Bullet pieces "shivering" without stop.

[vhalldez]

Hi friends...

I have a trouble here

I need to simulate stars fall and fill a container, but when it stop of fall..it still moving by your selves, "shivering" without stop.

I tried to simulate with Bullet Solver and RBD Emit, and both was with this problem..

I tried the parameters of Linear Threshold, Angular Threshold, Padding, incriase Substep...and nothing work...

Some one could help me?

[vicvvsh]

6 hours ago, vhalldez said:

Hi friends...

I have a trouble here

I need to simulate stars fall and fill a container, but when it stop of fall..it still moving by your selves, "shivering" without stop.

I tried to simulate with Bullet Solver and RBD Emit, and both was with this problem..

I tried the parameters of Linear Threshold, Angular Threshold, Padding, incriase Substep...and nothing work...

Some one could help me?

Hi,

maybe this can help

 

[ryew]

Sometimes scaling everything up by a factor of 10 before simulating and then scaling the result back down by the same amount to normal size afterwards can help with this particular problem.

[madebygeoff]

Scaling the sim can help (since by scaling the scene you're bringing your velocity levels up above the default thresholds), but it comes, obviously, at the cost of changing the scale of your scene. You're now running a sim on a scene 10 times as large and it will look it. Sometimes that's fine and for stylized stuff it might be preferable. But it's not accurate. It might be fine, but just be aware.

If realism is the goal, it's usually better to run sims of scenes built to the proper scale and to find the right velocity threshold and sleep pieces below it (which I think is what is the video above).

[ryew]

That's sound advice for many things in Houdini, however Bullet comes with it's own set of quirks and bugs - this one in particular has come up repeatedly in the forums as noted in the posts above.  Scaling is a trick both myself and my co-workers have repeatedly used to eliminate jitter on live-action feature films without detriment to the final look, it simply helps elminate the imprecision in very small-scale calculations causing the oscillation/jittering that even hard-coding sleep and thresholds don't completely remove.

[dleonhardt]

On 22.12.2021 at 1:42 AM, madebygeoff said:

Scaling the sim can help (since by scaling the scene you're bringing your velocity levels up above the default thresholds), but it comes, obviously, at the cost of changing the scale of your scene. You're now running a sim on a scene 10 times as large and it will look it. Sometimes that's fine and for stylized stuff it might be preferable. But it's not accurate. It might be fine, but just be aware.

If realism is the goal, it's usually better to run sims of scenes built to the proper scale and to find the right velocity threshold and sleep pieces below it (which I think is what is the video above).

If you properly scale all the forces in your scene and then scale down after the sim, there shouldn't be any noticable differences between the sims in terms of look and feel. Sure it's more involving to do this correctly, but you mitigate the symptoms of floating point imprecision. I've used this for really small scale FLIP in the past and you couldn't see a difference, just that the scaled up version ran a lot more stable.

[madebygeoff]

Interesting... In addition to scaling up the geometry of the scene, you'd also multiply all the forces in the scene (including gravity) etc.? I'll have to try this.