CGTalk - Shoulder Blues

Anchuvi

01-09-2003, 05:10 PM

I wonder if I can find some help out there...

I have a an arm setup for an in game character, this is a simple four joint arm - Shoulder > Bicep Twist > Elbow > Wrist...The arm works great untill I raise it above the characters head. I seem to get a twist of sorts right up near the shoulder, looking much like a sweet wrapper or the end of a cracker. I have tried many ways to figure out why it is doing it but I can't, its as if the shoulder joint twists around as it reaches its limit but no values are in the X rotation...

I hope I am explaining myself properly...

Any help !

MDuffy

01-09-2003, 09:10 PM

The problem you are running into is that your IK chain is passing the plane that it solves within, and so your calculated values are flipping from negative to positive. Or you have an orient or aim constraint that is running across the same problem.

The way I solve this problem is to put a node in the controls and a joint in the skeleton that sits above the shoulder in the heirarchy and allows you to change the parent coordinate system that the shoulder is solving in. That way you can use both the Shoulder_GimbalFix control and the Shoulder control to get your position. Normally you'll just animate with the shoulder, but when you hit flipping situations you'll switch to the GimbalFix control.

Hope this helps,
Michael Duffy
mduffy@ionet.net

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