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HelicopterMain Discussion › Why is my flight time different?
05-19-2016 11:22 PM  17 months agoPost 21
felixthemaster1

rrNovice

England

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I know nothing about gearing. I fly a 6s X3 with a 131T main gearand 11t pinion spun by a 1700kv motor. I use a cheap NTM rotor drive motor from HK so I am not sure if it can handle the extra load from a 12 or 13t pinion. Is this efficient at all? I get 4:20 flight times to 3.8v at 2700-2800 head speeds and at 2100, I get 6 mins (but tail won't hold in backwards flight).

Sorry if this is not the right place to ask.

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05-19-2016 11:32 PM  17 months agoPost 22
Richardmid1

rrProfessor

Leeds, England

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Your setup is fairly efficient, I'm guessing you fly fairly hard 3d?

Dividing your main gear by your pinion gives you your gear ratio, in your case 11.9. Times the motor kv by your pack voltage (22.2), gives you your max motor rpm. Motor rpm divided by your gear ratio gives you your rough max rotor rpm which you want to govern 10-15% lower.

60% of the time, it works every time!

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05-19-2016 11:33 PM  17 months agoPost 23
cudaboy_71

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sacramento, ca, u.s.

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It's as good as any:

131/11 = 11.9

1700kv (theoretical RPM/volt) * 4.2 (volt per cell) * 6 (cells) = 42,840 motor rpm

42,840/11.9 = 3600 headspeed (no headroom, no effeciency calculation)

A 94% efficiency calculation works well for Scorpion motoors--NTM HK motors, I don't know...so, 3600 * .94= 3384 max headspeed on fully charged pack. YMMV.

I also like to leave 10-15% headroom for a gov...so, 3384 * 85-90% = 2876-3045 RPM governed.

That's just ballpark, especially not being familiar with your motor, which packs you're running, or the ESC. But, you seem to be ok. As for your tail not holding, the fix is longer tail blades (if you have ground/main blade clearance), or a higher tooth auto gear to get the tail blades spinning more revolutions per revolution of headspeed.

if it ain't broke, break it.

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05-19-2016 11:42 PM  17 months agoPost 24
Richardmid1

rrProfessor

Leeds, England

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I never use 4.2 as cell voltage as it can be 4.15 straight off the charger with no load. Nominal voltage (3.7) gives you a fairly average flight voltage.

Tail will be very week on a 450 at 2100 rpm.

60% of the time, it works every time!

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05-19-2016 11:49 PM  17 months agoPost 25
cudaboy_71

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sacramento, ca, u.s.

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That's probably where that Scorpion 94% efficiency factor comes in, for me anyway. It's just a fudge factor.

But, I have run scorpions on all my helis from 250 up to 700. Using 4.2 and 94% puts it pretty well on the money.

But, you're right--change the voltage to a more realistic number and the fudge factor probably goes up closer to 100%.

if it ain't broke, break it.

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05-20-2016 01:52 PM  17 months agoPost 26
felixthemaster1

rrNovice

England

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I am just learning. Practicing upright circles and stall turns and inverted hovering. I do enjoy doing loops and the occasional tick tock.
Do you think it is beneficial for me to get a 4S Lipo and practice these things in slow mo with low headspeed and longer flight times?

As for no tail hold in super low 3100 RPM, I tried to get 70mm blades (I use 68 mm) but they are designed for 500 sized helis so their roots are too thick.

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05-20-2016 02:41 PM  17 months agoPost 27
cudaboy_71

rrElite Veteran

sacramento, ca, u.s.

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Capacity equals flight time. If you want to fly longer get a 5300mah pack instead of a 5000mah pack, for example.

If you start changing the voltage (going from 6s to 4s) you'll likely have to change pinions--maybe even motor. Kind of a PITA but an option for sure. Just make sure you keep the capacity up for flight time.

if it ain't broke, break it.

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05-20-2016 11:59 PM  17 months agoPost 28
felixthemaster1

rrNovice

England

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Seems like a 4S 1800mah lipo is the samish dimension and weight(80 gms lighter) as my 6s 1400mah. I have been advised to not go 3S as I won't get much power out of it. I am keeping pinions and motor the same of course, since I want the low speed, I am not trying to run the whole heli on 4s.

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05-22-2016 06:52 PM  17 months agoPost 29
Richardmid1

rrProfessor

Leeds, England

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Yes 4s on a 6s 450 is a good idea for long flight times. You mention 3100rpm which isn't low on a 450 and tail hold should be fine.

60% of the time, it works every time!

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05-22-2016 06:54 PM  17 months agoPost 30
felixthemaster1

rrNovice

England

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Oops, I mean 2100 RPM. My bad.

I should probably get the upgraded 14t tail shaft to speed up the tail.

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05-24-2016 04:17 PM  17 months agoPost 31
Richardmid1

rrProfessor

Leeds, England

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Fly it at 2100 and see what the tail is like, it might be ok with just an increase in gain.

60% of the time, it works every time!

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HelicopterMain Discussion › Why is my flight time different?
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