Re: A couple of RBD questions

["Morten Bartholdy" <xsi(at)colorshopvfx.dk>]

Thanks for the tips Kim. I am using 5.11 - 6.01, while it offered interesting new controls, was notoriously unstable - like it would dissapear in a flash when starting collisions sometimes...

 

I actually have been turning active/passive but find it unstable in the sense that my pieces pop to world center when activated - sometimes! But like you say, when it starts reacting sort of predictably it gets quite fun. What I have found though, especially in 6.01 is that cache seems to get half stuck sometimes. After removing rigid body properties and deleting caches, then reapplying rigid bodies, the new simulation would sort of remember the old activation point in time :/ So no 6.01 this time around either.

 

It sort of works now in 5.11 and I think I will plot it and take it by hand from now on. One thing I would wish for now is a way to select multiple objects and constrain them to nearest object. That would save me some time.

 

- MB

 

 

 

 

----- Original Message -----

From: Kim Aldis

To: XSI(at)Softimage.COM

Sent: Wednesday, June 27, 2007 12:52 PM

Subject: RE: A couple of RBD questions

If you?re using 5.11 or earlier it?s important you don?t parent any of your rigid bodies.

 

If you?re  doing a wrecking ball type thing, point of impact to start the breaking, I had a good deal of success animating active/passive on the blocks using their distance from a centre to decide the point in time at which to make the switch.  You may just get away with making the switch on all of them at the same time, when the wall starts breaking.

 

As far as actual shape/convex hull is concerned, you?re kind of stuck whichever way you go. If you make the blocks slightly small you get a kick as they settle, if you use convex hull you?re guaranteed interpenetration on anything except rectangular blocks.

 

It is workable though, I?ve had a lot of fun with exploding walls and things. The (very grumpy) chairman of the AE preservation society over there next to Alan did some pretty nice stuff with exploding buildings too.

 

From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Morten Bartholdy
Sent: 27 June 2007 11:09
To: XSI(at)Softimage.COM
Subject: Re: A couple of RBD questions

 

Thanks for the info Peter. Upon further investigation I think my problem lies int the fact that RBD seems to work poorly with actual shape vs. much better with convex hull. With actual shape I have to freeze transformations putting each wall piece center in the world centre, which makes subsequent plotting useless. If I dont do this my wall pieces fall through each other and start simulating from somewhere inside my wall breaking passive rigid body, which provides a useless sim. In a simple scene I can get everything to work nicely with simple rectangular bricks and convex hull, and even collide and react to changes in RBD settings in predictable manners. Not quite so with actual shape. I am afraid I will have to rebuild my collision objects so they will work with convex hull and fix the inaccuracies by hand - damn!

 

Morten Bartholdy
3D & VFX Artist

 

----- Original Message -----

From: peter boeykens

To: XSI(at)Softimage.COM

Sent: Tuesday, June 26, 2007 7:14 PM

Subject: Re: A couple of RBD questions

 

Im pretty sure I've done just this, replacing simulated RBD's with nulls, getting the animation as transforms to the nulls, and then parenting the highres geometry under the nulls, and it was on a few thousand, without any scripting and it didnt take all that long.

I'd recommend trying a scene with just 2 or 3 objects to try out what is the right order of doing things. I remember it being a bit quirky, and needing a few attempts to get it working.

 

I think you have to go to the beginning of your simulation, turn caching on and then run the simulation.

when you're at the end you can scroll through the timeline at will, proving that it does pick up the caches allright. Once you have those you can plot the transforms, and from there its whatever way suits you to get those fcurves onto the objects you want.

I dont recall if I constrained nulls to the rbd's and plotted those, or if I plotted the rbds themselves and copied fcurves across. But I think but worked, once you have the caches, and no sooner.

 

 

----- Original Message -----

From: Morten Bartholdy

To: XSI(at)Softimage.COM

Sent: Tuesday, June 26, 2007 3:05 PM

Subject: A couple of RBD questions

 

I am breaking a wall with RBD and am using a set of pieces which are slightly smaller then the ones I want to render so I can avoid interpenetration in the beginnnig of the simulation. Now I know I can transfer the cache to a clip in the mixer, but if I want to copy this motion to each renderpiece or constrain these to the RBD'ed pieces it starts looking a bit complicated. If I create a cluster with center my RBD is shot. Next thing I would try is to multi point constrain my renderpiece to the RBD piece but this requires me to create three clusters on each RBD piece and then three point constrain each renderpiece to those. Please tell me Softimage thought of easier ways to handle something like this with up towards 100 separate RBD pieces???

 

Another thing is my pieces tend to explode a bit away from each other even though I have made absolutely sure there are no interpenetrations at the bewginning of the sim. I have increased simulation and collision acuracy to very high levels without quite getting rid of this behaviour. Also I have elasticity all the way down to 0.001 since these are supposed to look like concrete pieces, but I still get weird styrofoam like bounce and sploinng-like fly away behaviour from the odd piece when it collides with something again after landing on the ground. I have tried messing with friction parameters without much luck.

 

I am guessing there a tips and tricks I still need to learn about the wonderful world of RBD'ing so if someone knows a way to dampen simulation collisions I would be happy to hear them, if someone in the know cares to share some insight.

 

Thanks!

 

Morten Bartholdy
3D & VFX Artist