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HelicopterScale Model RC Helicopters › Correct motor and gear ratio for electric conversion
02-16-2018 03:19 PM  63 days agoPost 1
CostaRicaHeli

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Costa Rica, Central America

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Hi all, I am planning on converting my Bell 430 to electric from gasoline. The current gear ratio is 9.1 and the RPM band of the engine output is around 11,000 RPM. I was figuring around 1200-1300 RPM for the rotor.

My question is this, which is better and why:

1) 6s setup, with a 580KV motor (22.2v x 580KV x 90% / 9.1 = 1273RPM RPM), or

2) 12s setup, with a 300KV motor (44.4v x 300 x 90% /9.1 = 1317RPM

If I could change the gear ratio form 9.1 to say 10 with a pinion I could lower it even more.

Why would I choose 6s or 12s? Flight time?

Thanks,

Franz

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02-16-2018 03:28 PM  63 days agoPost 2
coptercptn

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Mesa AZ. USA

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A lot depends on the size (weight) or the Heli. Watts per pound...
If light enough a 6S system is more than adequate, but if you need the power, and nose weight is an issue, the 12S will be more efficient.

Home of the "Sea Cobra".....

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02-16-2018 03:43 PM  63 days agoPost 3
ICUR1-2

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Ottawa, Ontario

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coptercptn
A lot depends on the size (weight) or the Heli. Watts per pound...
The watts needed would determine the battery size.
6S VS 12S depends on the load of the motor.
The higher the load = the higher the amps required.
To reduce the amperage we raise the voltage.
Amps make heat .
You may not need 12S perhaps 10S.
If you're able to raise the gear ratio you can lower the amp draw as well.

spending time, paying attention

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02-16-2018 04:15 PM  63 days agoPost 4
CostaRicaHeli

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Costa Rica, Central America

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Thanks for the help!

I think I can raise the gear ratio to 13.3 with the conversion kit. I already have 12s packs for my other 700s, so it would be ideal for me. As its a scale 800 ship, it may be heavy, maybe 15-20lbs? I'm thinking of 12s, 450kv where at 85% efficiency I'm getting 1250rpm (44.4 x 450 x 85% / 13.33 = 1273 RPM).

In terms of watts, this setup would be giving me 85amps x 44.4v = 3,774w max continuous. This is about 5hp. Sounds about right. How do I factor in the ship's weight to see if this is enough? What do you think? A 130amp ESC should be able to handle this.

Franz

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02-16-2018 04:35 PM  63 days agoPost 5
ICUR1-2

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Ottawa, Ontario

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CostaRicaHeli
How do I factor in the ship's weight to see if this is enough?
That would be 4 lbs to 1 hp. How many HP did the gas engine out put ? I don't have experience with scale models to know if this would be enough.
My experience comes from pod and boom 50 size and lower.

spending time, paying attention

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02-16-2018 04:41 PM  63 days agoPost 6
CostaRicaHeli

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Costa Rica, Central America

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The Zenoah 230RC outputs about 3hp, that's why I thought the 5hp setup with higher gear ratio would be more than enough. Still doing a little more digging but maybe there is a formula out there on watts/lb needed. Don't know. Maybe someone has this info, even if its on their own scale setup that works.

Anyway, thanks for the help!

Franz

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02-16-2018 04:58 PM  63 days agoPost 7
ssmith512

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Indianapolis, IN USA

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CostaRicaHeli
Still doing a little more digging but maybe there is a formula out there on watts/lb needed. Don't know. Maybe someone has this info, even if its on their own scale setup that works.
Accepted figures are roughly 55W/lb in hover (forward flight uses less). For a 4 blade head, maybe a tad more??

A 130A ESC on a 700 sized scale ship 12S setup will be MORE THAN PLENTY.

Steve

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02-16-2018 05:03 PM  63 days agoPost 8
CostaRicaHeli

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Costa Rica, Central America

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55 watts per pound
Thats very good info, thanks! You're right. At 55w/lb, and say 25lbs total weight, I would need 1,375watts to hover. This setup I'm suggesting should produce up to 3,774 watts, so its got plenty of reserve. As long as the motor can work in the 85%-95% efficiency range and the RPMs are what I want, it should work fine. Thanks again!

Franz

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02-22-2018 10:08 PM  56 days agoPost 9
CostaRicaHeli

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Costa Rica, Central America

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Update
I have settled on 12s 5000mah, KDE 295kv motor and keeping the original gearing and clutch. For this I am machining the clutch adapter for an 8mm shaft. Should have it within a week.

So max expected headspeed would be: 44.44 x 295 / 9.09 x 0.9 = 1298rpm and for a governed headspeed of 1,200rpm the efficiency would be at or around 83%, which sounds about right.

Flight time should be 8-10 minutes, but we'll see. Thanks for your help!

Franz

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02-24-2018 08:31 AM  55 days agoPost 10
Andy01

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Brisbane, Australia

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I have a Baumann EC-145, which runs 4x 820mm blades. I use a XNova 300kV motor (quieter & runs cooler than KDE), and CC Edge 80HV on 12s. I typically use about 1000-1200W to fly gentle scale circuits.

If you are using a CC (or similar) ESC, then governing to 83% may create some heat.

I also think that your chosen headspeed may be a bit fast for a 4 blade 800mm - I run mine at 1050rpm, and it is quite responsive. I get 8 minutes on about 3200-3400mAh, so with 5000mAh lipos, I could probably stretch closer to 10 minutes.

Colin

Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )

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HelicopterScale Model RC Helicopters › Correct motor and gear ratio for electric conversion
02-24-2018 10:55 PM  54 days ago •• Post 11 ••
CostaRicaHeli

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Costa Rica, Central America

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two blades
Thanks for your input. I have a two bladed head. That's why the headspeed is going to be between 1150 and 1250. The four bladed head will be for the future, hopefully.

Franz

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