Summary

The C-Rotor is a VAWT where it is not 100% clear, where and when it was invented. There is a pretty good documentation on www.daswindrad.de (in German only).

You can either print the bottom part only once and use the cover, or you can alternatively print the bottom several times and stack them (twisted by 60 degrees), using the cover only on the uppermost part. I am using 2 bottoms and the thing spins nicely in my garden at pretty low winds.

I glued all parts together with semi liquid cyan acrylate glue.

It is designed for use with 608 ball bearings ( 8mm rod, 22 mm outer diameter, 7 mm high). I am only using 2 bearings and do not install one in the middle to prevent mechanical stress. The bearing covers are protecting the bearings a bit from rain.

Comparison to Ugrinsky Rotor:
I have the C-Rotor and the Ugrinsky running in my garden since a while now. I did not make measurements and I did not test them under a load. However, comparing them as free running rotors over a longer time in many different wind situations, the Ugrinsky provides significantly better performance. It starts spinning at lower wind speeds and produces higher RPM. The C-Rotor is an interesting design but the Ugrinsky is better, in my personal opinion.