generative modeling for Rhino
I had a quick look and it seems the error comes from how you set up the distance relationships. If I understand your sketch correctly you want the bracelet hinges to be on a constant distance from one another. In other words the relative distance from one hinge to the next should be like a series of identical arc chords on a circle perimeter.
Actually what you have set up is a constant stepping in global Y direction (your x in calcola_distanza) and a constant angle increment (the y in the same). When you take x*cos(y) it works only for the first instance, but doesn't work incrementally. Why that is you can see in the attached screenshot. For now I have only pointed out the error - sorry not very constructive! - but tomorrow I will make an attempt to solve it too!
There you go - not super elegant since I had to cull some final list items to get it to fit...Probably it can be done better given some more time. But it should work.
(My solution is at the bottom of your canvas, I didn't delete any of your other things)