PDA

View Full Version : Wrist rigging question

greyface
09-24-2008, 02:47 AM
Hello fellow riggers, I have a question about forearm/wrist rigging:

I'm trying to isolate hand animation, I have a controller which the arm effector is position constrained to, and the hand effector is a child of. Arm is IK.

This way, I can move the arm into place and control the hand rotation with the same controller.

The problem is with the forearm twist: when everything is in neutral pose, the forearm is aligned to the hand, but when the arm moves around, and hence the elbow, the forearm has to align with the rest of the chain so naturally, it rotates.

Now the controller for IK/Hand rotation does not rotate and therefore there is now an offset between the forearm rotation and the hand... and the forearm appears twisted even though the hand is facing flat to the ground.

Any insight in how to fix this would be great :}

Thanks

A
Dichotomy
09-24-2008, 02:16 PM
are you using an orient constraint between the wristControl and the forearmJoint? that would cause it to change orientation with the chain and screw it up.
I typically parent the forearmJoint(s) under the elbow, then parent the wrist under the elbow as well, so that the rotation of the wrist and forearm(s) dont interact with each other.
You can then connect the rotation of the wristJoint (driven by the controller) to the forearmJoint(s)' rotation with a simple expression.
forearmJoint.rotateX = wristJoint.rotateX * .5;
which assumes that X faces down the joints on both. You could also tie the rotation to the controller itself, same script, change the name of the second value, i haven't really decided which I like better...
Its not 100% flawless, but it works in most situations.
wamo
09-24-2008, 08:21 PM
If i get what you mean correctly,i would say you have kindda linking problem, you'd better Link the Arm to a Handle,then make your ik chain between arm and wrist,link the IK goal to a new handle aligned to it,now make a total handle aligned on top of the Arm and link both handles to that.then you can follow what Dichotomy says about forearm joints,his expersion works well.

Now you isolate the arm animation!
PEN
09-24-2008, 09:01 PM
Does this help you at all?

http://paulneale.com/tutorials/twistBones/twistBones.html
greyface
09-26-2008, 08:33 AM
Thank you all for your replies!

Dichotomy:

The way I have it setup is I have some influence objects along the forearm, which twist when the hand control is rotated, and that is what I'm having a problem with, because they are parented under the forearm bone which rotates depending on the up vector! I guess maybe the influence objects must be parented a different way, so that they are isolated?

wamo:

You got me kinda confused there, I suppose you mean elbow, when you say 'Arm'?

PEN:

I will check that out, thanks!

--

Currently my hand root is parented under the arm effector, but its orientation is controlled by the hand control via an up vector. I've tried parenting it in other places, like the torso or cog, but i'm not too sure which is best.
CGTalk Moderation
09-26-2008, 08:33 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.