I'm trying to slice an object during a rigid body simulation.

imagine a fruit falling through a grid of laser beam. the object is supposed to be sliced in multiple pieces. i can't pre-crack the geometry as the fragments depend on how the object hits the lasers.

in the attached testscene, i already have a sphere falling through 3 “knifes”, it gets cut into 4 pieces using a sop solver with a cookie. inside the sop solver i'm also creating groups for the separated pieces using connectivity/partition

the problem now is that all the pieces are still simulated as one rigid body object. the solution i imagine is to dynamically create new rbd objects whenever there are new groups in the object's geometry, so far i haven't been successful…

now first: i would like to know from someone with more experience if this is maybe ridiculously simple, very complicated, or impossible for some reason.

secondly: i attached the scene that i use as the starting point of my tests for anyone who wants to take the challenge.

I'm doing something similar right now but with Wires. It's definitely not simple However, for RBD, I don't think it's impossible either. Don't be afraid of multiple solvers! I've already got 4 SOP Solvers with 4 SOP networks doing various things (sorry, it's for a real job, can't be more specific) plus the Wire solver and a Copy Solver.

Hope that helps I don't really have time to try it out, sounds like a fun challenge though.

Cheers,

Peter B

The other thing about simulations like this (and I'm saying this without having looked at your example or anything responsible like that ) is that it is often easier to break it down into passes. So first you create an animation that has the fruit falling. Then you use that as input to another pass (another hip file, potentially) that uses cookie to split the objects. Then you use that to create your simulation. etc.

Trying to make one big amazing network that solves the whole problem at once can sometimes make it too complex. Or maybe it's just my smaller, compartmentalized brain. But consider that as a possible approach.

At least your brain has compartments, mine is just smaller but with a single compartment. Hence the uber-network

Yes, you're quite correct, I should be breaking it down into passes, somehow. I've spent so long on this path that the branch to the path less taken is far, far behind me, obscured in snow and likely has the Black Knight on it, waiting to cut my legs off. Or something…

Cheers,

Peter B

thanks for your tips guys

pbowmar: what you wrote sounds a lot like what i've been fooling around with, as of yet without success… i have to investigate some more in this direction!

craig: valid, very valid. if i was smarter i would go down this path
but i still have hopes that this doesn't require some huge crazy network to do it! i'm trying to feel out the borders of what's possible with dops, and i think with this i found something ‘hard’ that is hard in houdini. most of the time hard things are actually easy..

the danger of getting my legs cut off if i continue on this path scared me a little though…

maybe i can try to do this in multiple passes but still kind of procedural. the problem is that for what i have in mind, i actually need to do it with something more complex than a laser or knife and also with a lot of rbd's