Rigging IKFK SWITCH WITH ULNA JOINT (MAYA)

[Dermont]

What I have done.

One way-
Only have the Ulna four bone arm as the bind rig place an IK for the twist control for the Elbow/ULNA/wrist
and have the IK and FK the Normal three bone set up.

Then place the Twist on both IK and FK controls in relation to the rotation of the wrist just with an ease out (I think that’s the right one) to it so you get a falloff for the effect you want.

The other way-
This is the more stable IMO. Use the Connection Editor Output the Rotation of the control and inputs the bones and just adjust the fall off with the the unit conversion node in the Hypergraph.

Oh for getting the bind part started make sure you have the IK/FK working and then parent the Ulna Elbow to wrist over it.

[lifire]

In my opinion, twist joints such as the radius/ulna are easiest to setup when they are not actually part of the system. Draw shoulder-elbow-wrist, then add a seperate joint or 2 directly between the elbow and wrist (point contraint to both), parent constaint them to the elbow joints, and control their orientation (in x, if that's down the bone) with the control object. Using more than one joint can help give the nice falloff our forearm actually produces.

[Dermont]

ooo the good old Chris Maraffi setup

[lifire]

That's not even close to what I was trying to say. Chris Maraffi uses a radius bone and an ulna bone, then he does an over complicated ik parenting solution. Just make 2 joints between the elbow and wrist equally spaced and parent constrain them to the elbow and drive their orientation in x by the arm or hand control. Making them part of another system that isn't parented directly in simplifies the twist and avoids the dreaded cycle.

[Dermont]

Terribly sorry for the mix up.

But now I am intrigued on your set up could you post an image?

[rigwrxxs]

parent extra joints? I haven't tried that method but it sounds like it does the same thing mine does. I actually start off with a 3 bone setup.

heres a little trick, create an EP curve from the elbow to the wrist, put your joints on a layer and template them, then get your joint tool back out and hold the C button (snap to curves) and you'll be able to make a joint perfectly between your elbow and wrist.

then I parent the wrist to the new joint and the new forearm joint to the elbow

the only tricky part is for setting up IK, you'll need to make the IK from the shoulder to the forearm, then you'll have to set evaluate nodes to ignore all and move the end effector to its proper position at the wrist. (if you script this process you dont even have to turn off nodes woot)

when its all one single joint chain, it allows you to add stretchy ik later, which is essentially scaling in a single axis down the joints.

[lifire]

Yes, if it is a single chain you can do the stretchy IK, but this way you don't have to have seperate IK/FK wrist controls (annoying if your wrist control has finger controls on it) and don't have to worry about effectors. This way you can also give it a falloff between joints.

As to make it scale, well, just plug in the "scale amount" number you're using for the other joints into the translate X child twist joint and that should work.

It all comes down to what you need to forearm to do and how realistic you need it to look. If you want a simple stretchy IK and you use scripts, yeah add one joint, move the effector and do a utility node stretch. But it's achievable either way.

Hope this image clarifies a few things. It's less complicated than I made it sound.

Sorry about the image, don't have PS on this machine.

[rigwrxxs]

very cool, i'll have to check into this method, the reason I didnt like using a single wrist controller before was probably because I was playing with single joint chain IK FK switching, and I didnt like how there still needed to be an IK controll and FK controller at the same time even though the FK would do all the rotates and the IK controller would do the translates. seemd very confusing to me, even more so than having 2 joint chains, not to mention i couldnt find a way to get it to stretch either.


thnx for the tips though

[lifire]

The thing about having different controllers for translate and rotate is that you can do script job so that when one is selected they are both selected. As long as the rotates are locked on the IK controller and the translates on the wrist controller, it will act as if a single controller.

At first I was skeptical about it as well, but my animators have had no problems with it yet as long as I include that script job or some other selection method for both controls.

Good luck.

Edit: I also find it quicker to use a script such as beJointSplit or simply parent constraining a single joint to both the elbow AND the wrist and adjusting the weight of those two to get it exactly between the two. Delete the constraint, orient constraint the joint to the wrist, delete that constraint. It just seems quicker than drawing curves and snapping.

Make a shelf item: delete `parentConstraint -insert flags here`; and it's even faster.

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