Scratch Posted November 15, 2011 Share Posted November 15, 2011 Hey od[force] community! This is my very first post, and I'm really excited about finding this forum! So first of all manny greetings from Austria! I'm exploring Houdini at the moment, been through some of the basics and at the moment I'm messing around with RBD (going through a Digital Tutors Tutorial). While doing so, I'm wondering how to correctly set the scale for my scene and objects in order to get a physically correct simulation result? I found HIP File Options within the Preferences saying 1m = 1 Unit, 1kg = 1 Unit. So far so good. But scaling for example an Apple (model provided by Digital Tutors) and a Groundplane to 0.1=10cm units (SOP-Level using a Transform Node) gives me very odd results. The apple is falling unrealistically fast. For the math part, it makes somehow sense, because Gravity is set to -9,8m/s^2) but it doesnt look real...I'm no physicist by all means, but it looks strange. The false scale values (the apple being about 2 units in size which would be 1m radius(!!) looks natural though. I'm confused So how do you approach this scale issue correctyl? Thx in advance for your help, and again cheers!! Quote Link to comment Share on other sites More sharing options...
MirrorSword Posted December 10, 2011 Share Posted December 10, 2011 Since your new to Houdini maybe you don't have the real time toggle activated. Its this little button on the bottom right corner of the screen that looks like a clock. http://www.sidefx.com/docs/houdini11.0/anim/playbar Quote Link to comment Share on other sites More sharing options...
3dbeing Posted December 10, 2011 Share Posted December 10, 2011 Perhaps you need to add a bit of drag? Otherwise your apple is falling in a vacuum. It's always beneficial to post your hip file when possible. Quote Link to comment Share on other sites More sharing options...
Scratch Posted February 6, 2012 Author Share Posted February 6, 2012 (edited) Hey there, I'm very sorry that I didn't write back earlier to thank both ouf you for your helpfull comments. I didn't get informed that there were reply posts to my thread. Realtime is checked, even though you are right, it took me some time to figure out that this button needs to be pressed *G* Drag, yeah would be right, but for now i managed to solve the problem without adding drag (eventhough it would be correct to do so. Simple test -> tried to keep it simple for the beginning). The problem had to do with the substeps of the simulation. It looked odd, because the solvers time sampling was too inaccurate. I modeled everything in real world size, applied real world physical data to the solver, increased the simulation substeps and it worked just fine! (I also had to tweak the "real" physical dataset a bit to make it look nice, but overall, it worked). So the answer to my question is yes, size does matter (and you have to have the right solver settings, hehe) Again sorry and thx for your replys!! Edited February 6, 2012 by Scratch Quote Link to comment Share on other sites More sharing options...
jim c Posted February 16, 2012 Share Posted February 16, 2012 One thing that maight matter - if you're playing back the *first* time (i.e. you have unsolved frames) and you have realtime checked, then you may very well end up skipping steps in the solver as Houdini tries to force things to match 24 fps or whatever rate you've set. I was always under the impression that you wanted to run the first solve with that toggle OFF, then once you've solved the frames you want, run it again with it on for the correct playback speed. Quote Link to comment Share on other sites More sharing options...
spev Posted February 17, 2012 Share Posted February 17, 2012 (edited) Keep real time off. Then sim it and flipbook it. The realtime may be unreliable with large data cache and slow machine. Flipbook is guaranteed to playback at right speed. Less stress this way imoh Happy simming Edited February 17, 2012 by spev Quote Link to comment Share on other sites More sharing options...
Scratch Posted February 21, 2012 Author Share Posted February 21, 2012 Thx guys for that superb input! I'm currently signed up at vfxleraning.com to take classes for houdini so hopefully soone I wont need to bother you guys with such basic stuff again. I will consider this for sure when we end up siming stuff! Keep you updated! greets from austria! Quote Link to comment Share on other sites More sharing options...
Netvudu Posted February 21, 2012 Share Posted February 21, 2012 Don´t worry about bothering us with questions. I mean, I´ve been here for a few years now and I´ve learned that some questions are always going to be basic for a few individuals around here, no matter how complex they seem to be in your brain Also, as I enjoy telling my students, questions never look stupid...the people asking them, that´s a different story Quote Link to comment Share on other sites More sharing options...
Scratch Posted February 21, 2012 Author Share Posted February 21, 2012 Thats cool to hear! Thanks! I'm making good progress at the moment in class. Diging through SOPs, doing my first expressions, stamping, channel referencing, creating custom interfaces, it is really fun and impressive what you can do with Houdini! I hope I will be able to post some of the results soon. At the moment we're just playing around with some testscenes to explore and explain certain techniques. I try to keep you updated! And again Thx Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.