CGTalk - Odd elbow rotation

AlanWeider

02-18-2008, 04:46 AM

I posted this on the Maya rigging board and did not get a response so I figured I would try here.

I have set up an rpIK chain and everything appeared to be fine until I realized that the elbow joint was rotating funny as I translated the IK handle. What happened is the joint itself would rotate on it's forward axis (for example if the arm were stretched out away from the body, then the rotation would be in the direction the character is facing). I can not seem to figure out what is causing this. Needless to say, the deformations are horribly wrong. The elbow rotates forward when it shouldnt' be.

The only thing I thought it might be are rotations not zeroed out. I did so, then reapplied the IK and the rotations ceased to be zeroed.

I apologize if this is a silly question. I am having a horrible time trying to learn rigging. My university has no one really knowledgeable on the subject and I am scrounging around for information.

Any help is greatly appreciated. Thank you in advance.

~Alan

prettyh8machine

02-18-2008, 11:33 AM

The rpsolver often does funny things so I can understand what kind of problem you might be having. Can you upload your scene file..only the hand? I'll see if I can fix it. I hope you understand that whenever the ikhandle itself goes past the object that is acting as a polevector, the ik chain does a flipping. Also, a bit of a care often needs to be taken in order to make sure that the rotations stay absolutely zero with consistent axes while making an ik chain. Please upload the hand rig somewhere and let us have a look at it.

Cheers

AlanWeider

02-18-2008, 05:46 PM

Here is the rig (Took me a while to realize you could post attachments).Thank you very much for taking a look :).

(http://www.uploading.com/files/GZALER8F/RIG_ONLY.mb.html)

ttyellow123

02-19-2008, 10:18 AM

The flipping problem on RPIK maybe come from the "joint prefered angle".
Since the arm joint chain you created is not on the flat plane, and the rotation axis is not pointing to the preffered direction (ex. Y-up). The RPIK solver will assume current joint chain's rotation as preffered angle, so the interpolated result will have weird behavior during some position.

Here are some suggestions. If you are using RPIK, make sure your joint chain is on the same flat plane. Otherwise, "set preffered angle" before applying RPIK (but sometimes still have flipping issue).

You can rotate the joint chain to the desire direction(rotation), then click right-mouse, select "set preffered angle", rotate the joint chain back.

Hope this may help

ttyellow^^

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