Shoulder Bones - necessary?

#1

Hello, folks. I’m new to this forum, and I’ve got a question about shoulder bones.

Pliable shoulders are important. The shoulders are the “eyebrows of the body” as somebody once said. John Keates just repeated this wise gnome, over at the Animation Master forum. :slight_smile:

Here’s my question:
In a rig, should the upper-arm bone (the humerus) be a child of a shoulder bone, so that when the character shrugs his shoulders, the movement is a nice little arc? Or would it be just as well if the humerus was held more loosely – without a shoulder parent. In this alternative case, shoulder-shrugging type movements would be achieved by merely translating the humerus bone. It’s possible to add fanbones and such in the shoulder area, to wed the humerus to the upper torso, so a parental bone is not absolutely necessary.

I guess my question is: Is it important for shoulder movements to be arcs? Or are the movements so limited that translations would work just as well? What do you guys think?

In my ignorant opinion, for most cartoony characters a pair of rotating shoulder bones are not really necessary; translating the humerus would be preferable because it offers greater flexibility. Only a photorealistic character would benefit from shoulder bone parents. But I’d love to hear other people’s thoughts on the matter. All feedback is welcome!

Sincerely,

Carl Raillard

#2

There are NO ‘shoulder bones’… shoulders rotate from further down in the back, not the neck
But I would say its important IF your character has Shoulders. some cartoony characters dont have noticable shoulder protrusions in that area.

#3

Hello! Thanks for nibbling, Pooby! :slight_smile:

To the best of my understanding, there are two shoulder bones, the scapula and the clavicle. The scapula is the flat shovel like thing that rests against the rear ribs. It floats up and down, compelled by the muscles attached to it. The clavicle is different; its proximal end rests on top of the sternum, right there at the little depression at the base of the neck. The clavicle actually does form a continuous bony link between the arm and the torso.

Lots of CG artists “fake” this complex bone arrangement by eliminating the scapula & the clavicle; they substitute them with a single bone. This artistic substitute bone starts close the spine (just below the neck) and ends at the shoulder socket area. It serves as the parent for the humerus.

I think most CG characters need something akin to this arrangement … otherwise they won’t be able to do shrug their shoulders, right? :shrug:

Up till know I’ve always thought this shoulder bone was necessary. But recently I’ve been having second thoughts about it. For starters, it’s not even accurate. The clavicle area shrinks and grows, due to the offset. The distortion is trivial, and nobody seems to fret about it. So I’ve been thinking: Why not get rid of the simulated shoulder bone altogether? It would be fairly easy to rig the character so that a freely translatable humerus will handle ALL shoulder-shrugging chores. In fact, Raf Anzovin uses something pretty close to this, in his commercially available Setup Machine Rig. http://www.anzovin.com/setupmachine/index.html

I just need a little feedback to help me make up my mind. Is the arc in shoulder movements noticeable?

If there is an outcry at getting rid of the beloved shoulder bone, or if my pal Stephen Millingen can persuade me otherwise, I am rather inclined to delete this sham shoulder bone.

My thick skull awaits all attempts at persuasion.

Sincerely,

Carl Raillard

#4

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