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Help getting RBD Glue Object collision scene to work properly


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Hey all,

I've spent countless hours over the last few days trying to get this scene to work correctly. Just started learning Houdini over the last 2 weeks.
The idea is a simple collision between some spheres and a fractured creature object. I've attached an illustration just to be absolutely clear as to what my goal is. I'm just trying to get the sphere to hit certain parts of the fractured object and have pieces of it fly out. Think of throwing a fast steel ball at a 6ft tall stone statue how pieces would break apart and fly away. The blue arrows represent the direction you'd expect the fractured pieces to fly and the blue bits represent the fractured pieces.
I've tried tweaking all the usual parameters(in glue constraint, physical tabs, sub steps, convex hull vs concave etc.) but I get either 1.) it all breaks apart 2.) A small breakage with the parts refusing to settle in their places, sometimes popping out unnaturally after a second or so 3.) The breaks run too deep to the underside of the creature, shooting for a few inches deep 4.)other various unnatural looking results.
I attached the .hip file as well along with the creature bgeo. Could someone kindly take a look and see if you can get some decent results or give some advice as to how to go about doing this correctly? Maybe I'm overlooking something or taking the wrong approach.

Thanks in advance for any help you can givehoudinifracture_illustration.thumb.jpg.bc3a7133de0266501e88f92ab6930614.jpg



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There is different way to do this. In this case Im using a pop metaball force. You can see that I using a switch to the metaball at Frame 7 when the ball hit the statue, and if you check the Sop Solver you will see exactly at that frame that I delete the constraints, check the blast node and the notes that I added, so you understand what Im doing.

You can change the force that is apply in SOPs to get the pieces to fly out more or less, also change the position of the metaball if you want as well.



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Hi Sepu,

Thank you so much for the quick response and help! I spent hours upon hours of trying to figure this out and here you got it done in an hour I bet haha

There seems to be an issue when I play the scene back though. I can see the switch at frame 7 but nothing happens, the ball just bounces off, no explosion. I apologize if there's something obvious I should be doing but I just started learning Houdini. Should it just sim as expected in your flipbook? I should mention that when opening the file I got a bunch of errors("Load warnings…") but I assume that's because the creature geo is offline until I relink it. 

Thanks again


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The group node. They split them up in different nodes, in 16 you have a group promote node, group expression, group by range, etc, before it was just group, group copy and maybe some other one that I cant recall right now.

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