How to deal with skinning on characters' shoulder？

vempdance · Jul 2017

when skinning the shoulder, I always get a bulge under the shoulder when move it up like this

Is anyone know how to get this part looks more nature? I know morph target is a solution, but is there any other way to solve this problem?

ActionDawg · Jul 2017

You simply need to weight those vertices more to the torso bones, so they don't get pulled around by the arm as much.

vempdance · Jul 2017

somedoggy said:

You simply need to weight those vertices more to the torso bones, so they don't get pulled around by the arm as much.

That will cause a big stretch between raised loop and those which are more affected by the torso bones. Especially with textures.

Mark Dygert · Jul 2017

Yep. You can't get around stretching, you can only manage it effectively. Do you want a weird bulge or do you want a little texture stretching?

You will want to weight that area partially to the clavicle but mostly to the spine.

Right now you are rotating the clavicle too much when you're raising the arm.You're example has the arm just above a T-Pose and the clavicle is already over extended. The clavicle only rotates 20+- degrees when the arm is at it's extremes and it doesn't even really need to move until the arm reaches a T pose or higher. You're example has the arm just above a T-Pose and the clavicle is already over extended.

The arms rotate a full 90. The clavicle is just a helper to pull the shoulder into the ear when the arms are straight up above the head, and to help out in subtle ways. They aren't arm joints.

vempdance · Jul 2017

Mark Dygert said:

Yep. You can't get around stretching, you can only manage it effectively. Do you want a weird bulge or do you want a little texture stretching?

You will want to weight that area partially to the clavicle but mostly to the spine.

Right now you are rotating the clavicle too much when you're raising the arm.You're example has the arm just above a T-Pose and the clavicle is already over extended. The clavicle only rotates 20+- degrees when the arm is at it's extremes and it doesn't even really need to move until the arm reaches a T pose or higher. You're example has the arm just above a T-Pose and the clavicle is already over extended.

The arms rotate a full 90. The clavicle is just a helper to pull the shoulder into the ear when the arms are straight up above the head, and to help out in subtle ways. They aren't arm joints.

Thank you for the reply. What you said is true, most of the time we have to balance between different issues. But still I will try to get the best result as I can. If I find some solutions before others told me here, I will post them out.

As the clavicle rotation, what I learned it can raise above 30 degrees up(http://www.hippydrome.com/ShldrUD.html), so I don't think my example is raising up too much(well maybe 5 degrees too much

, but it is not so obvious as I rotate it down).

musashidan · Jul 2017

What is the topology like? Do you have enough geo to support the deformation? Looking at the other arm in neutral state the lats appear to be joined to the biceps in a strange way.

Shoulders/hips are most tricky areas. As mentioned, a tradeoff is often required.

Mark Dygert · Jul 2017

vempdance said:
As the clavicle rotation, what I learned it can raise above 30 degrees up(http://www.hippydrome.com/ShldrUD.html), so I don't think my example is raising up too much(well maybe 5 degrees too much , but it is not so obvious as I rotate it down).

1) It can totally go wherever you need it, animators annihilate anatomy every day and it works great. Just don't treat it like it is the arm joint and don't ignore it. It has a limited range of motion. Personally on my rigs and in my animations I don't rotate it as much as you did, most animators I know don't go that far for a pose just over T (I just asked 3 of them), so yea be careful.

2) Hippydrome is based on pixar-era characters, exaggerated and bendy. He is also showing you the full range of motion of the clavicle he isn't showing how the arm moves when it raises. It's like showing someone doing the spits to demonstrate how flexible the legs are and then saying "oh that what people look like when they walk", of course that's hyperbole but you have to be careful and study how people move and take examples in context.

pior · Jul 2017

- You are lifting the clavicle too much, it should only start rotating up once the arm reaches the horizontal first, which is not the case on your screenshot.
- You definitely need to weight these verts to the torso (spine 2/3)
- Your model doesn't have armpits. Therefore, armpits/shoulder will not deform well.
- Based on the left of the screenshot (his right clavicle) you currently don't have the clavicle verts weighted to the clavicle bone.

vempdance · Jul 2017

Thanks for everyone's suggestions. I will check the anatomy and topology to make it looks more nature.
And for those one who has the same problem, I found a video by My Oh Maya here:

https://www.youtube.com/watch?v=5i-gxtXj1Ww&t=3s
He shows how to bake deformers to skin weight in maya 2017 update 3. So I could use deformers like pose space deformation to deal with those problem places. This method has limits he explained in the video and the comment below, but I think it gives us one more way to solve this problem.

How to deal with skinning on characters' shoulder？

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