1
$\begingroup$

I'm trying to rig a leg that has two thigh bones (one to move the leg around the hip and the other to rotate the thigh around the bone's main axis):

enter image description here

The IK constraint on the Shin bone reaches up to ThighB; ThighR has X and Z locks enabled on the bone's IK tab so as not to bend the leg between ThighB and ThighR. This works fine.

I tried to lock the ThighB's Y axis on the bone's IK tab but this has no effect - ThighB still changes it's roll when I move the leg (I also tried using a limit and setting a high stiffness, this also didn't work):

enter image description here

So I have two questions:

  • What exactly is the "Limit Y" / "Lock Y" option good for, since it doesn't seem to work as I expect it to?
  • Is there a way to keep the IK Solver from rolling/rotating ThighB around the y axis?

I'm aware that I could set up a second chain that just used a single bone and then copy the x,z rotation to the ThighB and the roll or the y rotation to ThighR, but I'm looking for a simple solution first.

$\endgroup$
0
2
$\begingroup$

With no pole, locking the Y axis works, and can be seen by locking/unlocking it in pose mode. However, what exactly it means to lock the Y axis isn't necessarily intuitive; in reality, orientations aren't sets of 3 independent axes.

There is one situation where locking the Y axis (of the first bone in the chain) will do nothing: when you are using a pole target. In this case, the calculations used to track the pole will replace the limited Y axis rotation of the first (only) bone in the chain.

Note that pole targets aren't necessary for IK; they're an option, and there are alternative controls.

If I wanted to create an IK thigh twist bone with a pole target, here's what I'd do:

enter image description here

The thigh bone of the IK chain is non-deforming. The deforming thigh twist bone is parented to it. Note the hierarchy: the deforming (upper, non-twist) thigh bone is not parented to it. Instead, it's parented to the hip (or whatever the IK thigh's parent is), and then acquires the proper orientation via a damped track constraint, in this case, targeting the head of the thigh twist bone.

$\endgroup$
0
$\begingroup$

Set same angle(so no lock, but if you want set min=max) to IK + rotation limit, local space)

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.