Wire Legs for Multirotors

A really useful multirotor is big enough to carry a camera or FPV yet small enough to take with you everywhere. A quad or tri rotor can be made more compact by folding the arms but how about some legs that fold out of the way? As soon as I saw the Qube H-copter from Aerovironment, I knew I had my answer. I like the Qube's wire legs for several reasons:
  • they fold flat
  • they are strong & lightweight
  • they have a very small cross-section to the wind
  • they are reliable. There really isn't anything to break...bend maybe.
The Qube mounts folding wire legs to round arms using custom plastic collars. But I wanted to attach my wire legs to 1/2 inch square pine arms. The first two photos shows my solution. Two tie wraps hold each of two identical custom hinges to the wooden arm. No holes are drilled into the wooden arm itself so its structural integrity is not compromised. One hinge pivots a custom cross arm and the other hinge pivots the 5/32 inch diameter piano wire leg. The end of the legs have rubberized ball feet made from a bead of JB Weld surrounded by a 1/2 inch ball of OOGOO. You could also use Sugru.
You could make these legs a lot shorter. As it is, this tricopter will bounce like a ball on a hard landing. I have not broken any custom parts yet.
Where does the custom hinge and cross arm come from? From 3D printers at Shapeways.com. I drew both parts in the free version of Sketchup 8 in one night and spent another night preparing (debugging) the designs for 3D printers. The requirements for printing 3D objects are much more demanding than requirements for simply rendering a pretty picture. I used both MeshLab and NetFabb Studio. The Shapeways website has all the information you need to get and use free or open source 3D design software.
A single set of 2 hinges and one cross arm will cost you about $14 in materials at my Shapeways store. I offer the design for free - I do not know if it is protected by any patents.
The $14 is not bad for a precision prototype but too expensive to use on a regular basis.  In my next post, I will show you how I made a silicon rubber mold from these 3D printed parts and knocked out strong epoxy parts for pennies.
Build log
3689514390?profile=originalA little background on this tricopter. I have an APM1 quad and a KK2 quad but this smaller 3DCC tricopter is great for sport flying because its yaw response is so good. It weighs - with an 800mAh 2S battery (but no camera) - 17 oz and flies for about 5 minutes. It flies faster, longer, and warmer with 1000mAh 3S battery but is still very lightweight. I keep my pockets filled with charged batteries.
The thing I like best about this tricopter is that it crashes into trees and falls out of the sky (a lot) but it rarely breaks anything more than a propeller (if that). I spend more time flying (aggressively) and less time repairing.  I fly HD video cameras and FPV with it.
Frame laser cut by Ponoko from Improved RC Explorer pattern by colorex.3689514413?profile=original
1/2 in. square pine arms, 10.5 in. long
3x 8045 slow fly propeller
OpenPilot 3DCC
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  • I was looking over alternate leg solutions this week also. Dubro makes a .60 size laminate 'bow leg' part for planes that coud be modified for multirotor use.

    Even when we are all 3D printing our aircraft, this topic will periodically pop up. It is healthy for the craft and shows us what the perspective of others can bring to the building table.

    Well done.


  • Nice, I like it.  I've also played around with a wire landing skid at the back of my heli to keep the tail rotor out of the dirt.  But mounting is always a problem.  I like the way yours collapses.  Hard to imagine AV would have a patent on that, but you never know I guess.

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