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The CyberHex

Cyberdactyl

Misfit Multirotor Monkey
#1
There’s been one aspect of all multirotors that has nagged me for some time.

And that is the insouciant concern for thrust column efficiency (TCE). Most builders take little notice of TCE, in that they design and build mostly for a handful of other reasons. Several commercial multirotors designers ignore this aspect as well. Many designers concern themselves with a single or combination of, initial cost, crash repair cost, crash management, size, weight, payload capacity, materials at hand, what they’ve seen before, etc. Rarely, if ever, is TCE even a consideration.

This is surprising in that low TCE can reduce flight time and lift capacity by as much as 25%. Most plate-type booms are in the neighborhood of 15%. Many configurations aggravate the TCE by placing the ESC flat, directly in the highest cross-section of thrust. Many place holes in the booms, however that is most likely for weight reduction, and the result is turbulence, buying very little increased lift.

But to give credit where credit is due, clean carbon fiber round booms have outstanding TCE. But I suspect CF tubes are chosen mostly for weight/strength consideration. However, even square wood, aluminum or carbon fiber booms have decent efficiency. Square booms do have a maximum thrust splash area, in that the leading edge is flat, but since a square tube or solid boom has a relatively small planform area, the thrust splash does not move into a critical region of gross inefficiency overall. I have seen double plates turned vertical, but generally the boom has horizontal structure between the plates, such as screws, standoffs, etc., to improve rigidity.

So, setting aside those designs which are either excellent or passable in TCE, I want to experiment with a paradigm shifting idea. To step beyond even the round clean carbon fiber boom, and get the TCE as close to 100% as is possible, by turning the grossly inefficient common flat boom vertical.

The idea was sparked by my ‘Racing Quad’ design I did several months ago. It basically utilized a symmetric shallow chord airfoil shape as the booms. It then occurred to me, if the boom could be made stiff enough, a simple flat plate could be used and could be built much easier and cheaper. So I began to design from that aspect.



The following hexicopter is made from 3/16” plywood for the booms and 5/32” plywood for the main plates.





I started by designing my general idea in SketchUp, then tweaking and changing several times until I had a rough structure, then trimmed the main plate and booms down to a size that was not too overly bulky given I was using an average strength material. I then printed out the shapes and spray adhered them to the plywood and cut them out with a band saw.

I coated the area of most active boom flex with epoxy, essentially adding a ~0.6mm non-reinforced rigid membrane tube.



I made a common ring-type harness. All connections are splayed wire T interface connections with a fine copper wire wrapping, then soldered and double coated with epoxy.

I suspect the reason why this design has not been done before, (at least I have yet to see it) is the problematic mounting of the motors on a very thin vertical plate. My solution is straightforward and simple. I used interlocking pieces, wood glued the pieces and reinforced them with two coats of epoxy on the surface. I also did not use the cross piece to zip-tie the motors down. They are only for lateral support, so there is no constant upward pull, or jerk moments on the piece, only compression.



Mounting the vertical booms to the frame is easy. I made blocking tabs and guides at every other corner, and did the same on the opposing plate, offset by a corner, so all corners have blocking and guide rigidity either above or below.



The two halves apart that are pressed together and securely clamped with six screws.



The result is an amazingly strong and rigid six sided box structure that can withstand dozens of kilos of shear, trapezoidal force.



I’m also utilizing clear shrink as my ESC mounting material. I’ve indented the booms so that the shrink does not interfere with the clamp region near each fastener, and to allow higher PSI at the clamp points and to allow the shrink to move freely during the heating process.

I’ve recessed the KK2.1 ‘inside’ the ring for protection and also recessed it back, off center about 20mm, so the Invensense chip is as close to the center of lift and the CG as possible. The battery is mounted on top to put the elevation CG closer in-line with the lift plane. The result is the elevation CG is about 1cm below the lift plane. I mounted the Rx underneath since I used foil tape to affix the motor wires to the booms and did not want to reduce reception by having the Rx and Tx LOS interfered at great distances. Foil tape is extremely strong in uniform tension, but yields easily when tearing.

Next came some rattle-can black and putting it together. Both went fast. I was a little worried I would need three hands to wrestle to manipulate it all, but it went together much easier than I thought. Having a block and guide only on one surface at each corner allowed me to slide and rotate each boom into position easily. Another aspect of such a design is I can slightly rotate each boom a degree or so for perfect vertical alignment before clamping down hard with the screws. One post design change I made was adding small wood pins on the outside corner where the boom is merely clamped and not blocked. I added the pins as reassurance against a catastrophic mishap if the clamping screws worked loose. I will loctite them as well.



