BuzzLightyear

Ola Tomas! I'll make the jump and install it now - many thanks. (I needed to make absolutely sure EI will continue to run - I can't live without it! ;-) Chip

Is anyone currently running EI under Mojave? I was about to upgrade from High Sierra, but am concerned that all the EI modules are listed in the "About This Mac/System Report/Software/Applications" area as not "64 bit apps". I'd appreciate knowing of anyone is running it without problems before I take the plunge. Thanks! Buzz

Tom said he will post the solution here on the website. It contains the working project file, several small Quicktime movies and an explanation of what I did to your original file with some JPEG images. It will all be self explanatory when Tom posts them soon :-) Chip

Hi Nori- I've sent you two Emails to your personal address recently - you should view them. (I thought they were getting to you.) The last one I sent showed the solution to your problem. I still can't attach files to the EI website. Once I hear from Nori directly, I'll re-send him the solution to his Bullet project. Thanks! Chip

Hi Nori- I sent you a solution last night to your direct Email. Your data is fine - it just required some modifications to your Bullet parameters. I think Tomas might post the files here for all to review to see how to approach your project. Let me know if you didn't receive the data I sent. I think you'll see that your approach is now right on track - good luck with you sim! Chip

That's correct Nori - With gravity set to 9.8 the simulation will appear to run very slowly. But this gives Bullet smaller time intervals to calculate the motion. Once the simulation looks correct, then render every "Nth Frame" (every 3rd, 5th, 6th, etc.) frame - whatever it takes to get the speed to look more natural. Setting the gravity to 200 makes everything very "heavy". Just like in the physical world, a huge chain where each link weighs hundreds of pounds will react differently than a lightweight motorcycle chain. Use 9.8 and then render every 5th or 6th frame. But remember to always run Bullet previews for EVERY frame. If you have "Nth frame" checked in the render window, Bullet will become unstable. It needs to calculate every frame for the math to work correctly. So don't forget to uncheck "Nth frame" before previewing the motion. Chip (P.S. Tom and I may have figured out why I can't attach files to my comments. If we get it fixed, that will help to explain how to get your file working :-)

Yes Nori - that's the approach. But just to be clear, only the low poly models are animated in Bullet. The high poly models can be added at any time later to follow the Bullet motion. I'm certain that once you build a low poly sprocket and reduce the number of cylinder faces and separate them with more space, your simulation will work. Let me know what happens :-) Chip (P.S. I'll try to attach a small image showing how simple my low-res models are. Use as few polygons as you can. I also noticed that it took me eight (!) different files to create this motion. I tried many different combinations of speed, friction, tension etc. before I got it to work. Finally, I noticed that you put a value of 200 for gravity. I would recommend putting it back to 9.8 and rendering the motion slowly. Then for the final file, render every 5 or 6 frames. Using a high gravity value might cause the chain elements to be very "heavy" and they might not react as they would under normal gravity.) (Sorry..., I couldn't attach the image. I'll see if I can find out why the attachments aren't working.)

I checked your file Nori, and the surfaces are still too close together and have too many polygons. Reduce the number so the cylinders are not as smooth (you only need 10 or 15 facets - don’t worry that it’s not smooth, you won’t see it in the final render). But the main problem is that your cylinder is too thin. The inner and outer surfaces are just a few pixels apart, so the normals on those two very close surfaces are confusing Bullet. In fact, you don’t even need the outer polygons at all. Just use a 10-15 cross section single surface tube. It doesn’t need thickness; all Bullet needs is a one sided tube to simplify it’s calculations. I would also add a little more space between the inner and outer tubes where the chain links are in contact. I took your file and made the first link static, and let the other links fall onto the sprocket. They fell fine, but as you noticed they continue to move (jitter) because Bullet is confused due to the close tolerance of your very thin cylinder. Try making it a single sided (zero thickness) cylinder with fewer cross sections. Also, your sprocket needs to be simplified. All those tiny facets in the teeth will also cause problems (too many conflicting surface normals). It's a pretty model, but too detailed for Bullet. Just like the simple links you created, model a very simple sprocket. Don’t bevel the edges or round the teeth at all. Make them square with as few polygons as possible. Once again, you will attach the high resolution sprocket later after Bullet calculated the motion with the low res models. Sorry I can’t attach any files or images, but I think you get the idea. Look at how crude my original low res chain links were. Model all your objects like that, and let Bullet work it’s magic. Then turn on the high res models, and it should look great. Chip (P.S. I can't view any of the online animation examples either. I wrote to Tomas to see if there's a problem with the EI server.)

Hi Nori, I looked at your files and your tolerances are too tight on the simple chain segments. There are polygons that are virtually occupying the same space, and Bullet can't calculate which surfaces are intersecting (because they intersect all the time). You have to build a very "loose" simple chain model that fits your sprocket very loosely. If you're going to try and drive the chain with the sprocket, once the simulation begins the chain will sag and drop into place on the teeth of the drive sprocket. Then you can move the sprocket slightly to tighten up the chain - but don't tighten it too much. If you look at the "Wall-E Treads" under the Dynamics examples, you'll see the chain slacken at the beginning of the simulation while Bullet figures out how the parts fit together. Then I moved the tensioning roller to tighten the tread segments before the drive sprocket begins to move the treads. When the treads were too tight on the drive sprocket, the treads flew apart. But they also came apart when the treads were too loose. It takes some experimentation to find just the right tension. But in general always leave enough space between your surfaces to allow Bullet to be able to calculate which surfaces are separate between different model parts. The simplified model needs to be an approximate representation of the actual geometry. Modeling it too precisely will cause Bullet to become unstable (as you found out!). Try re-modeling the simple chain to fit loosely on your sprocket to make it easier for Bullet to calculate the intersections. No one will see the simple chain segments in the final animation so they don't have to look realistic. The high-res models will follow their motion and look fine. Bullet requires a bit of trial and error. It helps not to think of your geometry too literally - think of what Bullet is trying to calculate, and build a simple model that makes the math easier for the physics engine to calculate. Good luck! Chip

