CGTalk - Help with arm rig

Transform Gizmo

12-15-2002, 05:06 AM

one particular feature of character studio that i have enjoyed, is the ability to set planted keys. for example, if you have a character with their hands on a table and you want the character to move around a bit, but have his hands remain still, in the same position on the table, or a character pulling down a lever, you can move all other parts of the character without making the hands rotate at all. i have found this a bit tricky to impliment on my own rigs. with my current arm setup(wich is just a HI solver from the upper arm to the hand), if you move your character, except for an arm, you notice that the hand rotates with the ik chain in the arm as it swivels with the motion of the body. i would like to be able to achieve something similar to planted keys in character studio with my own rigs. so would anyone happen to have a method for achieving this? perhaps a link or a sample file?
any help is much appreciated.

LFShade

12-15-2002, 07:02 AM

It's a bit complicated, but there is a way to rig an arm for this. Hopefully I can explain it without too much confusion. I'm going to have to assume that you have a basic knowledge of parameter wiring and custom attribute setup.

Create a point helper at the wrist and align it (pivot to pivot) to the hand bone, then link the hand bone to it. Link it to the forearm bone. Create another point helper at the wrist and align it to the hand bone, then link it to the forearm bone as well. Turn off all rotational inheritances for this point.

Select the first point helper you created and add an orientation constraint to its rotation track. Set the little terminator bone as the first target and the other point helper as the second target. Change the weights so that the terminator bone is at 100.0 and the point is at 0.0.

Now add a float slider custom attribute to the object of your choosing (I would probably just put it on the hand bone) and name it "Lock Hand" or something similar. Set its range as 0 - 100 (should be the default).

Wire the custom attribute to the first weight channel of the point helper's orientation constraint, and in the Wire dialog edit the expression so that it reads 100 - Lock_Hand. Wire the custom attribute to the second weight channel of the orientation constraint, using the default expression.

Now, when the Lock_Hand slider is at 0 the hand will be oriented to the forearm, and when the slider is at 100 the hand will remain oriented to the point which does not inherit rotations. You can keyframe the slider to blend between the two behaviors.

Here's a simple rig to demonstrate the concept (http://www.zeetec.net/host/lfshade/hand_lock.max)

Transform Gizmo

12-15-2002, 07:31 AM

hey, thanks a lot. That does the trick!

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