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Need advise with shoulder bone placement


rusty

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Hi,

 

I've always had a bit of a problem with the placement of the shoulder bone. With the pivot of the shoulder and arm on one end and the pivot of the arm on the other its placement is important.

 

Trying to match actual shoulder/arm motion with my model...

 

MatchDown.jpg

 

 

 

the first little 'got you' is that most others (and everyone with the Squetch rig I've decided to use) always seem to model and rig with the arms out but the shoulders down -- i.e. with the shoulder bone completely horizontal. So okay, I'm going to do the same.

 

Seems to me that you must figure out what two pivot points will work in all the positions of the arm. I've attempted to do just that...

 

(In the images below the shoulder bone is the one closest to the center, the upper and lower arm bones extend from that and, the three small bones that spoke out from the arm pivot are merely guides to help me keep the pivot point in the center of the shoulder)

 

 

 

 

 

Ergo, if I've done this somewhere close to right, would put the shoulder bone here...

 

 

 

...in my 'arm straight out but shoulder down' model. However, this seems too far inward and almost certainly, when rotated down, will cause the arm to rotate right into and inside the torso -- another problem I always have to do battle with. Seems like the arm hits the torso and goes flat... seems like you can attempt to emulate this or... do nothing and let the mesh pass into the chest because it doesn't look too bad.

 

Please tell me what you think:

1) of the shoulder bone placement

2) on how to handle the 'arm down mesh passes into chest problem'

 

Cheers,

Rusty

 

Edit: In looking at this post, LOL, seem like I could make the shoulder bone a tad longer (moving the arm pivot out) and this would still work and help with the arm down position.

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Real anatomy doesn't always apply, and weighting can do wonders.

 

And, as you realized, the shoulder bone should be longer. I tend to keep bones centered in the mesh, but you can't do that all the time. I would lengthen the shoulder bone near the seam of the shirt and probably lower the base of it. It's all of a matter of what you want the mesh to do.

 

For the most part, the biceps/shoulders/sleeves, I would weight between the shoulder/bicep/bicep fan/shoulder fan. Then add some weight from the chest to the sleeves. This would be a good start and see how things go from there. Once you get to a point where you don't know if you can get it any better with weighting, I would smartskin or add muscle motion to your animation.

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Thanks for the replies!

 

Mark, I will take your advise to heart. Probably some experimentation is in order (like I have the time!).

 

... I would cut the spline count down quite a bit.

 

Really? Well, old habits die hard -- for almost a decade I worked with polygons and even after 6 years of AM, this still looks way simpler then those polygon models. I'll have to look more closely at what others are doing. I know the geometry around the shoulders is not the best (and perhaps the worst)... I just stumbled on to that fact... but, for now, I think this will do... this uniform is only used in a couple of short scenes and it doesn't do that much.

 

Neither of your replies showed up when I did "View New Posts" BTW -- no replies to my posts ever show up when I do "View New Posts"... been this way for months... too weird.

 

Rusty

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... I would cut the spline count down quite a bit.

 

Really? Well, old habits die hard -- for almost a decade I worked with polygons and even after 6 years of AM, this still looks way simpler then those polygon models. I'll have to look more closely at what others are doing. I know the geometry around the shoulders is not the best (and perhaps the worst)... I just stumbled on to that fact... but, for now, I think this will do... this uniform is only used in a couple of short scenes and it doesn't do that much.

 

Sure, only use what is needed, no more, no less. If you need the shirt to bunch up and such, you might need that much geometry...it depends. Just remember that you are going to be weighting the CP's...the more there are that are close together, the harder it's going to be to make it move well. If you're going to use cloth, then you would need a body for the shirt to deflect off of and the shirt would have to have a high patch count to keep it from going through the body.

 

Neither of your replies showed up when I did "View New Posts" BTW -- no replies to my posts ever show up when I do "View New Posts"... been this way for months... too weird.

 

It could be that we posted while you were still on the forums, then when you logged off those posts wouldn't show up as "new" when you logged back in later.

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