Introduction
There's lots of talk of folded wings on here. About 6 months ago, I had an idea for a combination wing spar and power distribution board (PDB). Racing quads regularly use their circuit board material as both a structural component and PDB, so why not bring that technology into the fixed wings? The idea was to both reduce/eliminate fishing wires through the wings, and to make the wings much stronger at the same time. I plan for my next build to be the Guinea Pig, so I figured I'd start there.
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The spar PDB is designed to be hot glued directly to the back side of the existing wing spar(s). This will provide a continuous spar for the center 22" of the wing. Fiberglass PCB material is fairly strong on edge. The example to the left shows the installed spar as seen through the center access hole. I chose to solder on the appropriate male/female pigtail connectors at each end. You could also use 3-pin headers. |
Introduction video:
Although I dabble in electronics, this is the first printed circuit board I have ever designed. If this is something that interests you, but you don't know where to start, I highly recommend Chris Gammell's Getting to Blinky 4.0 series. I have heard the tale that the first run of boards for a new design rarely works (typically due to some design error/oversight), so I was very pleased when I got back a fully functional set of boards. Once I had tested them electrically, it was time to test them physically.
Torture Testing
Learning from Nerdnic's issue of having to balance the weights on top of his speed wing while he was testing it, I created a platform that would hang below the wing for stability. The platform had ropes over the top of the wing in approximately the same location as the rubber bands from a typical fuselage would go over the wing. I figured this would give a somewhat realistic representation of having that much weight inside the plane. I'm not sure exactly where the wings should be supported for this type of testing, so I went with about halfway out. On the Guinea Pig wing, this is roughly where the motor pods are.
Conclusion
Based on the results of this testing, I will continue developing designs to fit other Flite Test models. I'm currently working through the plans, while making lots of measurements and notes, to figure out if I could make a more generic design that would fit several planes without sacrificing functionality. Feel free to shoot me a message on the forums if you have specific models fhat you'd like a spar PDB for, or if there are any additional/different features you'd like to see.
Technical Details
Dimensions: 21.9" (limited by the board manufacturer) x 0.7"
Thickness: 2mm (thickest available from board manufacturer)
Weight: 38g (1.3 oz)
| The center section of the PDB contains the inputs and jumpers. These are all accessible via the center cutout under the wing. Testing will determine if 3-pin headers will be too hard to reach. If so, right-angle headers or pigtails can be used instead. There are 4 separate inputs and outputs. Since this is designed for the Guinea Pig, there is an ESC and an aileron chanel for each wing. In reality, they can be used for whatever you want (flaps, retracts, etc.). Just match the labels up to know which input goes to which output. |  |
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The four pins in the middle of the board are a jumper block that can be used for a variety of functions. Placing a jumper across the "AIL Y" pins (see example to the right) will allow one(it doesn't matter which one) aileron input to be used. The signal will be sent to both aileron outputs. This mimics using a servo Y cable. This configuration would be used to control both ailerons with one channel on the receiver. In similar fashion, placing a jumper across the "ESC Y" pins will mimic using a Y cable on the ESC channel. Place a jumper here if differential thrust is not being used. Both motors would be controlled by a single channel on the receiver. |
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| The jumper pins are spaced so that they may be turned vertically as well. When installed in this orientation, either right input goes to both right outputs and either left input goes to both left outputs. This configuration would be used for dual ailerons? I'm not sure it's useful, but it would technically work, so I included it. |
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The illustration to the right shows the left outputs (assuming the spar is installed on the back of the stock foam spar). These are accessible via the power pod holes on the Guinea Pig. Notice there is an additional output here. There are exposed pads for 5V DC power at both ends of the PDB. Since they are being powered by the BEC, they are intended for faily low amperage accessories (e.g. wingtip LEDs). It is up to you to determine what you can safely power from these. Receiver brownouts are a bad thing! |
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I have half a dozen of these current prototypes available. If interested, PM me on the forums. I'm not trying to make big $$$ or anything. I'll pretty much let them go for postage and the price of the board. This would just get rolled back into the development fund for the next set of boards. They're not expensive, but it adds up due to the minimum order at the board manufacturer. Also, I'd like to get them in people's hands to get some real-world feedback. It's one thing to test them on the bench. It's quite another to see how they work in the real world.
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This (great) article does bring up one of the problems that I see with foam when used as a weight bearing substance in a wing spar application. It seems that because it is "homogenous" (my word for lack of directional characteristics; no grain, no directional fibers, no lamination capability, etc.) it will not have the same wing spar weight bearing capability that something like fiberglass (FR4, G10), carbon fiber, wood, etc. will have when properly applied. I am still dedicated to Adam's. However, has designs go faster and become larger, wing spars will benefit greatly by the addition of something like the FR4.
I wonder if FR4 segments, whose length seems to be limited by available material sizes, can be spliced together (butt-joint with a small segment of the same material overlaying the joint, front and back, with "bolts" through all three layers) or laminated with a staggered configuration (like when bricks are laid)?
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I'm working through the same thoughts of joints and splicing techniques as I'm thinking about dihedral wings. G10 is available in bigger pieces, but it's somewhat pricey.
http://www.usplastic.com/catalog/item.aspx?sku=47295
I figure that most of the FT fleet could benefit from a (up to) 22" spar, so it's not really all that limiting to me. I'm working on the flat wings first. If I can come up with a slightly more generic design, so it will fit at least a few planes, that should allow me to place bigger orders (assuming there's a market for such a thing). The price goes down rapidly when I order more. This should allow for a price somewhere around $10(including shipping). Flite Test has allowed me to get into a hobby that I honestly never thought I could afford. I have heard others say the same. I'm keeping that in mind as I try to make my contribution to the community.
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