Collision In A House Of Cards

[pabush20]

Here's my problem.

I'm want to make a huge house of cards, then dynamicaly knock it down. The problem is that I'm having problems keeping the cards from interpenitrating and well, making them act like cards.

Right now i'm using a basic card geometry built from a grid and extruded. The cards are arranged into a simple house, and brought into the DOP net as a RBDGlueObject. I've gotten decent results, but i've had to crank the collisions divisions on teh glue object to something like 80x80x80, but this will obviously result in LONG solver times for any good sized house. Is there a better way of doing this? I'm getting frustrated at Houdini for what seems like just ignoring the fact that the cards are solid. I thought that coliding a bunch of simple boxes would be easy, but I guess not.

Example:

[Ratman]

D'oh, looks like Craig just made my post irrelevant

I really need to find time to get back to H

[craig]

Is there a better way of doing this?

Yes!

First of all, in the Collision tab of your RBD Object, in the Surface sub-tab, set the Surface Representation to Edges (the default is Points). This is a little slower, but for boxes and box-like shapes, it's more accurate.

Then second, in the Volume sub-tab, you may be able to set the Mode to Implicit Box, depending on how you are constructing your stack of cards. This is both quicker and more accurate, and should allow you to have fewer subdivisions.

And then, speaking of subdivisions, look at the attached - it's better to compute the SDF first, then arrange the objects, rather than have to crank up the SDF resolution to huge numbers. This file shows the same arrangement of dominoes / cards, but one with a good representation and the other not so good.

Finally, in the RBD Solver, set the Minimum Substeps and Maximum Substeps to something bigger than 1, and/or increase the Resolve Penetration parameter to 1 or 2. Don't do this right away - try the above fixes first, and then only do this if you still have penetration problems, since these changes will slow down the simulation again - and you may not need them if you do the first 3 things.

badSDFs.hip

[pabush20]

Ok, let's see. I'm using edge representation, so that's covered. how many subdivisions should I have in my base card model to start with? Will a 6 sided object work, or should I divide it up more?

I've tried using the implicit bounding box, and for the collisions, it's worked well. However, I can't use it. I'm bringing in my geometry already set up into the DOP network, so when houdini calculates a bounding box for the angled card, the card cuts at a an angle through a huge box, making it unusable.

Is there some way I could apply the bounding information to the objects, THEN arrange them into the pattern I want?

I havn't done anything to the Substeps yet.

And forgive me, but I can't figure out what you are demonstrating in the .hip file you gave. What should I be looking for in it?

Thanks.

[craig]

[quote

Is there some way I could apply the bounding information to the objects, THEN arrange them into the pattern I want?

Yes, and that was the point of the file. If you set the display flag on the RBD Point Object, you'll notice that each of the dominoes has a good SDF representation, even though they are rotated around. If you turn off the option "Rotate to Normal" in the RBD Point Object parameters, you'll see what is happening. We set up the normals on the guide geometry, then bring in a domino for each point on the guide geo. Since the domino starts out in the "correct" orientation, it gets a good SDF. Then it gets rotated into the position and angle that we want.

Oh, and you don't need to divide up your original geometry at all - in fact, I think that may be part of your problem, since you need "watertight" geometry.

[pabush20]

Oh ok, I see it now. The bad example is what my cars look like alot, broken up bounding boxes.

I understand how you arranged the dominoes into the circle, stamping them to points in the circle, and adding a normal to change their direction.

My question now is how would I arrange my cards into a much more complex arrangement? I don't just want to make a pyramid house of cards, My goal was to make a castle of cards, and for that I don't think stamping to points would work.

...Unless, could I make a curve for every place I wanted a card then apply the point data to that? Or even take the location data from my arranged cards and use that?

Edit: My profess and I got something figured out. I can arrange the cards how I want just using curves and normals. One thing I didn't get to test before leaving Houdini, is will the cads stay leaning against each other without them being a glue object? or will I have to take some inventive measures, like setting their friction really high then dropping it, or turning on their dynamics at the last minute?

[craig]

One thing I didn't get to test before leaving Houdini, is will the cads stay leaning against each other without them being a glue object? or will I have to take some inventive measures, like setting their friction really high then dropping it, or turning on their dynamics at the last minute?

Well, they will stay leaning against each other if the arrangement is stable, just as you would expect with two real cards. Or you could do something tricky (which I suspect will be necessary, in fact) - though I would tend to simply turn gravity off until you want the sim to start doing something. Much easier than fooling around with friction or glue.