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Xcompact project. Portable and flexible DIY frame.

Posted by Denis Krylov on December 4, 2015 at 5:00am

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Hello everyone,

I would like to share with you my latest project. Currently I am at the crossroads and would appreciate any feedback.

The main goal was to design a truly portable drone that fits into a backpack. I was unhappy with the foldable frames on the market, as they were all too large. The ones which fold in horizontal plane still have a problem with landing gear, and in umbrella-type frames you need to sacrifice the space for electronics. I ended up with such requirements:

  • Compactly folding core

  • Arms fixed with a screw (no plastic clips)

  • Detachable legs  

I've decided to use two 16 mm tubes as a frame core in order to make it strong and flexible. I've made two modules for front and rear arms. PMMA plastic is used to reduce the prototype costs (however, 3mm plates are surprisingly strong), later I am planning to switch to carbon fiber. The most compact folding is achieved when arms are above each other.

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Firstly I was attaching legs to the core tubes (PVC plastic). But then I realized that they can be fixed with the same screw as arms.  And this shortens the assembly time. Legs can have different length, mine are short just because I ran out of tubes.

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Following the modern trend I added a vibration isolated plate. The number of damping balls can vary depending on the load. Some balls have flexible position in order to fit to different core sizes.

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My current frame size is 710mm and it folds into ~ 370x170x120 mm, which is less than 8L volume.

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While the weather was not good for flying I decided to collect my thoughts. The frame is portable and also turned out to be quite flexible. Several holes can be drilled for the arm-fixing screw -> several square frames can be build from the same parts.

I started to dream about "Lego" for drones. The main point about "Lego" is that from the same parts one can build various things. There are some plastic analogues like RotorBits, however I was considering only carbon fiber and aluminum parts. Currently with my friends we are working on such set of universal parts for multirotors. Here are the characteristics we implemented in the kit:

  • Frame size D: 400 - 800 mm (8 - 18 inch props)
  • Folded size: L x 160 x 120 mm (L ~ D/2 + 60)
  • Variable arm angle, > 10 different square frames
  • Detachable legs
  • Arms and legs are fixed with an M4/M5 screw 
  • Quad or X8 configurations
  • Vibration isolated center plate
  • Different camera layouts
  • Optional: Retractable landing gear, vibration damping motor mounts, prop guards, integrated PCB

Personally I am really happy with the result.

Even my large 710 mm drone fits into a backpack. The frame is easily customizable: in order to change the size one simply slides the arm-modules, also variable parts can be attached to core tubes or to the center plate.

At this point I would like to hear your opinion. Did you also think about a truly portable DIY drone? Which characteristics would be the most important?

 

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Comments

  • Gary McCray December 4, 2015 at 2:16pm

    Hi Denis, 

    CNC milling aluminum is easy these days with proper carbide coated bits wet or dry.

    But CF plate really does require specialized micro crystalline diamond coated bits, carbide, just doesn't cut it and leaves a ragged edge.

    You might also look into G10/FR4 phenolic fiberglass plate, it is very strong and doesn't shatter or break as easily as CF plate (it is slightly easier to machine than CF plate).

    I use it in my CF tube H copters.

    Best,

    Gary

  • Denis Krylov December 4, 2015 at 1:59pm
    Gary, yes, I was greedy with material on the edges. Still the frame survived after a couple of crashes.
    I consider CF plates to be my next step. I was thinking about CNC milling both for CF and alu parts.
  • Gary McCray December 4, 2015 at 11:20am

    Great design, very innovative.

    I would suggest that the deployed inner frame plate outer arm retention screw holes may not have enough material at the outside of them for best resistance to less than perfect landings.

    easily solved by adding another quarter inch at the outside of the frame plates.

    Possibly the frame plates would be better made from CF plate or G10 or FR4 fiberglass.

    I have found CF plate, G10 or FR fiberglass can be reasonably routed with proper tooling (polycrystaline diamond coating) and is easily straight cut with a wet circular diamond saw (tile saw).

    Best Regards,

    Gary

  • Denis Krylov December 4, 2015 at 9:51am
    Alp, the prototype weights around 700-800 g. depending on the configuration.
    CFK version will be around 500-600.
  • Denis Krylov December 4, 2015 at 9:31am
    Motors are 380KV. 7 are good, one is slightly unbalanced (not sure if it was from the beginning or after a hard crash). Unfortunately, I can't compare
  • Denis Krylov December 4, 2015 at 9:25am
    Tony, I haven't done vibration tests yet. Honestly, I think that with plastic plates you won't see any reasonable damping.
    They are too soft. And with CFK I will definitely do some tests.
  • eUGENE December 4, 2015 at 7:50am

    Hi Denis,

    Its cool in my opinion. What about the weight?

This reply was deleted.