Editing IK Targets created using CAT

#1

I have been creating the IK setup for the arm on my CAT rig and I am a bit unhappy with the default placement of the IK Target when pressing the ‘Create IKTarget’ button. It places the target at the end of the wrist bone (or palm, as CAT likes to name it by default) so therefore rotations start at the end of the wrist/palm instead of at the end of the forearm bone. It seems to me that it would be prefferable to have the IK behavior terminate at the end of the forearm bone so that I could then freely rotate the wrist/palm via the bone or some additional controller. Any thought or reasons why that wouldn’t be a good idea? Seems like you would get IK functionality out of the arm and then the ability to control the wrist placement in FK (i kinda thought that was how people set it up back when i was learning rigging in maya).

I have noticed that if I set the ‘Num IK Bones’ in the Limb Animation panel under the motion tab to 2 instead of 3 this gets me closer to what I am looking for. The hinge behavior associated with IK isn’t triggered until the handle hits the end of the forearm bone in this case which is what I want but it still wants to place the target by default at the end of the palm and I get a slight rotation/movement when I drag the target from the end of the palm to the end of the forearm. I wasn’t sure if I could just fix this by freezing transforms on the target at the end of the forearm (or if I can even freeze transforms on an IK target). I also want to have stretch on the limbs so I would need the target to see the end of the forearm as the end of its trajectory, not the end of the wrist/palm bone, so that as I pull beyond this point I get stretchy behavior and not the slight rotation/movement I mentioned a moment ago.

#2

I’ve not messed with the Num IK Bones extensively. But quick experiments with it seem to yield decent results. Test it thoroughly, though, since CAT is fraught with with bugs.

An alternate approach might be to create an arm without a palm. (Just uncheck Palm in the Modify panel of the limb.)

You can then create an Arb Bone off the arm to serve as your hand bone. The one notable downside to this is that you won’t get access to the Digit Manager. But considering the Digit Manager has a fair number of bugs in it (namely saving/loading Preset Poses), I’m not sure this is that huge of a loss.

Regardless of your method, you might want to experiment with putting an Orientation Constraining your palm to your IK Target so that it will rotate with it. Good luck with it.

#3

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