Need help with rigging arm/shoulder area

Hi.

I am skinning and rigging a human character and I am struck with arm-shoulder joint area (and crotch-leg area, but I think that the solution will be similar).

I am doing skinning with vertex painting. But I cannot get it to work properly. I am able to skin it so it will look good if the arm is rotating up and down - but rotation in other axis (forward-backward) looks horrible and I cannot make it look good without braking previous deformation (during up-down rotation).

So I am curious. Is there any trick to get it work? Something like add extra bone? I found some tutorials about IK Solvers, etc., but my problem is actually the skinning.

I am sure that this is common problem in character rigging. So does any have a link to some advanced tutorial?

Anyway my model is a little more complex, here are screens:







Personally, I think the shoulder is one of the hardest areas to work with. There are a lot of areas you can run into problems. Topology can be one area, there is a few tricks to getting the edge flow right so the shoulder deforms well. Here’s a couple of links on that subject:
http://blenderartists.org/forum/showthread.php?t=55491
http://www.blendercookie.com/2010/03/31/topology-review-shoulder/

Another area can be weight painting, I’ve seen a lot of models where all the mesh that should move with a bone is painted red. You can vary the amount of weight painting to make it blend into other areas of the mesh. In 2.49 you can set the weight to 1/4, 1/2, 3/4 so parts of your mesh move less than 100% with the bone. In 2.5 there seems to be alot of improvement and you can vary the weight even more so. In the pic you posted where the arm is rotated forwards, I’d say that might be part of the problem, try spreading out the weight paint in towards the center of the torso some. See attached screenshots. I am always refining my weight paint as I rig, I’ll test a bone to see that it works properly and if the mesh deforms badly, I’ll go back and tweak the weight paint.

At first, I would focus on these two areas. I think they will solve 90% of the problems. Then there are a lot of other methods to further fix things up. The use of ‘fan bones’ - bones that are weight painted to a few vertices and move or stretch in relation to other bones. There are driven shape keys, where you correct the position of vertices by hand and engage the shape key as a bone moves/rotates. There is also the mesh deform modifier. And I’m sure there are other methods that I’m just not thinking of at the moment. I really think that if you don’t have good topology/weight painting then using other methods to fix things is just covering up the real problems.

Randy

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Thanks a lot revolt_randy. I am sure I will use you advice.

Looks to me like you have a pretty good start, topology looks OK if not totally optimal (what that is, I don’t know for sure :wink: ). I agree that weight painting is the key if you want to use a simpler rig – it sometimes takes a lot of “dabbing” at vertices in the cage to tweak the deformation to near-perfection, particularly in the shoulders, where the joint’s “Degrees of Freedom” make it a real challenge. As r’_randy said, try to spread the arm bone’s influence into the upper pectoral area above the breast some more, it should help.

Also remember that you can use weight painting on another bone to help finesse how one area of the mesh responds. For example, I use a “fan”-type bone for the breasts of my Katrice character (Kata), that not only moves their mass around but also tend to balance the influences in the upper pectoral/shoulder area. I have fan bones for both upper pectoral and trapezius areas as well, to pull the mesh into shape for the more extreme deformations. Even with those I’ve run into some poses that just can’t be made “perfect” – both topology and weight painting contribute to those problems.

One tip – try to keep the numbers of bones that influence any one region to no more than three, and best if you can do with only two. Balancing multiple influences can be a major headache! It’s sometimes impossible to tell what bone is causing what deformation glitch, because in effect, they ALL are! :eek:

Thanks for help, chipmasque. I will try some extra bones.

Hehe… I started a very similar thread a little while back.

You can read the discussion here:

Shoulder Rigging Challenge

FeelgoodComics did a cool shoulder rig. A little complicated for a novice, but an interesting rig to be sure. (He promised a tutorial on it… maybe someone should poke him and see how that’s coming :slight_smile:

I ended up spiraling into shape keys to solve the problem.

Basically, unless you are doing a rig for your demo reel, I would say you can focus primarily on deformations when the arm is in the down position. If you think about it, the arm over the head pose is very unnatural, and hardly ever occurs in real life. Arm by the waist, however, happens all of the time.

Post your progress, and guys will chime in with ideas as they have them.