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View Full Version : Bullet - great for Jell-O?



egearbox
03-25-2013, 10:35 PM
I've been experimenting with the Deformation mode in Bullet and it's great. But I can't seem to get the deformations to "stay" after objects collide - when Deforming object "A" collides with static object "B" it deforms, but then when it bounces off, it snaps right back into shape, like a Jell-O cube dropped on a table.

I've played with all the settings I can find, and this is the one behavior that seems fairly constant.

Here's a video of four boxes with various settings for "Linear Stiffness" and "Angular Stiffness" (From front to back: .5%, 1%, 5% and 10%):

http://www.youtube.com/watch?v=fXYpb_zdSJc

You can see the "jello effect" best on the second box from the front.

Anybody know a way around this? Or just save the deformed object and start a new scene?

Amurrell
03-26-2013, 06:50 AM
I tried linear stiffness 100% and angular stiffness at 75%. Mess around with shape retention to fine tune it a bit. A little wobbly in areas still, but maintains shape. Also the object is subdivided pretty well. Unfortunately I can't be much more help than that. Last time I came up with what you were looking for was on accident lol :)

lardbros
03-26-2013, 07:27 AM
Have you tried the damping setting? Just wonder if that may help a bit?

egearbox
03-26-2013, 03:07 PM
Have you tried the damping setting? Just wonder if that may help a bit?

I have fiddled with damping and it seems to just stop everything movement-wise. Maybe I can set an envelope for it and have it take effect after the collision. I'll try that tonight.

- - - Updated - - -


Have you tried the damping setting? Just wonder if that may help a bit?

I have fiddled with damping and it seems to just stop everything movement-wise. Maybe I can set an envelope for it and have it take effect after the collision. I'll try that tonight.

egearbox
03-27-2013, 11:14 PM
The problem I was having turned out to be two problems, closely related, and it's actually kind of interesting. I had created a simple two-segment cube to deform, figuring that would be faster. But it turns out that the less polys/segments an object has, the more susceptible it is to this "un-deforming" behavior.

The answer is the Linear Stiffness setting. I created a series of higher-and-higher poly cubes for Bullet until I started to see the behavior I was expecting. Then I tried to figure out what setting it was that was causing the problem.

8 segment cube: Deforms fine at 100% Linear Stiffness.
6 segment cube: 80% Linear Stiffness works.
4 segment cube: 20% Linear Stiffness works.
2 segment cube: NOTHING WORKS.

So I was using practically the only object that just plain won't deform. :(

Sample scene is attached, showing the "Broken" behavior - if you go into the Bullet properties for the box and change Linear Stiffness to 20% instead of 30%, it should work as you would expect.

113105

erikals
03-27-2013, 11:46 PM
lookie here >
http://www.youtube.com/watch?v=713S3BFSYpY#t=1m18s

http://erikalstad.com/backup/misc.php_files/smile.gif

egearbox
03-28-2013, 07:48 AM
If only I spoke Japanese. :)

erikals
03-28-2013, 07:57 AM
just pause video to check the settings. http://erikalstad.com/backup/misc.php_files/wink.gif

phillydee
03-28-2013, 08:27 AM
Really rough translation(my Jap isn't good anymore), what I picked up: he says that all three cubes use the same dynamic type. What's being used says "Deforming". He says they all have the same properties except the "Shape Retention" percentage. He then goes on to point out the box on the left has 0%, the box in the middle has 50%, and the box on the right has 100%.

erikals
03-28-2013, 02:37 PM
now i know who to call when i need a translator... http://erikalstad.com/backup/misc.php_files/wink.gif :hey:

phillydee
03-28-2013, 02:42 PM
LOL I'm no translator :P I can understand a little bit, but no where near it used to be. I can read hira/Kana 100%, but not as many Kanji as I used to :grumpy:

erikals
03-28-2013, 02:50 PM
still though, that's so much more than what the rest of us understand http://erikalstad.com/backup/misc.php_files/smile.gif

egearbox
03-28-2013, 03:30 PM
The boxes I was using had Shape Retention set to 0% though - no shape retention, zip zero nada zilch. Still wouldn't deform. Because it was such a maddening problem, I thought it would be good to share the solution with others to prevent hair loss in the LW community. :)

erikals
03-28-2013, 03:36 PM
...share the solution with others to prevent hair loss in the LW community :)

too late, friggin' genes...

egearbox
03-28-2013, 04:53 PM
Lol :)