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Old Mar 22, 2014, 06:18 AM
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Rewinding a Brushless Motor

I recently bought a motor from some really cheap Chinese web shop, hoping that it would have enough power for the job. Unfortunately, it doesn't. I looked at some similar motors from more reputable manufacturers (Omega 103g and Hacker A30-28S V3) and it's about 100W down in power from them. Can anyone here tell me how I could rewind the motor to get more power out of it?
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Old Mar 22, 2014, 07:09 AM
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specs would be helpful and/or pics.
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Old Mar 22, 2014, 12:57 PM
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Originally Posted by Su-33 View Post
specs would be helpful and/or pics.
It's an RCX 3536-9 910Kv 102g outrunner from MyRcMart.
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Old Mar 22, 2014, 05:06 PM
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This motor to 3s is good for.
APCe propellers 11x8.5, 12x6 even 12x8.
but not good for 13x6 and up.

with 4s only 10x5 to 10x6.

Manuel V.
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Old Mar 23, 2014, 08:41 AM
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Old Mar 23, 2014, 08:46 AM
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The RCX is 102g (910Kv), the Omega is 103g (1030Kv), the Hacker is 70g (1140Kv)... how can one compare apples with oranges?

Using 3W/g one can see that each has different capability... despite the 370W listed for the 102g RXC, ~300W is more plausible. The Omega will manage the same and the far lighter Hacker ~210W.

How did you determine that the RCX was "100W down" on the other two?
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Old Mar 23, 2014, 09:07 AM
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Quote:
The RCX is 102g, the Omega is 130g, the Hacker is 70g... how can one compare apples with oranges?
... Not to mention the differences in Kv which would result in very different power consumption figures for each motor using a given prop and battery.

I hate to see a lack of power blamed on a motor's perceived low quality when so little information is provided regarding setup and test conditions. Am I crazy, or is it just too easy to imagine a world where people assume a motor's price affects the wattmeter readout more than its physical characteristics? ...
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Old Mar 23, 2014, 11:52 AM
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Quote:
the Omega is 130g (870Kv)
There is an Omega 103g, which is said to produce about 425W with the same battery and prop (3s 2200mAh 25C and 12x6) as what I'm running on the RCX. I have flown a plane with the Omega, and has buckets of power. The RCX, on a lighter plane, barely provides enough power to go vertical.

Quote:
despite the 470W listed for the 102g RXC, ~300W is more plausible
The RCX is actually listed at 370W max, but I agree that it's not putting out anywhere near that. This thread was not intended to be a comparison between these motors, or a way for me to complain that I bought a lower quality cheap motor. I don't want hypotheses as to why it's not putting out the power I want. I want to learn how I can modify this motor to up the performance, even if only by a small amount.
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Old Mar 23, 2014, 07:22 PM
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Motors don't put out watts... they consume them. One plausible reason your RCX is "not putting out" the power you want is that you don't have a big enough prop on it... or you need to up the voltage.
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Old Mar 24, 2014, 03:17 PM
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Originally Posted by Dr Kiwi View Post
Motors don't put out watts... they consume them. One plausible reason your RCX is "not putting out" the power you want is that you don't have a big enough prop on it... or you need to up the voltage.
Even if I up the battery to a 4s, the max recommended for this motor, it'll still be "consuming" less power than the competition, and it will also cost me a new set of batteries, the capacity and physical dimensions of which I have no desire to calculate . I need to make the motor draw more current, either with a bigger prop or by rewinding it so that it uses more current. I am already using the biggest prop recommended for the plane, which leaves my only other option as rewinding it to a higher Kv. By increasing the Kv, the motor will have to spin faster, thus drawing more current and more power. Both the battery and ESC have the capacity to supply this power, but the motor is not pulling it in its current form.
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Old Mar 24, 2014, 03:48 PM
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Quote:
Even if I up the battery to a 4s, the max recommended for this motor, it'll still be "consuming" less power than the competition
How do you figure that? Switching to a 4S pack from 3S without changing the prop size would present an enormous power increase. Aside from the higher voltage itself, the motor will want to spin about 33% faster, resulting in a huge increase in current.

Quote:
I need to make the motor draw more current, either with a bigger prop or by rewinding it so that it uses more current.
No, you would need to rewind it so that it spins faster. It will likely draw more current as a result. Don't get caught thinking about the watts and amps consumed by the motor as the final indicator of performance. They can give you a rough idea, but a number of other factors are still at play.

However, you still may not need to rewind it. If the prop size on your model (which model?) is restricted, have you thought about using a three-blade prop? You can get more thrust from a limited diameter with an extra blade.
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Old Mar 24, 2014, 03:54 PM
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Quote:
How do you figure that?
The max power rating of this motor (370W) is with 4s, whereas the other motors only accept 3s max and put out ~420W.

I could go with a three-bladed prop, however, I already have loads of 12x6 two bladed props for this motor, and 3-blade props are not recommended for 3D. The model is a 3DHobbyShop 42" AJ Slick
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Old Mar 24, 2014, 03:54 PM
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3Dmad 5.

What are your numbers?

Propeller, Cel lipo, RPM, Ampers.

that's what you want?

Propeller, Cel lipo, RPM, Ampers.

Manuel V.
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Old Mar 24, 2014, 04:14 PM
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Okay, I found the Omega 103g 1030Kv motor... but 3W/g still indicates ~310W-in........ 425W-in is marketing hype.

If the Omega 1030Kv is consuming 425W with 3s and a 12x6, you can't expect the RCX at only 910Kv to consume the same amount with 3s and a 12x6... you could try 4s with a 12x6 but that would double the watts-in...... so you would need a smaller prop to keep it around 300W.
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Old Mar 25, 2014, 09:33 AM
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The Netherlands, GE, Nijmegen
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Quote:
Originally Posted by 3DMad5 View Post
Even if I up the battery to a 4s ...
'Our' PM BLDC (Permanent Magnet Brushless/Brushed DC) motors do not behave like a simple resistor (where mcurrent = voltage/resistance). Motor-current wants to go up squared ()with voltage and cubed () with Kv. Worst case, because battery voltage will decrease/sag a bit due to more current.

Going from 3 to 4 cells, keeping everything else the same gives an increase in current of (4/3) = 16/9 = 1.8, 80% extra, almost doubling current!

Simple table, without the e-blurb, listing the extra current when adding 1 or 2 cells
Code:
cells factor extra
1->2   4.0     300% 
2->3   2.3     130%
3->4   1.8      80%
4->5   1.6      60%
5->6   1.4      40%
or
Code:
cells 1  ->  2  ->  3  ->  4  ->  5  ->  6
factor  4.0    2.3    1.8    1.6    1.4
extra   300%   130%   80%    60%    40%
Why current wants to go up squared with voltage
www.wattflyer.com/forums/showthread.php?p=591935#post591935

Sticky: e-flight calculators (compilation)

Vriendelijke groeten Ron
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