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SplineSoup

Rigging a Thigh Roll

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Hey everyone!

I'm working on rigging a character for an upcoming short film and have a puzzle to bring to the table regarding hip/thigh rigging. While rolling the thigh bone on my character (and pretty much every library character), I observe a disconcerting tendency of the pelvis to simply collapse. To remedy this, I'm exploring the use of a chain of "fan" bones to distribute the roll of the thigh along a series of thigh cross-sections, giving the hips a much-needed break. I've currently tested my design with a simple tube model and the results look promising. It basically works like this:

 

Screen Shot 2016-07-21 at 4.35.42 PM.png

 

A chain of roller bones is constrained to the thigh and the thigh geometry is assigned to them. The rollers are constrained to Orient Like the thigh, but the roll is achieved by separate Roll Like constraints which gradually add up to the full roll of the thigh by the time they reach the knee.

 

ThighBasic_anim.gif

 

Spiffy! I was pretty proud of myself...until I brought this back to my actual character model and realized that legs are not perfect tubes!

 

The conundrum I'm facing now is that I want to apply this principle to a thigh bone that is not straight up and down and to leg cross sections that don't perfectly line up, vertically. Between proper bone hierarchies and constraint options, I'm currently stuck. I've attached the project file with my two concept tests. Any pointers on how to create a chain of roller bones that move with a thigh but maintain their own unique pivot points along the leg so that each leg cross-section rotates, more or less, around its center?

 

Thanks!

Thigh Roll Test.prj.zip

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...The conundrum I'm facing now is that I want to apply this principle to a thigh bone that is not straight up and down and to leg cross sections that don't perfectly line up, vertically...

 

I'll note that even though a real thigh is not a perfect cylinder, it does have a single axis that it turns around because the thigh bone is attached at a socket that it can not depart from (we hope).

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I did a Siggraph video covering this issue. I cover the fan bones for shoulder and thigh, and also smartskin:

https://youtu.be/gkBmYlRwP_8

 

Thanks for the tip. This is a fantastic overview of the rigging process and has so far shown me that I've been doing CP weighting in a pretty Jurassic way. I'm about 1/3 of the way through and ended up weighting the character's torso while I watched. Looking forward to the section on shoulders and hips!

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