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DOP groups for rbd Packed Objects


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I have a RBD sim, with 1 packed object which contains 9 elements.

I am trying to disable the gravity only on certain elements, within the packed object.


In order to achieve this, I would like to control the gravity node with a dop group.


I created a point attribute "falling" which I control in a sop solver, within the dop network.

Then I created a DOP Group that creates a group based on the following expression:






Now, this seems to work but ...not quite. 

I see elements that start fluctuating at a certain moment, but this moment doesn't match the moment when the "falling" attribute is triggered to 0.


To start, I'd like to understand if I am using the above expression correctly.


I am quite confused with the global variables $OBJID , $OBJ used with Packed Objects.


Could anyone shed some light on this?


I am on H13.0.547

Edited by mrWolf
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Check this thread:

POP forces and Bullet sim


hi Pradeep,

thank you for the example hip file, very much appreciated.

Your explanation makes sense and it works great !


I was trying to stay in the rbd land and use the old style way to drive rbd objects.

But I guess with rbd packed primitives , since we deal with points and transformation matrices opposed to real geometry, we are suddenly in a pop world instead !


I've read often here and there that it's possible to access the real geometry of a rbd packed primitive in a sop solver (meaning, unpack ... use and re-pack), but I wasn't able to accomplish this. Meaning that when I re-pack the element it's not the same as the one I unpacked (primintrinsic are lost when unpacking), so the sim breaks.

Is there a proper way to actually extract the packed data , within DOP, use it, and repack it seamlessly ?

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