MOTION DESIGNER: Rigid Body Dynamics Trick

[Mike Pauza]

I have removed my initial text. The idea was sound, but MD can't seem to get it's act together. Apologies for the inconvienance.

-Mike

[HowardM]

what?! what?! dont do that!
hehe no really, what did you want to try, maybe i can get it to work?

[Mike Pauza]

Just sent you a test model Howard. :)

[Mike Pauza]

Well. I was not planning on exploring where and how MD fails, but that might be good for everybody. Let me set up some scenes this week and show everybody what I come up with.

-Mike

[Mike Pauza]

OK. After some more experimentation I came up with a fair example of how to approximate rigid bodys using MD. MD has some real problems however, so attempt something similiar at your own risk. :)



For this example I droped a coffee cup (see the reference object on the LightWave CD) on a table. I wanted to see if MD was capable of handeling both rigid and soft versions of such a simulation.

"Remeshing" the cup was the first thing I did. If you hope an object to behave like it's a real solid, then you need to give it a real structure...like your actually building something. Using a "poly or subpatch soup" simply won't cut it. To rebuild the cup I began by creating a cube primitive. My cube primitive is a simple cube that also has 2 point polygons connecting every possible point pair. This gives you a primitive with 6 faces, 12 edges, 12 face diagonals, and 4 inner diagonals. This cube arrangement is much more structurally stable than just a cube, and is a common primitive structural engineering packages use to simulate solids.

Anyway, once the cube primitive is made, you need to revisit your childhood block building days...just stack these suckers up to approximate your model...point pulling and copying/pasting along the way will speed you up and give you a better model though.

Once this structure was completed, I merged points and unified polygons so that the cup would be just one continuous object, not just a bunch of cubes...this makes all those cubes act as one in the simulation. I then deleted all the inner face geometry that would not be seen. Again, rebuilding your mesh is infinitely better than using just a "regular object".

I then imported the object into Layout and assigned it very stiff springs, low air resistance, and high viscosity values. For low gravity / low speeds, this arrangement worked very well (MD sure is flaky) and I achieved rigid body animation though soft body simulation and stiff springs. I ran the simulation again with lesser spring values to create a jello-like cup animation.

This simulation method has the potential to create both soft and rigid body animation..and can actually sometimes do a better job with rigids that most current rigid body simulators can, since few of them have the ability to produce rotational wobble (due to non symetric balancing) and spinning top / gyroscope type motions....but, the immediate value of this method of simulation/animation is currently limited because of MD's major accuracy problems. Hopefully in the future there will be something better than MD that will make this type of animation ndispensible.

-Mike

[Mike Pauza]

For the few folks following this thread, here are some pics of cube arrays working together. These sims generated at about 10 fps without collision. They were stable with small deformations.

If you can view DivX and can stand a several meg download email me (sharonpauza@aol.com) and I'll send some vids.

-Mike