Hard challenge - Rice paper lamp

[hpekristiansen]

This is just a challenge for those who find it fun. I do not need help with or the result of anything - though I am interested in how people solve the problem. -I was not able to do it perfectly myself.

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My rice paper lamp has a bamboo stick in a spiral!

How can one make a spiral going down and back up on a sphere, where the down and up parts are perfectly joined without kinks?

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My own attempts:

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My lamp with just a spiral down:

A better spiral (not perfect, because of an estimated angle - notice the kink at the bottom):

[etfrench]

The helix can't have a constant pitch for this.  One way to change the helix at the top and bottom is to fillet the joints.

[janie.ypan]

Could you possibly post a download file for this? Thanks

[JulianGroeli]

You'd probably need to create a series of points in another program and import them to get a mathematically correct spherical helix.

https://mathworld.wolfram.com/SphericalHelix.html

https://www.mathcurve.com/courbes3d.gb/helicespheric/helicespheric.shtml

If you just want to get close you could do something like this:

https://www.youtube.com/watch?v=RoRPrilJ388

[hpekristiansen]

It is no problem to create a spherical helix in Fusion - no need for the API or any external program. The challenge is about connecting the helix that goes down, and the one that goes up. That is why I consider this a hard challenge.

[hpekristiansen]

This is a challenge - I am interested in seeing how you will solve it.

Anyway, I have attached the files, if you need inspiration or a starting point. (Note that I was not able to solve the problem myself)

[JulianGroeli]

@hpekristiansen OK, thanks for the clarification. 

See attached model for a reasonably close approximation given the tools available in Fusion. We could get closer to perfect with a "3D spline on surface" tool, or an adjustable pitch option in the helix tool (as @etfrench suggested), as some higher end CAD tools have.