Recreating Car Crash sim

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Hey all! Absolutely loved the Sneak Peek for h17 a few weeks ago. Downloaded it tonight, and I'm still lost.

Where under bullet can I make it soft body? Very lost as to what I should be using- the launch made it sound so much easier than 16.5
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Hi valkias,
I was the intern that created the car crash for the sneak peek, that's awesome that you want to recreate it! To answer your question, bullet doesn't explicitly have an option to create a ‘soft body’. To get that look, you could fracture your object and make soft constraints between those fractured pieces. Then, simulate on the fractured object and point deform your original mesh to the simulation. I used this method to create the car crash.
Edited by beneb - Oct. 18, 2018 14:32:13
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beneb
Hi valkias,
I was the intern that created the car crash for the sneak peek, that's awesome that you want to recreate it! To answer your question, bullet doesn't explicitly have an option to create a ‘soft body’. To get that look, you could fracture your object and make soft constraints between those fractured pieces. Then, simulate on the fractured object and point deform your original mesh to the simulation. I used this method to create the car crash.

Awesome work!

Still a little lost on the soft constraints- what do i plug in to where? What order?
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beneb
Hi valkias,
I was the intern that created the car crash for the sneak peek, that's awesome that you want to recreate it! To answer your question, bullet doesn't explicitly have an option to create a ‘soft body’. To get that look, you could fracture your object and make soft constraints between those fractured pieces. Then, simulate on the fractured object and point deform your original mesh to the simulation. I used this method to create the car crash.

Any chance you could share the hip file? Even if it doesn't contain the actual car geometry but just a cube instead?
>>Kays
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Thanks! I can't share the actual car crash hip since its incredibly disorganized and would never run without the actual car geo, which I can't distribute, but I will attach a quick file using the point deform with RBD soft constraints. I hope this helps!
Edited by beneb - Oct. 19, 2018 18:02:30

Attachments:
soft_constraint_PD_example.hiplc (318.8 KB)

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Thanks! I can't share the actual car crash hip since its incredibly disorganized and would never run without the actual car geo, which I can't distribute, but I will attach a quick file using the point deform with RBD soft constraints. I hope this helps!
thanks man!

I got it this far. Still not sure what isn't working

Attachments:
car crash test.hipnc (308.7 KB)

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valkias
beneb
Thanks! I can't share the actual car crash hip since its incredibly disorganized and would never run without the actual car geo, which I can't distribute, but I will attach a quick file using the point deform with RBD soft constraints. I hope this helps!
thanks man!

I got it this far. Still not sure what isn't working

I'm not much help without the actual car geo you're using - but, just plugging in a sphere instead of the file cache you're using I can't see what you've changed exactly to get it in the current state. That .hip's intent is more to show you the workflow and less intended to work with anything complex.
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Beneb: I was the intern that created the car crash for the sneak peek

Hi, Beneb awesome test! Did you also do the softcontstraints building destruction sample videos for the sneak peek? I am trying to recreate how those are done.
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beneb
Thanks! I can't share the actual car crash hip since its incredibly disorganized and would never run without the actual car geo, which I can't distribute, but I will attach a quick file using the point deform with RBD soft constraints. I hope this helps!

thanks for the file!

I was adapting it trying to break the soft constraints which worked ok
But now I an struggling on how to point deform based on that simulation.
Is this even possible in a dynamic way or would I have to define chunks that are broken before hand?
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Hello there,
I'm trying to create a similar simulation where the car hits a tube on its side using Beneb's method but I am completely lost(I'm also kind of new to Houdini). I've tried to recreate his workflow as best as I can understand but I'm at a point where my car just breaks apart before the first frame. If anyone has some time to spare, could you view the attached file and point out where I'm doing wrong?

Thanks in advance!

Attachments:
CarCollisionSim.hip (4.6 MB)
CarCollision.png (478.8 KB)

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For all I know Houdini can up to the task in a certain scale. To create a legit looking crash with scientific accuracy, I'd suggest using LS-Dyna, check out the link https://www.youtube.com/watch?v=FoRWNNIsKZA [www.youtube.com]

I wish houdini 17.5 could have an improved FEM model for crash sim
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and this one

https://www.youtube.com/watch?v=jTB1SbW_rmU [www.youtube.com]
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Hi, to use point deform you’ll need to separate the geo up into sections that don’t break. So mine was separated by material type. Plastic was connected to metal but neither separated internally just separated from each other. So you’re correct, you’ll have to separate them into chucks before hand, if you want them to break internally, and I would connect them with separate constraints.
Edited by beneb - Jan. 14, 2019 14:50:22
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Hello,
Do you separate the geometry with blast nodes and then connect them? I'm confused as I'm new to Houdini and if you do that, then how exactly do you connect them?
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beneb
Thanks! I can't share the actual car crash hip since its incredibly disorganized and would never run without the actual car geo, which I can't distribute, but I will attach a quick file using the point deform with RBD soft constraints. I hope this helps!

Thank you for this.

Is the only way to switch this (FREEZE THE DENT) and then sim, switching back to the normal glue constraint at a manual keyframe?

I have some poles on top of an object that I'd like to bend – but there will be many of them. So keyframing their switch seems a bit, well, not the houdini way…
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Hi - no problem! Ah, yes this is a fun challenge. There are a few ways to switch constraints during a sim, for this sim I used a sop solver inside the dop solver. In the sop solver, you can read many different attributes from your geometry each frame. One of these attribs is a point attrib called “angle” generated from the rbd sim. I took the “angle” and compared it to a constant that I used as the max bend and if it was greater than or equal to this then I switched the name of the constraint attrib to a glue attrib with a strength of -1. Hope this helps!
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If you really want to use bullet in this case, have a look inside Johnny's setup. Scene file download underneath.
https://vimeo.com/219270296 [vimeo.com]
https://vimeo.com/jacyslin [vimeo.com]
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beneb
Hi - no problem! Ah, yes this is a fun challenge. There are a few ways to switch constraints during a sim, for this sim I used a sop solver inside the dop solver. In the sop solver, you can read many different attributes from your geometry each frame. One of these attribs is a point attrib called “angle” generated from the rbd sim. I took the “angle” and compared it to a constant that I used as the max bend and if it was greater than or equal to this then I switched the name of the constraint attrib to a glue attrib with a strength of -1. Hope this helps!


This changes everything….. thank you. I really appreciate the help. Thank you.
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