View Full Version : Arm rig problem

06 June 2003, 03:44 PM
I am having a problem with the wrist on my character. It works fine if I don't set any keys on it but once I do it seems to get screwed up. This is my fist character rig so it might be considered pretty ugly, but I don't want to have to redo it if I can help it. I have posted a pic to show what is going on. The way I have it set up now is with an Ik chain running from the shoulder to the wrist. Then I also have one running from the wrist to the palm to allow it to twist. The problem is on the IK from the wrist to the palm. When I set the twist a key it, it gets messed up like in the pic. Anyone know what I am am doing wrong and the best way to fix it with out to may headaches. I have already weighed all the joints, so I would rather not do it over if I don't have to.

06 June 2003, 06:41 PM
hey thats a pretty cool model you got there. If I understand your question right you're trying to use an IK to control the twist of the arm. I don't think I would do it that way. I can't see the pivot points of your arm contol object, so I'm not sure how easily you'll be able to set this up, but I would use that one object to control the position and the arms rotation. First make sure that the control object is point snapped to the wrist joint (where your arm IK ends), then point constrain the IK to the control object. This will give the arm position control you need. Second orient constrain the wrist joint to the control object. You need to be very aware of the orientation of the local rotation axis of the wrist joint because if the wrist's LRA's are not aligned with the control object the wrist joint will flip to align themselves correctly.
That will give you the rotation and twist of the hand you want. Now wasn't that easier than having to key the twist of an IK to get the hand rotation. THere are several variations on this but I think this will work best for what you want.

06 June 2003, 06:59 PM
Thanks, I will give that a shot.


06 June 2003, 12:26 AM
I dont really understand exactly why you are rigging your character like this. Why have you got an IK handle going from the wrist to the palm?? If you want that area to twist (although it really shouldn't be necessary) you can just rotate the joint. There is no need for an ikHandle. For a very very basic arm setup, you should have an ikhandle going from the shoulder to the wrist and thats it. Then the fingers and the palm you can just setup using set driven keys. You can also still rotate your wrist joint even if its at the end of the ikHandle. If you want to rotate the elbow, you need to use a pole vector constraint to an elbow control. I'm not sure if I'm helping here, but it just seems like you're making things harder than they need to be. :sad:

Let me know if this doesnt help you and I'll try and see where I'm getting things wrong. :thumbsup:


06 June 2003, 02:10 PM
Yea thats what I ended up doing and it looks like it will be fine. Thanks for the help. :)

06 June 2003, 12:03 AM
i was taught this same method by a sony guy. there is no real right answer but i have found that it builds follow through into your animation which is what IK is all about.

when you move your wrist the arm will move but the hand points back towards its IK. you then just animate the hand coming into its position instead of having to backwards animate the follow through.

easier? its all up to the animator and the scene.

06 June 2003, 12:12 AM
Hey Mayic,

It really does boil down to preference. I am busy working on a tutorial right now on setting up an arm that has 2 joints between the shoulder and elbow and 2 joints between the elbow and wrist for better deformation purposes. It also has an IK/FK switch and some other cool things. Its going to be quite cool. :thumbsup: I'll let everybody know once its up.

I think arms should really have the ability to be animated both with FK and IK and to be able to blend between the 2. Also having a seperate rotate control that lets you rotate the hand independently of the translations orientation. :argh:


06 June 2003, 02:29 PM
I am busy working on a tutorial right now on setting up an arm that has 2 joints between the shoulder and elbow and 2 joints between the elbow and wrist for better deformation purposes.

Very cool, can't wait to check it out. When I was looking thru tutorials on doing the arms I didn't find alot about it.


06 June 2003, 05:07 PM
Definitely let us know when you have it done loked

I too would be interested in checking that out.


06 June 2003, 11:01 PM
I'm about half way there, so I should have it done in the next few weeks. Just depends on the amount of work I get thrown at me.

I'll definitely let everybody know once it's complete:thumbsup:


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