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Found 110 results

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. ## wire solver interacts with RBD solver

Hi all! I'm doing a rope sim with wire solver. And I wanna interact wire with RBD sim. I did each sim at the same time in the same DOP network. But it was not doing well. problems are... 1.Why the wire goes through the cube? 2.Why the cube breaks before the wire hits? Any solutions? Thanks. WireBullet_test.hip
3. ## glue constraint issue

hey !! why i'm getting this weird glue constraint issue the obj gets hit the glue broken then it gets attached again . thanks
4. ## update linear and angular vel based on another object in bullet sim

Hi, I have a case where I have, lets say an object which comes from bulelt sim, with v and w. Based on that object, I want to drive another bullet sim, updating v and w, so the rest would be calculated by bulllet sim. In the scene I attached it works pretty much, except it flips at some point. I understand that there should be some catches on quaternions. I suppose, there should be some sort of angle check and etc, but can't make it work... update_angularv.hip
5. ## Duplo Bear via Bullet Constraints

Here is a breakdown of how I made this bear made out of duplo blocks: The video isn't super comprehensive, I mainly cover setting up the constraints in SOPs, though I briefly touch on some other parts too. But the hip file is available to pick apart! Thanks! duplo_bear.zip
6. ## Bullet Going Through a Mechanical Heart

Hi, I'm trying to achieve a particular effect which I though would be relatively simple (see attached image.) I have a shot I'm working on where I have a mechanical heart and I want a bullet to go straight through it without losing impact, shattering the heart as it goes. I have pre-fractured the heart geometry with voronoi and used glue to anchor it in place. I then did a simple RBD sim as you normally would when fracturing objects. However, when I used a sphere as a placeholder bullet with initial velocity, it just bounces off the heart. Even when I increase the mass of the 'bullet' it still bounces off. My question is, how would you approach this? I'm completely lost. Cheers!
7. ## Bullet and Flips collisions?

Hi, Can someone please help me confirm is bullet is compatible or not with flip simulations? I set up a simple packed geo as a static object for a flip simulation. The geometry collision is properly calculated as convex hulls… (image1) But as soon as I run the sim this weird shape appears (image2) It is like if the flip sim automatically converts the collision geo into a weird resampled volume. is this true? Would this mean that the flip solver will automatically convert the packed geo into a volume? Feel free to look at my set up… I simplified the scene to run a test. (the hip file is attached at the bottom) bulletandFlip.hiplc I also added this post in SideFx forums as is driving me crazy trying to figure the solution... I have figured a work around transforming my collision geo into volumes and then just using regular static solver but I would like to have a clear answer about what is going on here...
8. ## Emit Coin Object and push them outward by new emitted coins

Hi, I want to emit alot of coins which will be pushed outwards the earlier borned coins Like a growing stack of coins. What is a good way to do this? Cause What bullet now is doing is leaving all the intersecting geometry Alone (no popping)
9. ## Control when attributes get overwritten in DOP's

Hi all! I'm currently trying to find a way that I can control when an attribute on packedrbdprims coming into DOP's gets written to from the "Overwrite Attribute from SOP" box and when it gets written to from the bullet sim I have set up. I have a set of packed primitives with rotation animation on them being fed into a bullet simulation, I'm also adding an "active" custom attribute which is being used by a SOP slover in DOP's with a vex wrangle inside it to activate them when the value equals one. What I also want to happen is have the orient attribute on each packedprim update from the existing vaules from SOP's right up until the point when the bullet solver takes over and begins writing to the orient value. I know that I can add orient to the "Overwrite Attribute from SOP" box but what I 'm hoping for is a way to disable this function for each object as they become active rigid bodies, essentially adding to the orient values that exist on that particular frame and continuing with the sims values. Instead of having the sim take the orient values that exist at the first frame or continually updating those values as the packedrigidbodys are influenced by the sim. I know its poor form but I'm afraid I dont have the project file on hand to upload, sorry guys :S hopefully I can upload it next week if anyone needs to see it. Any help would be massively appricated! Many thanks
10. ## Cloth/FEM and RBD/Bullet interaction

Hi I've been searching the forum on this topic but didn't find much. Is there a way to get a somewhat correct collision behavior between the cloth solver and the RBD solver running parallel in the same DOP network? I've a bunch of cardboard boxes that's suppose to stack on each other. I'd an idea that the cloth boxes that had come to rest would switch over to be a RBD objects instead, to optimize the sim. But first I got to get the solvers to interact. Any ideas? A simple test scene with the setup is attached (without the switching stuff). Thanks / John Edit: Ops double post :/
11. ## Rigid Body Simulation Question - Switching from animated geometry to simulated

