View Full Version : IK Arm won't stop shaking!!!

01-23-2005, 07:47 PM
I've got a pretty normal IK arm set up on a character. I have a null on the elbow so I can control how the arm sits. I need the null, but it seems to be making the arm constantly shake. If that was the look I was going for, then fine, but it's not so if anyone has a solution, please please please help.

03-17-2005, 08:30 PM
I had this problem with an IK arm. I moved my character to the origin and the problem became much less severe. Instead of degrees worth of movement in my bones, it was hundredths of degrees.

I got the idea from this discussion: http://www.cgtalk.com/showthread.php?t=122442

03-18-2005, 03:59 AM
Did you put a little bit of a bend in the arm bones at the elbow before you set up IK?

03-18-2005, 10:01 AM
You may want to consider re rigging the arms. Just name them the same so you don't have to remap the weights. I use a collar bone, a bicep bone, a forearm bone, and a hand bone. To rotate the elbow, I welded the base of a small bone controller between the collar bone and the bicep bone in modeler. This small bone is parented to the collar bone and the bicep is parented to the small bone. Now all you have to do with this setup is rotate the small bone to control the position of the elbow. The small bone is influenced by Ik. Make sure the collarbone is not afftected by IK:) This setup is inside Dan Alban's 'Inside LW 7' Let me know if you need a picture of what I'm talking about.

03-19-2005, 04:28 AM
thanks for the advice.

Dodgy, yes there was a bend in the arm before implementing IK.

jb - I'll try moving my character to the origin as that seems a little less complex than Mr.Westmas' re-rigging solution, which I will probably have to try immediately after moving my character to the origin.

Anyway, thanks for the responses. My only other option is to remove the elbow null or to refrain from using IK in the arms until I know what I'm doing. Or to only create characters without arms. Or to just go back to drawing cartoons on butcher's paper and sticking them on my fridge. I never had IK problems back when I was five. Of course I was using lightwave 2.4 back then. Still had the same interface mind you.

Don't post replies while drunk. Thanks.

03-19-2005, 08:03 AM
Look up a Tim Albee book too. He's a rigging pro! :p

03-20-2005, 03:14 AM
The IK will start flaking out if your character is very far from the origin, maybe a kilometer or more.
Do you have "keep goal within reach" turned on? If so turn it off.
Make sure your character is modeled to more or less normal scale. Sometimes if you have a very large or very small character it will do strange things to the IK. IF the character is very large try using very small goal strengths. If the character is very small try using very large goal strengths. On a normal size rig I typically go with 50-100 on the goal strength.
Are you using multigoal IK chains? If you are using IK to control the elbows positions you can sometimes get shaking as the arm goal and elbow goal fight for dominance.
Prebending the elbow will help the IK solve which direction to bend but usually shouldnt cause shaking.
Check and make sure you have a definate start and stop to your IK chain. Make sure the beginning has unaffected by IK turned on.
Also I typically dont use IK on the upper body unless some part needs to stick to a surface. If you need to use IK and FK at times I would apply IKBoost to the rig. :)