Last in the build was the organization of the wiring. Most important, this included stacking the motor wires under the 'trailing edge' of the booms. I also rounded the 'leading edge' or top of the boom to reduce the splash obstruction. I've yet to get the wiring 'looking good' along the trailing edge, but that will be done soon.

If this design proves itself, and so far it flies outstandingly well, I may remake it with 2.0 and 2.5mm G10. That would drop the frame weight by half, which is currently 415g (with screws). As is, the AUW is just under 1180g with 4S. So I suspect I could get a G10 hex of this configuration down to a AUW of around 925g. I would also fix the booms in place by incorporating the slot and tab technique used in most frame plate and boom designs. I almost did use such on this one, but wanted to retain a nice clean upper plate for esthetics and gluing blocks and guides were easier, faster and required less precision. And of course, making the boom even thinner would shave off another percent or so of thrust column obstruction, increasing the TCE that much more.



The final calculation tells me, while this hex has six booms, it has only 20% more planform obstruction in the thrust column as the already excellent thrust column efficient 10x10mm carbon fiber boom tricopter , and only ~75% of the splash obstruction.

And before someone mentions it, yes... I did strongly consider adding a raised mini bulge texture to the boom surface. The air velocity is high enough, as well there is enough vertical surface area to make it worthwhile. The technique I considered would have been laying a hex-shaped screen with openings of around 2mm across the flat of the boom, then buttering 15 minute epoxy across the screen. Waiting until the epoxy had set to a rather firm gummy consistency, then gently lifting off the screen. Allowing enough time to for the hex-shaped 'mounds' of epoxy to flow, round and harden to a nice mound. This uniform texture would improve the TCE by improving the boundary layer off the boom, as well as serve as the stiffener tube. This is something that would require extra effort, or similar could easily be done on the boom material itself during a mass produced manufacturing process.

My initial maiden was a crash. But purely because of my confusion. I connected everything up rather late one night and since the ESC power and control wiring 'appeared' to come from the end of the boom's motor, because of the way the booms are inserted, (LOL even though I designed it) I inadvertently hooked them up offset by 60 degrees. It did this weird Euler's Disk thing and the flight lasted about a second.

Of course, the most important feature is, how does it fly when properly connected? So far, better than I imagined! Rock solid and liquid smooth off of Steveis' stock setting of 1.11S2.

Please excuse the crude taping of the stacked motor leads on the trailing edge and the orange orientation tape. As to the slow fly props, I will switch to carbon fiber as my confidence grows flying it. I will also do a much better job of affixing the wires now that I know it flies great. :cool:

[video=vimeo;89800473]https://vimeo.com/89800473[/video]

[video=vimeo;89814090]https://vimeo.com/89814090[/video]
 
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jhitesma

Some guy in the desert
Mentor
#3
Looks great. I could see that design being made out of a bunch of different materials or even 3d printed.

I'm half tempted to try and make a quad off that design setup to fly H style so it looks all crooked in the air just to mess with people :)
 

crlock

Senior Member
#5
allow me to take my hat off, that is an awesome design cyber, i'll definetly take in account the TCE for my next build, thank you.
 

FinalGlideAus

terrorizing squirrels
#6
Nice one Cyber. Looks cool!

Whilst building my FPV Tri I was thinking similiar things but got a headache when I the started incorporating forward/sideways/backwards flight into it. I'll be watching this one closely.
 

Cyberdactyl

Misfit Multirotor Monkey
#7
Thanks everyone.

I'm relieved it flies so solid. But one thing I'm perplexed about. Is it the configuration or the new KK2.1? This is my first KK2.1 and Steveis.
 

DDSFlyer

Senior Member
#9
Sweet looking hex! And mind boggling pains taking effort to put into the design and explanation of it...cheers and I bow to your knowledge.
 
#10
Thanks everyone.

I'm relieved it flies so solid. But one thing I'm perplexed about. Is it the configuration or the new KK2.1? This is my first KK2.1 and Steveis.
There is a lot of merit in a good frame. One that doesn't flex, one that doesn't have wires loose to rattle, and less thrust obstruction for less noise and turbulence. However, the KK2.1's sensors are faster and the calculation changes Steveis made is a substantial improvement as well.
 

Cyberdactyl

Misfit Multirotor Monkey
#11
Thanks again everyone. :)

Looks very cool! Can't wait to see how it flies!
You must be using a tablet or something Scratch, there's two videos linked.

