Basic cone constraint problem

[localstarlight]

Hi,

I'm pretty damn new to Houdini. I'm trying to set up a basic cone constraint network for some voronoi fracturing on a cube. I've managed to get glue constraints working fine, but want to use the cone constraint since it seems useful for flexible breakage/destruction rather than the rather binary on/off nature of glue constraints.

I've attached my project file, which just contains a box, fractured and with cone constraints added. I'm not sure why the box goes completely mental from frame 1 – what's going on here?

I was hoping the constraints would just hold the box pieces together until some force was exerted upon the constraint network, but it seems like the network is exerting force upon itself and I can't figure out why.

Any help massively appreciated!

Thanks,

S

ConeTest_01.hipnc

[carlo_c]

I had a quick look at your file, I'm not sure if this was the definite reason for the box pulling itself apart but I lowered the max search points to 2 so that I have a lot less constraints. I also zeroed out the constraints scale using the primitive SOP, the constraints need to "live" in between the pieces and sit on top of each other (if I remember right) and so this will do that.

I added a sop solver to your DOP network too so it fractures, have a look inside and check the attribute wrangle to vary the strength needed to break apart.

ConeTest_02.hipnc

[localstarlight]

Hey carlo,

Thanks so much, that seems to be the key! I didn't realise the cone constraint primitives needed to have zero scale in order to work – thank you!

I'm trying to create a different setup based on what you just showed me, but having a different problem now, can you take a look at the new file?

For some reason, if I attach the SOP Solver, it messes it up. Without the SOP Solver attached, I get all the data in the Geometry Spreadsheet (angle, torque, force etc.), but as soon as I connect it, all that data disappears. Inside the SOP Solver, it doesn't seem to be pulling in everything correctly, because the constraints just cease to exist instantly. I've been looking back and forth between your example and this new one and can't for the life of me figure out what's different.

On a side note, do you know why the constraints in the splintered wood 'bounce' for a couple of frames before settling? This would be no good, because it disturbs the geometry before anything has actually happened to it dynamically, so would love to know how to fix that.

Thanks so much.

ConeTest_03.hipnc

[carlo_c]

Had a quick look at the file (caught me just in time!) was as simple as not having the display flag set to the attribute wrangle. This is important in the SOP solver as the display flag is the output, in your file it was set to dop geometry

 

Oh as for the bounce, I think that's just the settling of the sim, you can have a glue network to keep it all rigid pre-fracture or use the active attribute to activate (bad use of the word twice there lol) them just before impact/collision/explosion etc!

Edited July 27, 2016 by carlo_c

[localstarlight]

Ah, it was just a damned display flag! Learning Houdini reminds me of when I was first learning to code, trying to track down a single semi-colon or whatever that throws the whole thing into chaos...

Will explore the possibility of using a glue network or active attribute to bring in the cone constraints when needed – thanks!