I know that you can use constraints to hold separate parts of a model together in an RBD simulation, but is there a simpler way without using constraints, like parenting them together to be regarded by the solver as one piece, or would this not be possible with RBD sim?

For example, If you want to keep a car tyre and wheel rim connected after a crash.

pack them together as a single packed prim

Thanks, that works, but I would also like to fracture the two connected objects and apply constraints while treating them as one object. I am probably asking too much to do this without the more complicated constraint method.

I can add constraint to the two parts, but the constraints will not link the two together, rather the constraints are built separately on each part.

before fracturing you can assign the same s@name to your elements that you want to be together

then in RBD Material Fracture or Voronoi Fracture nodes set Connectivity Partition to None

it will treat those pieces as one and still fracture and create constraints based on the voronoi cells only, ignoring the connectivity

Amazing Thomas!

I tried this setup and it seems to work. Does it look correct?

Houdini setup [ibb.co]

yes, that should be correct

Voronoi Fracture should already compute constraints for you so you can also just connect RBD Configure (instead of Assemble) and RBD Constraint Properties after and pass both outputs from Voronoi Fracture through them

Thanks for your added info.

I used it to simplify my setup, and also did away with the Attribute Wrangle to set s@name, since a Merge node seemed to be all I needed. How does it look to you? Setting Connectivity Partition to None was the key -- thanks again, brilliant tip!:

Simplified setup... [ibb.co]



Project hip file... [uploadnow.io]

more like this

Thank you for the updated file. I am glad you made me realise that the newer Voronoi Fracture node builds constraints. I was still thinking of the old version where you had to build them separately with the Connect Adjacent Pieces node.