Hey Stathis - wow! you've been busy 🙂
So awesome to see what people are coming up with independently. Thanks so much for sharing your work with us and everyone who reads the posts!
Okay some feedback!
It looks like something isn't quite right either with the setup of the line of action nodes, or with the excitation of your fibers. I'll explain my reasoning based on what I can see.
If you look at this frame below in your video, you'll see that the chest etc is all pretty much still in default pose but the pecs, obliques, abs and traps are all firing 100% (fibers are rendered yellow)
Ideally you want the fibers to excite gradually as the curve that feeds into the line of action node becomes shorter. It seems to be about right on the upper legs, for instance. On a related note, the fibers are firing but they don't seem to be contributing to the shape change of the muscles. For instance in the frame below, I would expect the abs to compress and tighten as your character crunches down, but instead they collapse in:
A secondary node on this part of the anatomy is that you probably want to represent the internal organs of your character with a volume in there, to help prevent this sort of collapsing. If you look at Lonnie's thread on making a human with Ziva: (https://community.zivadynamics.com/d/38-making-max-with-ziva) You'll see he solves that volume first.
It also looks like adjacent muscles which should have similar excitation are quite different from one another. See below:
One final note on the firing. If you look at the excitation rendering of the pecs, over the course of the video you posted, you'll notice they seem to go from zero to fully excited (off and on) within very short time frames. And it does feel somewhat unmotivated.
Again you would expect to see the muscle shape change quite a bit when these excitations change.
My guesses are that firstly: the curves feeding into the line of action nodes might not have been attached (riveted?) to the correct bones. Also did you change the default values on the line of action node? if you changed pos sensitivity from 1 to 10 for instance, the fiber might excite too quickly.
Secondly there might be a mismatch between the strength of your fibers and the stiffness of your muscles. I would probably guess that your muscles are quite stiff and the fibers are relatively weak. Could be wrong, just my intuition. Or perhaps you've set your contraction limit to 1 on the fibers, meaning they can't contract at all.
My next observation was that I'm not seeing a huge amount of secondary, independent motion on the muscles. You mentioned you've got fairly dense tet resolutions for the muscles. This would indicate to me that one would expect to see a lot of secondary motion including perhaps some wave propagation when the character moves. There could be a couple of reasons for this.
- The stiffness of the muscles (Young's modulus on the zMaterial node) could be on the high side.
- You might have a few too many attachments between muscles, meaning that the system becomes 'over constrained'. The over constraining could be contributing to the jittering you're getting on some of the muscles. As a general rule, be sparing with attachments. Origins and insertions first, then attach between muscles if you need to.
- The solver scale might be too large compared to your character. If you look at the zSolver1 locator in your maya viewport. You'll see that there is a 1m label on one axis. This means that according to the solver, objects that are about the same size as it, are about 1 meter high (or wide, or deep) It could be that according to the solver, you character is only 1cm tall for example. A quick google tells me chimps are ~1.2m tall, so the zSolver1 node should be slightly smaller than the height of your chimp geo.
As for not being able to solve on more than 1 substep. I'm not sure about the cause of that one. If you're able to send a scene to firstname.lastname@example.org, I'd be happy to investigate your character at my end.
On the whole it looks like you've got a great grasp of the pipeline and requirements for building and simulating characters. I'm excited to see future iterations on this project 🙂