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Old Jan 11, 2009, 10:47 PM
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Ducted Fan QuadCopter

I would like to build a quad using ducted fans.

I am a working cinematographer and don't want open blades on the set.

It needs to be able to lift five pounds. I read in a post on another thread where someone had lifted a brick. Bravo!

It needs to be rock solid and capable of doing smooth basic moves: TRUCK, PAN, PULL, PUSH and PEDESTAL (CRANE). I'm not going to chase a train through a tunnel with this; just nice smooth establishing shots.

In addition to the obvious danger, yaw is the biggest problem with RC Heli shots. It is endemic with the design. I seems as though a quad with four or five foot arms would be rock solid.

I have been rummaging through quite a few threads in several forums and the best example of the kind of shots I'm looking for are OMM's, tree Tops shot. I've seen a lot of shots from "professionals" that weren't nearly that smooth.

http://www.rcgroups.com/forums/showp...postcount=2375

So I guess the first question is if there are any controllers that handle the thrust vectors of ducted fan units?

I currently fly a Blade400 (but not all that well), and am rather handy with a soldering iron.

Suggestions, tips and cautionary tales are all welcome,

Cheers,
Scott Billups
Hollywood, CA
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Old Jan 12, 2009, 03:42 AM
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Good Lord man, something with the proportions you've described and the capabilities you're specifying might very well require some sort of FAA licensing or some such.

At first, as I skimmed through your message, I for some reason decided you were favoring ducted fans in the hope that they'd be quieter than conventional rotors.

Just as I was getting ready to tell you how monstrously loud it would be to have a bunch of jet engines hovering over a set, I re-read your post and realized it was a safety concern, and probably a valid one.

If open blades weren't an absolutely insurmountable deal breaker, I'd suggest taking a good, long look at the top two Draganflyers ($2,500 and $15,000 respectively):

http://www.rctoys.com/pdf/draganflye...ison-chart.pdf

Depending on budget and time constraints, buying or renting one of those would have at least one major benefit in that it would save you from having to re-invent the wheel. Besides the fact that the R&D was done a long time ago, Draganflyer has probably put a lot of thought into preventing the type of failure that could plunge hardware into a populated area and its manufacturer into years of litigation.

But you're not trying to avoid re-inventing the wheel, are you? You'd prefer designing something to address all of your requirements, as opposed to trying to compromise and tailor your needs to fit somebody else's product, yes?

Heck, even if your ducted-fan platform represented a huge investment of money and time, being the owner and operator of such an asset could pay huge dividends, especially when your colleagues see the results and realize you're the only game in town.

I do, however, find the sheer hugeness of what you envision, and the corresponding power requirements, to be somewhat daunting. In contemplating this, I've got just one inspired bit of brainstorming for you:

What would happen, I wonder, if you could build in some degree of lighter-than-air technology? I'm not suggesting you turn it into a glorified hot air balloon or anything, but partial lighter-than-air dirigible/plane hybrids are all the rage with certain inventor/futurist types.

I'm picturing some type of rigid structure with internal chambers filled with enough helium that the ducted fans would have slightly less work to do, while the increased energy efficiency would yield longer flight times.

In order to make a difference, those chambers would have to be cavernous enough to hold one heck of a lot of helium. On the plus side, because the vehicle wouldn't actually be lighter than air, you wouldn't have the kinds of challenges that a blimp or zeppelin faces when the weather turns nasty.

Just a thought.

I got a million of 'em....
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Old Jan 12, 2009, 03:59 AM
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Hi Monger,

okay I will try to share my little experience about quadrocopter with you as much as I can.

1-ducted fan quadrocopter are much much more noisy

2- Ducted fan quadrocopters are likely to be less stable than the exposed blades type, so if you still want the ducted fan type I suppose you need more than 4 rotors , something like 6 or 8 rotors to achieve the same stability

3- Another alternative of the ducted fan is using an exposed propeller type with some sort of protection that surround the the whole quadrocopter, something like a two piece cage (top and bottom ) that allow the airflow to pass through and at the same time cover the whole craft and your camera should be mounted on top of that cage.

