Follow position and rotation in dynamics

[rafaelmoco]

Hi guys;

I'm a Cinema 4D user trying to migrate to Houdini. In the past days, I tried to replicate a very common o effect in Cinema 4D dynamics. In there, you can use follow position and follow rotation to try to restrain a dynamic object in your original orientation and position

 

I'm tried to replicate this in Houdini, but without success. Maybe I'm trying to figure out myself using the wrong tools, or searching for the wrong terms in Internet, but I still can't find a good solution

I made a video, showing the effect in C4D. It's very simple, but a fast way to fill volumes with objects, without any collision 

 

 

Any thoughts? 

[mestela]

Interesting question. Had a go, I'm sure there's a more efficient way of doing this.

Seems that Bullet fights hard against this problem; from what I've read it detects if shapes intersect at the start of a sim, it treats them as glued together, which is exactly what you're trying to avoid here. 

At first I thought 'ah, I'll scale the shapes really small at first, or shrink their collision geo really small, and quickly expand to full size', but there doesn't appear to be a way to do this with Bullet either.

In the end I gave all the objects a starting velocity away from the origin, but then give them a force to try and attract them back to their starting position. This bit of jostling is enough to keep Bullet happy, and the shapes re-settle into a deintersected arrangement, more or less.

rbd_deintersect.hipnc

[rafaelmoco]

Thanks for the help!

For sure, is a clever way to deal with this "problem". I didn't know bullet treated intersecting shapes as glued together.  Actually it's rings some bells for me in other problems I was having with simulations

Thanks again!

[mestela]

Huh, the ghost of odforce posts of the past came to visit me. There's a better way:

 

http://www.tokeru.com/cgwiki/?title=HoudiniDops#RBD_deintersect_the_easy_way

[Atom]

I was playing around with trying to mix the two styles but I still have this initial explosion of particles before things settle down. What causes that? Are two sets of RBD objects being created on top of one another? Even if I zero velocity I still get this extreme force outward.

ap_rbd_deintersect.hipnc

Edited January 16, 2019 by Atom

[Atom]

Ok, I think I figured it out. After looking over Matt's scene I noticed he is skipping the first frame with a conditional switch. Once I put that in place it started behaving correctly.

Edited January 22, 2019 by Atom

[sandidolsak]

Hello,

does anyone have an idea how to do the same with a simulation where particles are advected and spawned (added) each frame?
So you would have an object that is dynamic following a particle around with new object added for each new particle created.

Thanks,

Sandi