I'm trying to animate the hand of a character with IK.
And the hand should often be in a stretched pose..
How do I overcome the elbow snapping problem?

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Fiery

Here is a plugin for xsi by Andy Nicholas that solves this problem: Soft IK in XSI

Another trick is to never build the bones in a straight line. When the leg or hand geometry is straight the knee and respectivley the elbow joint should be at a 8-10 degree angle. It softens that snapping motion a lot. Then you just have to set a rotation limit to keep the elbow or whatever from “breaking” the other way.

You can also gain more control by animating the clavicle so that you don't get a straight line.

Yet another way is to write a script that will stretch your forearm bone whenever the IK effector will reach the point when the snaping motion starts.

Yet another solution for your problem would be to use FK instead of IK

Hope it helps.
Cheers!
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Andyba, 3d artist
skills: 3d modeling, texturing, rendering, 3d character animation, compositing
3d software experience: 3ds max, Maya, Softimage XSI, Deep Paint 3d, Body Paint 3D, Wings 3D, Z Brush
2d software experience: Adobe Photoshop, Adobe After effects, Macromedia Flash, Freehand