View Full Version : Seeking dynamics help

05-21-2004, 01:10 AM
This thread may not belong here, I wasn't sure where to post it. Mods: feel free to move it.

Something isn't getting through my thick skull. I've been over just about every setting I can think of.

I have a ball that rolls down a ramp, then it falls onto a series of little trampolines. The trampolines have cloth effects and collision applied to them. They bounce the ball just fine, but they aren't effected by it. They do that "starting sag", but then they act like rigid collision objects from then on out.

This isn't for a job, just playing. I'm just trying to cram all this info into my head for when a real job comes along.

If anyone wants to play wth the scene, let me know if you come up with anything that makes the cloth act like cloth.


Thanks in advance, guys. I guess we're all pretty much learning this at the same time, without a manual to back us up =)

05-21-2004, 06:45 AM
You can get cloth and hard to interact, but you have to layer the dynamics with collisions on both objects. Look at this demo scene where the ball impacts on the cloth, you get little dimple where it hits...

I've noticed lots of little inconsistencies withing the dynamics as well, for example gravity you can set in Hard or cloth FX, but not in Soft, but you can specify a vector in cloth for gravity, whereas hard only allows up or down. You can kind of get Soft to react to gravity, but setting it in the Deformer tab, under Keep root, but it all seems a bit muddled. The manual isn't a big help as it seems to have been written by Ino without much in the way of after translation editing...

05-21-2004, 02:11 PM
Actually, Dodgy, your file does the same thing mine does.

The ball reacts to the cloth, but the cloth doesn't react to the ball. If you remove all effects from the ball, the cloth does the exact same thing.

I've seen cloth react to other objects, I can't understand what the problem is here.


05-21-2004, 02:27 PM
I can't get cloth to react at all, even with a simple scene. 1 sheet, 1 ball.

Anyone have the secret decoder ring handy?

05-21-2004, 03:32 PM
Hold on, on the interaction setting for the box, I had it set to Box, this makes a difference. I think..... :)

Definitely try it with a box, it's much easier to see if something's happening...

Hmm, when I push up the collision distance (on the box) way away from the box I have dropping into my cloth, I definitely get dimples in the sheet, but when I drop it back to 0m I don't get the dimples. This is with both sheet + box with separate collision FX on.

Fiddling with the Collision radius seems to alter the interaction between the box and cloth from no dimpling to getting so excited that the box gets flung off the cloth, with dimpling in the middle somewhere.

05-21-2004, 05:14 PM
I just had a hell of a time on a project that required dumping a load of bricks out of a wheelbarrow, then into the back of a dump truck, driven a short distance, then dumped from the dump truck. Whew.

Didn't seem particularly difficult initially, but the biggest problems I had were 1) getting the bricks to settle down (stop bouncing and jittering), and 2) getting them to stay in the containers and NOT drop out of the bottom (or the sides) - even with collision probability cranked up to 200 or 300% (though I don't see the point of a setting above 100%).

The one saving grace is that editing motion after the simulation is is completd is pretty easy, so deleting stray bricks and pushing thhem back within bounds was pretty easy, but the simulation itself was horrendously difficult to acheive results that were worth editing.

I give it a C- . Needs lots of work.

05-22-2004, 11:23 AM
Hey Michael,

I've been playing around with your scene, and I've just scratched the surface here, but I can say that to some extent I've gotten it to work the way you want.

First, the trampolines need to be subdivided a few times to give it enough vertices to react properly.

Second, set the bind/bounce power lower, like 150% or so. Otherwise the ball seems to bounce out before the trampoline has a chance to react.

Tweeking all the spring/viscosity/etc settings to get it to really react right is the tricky part, especially without a manual...


05-22-2004, 06:12 PM

Thanks for the advice, but I'm not getting anything after following your tips.

Do you have a movie or updated file there to show what you're referring to?

Is it really this difficult to get an object to deform cloth? We have to be missing something pretty basic, because the other possibility is that the dynamics are just broken.

05-22-2004, 10:16 PM
I was able to get a ball to deform a cloth sheet..but when I have tried to apply the same techniques to your scene, I do not seem to get the same results...I have been fooling around with it for about a half hour now, and can't seem to get much farther. Here is the very simple scene that I set up...take a look and see if it helps you at all...good luck.

05-23-2004, 01:26 AM
After a few minutes, I got this result.

I think little better but need to stabilize the sheet a bit.

Have a look to the settings but not to close : I don't understand all parameter, I just try....

05-23-2004, 01:29 AM
A little test with a jelly object in stairs (I tried in 7.5 but it never work).
Thanks LW8

05-23-2004, 10:32 AM
Here's something for you to check out. I used the same trampoline object you had in your scene, but it's been subdivided a few times.


05-23-2004, 03:21 PM
Here's my simple box and cloth setup, if you adjust the collision limit on both collisonFX's you get differing results. Have a faff.

05-23-2004, 04:32 PM
"jelly object"

two thumbs up! :)

05-23-2004, 05:49 PM
Love the jelly object. How about sharing the scene to educate the rest of us?

05-23-2004, 07:42 PM
I apologies Dodgy and ericsmith to stay in this thread, but it seems to be the good place for dynamics..

Here is "jelly" files.

Feel free to improve it and give feedback.

( I left these odd parameters as is, that's work, so is ok )

05-23-2004, 08:12 PM
ok....the Jelly scene is just too cool...fast to calculate and looks damn smart....thanx for teh file...I plan on building a demo scene with is kinda setup.....too cool!

05-23-2004, 08:17 PM
Thanks alot titane357. I never would have guessed that such astronomical settings on spring and substructure (in a cloth preset,yet) would generate such a wonderful response. Great discovery!

05-23-2004, 09:15 PM
Damn, step away for a day and miss the world!
Very cool thanks for the scene!
Did you guys ever see the Siggraph Papers test of a rubber Buddha? CHECK IT OUT IN MIDDLE AMONG OTHER KICKASS STUFF! (http://graphics.stanford.edu/~fedkiw/)
looked incredibly real, like a thick rubber dog toy, JUST LIKE THIS! ...and I looked at it and thought, hmmmm, can LW do that...nah...and you proved me wrong!

by the way! Jack up the Compress Stress to thousands range, and you the object will keep its shape a little more!

05-24-2004, 02:26 AM
MMMM nice!

MMMM jazz....

05-24-2004, 02:40 AM
Thanks for the generosity. This is the type of thing I want to learn more about as soon as I get my LW8. :)

05-26-2004, 08:16 PM
Sorry to leave this thread hanging. I want to try out the very cool looking sample files provided, but my machine clearly does not like the new dynamics.

It's constantly freezing up, "not responding", "control" almost never stops the calculations, and "gravity" continues to flip-flop on me. (sometimes I hit calculate, everything works fine. the next time I calculate, all my objects float off into space.)

I've just about had enough, at this point. I'll just have to move on to something else until NT sorts out their mess.

08-08-2005, 03:17 AM
Hi Dodgy,

Thankyou for the scene files. I'm having fun messing around with the settings. I'll post my findings:)

You are an increasing source of inspiration. Your work rocks:)


08-08-2005, 04:10 AM
Yes, I just sat and stared at the jelly object for ages! Seriously cool for something so simple!


08-08-2005, 09:10 AM
I think dynamics in LW 8 can do amazing things but they are not very well documented.