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Old Dec 29, 2012, 06:01 AM
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Alright then, next thought: what formula best converts the power required to drive a single prop vs multiple props? Probably easier to account for the individual rotor power requirements... Also the relationship between a single disk area and multiple ones... 30 size helis have like 1,900 sq in. 450’s have like 600? So 2,400 sq in or so is kinda close, plus with FP cambered blades… sounds like it has a chance. What size props would go on a 6lb quad anyhow?

And I heard somewhere that full scale heli transmissions are like 99% efficient, but belt drive systems at this size are closer to 90-95% ... That penalty might apply to all four arms. Perhaps three would be easier to drive?
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Old Dec 29, 2012, 08:55 AM
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just use available data

I have no idea what to include when converting lift from the different blade sizes.
Disk size has not a linear relationship to lift at the same rpm.
I think the differences in tip speed where the most lift is generated is the biggest reason for that.

Anyway the data already exist ; we know what performance 450 class helie's have and it should be easy to find out there lifting power at a known rpm.
In hover the lifting power is the same as the weight so when we know at what head speed and blade pitch it hovers we know the lifting power,

A tricopter is simplere in some ways but the need to have one rotor twist makes that a bit more mechanically complicated so that might not be the best solution.

Regarding fixed pitch blades ; they are usually very thin and flexible (like my esky hb fp) so its easier to use wooden or or even carbon blades.
Those can also handle the required rpm better.
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Old Dec 29, 2012, 12:02 PM
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and yaw could be done by a additional tail but used in a conventional way
Or just let the FC control like it already does in electric quads: by varying the motor rpm.
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Old Dec 29, 2012, 01:04 PM
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would not work

that would require more then one engine and the throttle response is not exact enough on engines to be useful

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Originally Posted by VytasandRio View Post
Or just let the FC control like it already does in electric quads: by varying the motor rpm.
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Old Jan 02, 2013, 10:38 PM
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How about using a tail like in a tricopter?
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Old Jan 04, 2013, 01:57 PM
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So my TRex 450 runs about 900 grams ready to go... x4 rotors = 3.6 kilos or nearly 8 lbs lifting capacity at hover power.

I’ve read somewhere that 100 watts per kg is a good rule of thumb for an electric to hover. How many watts equivalent can you get out of a .30 size heli engine?

If 1 hp ~ 745 watts (Google), then the TT .39 in my Century Hawk Pro (rated 1.35 hp @ 18,000 RPM) is capable of about 1kW, and can lift 10 kg…

Since I doubt my Hawk could get off the ground at 22 lbs… the math probably doesn't quite work that way. I’d imagine shooting for the 6 lb weight of the Hawk would be a safe bet (if using a .30 size power train). With a governor and some strong/quick servos driving pitch at the corners…
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Old Jan 04, 2013, 02:00 PM
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So that parts easy... plenty of power. Now how do you drive 4 sets of 450 mechanics (with 2 counter rotating), off a .30 size drive train..?
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Old Jan 04, 2013, 03:06 PM
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So that parts easy... plenty of power. Now how do you drive 4 sets of 450 mechanics (with 2 counter rotating), off a .30 size drive train..?
The solution was already given to you. Drive belts. Imagine that the center motor is the tail and use the drive belt to drive the rotors. Give a half twist to the belts you want rotating in the other direction.

As an option, you can use a tail shaft driven system. Again the center motor takes the place of the tail and drive the rotor heads that way. If you install the 90degree gear up-side-down in two of the rotors, you will get the oppsite rotation you are looking for.

Rafael
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Old Jan 05, 2013, 03:59 PM
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Drive belts, yea I caught that bit but how do you get four drive belts into and out of there? On second thought, you don’t need to get them into the gear train. Stacking four gears (or a single tall one) on the main shaft and running belts to the corners could work. Wouldn’t be as compact as a typical quad…

Ok, so next; a .30 size heli hovers around 1500 rpm and is happy around 1800 for aerobatics… so to get the 2,500 to 3,0000 range expected by a TRex 450 rotor head would take a 1.67 to 1 ratio from the center main shaft to the 4 corners (hope I did that the right way…). The first Google hit for robot gear belt offers (conveniently) 15 and 25 tooth gears (getting us pretty close to converting 1,500 rpm to 2,500 rpm . I imagine bigger gears would probably run smoother (maybe 18/30) but that’s just a guess. No idea if these gears and belts are up to the task, but the parts are out there...

HobbyKing has a 450 clone for $28...

All the thoughts are coming together...
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Old Mar 24, 2013, 11:57 AM
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IMG 1284 (5 min 25 sec)
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Old Mar 25, 2013, 02:09 AM
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How refreshingly terrifying

Now all it needs is an onboard generator, a couple hours of fuel and an ardupilot... Then set it to wander back and forth just ouside the Oregon/California border...
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Old Mar 26, 2013, 05:41 PM
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Its a Hybrid!
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Old Mar 28, 2013, 02:36 PM
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next step is it with a turbine pointing down.

If only i had the money to try
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