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04-27-2010 08:14 PM  8 years agoPost 1
Flying Brian

rrElite Veteran

St. Clairsville, Ohio

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......

"I just don't Listen" "

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04-28-2010 01:27 AM  8 years agoPost 2
Flying Brian

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St. Clairsville, Ohio

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Alright, I'm having a hell of a time trying to figure this Ratio/KV thing out here. And quite honestly, I don't want something I have question about. So if someone could help simplify this for me, That would be wonderful.

OK, I have a Ratio of 8.4:1, This is what I did "multiply the Kv (rpm/volt) of your motor by the Vl (loaded voltage) of your battery and then divide by the desired head-speed

So I used a random KV of 630KV X 37 DIVIDED BY another random number (HS) of 1900rpm

I'm coming up with 12.26. What does this number stand for?

"I just don't Listen" "

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04-28-2010 01:42 AM  8 years agoPost 3
Heli 770

rrProfessor

USA.

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Why don't you go to Ready Heli and use Mr. Mel's head speed calc. It has tons of options to use.

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04-28-2010 02:06 AM  8 years agoPost 4
Flying Brian

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St. Clairsville, Ohio

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Everything I'm showing on Ready helis calculator is well over 3000rpms

It is asking me for a final Gear Ratio, and Im using 8.4:1, is that correct?

Running the calculator is all well and good, but I don't goto the field with a laptop.

"I just don't Listen" "

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04-28-2010 02:22 AM  8 years agoPost 5
Warrick

rrApprentice

Perth, Western Australia

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Hi Brian,

The number you came up with is the required gear ratio your heli would have to be setup with to achieve your desired head speed at 100% throttle (without bogging).

Note when you fly your heli with that ratio under load your head speed will decay by a figure between 100-200 rpm depending on the size of your model, the blades your swinging, pitch and a few other variables.

Ideally you want to have a around 200rpm head room available and then utilise your ESC's govenor function to keep your head speed consistant or just run 100% and deal with it.

My Ion-X2 (12S with 560kv motor) has a ratio of 11.625 which at 100% throttle gives me around 2,138~ on the head (non bogged). I then govern the head speed back to 1950 and it flys beautifully.

So utilising the formula you where using before...

(Volts * kv) / (desired headspeed) = ratio

(12 cells * 3.7 nominal voltage) = 44.4volts

44.4 volts * 560 kv = 24846 motor rpm

24846 motor rpm / 2138 = 11.62 ratio.

Then you need to work out what pinon/gear makes that ratio up so you can achieve that on your heli.

The other thing you can do is work out what the maximum head speed you will get on 8.4:1 ratio.

(Volts * kv) / ratio = head speed.

i.e.

(44.4 * 560) / 8.4 = 2960.

if you were running a 12S setup with a 560kv motor.

Mr Mel's head speed calculation tool is quite good to work out good options for your heli as Heli770 suggested.

Hope that helps

Cheers,
Warrick

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