Hi all, I am trying some simple tests in dops using the bullet solver. I have hit a few stumbling blocks and would appreciate any input from you friendly people What I'm trying to do: I am trying to get a scene showing a pillar being picked up by a crane (like the ones in fairgrounds where you can use it to grab soft toys), the base of the pillar stays where it is and the rest of it gets picked up by the crane. As the pillar is picked up, the lower part of whats left is crumbling away as the whole thing moves. The setup: Because this will eventually be put into a game engine, I have to keep the number of fractured pieces down, so I split the pillar (Top, Bottom), and then I split the Top even further to isolate the "destructible" area. I fracture this area and animate both objects to be moving with the crane (transform sop within the SOP level) I then bring these objects into a dop network as RBD packedobjects but I can't seem to bring in the animation that is attributed to them. I change the "Initial Object Type" to all the the available selections int he dropdown, including Create animated static objects" but this doesn't seem to do anything. I do know you can do this on an RBD fractured object using the Use Deforming Geometry checkbox, but I'd prefer to work with packed geometry to reduce simulation times. Ideally, I would want the destructible area to just be parented to the Top of the pillar and then I can make it crumble by breaking the constraints. But I can't seem to do that either. In 3DS Max, in PhysX, there is an option to tag objects as "Kinetic" and then choose which frame to make them "Dynamic". That's a very rigid way of working and I'm certain there is a much more flexible way to do it in Houdini but I am still a beginner, especially when it comes to rigid body simulations. So to summarise, the questions I am left with are: How can you bring in animation on an RBD packed object? What would be the best way to achieve what I am trying to do? Thanks
12. ## Impact Data from Particular Object Id

Hello guys, How can i use impact data when an object hits a particular object in my case a ground plane to break the constraints, For eg - i have certain glued objects falling on the ground , some of them are breaking in the air while they release due to impact generated while i want they should only break once they collide with the ground plane else their strength should remain -1. So how could i extract object id of ground and use that as an impact data.
13. ## Packed RB Morph - from one shape to another

I'm looking to transform one shape of packed RBD's into another. I've looked at the forum and a few of the examples. Specially the lego car which is awesome but they all tend to transform the same set of Packed RBD's from a rest shape to complete form. I am looking to transform from one shape of object to another shape of object. this is a pure Position and Rotation transformation and I think I'm just not understanding the way rotate work to show this I've made a simple houdini file. Any Help to better understand this would be appreciated.
14. ## Packed RB Morph - from one shape to another

I'm looking to transform one shape of packed RBD's into another. I've looked at the forum and a few of the examples. Specially the lego car which is awesome but they all tend to transform the same set of Packed RBD's from a rest shape to complete form. I am looking to transform from one shape of object to another shape of object. this is a pure Position and Rotation transformation and I think I'm just not understanding the way rotate work to show this I've made a simple houdini file. Any Help to better understand this would be appreciated.
15. ## Packed RB Morph - from one shape to another

I'm looking to transform one shape of packed RBD's into another. I've looked at the forum and a few of the examples. Specially the lego car which is awesome but they all tend to transform the same set of Packed RBD's from a rest shape to complete form. I am looking to transform from one shape of object to another shape of object. this is a pure Position and Rotation transformation and I think I'm just not understanding the way rotate work to show this I've made a simple houdini file. Any Help to better understand this would be appreciated. packedgeo_shapetoShape.hip
16. ## Multiple Solver Interactions

I'm gradually trying to learn various of Houdini's solvers (primarily cloth, pyro, and bullet for now) and I'm slowly getting to grips with how they work individually. What I'm struggling to understand, and also struggling to find good learning resources for, are the ways to create interaction between multiple solvers. I'm interested in setups for one-way interaction (eg. pyro affected by bullet/rbd sims) but even more keen to understand two-way (or more) interactions. For example, how to have cloth and bullet (and perhaps pyro as well) all working mutually in a dynamic simulation, all affecting each other. Can someone point me in the right direction towards learning how to combine different solvers together? Are there generic ways for doing this (in other words combining cloth and bullet would involve the same understanding/setup as combining pyro and cloth), or does every solver/combination have its own idiosyncrasies when trying to combine? I found this video about combining pop and bullet solvers: https://www.sidefx.com/tutorials/combining-solvers-with-a-multi-solver/ I assume a good understanding of the multisolver is key here. But the multisolver doesn't accept the cloth solver as an input, so it seems like there must be more to it than that... Any help much appreciated!
17. ## SOP GEO - FIELD FORCE - BULLET

Hey guys, working on a destruction peice and wanting to take the velocity from my charachter and put it into my bullet sim - So decided to try and use a sop geometry node to bring in the calculated velocity (from a trail and fluid source) - which is working perfect. But my sop force doesnt update each frame, its static - ive tried changing the expression from \$T to \$F and other things, not sure if its a limitation or if im doing something wrong? i will attatch a file but will be missing the geo but atleast you guys can see the setup Any help would be great! Thanks Destruction_v3_t2.hip
18. ## bullet Instance Pack Trouble

