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vonpietro
07-25-2018, 12:27 AM
GOt a questio nabout bullet.

i made a cage fall on a plane, pretty simple gravity thing.
the problem is when the cage hits the plane it bounces as one would expect, but then vibrates.

nothing i threw at it worked, playing with dampening all values, and adjusting gravity after it hits ect.
nothing with any values will stop the cage from vibrating after it hits.

i noticed i was useing mesh type.

i switched to box and low and behold and no vibrating whatsoever.

why is it that the mesh type introduces so much data that it vibrates, i've experienced this with a lot of my bullet experiences specially shattered pieces that wont stop moving while using the mesh type parameter.

i need to use mesh type for things, not being able to use it becuase of the unwanted jittering or nonresting over time is a real problem.

is this a bullet flaw?

prometheus
07-25-2018, 09:42 AM
GOt a questio nabout bullet.

i made a cage fall on a plane, pretty simple gravity thing.
the problem is when the cage hits the plane it bounces as one would expect, but then vibrates.

nothing i threw at it worked, playing with dampening all values, and adjusting gravity after it hits ect.
nothing with any values will stop the cage from vibrating after it hits.

i noticed i was useing mesh type.

i switched to box and low and behold and no vibrating whatsoever.

why is it that the mesh type introduces so much data that it vibrates, i've experienced this with a lot of my bullet experiences specially shattered pieces that wont stop moving while using the mesh type parameter.

i need to use mesh type for things, not being able to use it becuase of the unwanted jittering or nonresting over time is a real problem.

is this a bullet flaw?

Not sure wether or not Blenders physics engine is based on Bullet, what I do now that I was surprised to discover that I can fracture pieces and let them drop to a collision floor, and they DO NOT JITTER!! at all in blender and comes to a rest quite naturally...so that is awesome.
I have to check out if really is based on bullet engine, if it is..it may be that the lightwave bullet adaptation just isnīt as good in that area.

Ma3rk
07-25-2018, 10:14 AM
What you might consider is a lower rez mesh for your initial mesh object if possible. You can swap out afterwards. Also, check your Collision margin and the Dynamics FPS. Have you tried ramping the Bounciness down to 0% for both the object & the ground plane?

Greenlaw
07-25-2018, 10:37 AM
Was your Bullet setup using a single-layer Parts Body, or multiple layers/objects?

I find that a Parts object is subject to jittering probably because there is a higher likelihood that some little bit of itself will almost always be colliding with itself, or some stray part has fallen past the ground plane and is infinitely falling, so this single Parts Body object is never able to come to a full 'rest'.*

This generally isn't an issue when the 'parts' are separated into layers or object files. (Which I think is how it works in other 3D programs anyway, which be may be why you don't see jittering as much there.)

If you have a lot of parts in your mesh, try running one of those 'object splitter' scripts/plugins that put each part into its own layer and see if that helps settle the jitters. If you don't want to see all the separated items in your scene editor, just parent them to a null and collapse the null.

FWIW, I typcially use Parts only when I know I'll be cutting out of the action before the Bullet Dynamics settles down. If I need to see it all the way through (which I find is pretty rare in an actual production shot,) then I'll use separate layers or objects.

Using a Parts object is convenient and useful, but be aware of the issues that can come along with it. In some situations, IMO, it's better to avoid Parts.

If you're NOT using a Parts object, well, never mind. :)

*Note: This is based on personal observation and not an official explanation. I asked tech about it a long time ago but never got a reply. Regardless, having used LightWave Bullet successfully in many shows, I still think the above is correct.

Tim Parsons
07-25-2018, 10:48 AM
I fix the jitters as well as re-time perfect bullet sims with Chronosculpt. It's free and simple to use, download it and put it to use.

vonpietro
07-26-2018, 09:01 AM
the object is just a cage with a chain sticking out of its head straight upwards.
all one object.

hi greenlaw - I originailly used parts for the chain, and it was working ok, but i see what you mean about a part of the object passing through the floor, it wasn't flush, and that may be it trying to push itself back to flush and then falling again thus the jitter. I have to check collision distance to see if thats the culprit or if that might fix it. Thanks for the insights into dynamics, very helpful.



the cage is just built out of a few cyclinders spaced apart.

Some good suggestions i did not think to make lower poly obj, or play with collision distances.

i did try bounciness to 0 still get quite a bit of jitter. even with dampening all the way up. the problem is when you make extreme values you dont get a good sim usually.

My point is i'm trying to fix a problem that i think newtek needs to address. My cage should not be jittering after its simply dropped on a plane. I'd l would like to see some of these problems addressed by newtek instead of having to find ways around them. its always been a problem using bullet.

Changing the type from mesh to box and it works - no jitter watsoever. but it may have worked for this instance, but what about when i need that mesh to work, even reduced poly most likely will give jitter results.
i've tried this before with fractured items and all the pieces jitter across the floor, it seems like a problem with bullet implementation (a big one too).
its like they dont release enegy or are picking up energy just sitting there and jitter eternally usally. (or its the problem greenlaw outlined perpetual falling through the plane)

i have chronosculpt, never used it. can you just dial out the jitter with that program?

Tim Parsons
07-26-2018, 09:36 AM
i have chronosculpt, never used it. can you just dial out the jitter with that program?

Yes you can. But as others have suggested it is ALWAYS better to use low poly stand-ins for your Bullet sims and replace with your regular models to render. Chronosculpt is very easy to work with, the hardest part is figuring out the MDD/FBX file business to go from LW to CS and back. Using CS is a breeze otherwise.