Shrugging and Flying

Wherein Verachantesse Does Shouldery Things -

1 1 It was time for me to do a shoulder rig. This will be a bit more of a technical post than some of the previous ones, since I feel like this is an area where now I have something to contribute.

I can’t find any good Blender shoulder rig tutorials out there. Every shoulder rig is some super simple toy setup with a few shape keys to get good deforms in a few poses. There’s nothing to give good deforms in most/all poses.

This is my first foray into fixing that for Blender.

First, I found a Maya tutorial that had four muscles and a corrective bone for the top of the shoulder. That was pretty legit, so I watched it a few times.

Then I spent a few days making a shoulder rig in Blender. It doesn’t really work the same as that Maya rig, but it does use some of the concepts (like keeping scapula and pectorial rotations roughly constant).

Now I’ve got my own shoulder rig, so I need to document how I did it, both for my own future self, and for anyone else who wants to make good shoulders with armatures.

The Video Tutorial

1 First, here’s a video tutorial. Give it a watch. Notes:

  1. When talking about the Lat, I mistakenly point out the Pec deform instead. Just use your imagination to understand what I mean.
  2. When talking about the breast bone constraints, I mix up the limit-distance and copy-location constraints for a moment, but I figure it out shortly after.
  3. The sternum and trap-stretch bones I say are non-deforming, but I mean they are non-moving bones. The sternum for sure is a deforming bone and needs to be. I am uncertain if the trap-stretch bone should be deforming or not. Probably not.
  4. As mentioned a couple times, there are no weight paints or corrective shape keys, so there is some nasty twisting and problems at the upper-arm, but that is for another video/tutorial.

The General Idea

1

Here’s a quick summary for those with short attention span.

First, generate a Rigify rig.

Get the arms, fingers, face, feet, knees, elbows, etc all set up as nearly perfectly as you can.

That will take you several days to weeks, depending on how much time you can spend per day on it. Take your time. Let this shoulder thing simmer in the back of your mind while you do that.

Got it done? Great!

Now, kiss that beautiful metarig good-bye. It won’t be useful anymore.

Quick Bones Overview

1 Add some bones with constraints:

  1. Sternum. Deform. No constraints.
  2. MCH-TrapStretch from base of neck. Non-deform.
  3. DEF-trap bone, child of scapula, stretch to MCH-TrapStretch.
  4. DEF-lat, child of spine, stretch to ORG-upperarm, about 10% down.
  5. DEF-pec, child of breast, stretch to ORG-upperarm, about 10% down.
  6. DEF-breast, near the existing breast bone, child of clavicle.
  7. ORG-scapula, where you want your scapula, child of spine.
  8. DEF-scapula, near the ORG-scapula bone, child of clavicle.

Setup everything so it looks great!

Done.

Okay, I’m being facetious. Let’s get a little detail.

Two Views of the Bones You’ll be Adding

1 1 Here are a couple of angles showing the bones you’ll be adding highlighted in cyan/light-blue.

You basically want the breast to translate up, down, forward, back, but not much right/left. You also want it to rotate mostly left/right (on Z axis) but not so much on the X or Y axes. Use copy-rotation and copy-location constraints to do that. Also use a limit-distance constraint to keep it from traveling too far in any direction.

The scapula you don’t want rotating much, or to travel too far from its original location, so you have a limit-distance and copy-rotation constraint on it to achieve all that.

The video has the exact details if you want to copy the rig precisely, but your character will probably need different values for the constraints, so the general idea is what’s important.

You Go, Girl

1 Here’s what she looks like when she’s happy with her shoulders.

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