Tube Quad Design – Fail

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I have been designing and building racing quadcopters for a year or so now.  A lot of times things don’t go as planned and there always is improvements… instead of trashing the idea I thought I’d put it out there for others to look at!  The design is downloadable here if you have Autodesk Fusion 360: http://a360.co/2rBpIk5

Tube Quad design.

I decided to focus on 10mm carbon tube for this design.

Benefits

Cheap – $21 (http://amzn.to/2qlQ5Gc) for enough carbon for 2 quads with 5 inch

Aerodynamic – Flat piece of carbon used normally sucks for aerodynamics.  All the thrust that the props are producing hits a square area and creates a ton of turbulence.  Not to mention that the quad is moving through the air with a couple of flat pieces sticking in the wind.

Ridgid – The tube has no flex to it.

Fits around a 22xx motor perfectly.  Correctly orientated the motor screws are a little under 10mm apart.  Perfect for a slight interference fit.

Softmount Everything – Since I was using TPU to isolate the motor both right on the motor mount and connecting to the main body.  It would reduce gyro noise to a minimum.  After up and flying and looking at betaflight blackbox logs, the noise was amazingly reduced.

Propsize – Very easy to change from 5 inch to 6 inch, just have pull the motors out a little bit.

 

The Build

 

3d printable mounts were designed to hold the carbon tubes in places.  A 4in1 esc design was strongly prefered so a ESC wouldn’t have to hang out on the tube.

For quick prototyping.  Grabbed a few Hyphy 3d printed designs for camera and antenna mount.  Found here: https://www.thingiverse.com/thing:1926684 and https://www.thingiverse.com/thing:1926684

Use my CNC router to cut out the top and bottom plates out of 2mm carbon that I had handy already.

 

Also took a piece of scrap carbon from another quad for the top plate.  Drilled holes with a hand drill to make them line up.

One hold on each arm had to be drilled to hold the center tube in place.  This was easy to due since it was guided by the TPU in place.

 

After that, put it all together all the electrics which was an easy build due to the 4in1 esc and omnibus flight controller board.

 

The Flight

After finishing putting it all together, the first of the drawbacks started to come out.  It was a heavy build, I overdid it on the TPU and there was probably 10-30g of extra material that was adding to the weight.  The actually flight was very very good, but you could notice the extra weight.  During this time, I optimized TPU to reduce it as much as possible.

Every crash knocked the motors on the TPU mounts out of alignment.  It turns out the TPU and interference fit was not enough to keep everything from moving in a crash.

The final issue.  Took it to a race and cracked one of the tubes where bolt was through the carbon on the main plate.  It was still fliable until I had another crash which broke the tube.

 

The Verdict

  • The carbon tubes aren’t strong enough to handle the crashes.  Maybe 12mm tube or better quality 10mm tube would work, but in its current form… it won’t work!
  • TPU is heavy.  Reduce it as much as possible.
  • Round tubes are hard to mount.

 

The Future

Since I decided I didn’t like the tube design there are lots of other great designs out there.  Here are a couple.

http://hyphymultirotors.com/product/le-hyphy

http://www.armattanquads.com/scx-200-1/

https://xlabs.myshopify.com/collections/all/products/shrike-style

I have a SCX-200 right now and am getting a hyphy frame.

 

 

Keep building!

 

 

 

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