.

Minor variations in magnets, windings, clearances on motor parts, bearing drag, position of the magnets relative to the hammer heads, and other things like that will always produce a range of variation from one motor to another as far as the Kv ratings you get and how it compares to the "called" Kv.

Jack
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Old Apr 03, 2015, 10:09 PM
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Oh gosh I fully agree on all points. I learned my lesson a long time by accident. I'm farther into it now than I was when I bought a new Turnigy 3542-1100 KV. It was advertised as a 1000 KV that the factory labeled wrong and it was mentioned on the page that had happened. I had been running it on a 3 cell with an HK APC style 12x6, previously Tower Pro that Headsup was selling, for quite awhile. It flew a 4.75 pound Nitro plane L-4 for around for quite awhile. I even flew it on a 5.25 pound cub with a 4 cell and a 9x6. I tell ya that thing got hot. You have to admit those Turnigy's are pretty darn good. Now it's flying an E-flite Cub 25e on a three cell and a 10x5 HK. It flies it real well. I've had it for over 4 years. It was only a week ago that I got my pull scale and decided to check it. I have not checked it yet with the 10x5 because I put an 11x5.5 on it that I havn't flown yet. It gives 61 oz thrust. So I did a KV check and it's at 1225. They must have put an 1100 can that was supposed to be a 1000 onto a 1250 stator. It pulls 41 amps that way. Now I check all my motors. The scorpions are the very few that are always within 5KV of advertised.

I do it the same way you do. I thought about the drill press thing but first I have to have one. There are a lot of tools I still want to get. wish I still had access to this big flat CNC cutter where I used to work. I have tons of cad drawings. I drafted all the cuts that machine does. I thought about buying the right blades for it and running some of mine through it. A Big GIANT B-17 cut in just a few hours. he he.

Bob
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Old Apr 04, 2015, 06:32 AM
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Quote:
Originally Posted by bnesbitt View Post
... Most magnets begin to break down at 175C ...
Typo, should be 175F, or 80C. The stronger the magnet, the lower the achievable maximum operating temperature. See this magnet grade table
www.supermagnete.nl/eng/data_table.php

Vriendelijke groeten Ron

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Old Apr 04, 2015, 07:50 AM
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Ooooppsss yes typo
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Old Apr 07, 2015, 04:14 AM
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Quote:
Originally Posted by bnesbitt View Post
Original KV 1127 9 Turns per leg .21mm wire @ 6 Strands
Current KV 1224 9 Turns per leg 29 AWG Wire @ 3 Strands

Yes thats right. I don't know why but the KV is now higher since I checked it right after I rewound it. I always do a check at least 4 or 5 times too.

OK The RPM check with a GWS 9X5 was 9086 compared to Scorpion
Scorpion and GB Test data says it should turn 9300.

Topping off the battery to test with a new can with new magnets.
Hi
My S2215-18 sample was measured at 1131 rpm/V (value I embedded in Scorpion Calc)
The copper wire filling/organization inside every slot could act slightly on the Kv
Do you have pictures of the stators (original and rewound) ?
Louis
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Old Apr 07, 2015, 04:40 AM
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Hi Louis

I don't have pictures of the original because it had two broken wires. I bought it used along with a few others really cheap. It had 9 turns DLRK with .25mm wire. It did start up with a stutter and turned 1206 KV. I think it was probably rewound ptior to me having it or it might be an 1800KV version with a couple of broken wires making it turn slower. As you can see, I can get better fill. When I went 10 turns, it was only 1080 KV. I tried 4 strands of 30 awg for 10 turns but it wouldn't fit. I might try again or see what I get with 31 awg. The wire got here last night but I'm in the middle of turning a 30x14 stator.

Thanks

Bob
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Old Apr 29, 2015, 10:35 AM
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Sorry it took so long to keep this thread going. It's been busy. Plus, initially I was looking to make the motor perform to at least OEM specs so I wound it a number of times using different turn counts and wire sizes to achieve the best possible results. Here are some quick results with a comparison to test data obtained from Scorpion. FlyBrushless prop data is very close to Scorpion so I didn't include theirs although flybrushless.com is a very valuable resource.

My current wind

7 strands 32 AWG .2032 mm wire at 8 turns per arm Delta
1121KV
10072 RPM
35.2 oz thrust
14.7 amps

S-2215-18 Original specs from Scorpion site

6 Strands .21mm wire at 18 turns in the slot or 9 turns per arm Delta

1131KV
GWS 9x5
9300RPM
29.31 oz thrust
13.61 amps

S-2215-18 My original wind with 3 strands of 29 AWG .2870mm wire at 9 turns

1175KV
GWS 9x5
9000 RPM
26.7 oz thrust
13.6 amps

I'll be posting results using various props from both the 9 turn with 29 awg and the 8 turn with 32 awg. Also, I have two of these motors so I'll be experimenting with different wire sizes on the one with 29 awg because obviously that's not the optimum results. If anyone want's to suggest a single strand or two strand size, my ears are open. I've tried 3 strands of 28 for 10 turns and it won't fit. I'm considering two strands of 27 awg.
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Old Apr 29, 2015, 12:35 PM
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Good job. You wound up (pun) with basically one more strand in the bundle and two turns less than the manufacturer. Maybe you should concentrate on 8 turns to better match your prop. Say 3 strands of 28 8x
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Old Apr 29, 2015, 12:48 PM
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Thanks for saying

3 strands of 29 awg at 9 turns made it 1175KV. I imagine 3 strands of 28 at 9 turns would make even faster and less efficient with a 9" prop. 10 turns with 29 awg made it 1080KV I think that might have been too slow for a 9 inch prop. However, it might have been better for the Vess 9x6. I prefer to be in the 1120 - 1140KV range as it will give me a wider range of props that I can use. In any case, I think a Vess 9x5 would be better than the 9x6 for both winds.

