Armature+Weights = shoulder, elbow + arm-pit

Hey everyone,

Anyone know of a really good tute on armature/weights in the problematic shoulder areas, knee joints, etc.? I’m getting the typical problems:
a) upper arm cutting into torso-mesh when lowered
b) unnatural deformations at elbows
c) or else a generally ‘rubbery’ appearance; as the arm stands away from the body and bends like a hose when lowered (to avoid cutting into torso)

Before resorting to something like shape-keys to fix deformations, I’d like to make sure I have a real understanding of advanced weight-painting, AND creating a mesh that is truly suited to deformation in the first place.
for example…
Should a characters arms, etc, really be modelled straight out, as in most examples? And what should a proper mesh be for the shoulder/elbow folds?

Any help would be very appreciated…

John, the basic problem is that CG skin doesn’t maintain a fixed distance from CG Bones. The vertices are connected to each other, the bone just gives them a displacement or rotation from their previous location. The question is really not how to eliminate deformation, but how to minimize it. The simple solution is to do your modeling with the limbs near the center of the expected range of motion. Arms lowered half way to the hips, elbows bent at a 90 degree angle, fingers curved as if holding a softball, and so on. Then do some experimentation to find how far you can bend the joint before the inevitable deformation becomes too noticable. I find it’s generally around 60 to 90 degrees.

Since real range of motion runs from 160 degrees or so for an elbow or knee, up to 360 for the shoulder, you won’t find an ideal solution, just a compromise. That’s when people start resorting to extra deformation bones, fancy contraints, shape keys, py drivers, and so on.

Weight painting is somewhat of a chimera: it will help increase the range of motion, but never to the point where you want it. Since weight painting is fairly tricky, you may wind up with the impression that if only you were better at it, you could achieve the results you want. Unfortunately, that seems to be an attractive but blind alley.

tolobán is probably the expert at avoiding deformations who posts here regularly, check out his thread on Muscle simulation experiments (nude female model). There are links in that thread to other methods, as well. Toward the end of the thread he shows a good set of shoulder edge loops, and I suspect something similar would work for elbows and knees as well.

Hey - thanks very much for that explanation! really, it does help explain that to me finally.

i’m gonna remodel the arms downward, and allow for more depression in the torso frist off, and try it again