View Full Version : Need help with rigid body friction parameters

01 January 2009, 07:55 PM
Hello everyone,

I've been using XSI for over a year now, but only recently have I begun to learn how to use rigid body dynamics and the simulation settings.

I know it's cliche and almost taboo, but to learn how to use the system I'm blowing up a box.

It's not the n00bie 'Oh man I'm totally gonna animate explosions!' ideology, but rather I thought it would be a good exercise to learn how XSI's rigid body system works.

So far so good. I downloaded the Shatter script from , used it to break apart a polygon mesh, applied the shattered pieces to a rigid body state, set a grid below it to a passive state, and simulated it. The result was the exploded pieces falling to the grid and stopping.

So far so good.

I then made another passive object, set it invisible, and had it slam into the shattered parts, thus throwing them outward in an explosion.

That result was satisfactory. So I have an exploding box, oustanding.

I'm happy with the results, but I can't tweak it just right. The problem that I'm having is that the rigid bodies, as they fly away and hit the 'ground' grid, they slide as if they're on ice.

I can't seem to get friction working properly. I've tried adjusting the static and dynamic friction properties for each of the rigid body pieces, as well as adjusting said friction properties on the passive grid. Neither adjustment made an effect on the actual simulation.

So how exactly do I up the friction? I would like the pieces to slide to a quicker stop and possibly roll a little, as if they were hitting grass and not ice.

Here's a test render. You're looking for the final 3 clips primarily. You'll notice the fragments hit the ground and continue sliding for a bit:

Any suggestions?

01 January 2009, 06:01 PM
I think your problem is not in the friction, but in the Mass and Density of your objects.

If you find the explosions to be fine, than just animated the Mass so it gets heavier when it its the ground.

You find the Mass in the Rigid Body property of the object.

01 January 2009, 07:30 PM
Cool, thank you very much!

Mass tweaks worked well. It also seems that there was a memory issue that was keeping me from seeing progress. I restarted XSI when I got home from work, and the new friction settings had been applied and looked much better!

Thanks a lot!

Now, a new question: Here's an updated render with the passive grid set to invisible:

A lot of the rigid body pieces are falling through the grid, some after having lain upon it for a number of seconds (notice the large piece falling through towards the end).

Is there any way to prevent this? Perhaps it's extraneous gravity pulling it through? Gravity force aplitutde is set to 98.1, which I believe is a rather normal amplitude.

Perhaps object mass?

01 January 2009, 02:32 AM
I'm not sure, but try to subdivide the grid once or twice. I'm not sure if it'll affect the results, though.

01 January 2009, 01:46 PM
Try to use a box instead of grid.

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