I think I would need 10 turns with 3 strands of 28 awg. I think I tried that and it wouldn't fit but I can double check that.
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Old May 22, 2015, 05:16 AM
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How would this work sgl strand Rewind 9T of 23 awg Delta?

Hi Bob
You're blazing a trail for me, my Scorpion 2215 & 2212 kits are supposed to be coming in a day or 2 and I want to wind either a 2212 or 2215 half parallel dLRK either Delta or Wye. Did you get Jacks 8pg guide on this, it's very good. I have been looking for others winding these motors like mine and just learning how to do this.
For practice and I was curious to know, this first wind is under-filled compared to the stock wind, I am not sure how this would affect the kv issue you mentioned but the first thing I wanted to do was figure this wind for wrapping with solid wire. Did you intend a match as close as possible to the wire fill ( it figures to me like the fill is under the stock ) and know or intend it to be a little under? Four of the 0.21 strands would not have fit? Would the following be too hard to wrap?:
*********************************
Greater copper fill sgl strand wind for a small amount of over fill:
Rewind 9T of 23 awg Delta ( your original idea BUT over stock fill )
*********************************
Bob, look at the picture, it's easier reading, where I was saving work and figuring this.

Electric Motor Des. Const
Rewinding Scorpion S-2215-18 Thread by bnesbitt 3 April 2013
Original KV 1127 9 Turns per leg .21mm wire @ 6 Strands
Current KV 1224 9 Turns per leg 29 AWG Wire @ 3 Strands
I don't know why but the KV is now higher
0.21 mm wire radius = .105mm
Area = .03463605901mm^2 Cross sectional Area of .21mm wire

Rewinding Scorpion S-2215-18
Stock 9T ( 6 strands of .21mm )

Area of 6 strands or .21mm = 0.20781635406mm^2
Dia is needed

( Area / π )^.5
( 0.20781635406 / π )^.5 = r = .257196423008mm

Scorpion Stock copper fill Dia = 0.514392846 mm
awg 22 = 0.64516 mm
awg 23 = 0.57404 mm
awg 24 = 0.51054 mm

Stock = 9T of awg 24 This is a little under the copper fill of Dia = 0.514392846 mm


Rewind 9T ( 3 strands of 29 awg )

What are 3 strands or awg 29 in Area, do they = .514 as above
3 strands of 29awg (0.28702mm) = .86106
rad = 0.14351mm
Area = pi x 0.0205951201
Strand Area= 0.064701478006mm^2 ( one strand of 29awg )
Cross Sectional Total Area of Turn
3 x Strand Area = 0.194104434018mm^2
Area of Turn = 0.194104434018mm^2
Rewind Dia of Turn ( copper fill ) = 0.497133222788mm


Scorpion Stock copper fill Dia = 0.514392846 mm
minus the Rewind Dia of Turn ( copper fill ) = 0.497133222788mm
------------------------------------------------------------------
Rewind fill is 0.017259623212 mm under diameter of stock fill
23awg 0.57404 mm + 0.0769 mm over stock fill
24awg 0.51054 mm -- 0.01726 mm under stock fill
π π π π π π π π π π π π π π π π

Greater copper fill sgl strand wind for a small amount of over fill:
Rewind 9T of 23 awg Delta ( your original idea BUT over stock fill )

The first thing I thought to do was compare the copper fill and both winds have 9T, and found your rewind was under the stock fill. I have never wound a brushless motor and don't have parts or wire or wire gauge here yet.
I am in the planning the wind then I'll order, I want to optimize either the 2212 or the 2215 to a Kv that would give 10,400 rpm on 7.4 volts driving the GWS 9 x 5 DD.

I just re-read your last post saying you would prefer a higher Kv in the 1170 range that would give you more prop range. You might be using the small wire to be able to wind in smaller incremental differences or just prefer it to using a single strand of 23awg?

Oh while I was studying your wind ideas I came across this page for wire, you really might want to bookmark this, I was using it to check myself, they did round some stuff to 4 digits that for me would have been intermediate figures but this is the site description Link underneath:

Conversion and calculation − cross section < > diameter

● Cable diameter to circle cross-sectional area and vice versa ●

Round electric cable, conductor, wire, cord, string, wiring, and rope
along with other resistance for wire etc.

http://www.sengpielaudio.com/calcula...ss-section.htm
One thing to add curious about, the smaller wire is going to have more resistance than a solid strand. These points about underfill and resistance make me wonder about your choice. I did however see Rons post about getting a better copper fill with your multistrand technique, and yet see so many wind projects where single strand is chosen and explained as it is better and also that the choice for the multistrand is that it is simply easier to manufacture production style. It seems like one idea the multistrand fill idea is pitted against the solid strand idea. Less resistance is supposed to be much better for efficiency and less heat in the motor too. The more resistance, the more the heat inside the coils, no????? Like a load resistor in one of the old solid state table radios I worked on as a technician years ago, that resistor was like 5 or 10 ohms 50 watts ceramic and radiated heat, it would blister your finger quick. This was inline I think with the 120v AC line, now the wires carrying the current next to the resistor had 0 ohms carrying the load so they did not get hot like the resistor. Large sgl strand wire lo resistance VS small multi strands higher resistance????


Still learning and it might help me to hear the reasons for your technique.
Thank you, like to hear why you did not wind it solid 9T of 23awg. This is similar to what I would be planning to wind mine except for maybe 1500kv to run on 2s. I'm still forming ideas about this and also need to learn to use a good wind calculator program. and which wind for this goal half parallel Delta or Wye.

Leonard
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