Hi!

I'm facing a problem, and can't figure it out alone… (yes, that mostly always the reason someone post here i guess :p)

I'm trying to make some particles firstly go in a spiral motion around a curve (I've succeeded in this part with a line with edge_dir, then a wrangle with pcopen, and some cross products), but i want at some point (based on age) for the particles to end in tiny spirals… Like the effect in the frozen movie for exemple.

As my particles are firt moving in the XZ plane, i just made a first test by cross-producting the vel by an {0,1,0} vector, but evidently, as soon as my particles move in the Y direction, this method stop working!

So i think i just need some “up vector” from the particles, but that were i'm stuck!
The particles could be with any velocity direction and “spiraling” in any direction too…

So, does anyone knows how i could find this upvector, which should be pointing down when the particle is at the “top” of a spiral and need to get down, etc?

I hope i explained it well enough, sorry for my english!

Thanks a lot in advance!
François.