Hi guys , Based on the tutorial Applied Houdini - Rigids II Structure Destruction I'm try same effect , But i have trouble is instance pack , i m use same techniques in this scenes . But i don't know why matrix replace does not work . Hope your help .Thx every body. Please find attached for details

i have managed to create a network of masked gravity force to drive the RBD packed objects but I'm a little confused about how to proceed further. i need to control the moving pieces of geometry more effectively with further forces as well as create debris from the cracks or where it fractures. any direct help (i have attached an example file) or pointing me towards resources where i can learn further would be cordially appreciated. thank you and best regards fracture.avi fracturingGeoMaskingForce.hipnc
20. ## Copy SOP - Dynamic Objects

Hey guys, Im creating some procedural Sawdust using the copy sop onto a point selection - i want to sim the objects then dropping onto the terrain for placement, but so far have had no success - tried changing collision modes in Bullet but think the main issue is its all connected as such? (have tried convex hull and per connected set of primitves with no luck etc) and cant think of a way using the skills i have to select every peice of geo individually and then make dynamic quickly without doing it manually (which with thousands of peices of geo is not a good idea) Any help or ideas would be great Thanks Chris
21. ## Copy SOP - Dynamic Objects

Hey guys, Im creating some procedural Sawdust using the copy sop onto a point selection - i want to sim the objects then dropping onto the terrain for placement, but so far have had no success - tried changing collision modes in Bullet but think the main issue is its all connected as such? and cant think of a way using the skills i have to select every peice of geo individually and then make dynamic quickly without doing it manually (which with thousands of peices of geo is not a good idea) Any help or ideas would be great Thanks Chris
22. ## bullet custom deformable metal constraint

Hi everyone, I made this setup to mix constraints between conetwist and glue, depending on angle value, i set the constraint_name in a sop solver plugged in the constraint network node, it works quite well but the resulting object is floating in the space... is anobody here can check my file and tell me what's going on!!!? apparently its not a subsanple or CFM, ERP issue ( i checked all this parameters and, nothing...) thx by advance, Best regards H TEST_PACKED_CONST_METAL_V002.hip
23. ## Houdini Pipeline Engineer / Technical Director

Hi, I am an experienced Software Engineer with a good eye for Visual Effects. I have over more than 10 years of experience in developing advanced software systems for simulation and animation companies. In addition, I've invested that last 5 years exploring and educating myself all about Visual Effects. Below is my demo reel. Please check https://www.linkedin.com/in/khaledabdelhay for more details on my technical/artistic skillset.
24. ## Access Bullet AutoFit Orientation

Hello there, For my current project, I have a subset of randomly oriented geometry (mostly box or capsule like shapes) in one .obj I would like to orient all of them along their main axis. I remembered Bullet had a Autofit feature, that would fit specific geometry (Sphere, Box, Capsule, etc) to your geo. I tried looking up the source code for this, but I don't think the effort would be worth trying to understand the whole code (I'm a very beginner coder unfortunately), and secondly I think the bullet solver inside houdini does a pretty fast job as is. My approach is now to import all the objects to bullet, calculate the AutoFit there, and then get the orientation for each object. But how exactly can I access the Bullet Collision Orientation? In my subdata it shows no orientation (obviously, because my parent node is not rotated or transformed), and in the bullet data tab i cant seem to find any orientation. Is this even possible? Or can someone here share and explain the AutoFit code inside Bullet? (Just Kidding ;)) Best Regards Bajt *edit : I just remembered one more question, even though it's not directly related to this one: Is there a way to calculate the best fitting primitive for a shape? I read the paper https://www.cs.drexel.edu/~david/Classes/Papers/MeshlessDeformations_SIG05.pdf , but when i understand this correctly it only works if point numbers and number of point match in both point clouds. Maybe its possible with bullets autofit algorithm?
25. ## Bullet penetration

Hello I have scattered points, a lot of them and I copy some simple objects, which represents roughly my Hires Geo. Problem is, that whole system is procedural, so I never know if Ill be simulating 20k or 50k objects. Ofcourse more objects, more penetration on first frame. So I have an idea, to do a small sim, where on couple of frames play new bullet sim and all penetrating objects will move until theres no penetration (say time shift 10-20f). Then I`ll start my main sim without penetration (a lot of different constraints, some groups of active objects.....) But problem is, that bullet do nothing even there`s a lot of penetration. I cant find any parameter in bullet solver, rbd packet prim, which will help me. Ofcourse Ill be happy to hold main shape as close to original as possible. There is simple scene. Thanks a lot. bullet_penetration.hip
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