Cardan shaft, cardan coupling lego technic compatible

Cardan shaft cooperating with lego technics. This is the most difficult project that I managed to run on a 3d printer. The biggest problems caused me retraction, which deformed small elements, which is why I used an element that should be removed after the printout. It does not change the fact that the shaft is not able to carry large overloads and there are problems with moving the drive after exceeding the angle of 40.