CineRace20 Sturdy Frame

**Update 2022-03-15**: Uploaded new model CineRace20_Frame_TPU_2022_02_14.stl with
* improved printability
* better tolerances for easier assembly
* stabilized conections of ducts and motor mounts

After many testing flights, I'm finally convinced that the design indeed is by far more sturdy than the original frame. Since I switched to the 3D printed version I never again had to reassemble my CineRace (like I had to before almost every time I was flying it).

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I was unsatisfied with the stability of the original Cinerace20 frames made from hard plastic. So I tried to come up with a more stable variant.

For maximum stability, I printed the part as a composite of PETG (black) and TPU (red). However, it should be possible to print it from PETG or TPU only.

**This is work in progress! I am happy with the result so far - it didn't break yet. :-D. However, there are drawbacks:**
1. Increased weight. Due to the thickness, the total weight of the copter is approx. 20g