[img]http://i.imgur.com/7NO2gvi.png[/img]
The idea was to use carbon fiber arrow shafts as the main structural elements, and to use full length tubes that go through the frame instead of cutting them in half and having 4 separate arms to try and attach/immobilize. I created a "frame sandwich" that holds the tubes in a stacked X shape. The top piece of the sandwich incorporates a vibration isolating mount for the flight controller, and the bottom piece fits the speed controller. More on those later.
[img]http://i.imgur.com/gI1d3Q5.png[/img]
The motors mount to a tube clamp that serves both purposes, instead of having a tube clamp separate from a motor mount that have to screw to each other. This is another advantage of the smaller diameter CF tubes, they fit inside of the motor's mounting pattern!
[img]http://i.imgur.com/dKy18xZ.png[/img][img]http://i.imgur.com/vPvXL1i.png[/img]
As you've probably noticed from the last picture, in all of the places where plastic needs to clamp to carbon, I've used o-rings around the tubing that fit into a groove on the mating plastic piece to isolate the plastic and carbon from hard contact with each other while keeping a tight grip. Hopefully this reduces vibration transfer.
The flight controller is floating on 3 platinum silicone dampers that I designed and printed a mold for: http://repables.com/r/431/ I arranged the isolators to all be 90 degrees away from each other so that differences in their strength wouldn't dampen vibration in any direction any differently. (54.74 degrees are the elevation angles of the 3 sided right angle pyramid model that I based this on, if you're curious. It's the same thing as one corner of a cube) I also made a "slot" for the flight controller circuit board to slide into out of silicone aquarium tubing both to dampen more vibration and because I'd heard horror stories about shorting the boards with metal hardware and I was too impatient to order plastic M3 screws
[img]http://i.imgur.com/4Og2iiT.png[/img]
The speed controller is a 4-in-1 unit called the QBrain that adds a little bit of weight, but tidies up the wiring and power distribution of the whole aircraft. Instead of having metal hardware to clamp it down, it fits between the main arm-body's bottom piece and the adapter for my tube landing gear. I added little captive slots in both pieces for zip-ties to clamp the ESC sandwich together. (So there's a flight controller / silicone tubing sandwich on top of a carbon fiber frame tube sandwich on top of a frame / ESC / landing gear sandwich.... I'm hungry)
[img]http://i.imgur.com/uAIXou0.png[/img]
Other design considerations that I included are that the frame sandwich uses a standard 45x45mm mounting hole pattern, sou you could conceivably add your own frame accessories from places like HobbyKing. I also made my landing gear mount tube spacing 60mm on center to match some of the off the shelf items out there (they do use a different diameter of tubing, but that would be an easy enough modification at a later date). I'm also trying to make cutouts in some of the pieces for wire management. You can see a little bit of that in the second picture down. Hopefully I end up with a pretty presentable finished product!
I have some of the last few parts designed roughly, but I need some more time to print them and tweak them before they'll be done enough for me to use. It's been a really fun project so far, and I hope it turns into a really cool copter when it's done. What do you think? Any design tips?
