Maya nParticle instance rotation baking (I promise not the same old boring stuff)

Rigging
1

Hi. So here’s the conundrum. I am trying to make nParticles roll (yes roll, usually nparticles actually slide, fine if they’re a solid colour but not fine in this case) down a hill. I have an expression that takes velocity and uses this as a multiplier for the instanced geometry’s rotation. This works great and it looks pretty much like the particles roll nicely down the hill. Problem is when you cache the particles they no longer have velocity info and thus my expression for rotating my instances no longer works?

Any suggestions. Coincendatally has anyone else tried to make nparticles roll along a surface. I’ve got a quick and nasty solution for now but I’m planning on refining things so the particles roll along any surface perfectly.

Any help would be appreciated. And it’ll mean I get to go home tonight at some point.

Thanks.
Benjamin.

2

Have you changed the cache settings on the nParticle node? I believe by default it only caches position and colour.

3

Okay here’s my noob question. Where the heck do I change the nparticle cache settings? I’ve looked on the nucleus and the nparticleshape nodes I’ve checked through the menus I’ve read the help files I can’t see a way to do this. I’m just now trying to use the worldposition to get my velocity. After the particles are cached. Seems like a fairly simple procedure just sample the previos worldPos the the current world pos and use the distance between these to find the velocity. But if there is a way to just cache velocity please do tell.
Thanks.
Benjamin.

4

There is a section on the nParticleShape node called caching.