[Solved] Convex Bodies Jump on Static Mesh (3.12)

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[Solved] Convex Bodies Jump on Static Mesh (3.12)

Postby AntonSynytsia » Fri May 23, 2014 10:21 pm

Greetings,

I came across this glitch, and need help on how to resolve it:


  • When the solver model is exact convex bodies seem to jump on a static mesh tree body.
  • When the solver model is changed to interactive the jumping stops, but starts again if you change it back to exact.
  • If the floor body is a static convex body the jumping does not occur on any solver model.
  • It seems bodies jump on static mesh tree body, but not on a static convex body. Weird


Details:
    '
  1. All bodies are set to default material.
  2. No collision callbacks were assigned to the default material.
  3. Current update rate is 64 times per second, but making it small doesn't remove the glitch.

Awaiting help,
Anton
Last edited by AntonSynytsia on Mon Aug 18, 2014 8:39 pm, edited 1 time in total.
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Re: Convex Bodies Jump on Static Mesh (3.12)

Postby AntonSynytsia » Mon Jun 02, 2014 3:43 am

Same effect occurs in Newton demos sandbox when bodies are in contact with tree collision.
Image
I recompiled demos sandbox with MAX_FPS set to 60.0f so that the effect is more visible.
BTW, when I change solver model to interactive the moving stops (even if the auto-sleep state is off).

This is not really important to me, as I can always use interactive solver model, but exact solver is 8)
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Re: Convex Bodies Jump on Static Mesh (3.12)

Postby AntonSynytsia » Wed Jun 04, 2014 1:37 am

Its seems setting contact softness to 0.01 will prevent body from jumping... That makes sense actually.
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Re: Convex Bodies Jump on Static Mesh (3.12)

Postby JoeJ » Wed Jun 04, 2014 4:40 am

I was confused by 'softness' too and copied following comments from forum, it may help you as well.

As far as i understand it is a value controlling how fast interpenetrating bodies seperate.
It's not a physical value, but more a 'recover from illegal state' thing.

I guess there is indeed a bug related on convex - static mesh / exact solver that Julio should fix before you can offer the exact solver as an option.




//NewtonMaterialSetSurfaceThickness // Thickness is how cloase the collision will be, you can for example set a small sickness value and the shape will not touch.
//NewtonMaterialSetContactSoftness // softness in hwo fast penetration will be resulved (by penaltry force proportinal to the penetration.)


/*
softness and elasticity are very different things.
one is a function of penetration distance
and the other is function of relative impact velocity

elasticity is the coeficient of restitution according to the equation of impulse. eleaticity is proportional to the relative velocity of impact at a contact.

softness it there to resolve interpenetration only.
Softness is the penetration coneficient that is use to convert teh interpenetration is disatnce to an inpulse veliocity to recove from penetration,
the velocity is then added to the impact velocity.

in future versions of Newton softness will be eliminated all together.
you can leave the softnes coficient to the default and only work with elaticity.



yes elasticity is what some people call restitution

softeness is a penalty acceleration that is added to the contact point if they penetrate.
it is not propotional to the penetration, instead the penetration is use as a switch to decide if using the softhness or not,

In Newton this parameter is not visual, is is in fact translate to an impulsive force add to the contact point, and it is one of the reason collision can go bad if you set that value to anything too high.
the parameter have not physical explanation other that recover bodies from penetation.
so the physics of it are umpredicatble since I do not have any physcial/mathematical expresion to add it to the engine.
like I said, set it to zero, the engine do recover from penetration graciously by separating the at a constant speed when they penetrate.



*/
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Re: Convex Bodies Jump on Static Mesh (3.12)

Postby AntonSynytsia » Wed Jun 04, 2014 8:29 pm

Thanks for info, JoeJ.

I hope Juleo looks into that bug because bodies don't behave normally on teh tree collisions.
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Re: Convex Bodies Jump on Static Mesh (3.12)

Postby Julio Jerez » Mon Jun 09, 2014 7:03 am

didn't setting the softness to 0.01 fix it?
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Re: Convex Bodies Jump on Static Mesh (3.12)

Postby AntonSynytsia » Mon Jun 09, 2014 5:10 pm

Julio Jerez wrote:didn't setting the softness to 0.01 fix it?

No it doesn't fix it, but it makes that penetration effect less visible.
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[Solved] Convex Bodies Jump on Static Mesh (3.12)

Postby AntonSynytsia » Mon Aug 18, 2014 8:38 pm

I can no longer reproduce this issue in 3.13

Thanks for fixing this Juleo.
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