I believe I've seen this design somewhere, I will try to find it for you

but I strongly recommend that you post your question in this active thread

http://www.rcgroups.com/forums/showt...0#post11326442

You will find even more solutions, ideas , and much more experienced people

also the aerial photography section section of this forum

Good luck

Khaled
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Old Jan 12, 2009, 12:48 PM
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Noise might not be an issue, as filmmakers often have their cast go into a sound booth and re-record their own dialogue well after a scene's been shot. Likewise for sound effects.

That instability thing, however, is a much bigger challenge.

Khaled, I've seen UAVs similar to what you're describing. I'm not completely sure on the locale, but I believe there are police agencies in the UK experimenting with surveillance drones that basically look like big, fat, flying saucer or hamburger-shaped enclosures with rotors and cameras hidden within. Each one almost kinda looks like a single, disembodied, ducted fan engine that floats above your neighborhood with no corresponding plane attached to it...
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Old Jan 12, 2009, 12:59 PM
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Uh, oh; they're already in The States!

http://www.popsci.com/military-aviat...-new-spies-sky
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Old Jan 12, 2009, 05:12 PM
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flightsuit

Wow ,,, that looks scary ....not friendly at all

I wonder how the directional control is done, since it is a single ducted fan

Khaled
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Old Jan 12, 2009, 05:22 PM
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Quote:
Originally Posted by khaled_abobakr
flightsuit

Wow ,,, that looks scary ....not friendly at all

I wonder how the directional control is done, since it is a single ducted fan

Khaled
Maybe it's a pair of counter-rotating blades. The speed of one of the blades is varied to allow torque to rotate the airframe, thus allowing steering?
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Old Jan 12, 2009, 07:06 PM
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My understanding and/or memory of it is that Honeywell uses thrust vectoring shutters. Honeywell gets lots of press in the military circles with numerous articles on the ASD and DID email new wires.

Dan
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Old Jan 12, 2009, 07:11 PM
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Link

http://www.asd-network.com/press_detail_B.asp?ID=18319

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Old Jan 12, 2009, 07:13 PM
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Quote:
Originally Posted by khaled_abobakr
flightsuit

I wonder how the directional control is done, since it is a single ducted fan

I think Windbreaker nailed it. Twin, counter-rotating ducted fans. Yeowza!

I was taking flightsuit's advice and was just ordering a Dranganflyer to play with, but this thing is more of where I think the design for a motion picture rig needs to go. Looks like they dropped the CG as well.

I think I'll be better off getting some ducted fan units and just playing with them. Maybe a massive gyro wouldn't hurt either.
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Old Jan 12, 2009, 09:17 PM
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Originally Posted by otlski
Yep. Ducted fans it is. Great link Dan.
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Old Jan 12, 2009, 11:20 PM
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Well thanks for taking my ideas seriously, regardless of what you ultimately wind up doing! One other possible benefit with Draganflyer is that they purport to offer training of some sort. I have no idea how comprehensive that training might be, but I'd imagine it could go a long way towards addressing your safety concerns, both from a practical, real-world standpoint and in terms of being able to provide insurers and legal departments with credentials, or at least some evidence of expertise and reasonable precautions.
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Old Jan 13, 2009, 06:32 PM
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Quote:
Originally Posted by Monger
I think Windbreaker nailed it. Twin, counter-rotating ducted fans. Yeowza!
I think I'll be better off getting some ducted fan units and just playing with them. Maybe a massive gyro wouldn't hurt either.
Hi Monger

only very few of this type of "Aerobots" are actually fitted with CR-fans (counterrotating). Exit guide vanes eliminate the rotor torque.
Here is an elderly pamphlet of such a device which provides some info of the control arrangement. AFAIK is the I-Star one of the progenitors of the Honeywell VTOL UAV.

I don't think that you will get very happy with the current crop of EDFs. They are all designed for model (horizontal) propulsion with small air mass and high exit velocities. What you are looking for are lift fans with large air mass and moderate acceleration. If you are serious - a good friend of mine designs and builds those to order, even with variable pitch if necessary. A typical lift fan for your job would be around 12" diameter and uses around 800W. They can be kept quiet on account of their low rotational velocity.

Regards

Wendi UK
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Old Jan 13, 2009, 06:52 PM
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Originally Posted by Wendi Smol
If you are serious - a good friend of mine designs and builds those to order, even with variable pitch if necessary.
Thanks Wendi, I'm very serious. Please have him contact me.

Scott Billups
sbillups at aol.com
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