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Kdeg

Custom force not affecting RBD sim

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Hello,

For some reason I can't get imported forces to affect an rbd sim when there is an active object constrained to a static object with simple glue. Even when the glue strength is set to minimum and the force is considerably scaled up, there is still nothing happening. The sim works fine if I remove the constraints between active and static objects and only keep the constraints between active pieces.

I attached a simple setup below with the two configurations.

Any Idea why the one with inactive objects doesn't work?

Thanks.

force_test.hipnc

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forces never break constraints...two ways to break constraints : either (1) break them manually , (2) objects hitting each other (e.g. a ball hitting your target breakable object). It does not really matter how much force you apply, they won't break even the slightest constraint...

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I confirm. The RBD solvers works through « impact » data that propagates.

They do not calculate what is called shear and stress within the structure : this kind of calculation is done in a FEM solver. You can also get a similar behavior with Vellum.

The good news is that there is one in Houdini :-)

 

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Thanks for the response guys.

I apologize I  think I used the word "force" wrongfully. I'm actually manually adding velocity to specific rbd pieces in a sop solver. It does break glue constraints when there are no static objects constraint involved. You can see this in the file I attached. I just can't figure out why it ceases to work when constraints between static and active objects are involved.

 

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If I understand you correctly, then it's the same concept: if there are constraints bet active and passive pieces and you apply force or velocity on an active piece, the most probably it won't move because it's attached to a passive piece by a constraint...so the same idea: if there are constraints, then having force or velocity on pieces won't break them (so break them manually or via impact)....I am not sure if this answers your question? 

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3 hours ago, Kdeg said:

It does break glue constraints when there are no static objects constraint involved.

It's because impacts are happening between static and active objects. Bullet solver breaks glue constraints automatically when impact attribute of constrains greater then strength. You can broke constrains manually with sop solver dop.

Look at this topic, I posted an example file there, how to broke constraints manually.

 

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On 10/4/2019 at 8:00 AM, StepbyStepVFX said:

I confirm. The RBD solvers works through « impact » data that propagates.

They do not calculate what is called shear and stress within the structure : this kind of calculation is done in a FEM solver. You can also get a similar behavior with Vellum.

The good news is that there is one in Houdini :-)

 

Wow this is great. now watching thanks.

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