Hi everyone,

I've post this in the apprentice section but maybe it was not the right place, so I repost it here.

I'm trying to control the rotation of my particles when a collision append.
I've uploaded an image to explain this simple case.
At collision, a particle is re-oriented to the new direction, but it's an “On-Off” effect.

I would like to control the rotation after collision to damp the rotation on several frame.

Am I clear enough ? i hope.

Thx for your help.

You can use the soft limit POP but it is only useful for simple collisions.

Here is another method that should work with all kinds of geometry. It calculates the distance to the nearest collisiongeo point and switches on an attractor force.

You need to enter the force by hand.

I tried to calculate the force with a voppop (needs some vector math) but I don't know how to get parameters from external sop nodes into the vops. I thought op: would do the trick but I am missing something.

milwatt
Hi everyone,

I've post this in the apprentice section but maybe it was not the right place, so I repost it here.

I'm trying to control the rotation of my particles when a collision append.
I've uploaded an image to explain this simple case.
At collision, a particle is re-oriented to the new direction, but it's an “On-Off” effect.

I would like to control the rotation after collision to damp the rotation on several frame.

Am I clear enough ? i hope.

Thx for your help.

Sounds like something you could do in CHOPS.

Sounds like something you could do in CHOPS.

Maybe. I want to try it.

Does anybody know how to get at the particles frame? We can display it as gnomon but I can't find out what it's called.

I believe the gnomon is just a reflection of the particle's velocity vector (Z), the up vector (Y) and the cross product of the two (X). The velocity is no problem and there's the Up Vector POP for that. You can do the cross product of those in expressions, VOPs or CHOPs.

Thx guys.

Soothsayer : Thx for the scene (it's so cool for a noob like to get a scene to really understand houdini's philosophy). It's not really what I want to do, but it's really interesting.

mawi : maybe, maybe, it's like science fiction for me . If you could post a little exemple, like Soothsayer did, it would be nice (If you got time ).

Graham : I've try with UpVector and Rotate, but I don't really got the control I want (due to my lack of knowledge with Houdini).

My sketch is a little bit too simple, I would like to be able to control rotation in any axis, to damp or accelerate rotation, and fix the fact that when a collision occurs particles a ‘poping’ in the new velocity direction.
(In maya I combine before dynamics and after dynamics expressions to modify particles the way I want).