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neurostudio

RBD concave thin wall collisions not detected

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hey guys i am having a little bit of an issue with this test.
 
i picked up this setup from another thread on this forum however in this particular scenario it doesn't seem to work as i am probably missing something.

basically the pieces getting activated and falling, do not collide with the inner shrunk body volume i created and - since i am a houdini newbie - i am struggling to figure this out :)
 
tried to change geometry representation to concave, tried to increase resolution of colliders, but nothing worked so far.
 
i'd be really grateful if anyone could suggest a possible solution.
 
here's HIP and assets in case you want to have a look.
 
thank you in advance.

ALTzdRVw.jpeg

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You should use convex pieces with Bullet, the convex decomposition SOP can help with that.
convex pieces are slow and (very) buggy.

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Posted (edited)
7 hours ago, bunker said:

You should use convex pieces with Bullet, the convex decomposition SOP can help with that.
convex pieces are slow and (very) buggy.

Hey Julien,

I am gonna give that a shot and report back. thank you :)

 

Edited by neurostudio

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10 hours ago, bunker said:

You should use convex pieces with Bullet, the convex decomposition SOP can help with that.
convex pieces are slow and (very) buggy.

Hey Julien, 

I have been implementing convex decomposition (probably the wrong way), and made a bit of a progress. 

Would you mind having a look at my file? Assets .abc is included.

https://www.dropbox.com/s/eaheclpww2w090l/FRACTURE.zip?dl=0

thank you :)

 

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I had a look at your HIP file, there was a few issues.
- the left side of the body didn't have a name attribute, same of the new faces from the PolyExtrude
- convex decomposition won't be consistent on animated geometry

a much better way is to create all your pieces on frame 1 and pointdeform them to transfer the animation.
for the activation, you can use a wrangle in DOPs and lookup your pointcloud directly.

girl_fracture_05_convex_decomposition2.hiplc

hope that makes sense.
 

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3 hours ago, bunker said:

I had a look at your HIP file, there was a few issues.
- the left side of the body didn't have a name attribute, same of the new faces from the PolyExtrude
- convex decomposition won't be consistent on animated geometry

a much better way is to create all your pieces on frame 1 and pointdeform them to transfer the animation.
for the activation, you can use a wrangle in DOPs and lookup your pointcloud directly.

girl_fracture_05_convex_decomposition2.hiplc

hope that makes sense.
 

Thank you so much :) Gonna dive in now and see if I learn something. Will let you know!

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1 hour ago, neurostudio said:

Thank you so much :) Gonna dive in now and see if I learn something. Will let you know!

i had a look at your setup and certain things definitely make sense, even for a newbie like me! thank you!

however, collisions are still not working and the pieces fall straight through the collision volume. trying to figure it out!

 

 

Annotation 2020-01-06 131753.jpg

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not sure what the dark blue object is but it should also be a convex packed primitive object.

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Just now, bunker said:

not sure what the dark blue object is but it should also be a convex packed primitive object.

it's just the collision representation of the inner volume :)

got it. i'll try to do that now!

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Posted (edited)
1 hour ago, bunker said:

not sure what the dark blue object is but it should also be a convex packed primitive object.

julien, i think i am getting there :)

now  i need to exclude the collider (which is now a packed object) from the activation pop wrangle, but i really can't think of how.

 

 

 

girl_fracture_07_convex_decomposition.hiplc

Edited by neurostudio

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Posted (edited)

you can use the name attribute to filter out objects to activate in the pop wrangle:
eg: if your collider is named "collider"

if(s@name!="collider"){
// activate the other pieces

}

Edited by bunker

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2 hours ago, bunker said:

you can use the name attribute to filter out objects to activate in the pop wrangle:
eg: if your collider is named "collider"

if(s@name!="collider"){
// activate the other pieces

}

thanks julien!

now the collider is excluded, however the pieces collisions are not working properly. 

trying to figure this out :)

alession odforce_01.hiplc

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The blue collision object you are visualising... is that created using a static object dop? If so, are you visualising the "Collisions/RBD solver/Volume" tab rather than "Collisions/Bullet Data" tab??? I think you may not be seeing what the solver is seeing. 

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of cource, you're using volume collision (blue) that's not going to work. Bullet uses Packed primitives only.

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22 minutes ago, bunker said:

of cource, you're using volume collision (blue) that's not going to work. Bullet uses Packed primitives only.

i am using packed prims now, but still not working correctly.

still trying to figure it out.

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10 hours ago, bunker said:

you should watch this, it's still relevant: https://www.sidefx.com/tutorials/h13-masterclass-bullet/

hey julien,

i kinda solved it... i got a little confused along the way, but tidied up things in the end :)

ended up getting rid of convex decompositions for both collider and rbd object.
used concave representation for both and reduced collision padding and split impulse threshold by a lot.
of course now it's super slow and the result isn't super stable, however it will work for what i need.

 

thanks guys for the help !
 

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Glad you got it working, and of course whatever gets the job done is great. However, I would encourage you to investigate using convex hulls for all collisions. You will see vast improvements in speed and stability. They can be a little trickier to set up, but the rewards more than worth it. 

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7 minutes ago, woodenduck said:

Glad you got it working, and of course whatever gets the job done is great. However, I would encourage you to investigate using convex hulls for all collisions. You will see vast improvements in speed and stability. They can be a little trickier to set up, but the rewards more than worth it. 

will do cause honestly the sim is a little jittery and not all collisions are perfect :)

maybe i'll try this method next time.

thanks!

 

 

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