Concave to Concave in Bullet!!!!

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hello guys….
i dealing with the problem in bullet engine i don't know it's bug or not but in simulation for correct collision with the same setting i get really unstable result.
for example if you have two object and you force for have correct collision geometry representations set to concave for both objects , simulation will be unstable!
see attach project to see what i say!
if we can use compound in bullet collisions how can i convert apple to compound?
it's true that compound geometry representations just work with combination of boxes, spheres, and cylinders????
any help will appreciate.

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Unstable!.rar (108.1 KB)

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i think its because the amount of substeps in your bullet solver. I just tried it with Number of Substeps on the default 10 and i becomes much more stable.

Also the apple a convex hull should do the work since you don't have anything colliding between the stem and the apple itself.
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robonilla
i think its because the amount of substeps in your bullet solver. I just tried it with Number of Substeps on the default 10 and i becomes much more stable.

Also the apple a convex hull should do the work since you don't have anything colliding between the stem and the apple itself.
can we use compound geometry representation for apple?
if we can how can do that?
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if by compound you mean to create proxy geometries for each piece and have that as a separate hull, yes we can.

Look at the attached scene. I created in the apple network a proxy apple made of 2 separate geometries, the apple and the stem. Then use that in the as the DOP object. If you check “Create convex Hull per set of Connected Primitives” if will create a separate hull for each piece.

And then just import the sim back to SOP, and move the hi-res apple as you were doing before with the Dop import set as Transform Input Geometry. Just be sure to match the pivots of your proxy and hi-res to get matching transformations.

I couldn't get rid completely of the jitter, i think is still a problem of bullet solver handling the concave platter. You could either make a proxy geo for the platter too to avoid using concave collisions, or use the rbdsolver since its not a heavy simulation and it does give you really accurate sism.

Some other thing to consider: remember that Houdini manages units as meters, so your apple in that scene is around 1 meter radius falling 4 meters onto a 10 meter plate. If you want accurate movement i would recommend to match the scale to real world or change your units on the scene (if you change your units, is better to do it before creating the Autodop since all the default values are dependent to the units)

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Fall_withProxyGeo.hip (359.7 KB)

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it's very useful thanks.
in houdini help wrote for compound geometry representation:
Creates a complex shape consisting of Bullet primitives (including boxes, spheres, and cylinders). You will need to use the Bake ODE SOP.
so i think the other way to done this sim apple make with a lot of cube or sphere so we can set geometry representation to compound.
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ohh you meant that Compound geo..

ok after figuring out how it worked (actually by watching the other thread you posted where goldleaf provided an example) I assembled your scene to work with ODE primitives

I changed both the tray and the apple, you could create better representations having less primitives but I did it quickly just for demonstration sake.

Note that before baking the ODE I specify each type of the primitives I want to be used by a point attribute primType. You can check the values for each prim on http://www.sidefx.com/docs/houdini13.0/nodes/sop/bakeode [sidefx.com]

With this approach all jitter is gone because we stopped using the concave plate.

the process is the same to the proxy geo one I sent before, but instead of creating different hulls for your proxies it uses the internal primitives you specify on the primType.

I never used compund objects bef0re, im used to create lo-res proxies but it was interesting to learn this too.

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Fall_withCompoundGeo.hip (365.9 KB)

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thanks it's best and i completely under stand.
in final in RBD engine how can we disable simulation automatically for any objects in simulation when they have less velocity than we specify for them( like sleeping option in bullet) ? i heard before we can use dopfield expression but how?
thanks.
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Attach an RBD Auto Freeze Dop and that should do the trick, i'm almost sure it works for both solvers.
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thank you it's work best.
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