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Old Feb 14, 2013, 05:04 PM
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P.S. when one steps outside of the box, anything is possible, Haha!
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Old Feb 14, 2013, 05:07 PM
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My present 4S battery weighs in at 480 grams, found this 5S same C rating but 4000mah weighing in at 460 grams

ZIPPY Compact 4000mAh 5S 25C Lipo Pack (USA Warehouse)
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Old Feb 15, 2013, 05:06 PM
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It was never my intention to transition the rotors to a full 90' horizontal position however, if required, I can get allot more travel by shortening the push-rod and repositioning the servo horns. At present, I am only using 50 percent of the servo swing. The theory is, when the props are rotated to 45', there is 70 percent downward thrust and 30 percent forward thrust. This is calculated as COS(angle) and at 60', the forward to downward thrust ratio are equal. In this position, the wing loading factor is at minimum and I can gradually increase the airspeed to find the optimum performance points. also at this position, all three axises are managed with thrust vectoring thereby eliminating the requirement for control surfaces and additional servos. The present ailerons are flaps only and may not be include in feature versions. After the initial rolling takeoff test, I may adding some code to use the Weight Shifter to assist in pitching the aircraft as well and keeping it level.
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Old Feb 15, 2013, 07:16 PM
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Just thought I'd add some design concerns for ducted fans. To work these things have to be highly engineered.


First, you have to have more than just a tube. For them to truly add thrust they need a rounded inlet. Design of the inlet is crucial. Diamter is most important, shape is secondary.

Two, tip clearance is Absolutly critical. 0.1% of the rotor diameter has found to be optium.

Three you have to have a expansion angle to the bottom of the duct. 5 degre has found to work well for static thrust

You only need a "Rigged" inner wall right around the rotor. The rest of the duct can be foam or fiberglass. I think the cardboard concret tubes is an excellent idea.

Tip clearance is a big issue. I have heard people using AstroTurf to bring the clearance down.
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Old Feb 15, 2013, 07:20 PM
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AstroTurf = synthetic grass?
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Old Feb 15, 2013, 07:39 PM
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Yea, you maybe on to something. I have seen small brush like hairs in vacuum pumps. Just may work. I am going to try lining the tubes with the astroturf the next time I try installing the ducts. Thanks for the suggestion.
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Old Feb 15, 2013, 09:17 PM
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Yea that green turf stuff. Lots of other material could be tried. Soft side of Velcro. Tooth brush bristles....
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Old Feb 15, 2013, 11:59 PM
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Quote:
Originally Posted by icbribob View Post
First, you have to have more than just a tube. For them to truly add thrust they need a rounded inlet. Design of the inlet is crucial. Diamter is most important, shape is secondary.

Two, tip clearance is Absolutly critical. 0.1% of the rotor diameter has found to be optium.

Three you have to have a expansion angle to the bottom of the duct. 5 degre has found to work well for static thrust
these may be refinements on my previous comments and experience from embry riddels 2012 ducted quad....

that 5 degree comment is interesting... so we must match the high velocity slipstream, to the normal air around the duct via expansion. (like a rockets exhaust bell, the duct would then also see small upward force, and the usuall vibration)
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Old Feb 16, 2013, 12:01 AM
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Really neat idea
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Old Feb 16, 2013, 12:32 AM
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If you increase the blade count, It would be interesting to hear what an asymmetric propeller blade spacing would do to the sound signature.


http://oh1ninja.la.coocan.jp/details...20rotor_e.html

http://en.wikipedia.org/wiki/Fenestron
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Old Feb 16, 2013, 02:50 AM
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the abovepic shows varied angled blades with respect to each other, thus the emitted noise is at several frequencies instead of one, thus it appears quiter.

for drones in urban areas and battlefields, this may prove important.

as i and others have previously stated, notice the roundness of the circumference, and the tiny gap from tip to duct...
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Old Feb 16, 2013, 07:38 AM
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I have been struggling with finding suitable rotors for my application. I am using 4 blade 20 inch zingers. Not happy, but they seem to be working.

Oh and one other thing on ducted design. You only get th benefit of the duct above about 5500 rpm. Below that the duct performs just like a naked prop.

They other really tough thing to get your mind around is the fan will become starved for air along the leading edge as you increases the angle of attack. At hover you get nice equle air pressure on all parts of th rotor. Tilt to soething like 45 degree, and move forward and the leading edge gets less air pressure, resulting in unequle thrust, leading to the nose of the craft diving. This effect is why true VTOL drones like the T-hawk are software limited to I belive 30 degree of pitch, and a low air speed.

It gets worse, on VTOL ducted uavs, usually the control of the craft is with control surfaces in the air flow. When the ducted gets starved, the control surfaces we unequle air flow, resulting in control unstablity.

It gets really confusing.

Basically, if you are doing testing, start with a good duct design. Or like rimshot eventually did, build it uneducted and come back and build in the duct.
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Old Feb 16, 2013, 09:04 AM
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I think I may have found a cheap suitable and easy access to some fans with the ducts. Will not know for sure until I get one of these fans here to see how the conversion will go.



12" UNIVERSAL SLIM FAN PUSH PULL ELECTRIC RADIATOR COOLING 12V 1730 CFM

Can be Configured In "Push" or "Pull"

http://www.ebay.com/itm/261128037749...84.m1438.l2649
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Old Feb 16, 2013, 02:18 PM
I DESIGN QUADCOPTERS
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Quote:
Originally Posted by rimshotcopter View Post
I think I may have found a cheap suitable and easy access to some fans with the ducts. Will not know for sure until I get one of these fans here to see how the conversion will go.



12" UNIVERSAL SLIM FAN PUSH PULL ELECTRIC RADIATOR COOLING 12V 1730 CFM

Can be Configured In "Push" or "Pull"

http://www.ebay.com/itm/261128037749...84.m1438.l2649
Nice
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Old Feb 17, 2013, 12:28 AM
figuring it out...sort of!
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Brushless!?
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