Real-Time Physics Simulation Forum

Re: Restitution dependend on timestep

2022-09-24T10:36:16+00:00

I tried this with version 3.25 with the same problem.

You can find my example code in this issue I posted on GitHub:
https://github.com/bulletphysics/bullet3/issues/4341

In my case it works for a btBoxShape but not for the same box implemented as a btConvexHullShape. It also fails for a sphere like in OPs case.

I'm totally not an expert, but the fact that it works for btBoxShape and not for btConvexHullShape makes me think that this should be "solvable"? I went through the code a bit but I don't find anywhere where restitution is handled differently for btBoxShape and btConvexHullShape. Obviously it is different, but I can't find how. Can somebody point me in the right direction? Maybe it's something I can help with.

Statistics: Posted by bbird5490 — Sat Sep 24, 2022 10:36 am

Re: Restitution dependend on timestep

2018-05-12T13:11:51+00:00

Hello,

I've experienced same issue on Bullet recent version (2.88)

Is there any advanced yet?

Statistics: Posted by kangd — Sat May 12, 2018 1:11 pm

Re: Restitution dependend on timestep

2017-09-05T16:22:51+00:00

I searched and found the old thread about this problem:

I misremembered the double precision relevance. It was mentioned but it was the same case as here: already being used.

It is a real bug with a reliable repro recipe.

Statistics: Posted by drleviathan — Tue Sep 05, 2017 4:22 pm

Re: Restitution dependend on timestep

2017-09-05T07:36:34+00:00

Thank you but I am already using double precision. In any case I can't imagine that the values dealt with here get so small that numerical precision errors cause such a big deviation. And why would that only affect the ball and not also the much more unstable (in theory) box?

Statistics: Posted by thantalos — Tue Sep 05, 2017 7:36 am

Re: Restitution dependend on timestep

2017-09-02T16:48:07+00:00

I think someone else noticed this problem a while ago and as I recall: you need enable double precision floats when using very small timesteps.

Statistics: Posted by drleviathan — Sat Sep 02, 2017 4:48 pm

Restitution dependend on timestep

2017-09-01T10:01:26+00:00

Hello guys!

I've been experimenting with bullet and came across a problem I can't explain it and I can't find any information on the problem.
My setup is as simple as possible: a small box and a small ball falling on a fixed large box. Restitution values for all objects are 1.

Everything seems fine when I run the simulation slower than 500Hz (stepSize > 0.002). If I go above 500Hz, the ball suddenly doesn't work correctly any longer. It seems to loose energy, while the box is still behaving correctly.

Sphere z-Position at 400Hz (blue) and 500Hz (red)

Deactivating split impulse adds energy to the system as expected, independent of step size.
Friction parameters have no effect.
Number of iterations has no effect.
Changes to any ERP parameters have no effect.
It seems to be solely dependent on the real step size, using subSteps doesn't change the behavior ("real step size" = fixedStepSize/numSubSteps).

Shouldn't the simulation be more accurate at higher frequencies?

If there is any additional information I can give you please let me know.

Cheers!

Statistics: Posted by thantalos — Fri Sep 01, 2017 10:01 am