Hi,

real noob question:
i am trying to learn how to do a car crash. i have done a couple of tutorials, but in all of those the object is only dropped from some height onto the ground. i can do that now(WOW). when i have dialed in all the soft constraints and plasticity and it looks good, i tried to animate the object and active/deforming state so it has more velocity. if i do so the settings are not working anymore and i cant seem to get them right, with increasing the values. i tried all sorts of stuff, but the pieces just fly off and look really weird.

can someone point me in the right direction ?

Pieces flying off might not be that unrealistic. I've found parts of cars 3 blocks away from wrecks that happened at only 25mph.

your right, but the soft constrained pieces do that too and stay bound. so it looks silly and i cant find any tutorial where you have an animation before simulation. thats really odd as you see that stuff all the time in movies and houdini is supposed to be THE software for stuff like that. i am sure it is, but i really hope you dont have to script a ton to do so. i have attached the file. the right tree works with dropping.

As a total beginner I tried doing car crashes and ran into the same issues as you. In my research I found that for a visible large deform of the car requires very high forces, at which the bullet solver just flips out and produces unexpected results (going through collisions, popping, etc.). If you look for car crashes done in Houdini on Youtube, most of what you find is slight dents and stuff that doesn't really look like a heavy impact. I think I read somewhere that for a deformation like that you want to convert the car's carosserie to a vellum cloth for a couple of frames, let it bend and twist, and then do your rbd stuff.

Hi, thanks for your answer. I had hoped that it would be easier in houdini. i tried it in other software and it just didnt work. So vellum ... another thing to wrap my had around. Do you think it would be possible to just scale down the velocity ?

OK, figured out a solution. it works if i do the transform animation on the unfractured object and then transfer the velocities onto the proxy geometry. this way i can even scale the velocities with the trail node. the simulation works now.