I'll post some aerial video soon. It 'feels' and appears like there's little to no vibration, but I'll solid mount my 808# 11 to it for the acid test. :cool:

This is my first hex, and I was struck my how much downwash there is. Of course some of it is the fact that its AUW is almost 1200g, but I can feel it when it's hovering 30 feet over head.
 
#12
Thanks again everyone. :)



You must be using a tablet or something Scratch, there's two videos linked.

I'll post some aerial video soon. It 'feels' and appears like there's little to no vibration, but I'll solid mount my 808# 11 to it for the acid test. :cool:

This is my first hex, and I was struck my how much downwash there is. Of course some of it is the fact that its AUW is almost 1200g, but I can feel it when it's hovering 30 feet over head.
What the heck!

I don't see any videos or links... And yes, I'm using a tablet. I'll have to get to a PC and check me out.
 

cranialrectosis

Faster than a speeding face plant!
Mentor
#13
I have been looking at reducing TCE since I first saw and understood your Racing Quad and have been eagerly awaiting this thread since you started teasing it a week or two ago.

I rebuilt my Knuckle H Quad into an I quad as a result of your postings and theory on TCE and the difference for me is <>20% more power/battery life. All I did was get the knuckles and ESCs out of the thrust column and WOW what a difference.

This build takes TCE accomodation to the next level AND it provides a frame with the bulk of the weight in the center for better acro.

Last year, I tried the offset booms that run down the side of the center hub on my anycopter to increase the amount of wood in the center hub to make it less fragile and rely less on the two screws that attach booms to an anycopter's hub. I also screwed up the ESC config due to the offset and instaflipped my quad. :(

Ultimately, the Anycopter center hub was too small to make it work. You built your own center hub and included recessed slots in the center hub to fit the ESCs. Nice work around.

As per usual, CyberD, you have raised the bar on what we home builders can do and where beginners may move on to after we learn to build our first and fly.

I would love to see this build on the FT site proper. Your dialog on TCE is clear and concise and your build demonstrates your theory VERY well.

Well done, CyberD.
 
#14
CyberD, my hats off to you. This has been a pleasure to read and learn. Your build is amazing and the fact that you can bring it to fruition is amazing in itself as well. Love the build and am anxiously waiting for more.
 

Cyberdactyl

Misfit Multirotor Monkey
#18
I realized I didn't share any clear shots of it complete.

So far it's flying great. I changed to CF props. I'm very tempted to remake it with G10. Because of the substantial increase of G10 strength, I would keep the same motor-to-motor distance, but reduce the frame diameter, as well as the interior diameter would be enlarged, making the plates more like a thin ring. Also the booms would be ~60% thinner and around ~75% the height.

I really need to come up with a more attractive method to stack the wiring. I'm thinking of doing away with the bullet connectors, or at least shorten them and have them under the root of the prop where there's almost no thrust.

I would prefer to use the same harness and electronics. . . it was some effort. :eek: One thing I think I would do is extend the three legs another 25mm to get my GoPro underneath easily. As it is now, any mount would have it brushing the ground. I'll try and put my card cam and VTx on it this weekend, if I can find the time. . . it's so much fun to fly, I don't want to build at the moment. :rolleyes:







 

DDSFlyer

Senior Member
#19
That is such a sweet looking build. As far as the bullet connectors go I would agree with you, just some extra time soldering would either relocate the bullets or get rid of them entirely. Would you think of some extensions under the arms to hide the wires (like some plastic fins?) Maybe if you could make the arms out of G10 you could inset some grooves? It'd be hard to make them so thin though...just some thoughts
 

Cyberdactyl

Misfit Multirotor Monkey
#20
Absolutely DDSFlyer! :D I had similar ideas.

One was to build the booms from three epoxied G10 plates. Sandwich a ~2mm plate (or whatever the wire diameter is). The outer two would be pretty much as thin as I could find, maybe 0.5-0.7mm, or just enough that I could press the wires between the outer plates snug and tight. The wires would be totally hidden.

0.6mm + 0.6mm + 2.0mm x 20mm G10 would be plenty strong and stiff enough for a hex with 1300Kv motors. :cool:



Another, more radical idea, was to use strips of copper plate. . .maybe around 20mil and 4mm wide (or whatever width that would be required) and epoxy it to the plate and cover it in some fashion. . .with epoxy, tape, etc. Either way, the TCE would be so high as to be a removed variable in calculating the overall efficiency. I'm looking to have considerably better TCE than a clean round CF tube.
 
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