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# MJNorris

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• Rank
Peon

• Name
Matt
• Location
UK
1. ## Physically accurate friction settings

Hi all, I'm trying to create some physically accurate bullet sims using real world values for mass/density and friction, so I've been looking at some engineering tables for friction coefficients: http://roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm What I'm confused about is this: It seems that real world friction is calculated based on the coefficient of friction between two objects, eg wood & wood has a friction coeff of 0.25 - 0.5; wood and concrete 0.62; wood and metal 0.2 - 0.6. So friction is not a material specific attribute, so if I have 3 houdini objects, one wood, one concrete and one metal, how do I create realistic friction settings for each combination when I can only set a single friction value per object? Is it even possible? Also, how does Houdini calculate friction coefficient between two objects? Does it multiply the friction values? Or average them? Any help is much appreciated Thanks in advance!
2. ## EXR meta data issues

Thanks for the help, makes a lot more sense, although I'm finding it a bit temperamental, sometimes working, sometimes not. I'll keep investigating. Thanks again
3. ## EXR meta data issues

Hi there, I'm trying to set custom data as meta data using the mantra render attribute: "vm_image_exr_attributes" according to the docs i should be able to parse the attribute a python dictionary object, however whenever I try to do this: test_dict = {"count" : 0, "path" : "/jobs/"} my_node.parm("vm_image_exr_attributes").set(test_dict) I get the following error: TypeError: in method 'Parm_set', argument 2 of type 'std::map<std::string,std::string,std::less<std::string >,std::allocator<std::pair<std::string const,std::string > > > const &' What I am trying to achieve is a dictionary comprised of file paths that I can then check in nuke. Can anyone shed any light on this? thanks
4. ## Trouble with debris shelf tool

Hi All, I'm relatively new to Houdini and I'm working on a destruction sim of a car hitting a crystal/ice statue. I'm really close to getting a result that I'm happy with but I've hit a brick wall trying to get a fine spray of particles as a secondary effect. Here's what I have done so far: 1. import statue GEO and use a combination of cookie SOPs and Voronoi Fracture to pre-divide the mesh into groups. 2. create an RBD sim using the RBDglueObject node, bring in the low-res car proxy and use it as a collision object. 3. smash car into statue. 4. cache out the RBD as a .bgeo sequence. 5. read in the cache and everything works fine! 6. press the debris shelf tool, this is where things start getting confusing. so I'm getting several odd results, firstly I have to run the sim from frame1, despite having set the debris_sim node start frame value to the correct frame (512). I'm also really confused about the relationship between the constantBirthrate attribute of the POP_replicate node and the constantBirthRate attribute of the POP_source node. My end goal is to use the particles to instance some very simple geo with a copy SOP, however when I do this I find that where I thought there was just one particle, there are actually a load of particles, all occupying the same space, resulting in loads of copies of geo overlapping each other! I haven't uploaded a scene file because my scene is a little heavy but if anybody needs one I'll upload a simplified version with the cache as a .zip Many thanks in advance and any advice or help at all is much appreciated. M.
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