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View Full Version : Forearm Twist - Negate XROT problem

AcrylicStudios
03-25-2009, 12:33 AM
Hi guys, got a really big problem I need some v quick help fixing.

basicly

I want to my character to be able to pick up and hold objects, using IK, to do this the hand must remain static so that the body and rest of the arm can move around it

The hand is merely position constrained to the wrist point rather than directly linked in, I have an orientation constaint in the rotation list which is controlled by a custom attribute slider to orient the hand to the lower wrist bone when set to 100 and off when set to 0, I also have forearm twist and to prevent double rotations to the hand i have a negate x rot expression on the hand, beneath this i have a euler xyz to allow manual rotation.

the problem is when i try to rotate the hand and orientation slider is set to 0, so I can use the IK to pick up objects, there seems to be a horrible gimble lock on the hand and it wont rotate correctly. it makes picking things up impossible.

anyhelp would be great, i'm working on a live project and time is of the essence

picture

http://forums.cgsociety.org/attachment.php?attachmentid=140238&stc=1

thanks guys
PEN
03-25-2009, 02:58 PM
Easy answer, never do what you have done. Trying to drive an object with an orientation constraint and then an Euler above will cause problems as you can see. Instead add another helper above the wrist control, add the orientation constraint to it and then just manually drive the wrist controls as you would any other. This way the wrist blending option is happening above it in the hierarchy.
AcrylicStudios
03-25-2009, 11:09 PM
Thanks for your response Paul, I'm a great fan of your tutorials.
I have tried your advice, however it means going back and re-setting up forearm twist as your method removes the forearm twist I had set up via wire parameters and doesnt allow for the hand to operate in an IK mode ie following the lowest forearm bone .

I'm probably confused due to my frustration and panic, perhaps I could send you a copy of the rig to examine?
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03-25-2009, 11:09 PM
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