Wow AVT! Your “Bot in a Day” is super! He looks amazing, and especially for a one day(!) effort. I know zip about Zbrush, and have to model “the old fashioned way” ;-) My Bots take immeasurably longer, and I’ll try and attach a image of them. But for some reason, I’ve never been successful in attaching files to my posts, and sometimes have to have Tomas upload them for me. I can’t figure out why they won’t attach - I’m using Safari like most Mac-Heads do. I copy and paste the image, and it appears fine. But when I log in and look at the posing, it's gone! (The attached Bots were Modeled in EI Modeler, Maya or MacRhino.) And thanks again for your IK help. The rig works great, and I’m going to fully rig the rest of the character today. He’ll be a combination of bones and deformers, and it should work out great. Thanks for the robot teaser - he’s excellent!! Buzz Yup... I posted it and the pasted image disappeared. Never could figure out why...

MOST appreciated AVT! Yes, I definitely wasn’t getting it, because I was trying to build a rig with a _single_ connected chain. It never occurred to me to keep the foot completely separate from the upper leg, and then select three effectors to move the whole foot, and upper leg IK handle at once. Trying to build it with everything connected was my problem. (I was clearly looking at human anatomy a little too literally, and not considering the flexibility of bones.) Thanks for the insight. I added a Global Mover to your example, and will re-create your rig and re-animate my character today :-) Buzz

Hi again ATV- I think I’ve got it now, thanks. I actually got it to work with an inverted IK chain, but it’s a bit limiting in some ways. I’ll play some more with it, but your “normal” direction chain should work just fine. Thanks for pointing me in the right direction - sorry for the confusion in my last posting. It’s been ages since I played with IK bones! ;-) Buzz

Hi AVT- Thanks for your prompt reply :-) I was sort of doing what you described, but tried your exact instructions as well. But I keep getting a circular link at the last step, which was my original problem. Here’s what I did: 1) Pelvis Box Null created 2) Thigh and calf bone created - stop. 3) IK handle between calf joint end (ankle rotation location) and thigh. No problem, IK works fine. 4) Created single bone in foot from ankle to toe, added IK. (I only need to point the toe, not bend ball of foot. So I didn’t add a second bone at the ball of the foot.) 5) Parented Foot bone to Joint End of calf (ankle rotation location). 6) Parented Thigh bone to Pelvis Box - no problems. Result: As expected, IK works fine when moving ankle; knee bends and foot moves with ankle IK handle. (However, foot does not remain level as it does when inverting the bone chain. My goal is to have the knees flex when I depress the Pelvis, and the foot remains level and stationary on the ground plane.) However, I can’t create another IK handle between the upper leg bone (Thigh) and foot bone due to a circular link (from calf to thigh). So when I move the Pelvis, the entire leg chain moves and the foot doesn’t remain on the ground, flexing the knee automatically. Does that make sense? I’ve done this years ago, and it was really simple. As you described, it’s just a matter of linking the parts correctly, and everything works. Question: Did I misunderstand your last instruction? 5. Parent Upper leg bone to Pelvis and IK to foot controller. Does that mean “Parent upper leg bone to Pelvis” and “add IK between Pelvis and foot bone”? - Or - “Parent upper leg bone to Pelvis” and “add IK between upper leg bone and foot bone”? Both result in a circular link, as expected due to the IK handle in (3) above. So I think I’m still not quite getting it…

It’s been ages since I needed an IK skeleton for a figure, and clearly I’ve forgotten the procedure. I need to articulate the legs separately as usual, but also want the knees to bend automatically when the pelvis is pushed down while the feet are planted on on the ground. Think of a simple pelvis, with two legs and feet for arguments sake, with bone order starting from the thigh down to the toes. It’s simple to add and IK handle between the heels and hips, and the toes and heels to control them. But the only way I can get the feet to remain planted while pushing downward on the pelvis is to reverse the bone order (i.e. starting at the toes and going up to the hip). But I clearly remember there’s a way to do this in the normal top-down bone configuration. An explanation of the setup would be appreciated. Also, I don’t actually need a reverse foot setup, but it would be useful to know. I’ve looked online and found several setup examples for Maya, 3DS, etc.. But I don’t believe they are applicable as shown when using EI (different procedure for bones and constraints). But if anyone has a clear example of a reverse foot as well, that would be appreciated. (I thought there was an example on the EI website of a full IK skeleton and reverse foot, but can’t seem to find them now.) Many thanks for any input :-)

Thanks Frank- I'll look into ViaCAD as an option. The 2D version says it will read 3D files, but it doesn't explicitly say it will export them. If it can, I'll definitely buy it (or the 3D version if necessary). Thanks again for all your input! Chip