CGTalk - Thinking about wrist problem

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Stroker

12-08-2002, 05:34 PM

I'm still fairly new to rigging, so bear with me.

Been thinking about the wrist problem. For a new guy like me, sounds like a good exercise. Somewhere around here, someone mentioned using an extra bone, and that's the idea that stuck with me. So I thought about it and thought about. Eventually I came up with the idea of "doubling back".

Basically, and extra radius-"finger" bone that runs back along the ulna and connects to the elbow. Make sense?

Okay, set up the bones. humorous and ulna. Then the radius seperate of that and running backwards along the ulna. Then a silly box for a hand.

Hierarchy like this: humorous > ulna > hand > radius.

Make a point helper object. Link it to the ulna and align to the pivot point (position and orientation) of the ulna.

Make the IK chains. One from the wrist (end of the radius) to the humorous. Other one is just the radius all by itself (the little knob at the end of the bone to the bigger part).

Grab IK_Chain_Radius and link it to that helper point that's on the elbow.

So far it seems to be moving around pretty good. Well, good for a prelimary fiddle rig.

I still have yet to Skin it. I'm sure once I get to it, I'll have some serious tweaking to do with various things. For one, it looks like I will have to shorten the radius considerably - funny motion going on when I bend the elbow. Tweak envelopes (I bet these are going to be a pain), pivot points, and things.

I am a big proponent of figuring these things out for myself (experience is my greatest teacher), but I would like to hear what you veterans have to say about what I have so far.

LFShade

12-08-2002, 05:48 PM

I've tried this setup myself, and my conclusion was that it's just too difficult to skin. I really like the motion; it's reasonably accurate to how the real bones move under the skin in the forearm. But, short of using a plugin like ACT to get the "muscles/skin sliding over bone" effect, the result after skinning always looked really wierd.

Give it a go yourself, though. Who knows, you might end up with a better result than I did. I wasn't too experienced with skinning at the time I tested my radius/ulna rig, and I gave up quickly.

Stroker

12-08-2002, 06:43 PM

I think I figured it out. There were two main things that I had to play with.

1) Radius bone/envelope. Pretty much has to run down the center of the forearm instead of off to the side.

2) I had the radius bone envelope set to Absolute instead of Relative. Man, this was driving me nuts because fall-off wasn't working the way I wanted.

That's pretty much it. Well, I still have to figure out how to prevent the forearm from "squishing in" when I rotate the hand, but I don't think this will prove too difficult.

Other than a little bit of squishing, it works pretty damn fine. At least to my satisfaction for my skill level.

Back to the grind.

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