250 Mini Quadcopter evolution

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Crashed and broken

The current incarnation of my mini quad.
This quad started off as a Turnigy Micro quad V2 from HobbyKing. Being my first quad, I crashed that frame more times then I can count and fixing it became increasingly more difficult. The original frame has many weak spots in the frame design, and breaking it is just a matter of time (if you crash a lot). I never had a chance to properly tune the KK2 controller board, hence the ample crashing in my back yard. 🙂

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Shiny new printed frame

In that summer (of 2013) I decided I needed a new frame so I designed and 3D printed a new frame. At the same time as the transplant to the red frame took place, I also changed the brain of the quad. I bought and installed a CC3D controller from OpenPilot. This frame was based on the design from this Flame Wheel design from Thingiverse.
With the plastic frame and the CC3D I began to learn to fly the quad, mind you there was still a lot of broken propellers (read; crashing). There were many attempts to tune the CC3D board but there were always some twitches present in the flying characteristics that I could never sort out.
Midsummer 2013 I bought a X1. I read about it being inexpensive (which it was at about $40 shipped) and it incredibly stable and easy to fly. For me the X1 set the standard I would be aiming towards in terms of stability and ease of flying.

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In august I redesigned the frame to take out some weight and make it stronger at the same time.
I decided to go with a carbon fiber boom design, and use 3d printed parts only where connections needed to be made.

The result of a few weeks of work was this new quad which ended up being lightern the the original frame and WAY stronger and more resilient to crashes.

The motors mount through a small adapter to the square tube, and the square tubes attach to the frame through another adapter. One of my design criteria was that I didn’t want to glue the booms to make it easy to fix.

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motor mount 01The center body that receives the four booms is printed in several pieces. This was due to the fact that the FDM (Fused Deposition Method of filament laying) process of building parts has certain a certain weakness when it comes to the material strength between the deposited layers. If I was going to grow/build the part as one component, it would very likely break. By building the assembly in several parts (that get glued together in the end) strength is catered for in every component.

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And so far, after many more crashes, hard landings and broken props, the carbon fiber boom seems to be the weak point. The square tube I used is 6mmx6mm Carbon tube from HobbyKing. The problem with it is that the tube has very little rigidity in torsion, and once it sustains a good hit that twists the boom, the tube delaminates causing it to loose nearly all it’s torsional strength. It still resists bending, but torsionaly it’s a wet noodle.
If I could only find aluminum tubes, everything would be awesome.
Not cool.
The quad still flies.

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