I've setup an IK rig that uses an IK pole to aim the knees, and I'm wondering what is the best way to have these IK poles follow the rig? Ideally, the pole would always be directly relative to the knee it controls, like a planet orbiting the sun. But I can't seem to parent it to the leg without causing strange issues (because the leg is changing relative to the pole and the pole relative to the leg).

Any ideas on how I can accomplish this without the feedback loop issue?

Another secondary question related to IK - how do you toggle IK on and off during animation? I thought about using a driver linked to the influence factor that could be rigged to some type of user control, but it seems like it should be easier than this?

  • $\begingroup$ have you tried to parent the pole to the foot or to the IK controller? About your second question: you could simply use the IK constraint visibility, deactivate it and put an keyframe? $\endgroup$
    – moonboots
    Jul 18 '19 at 7:09
  • $\begingroup$ For toggling IK, do you mean to change the influence slider between 0 and 1? I'm not aware of a constraint visibility adjustment? $\endgroup$
    – Robert
    Jul 18 '19 at 12:50
  • $\begingroup$ the eye icon can be keyframed $\endgroup$
    – moonboots
    Jul 18 '19 at 12:52

I've found what looks like a good solution. Still need to test it in animation editing. In case anyone else is attempting to do this, this is what I've setup:

  • Create a new child bone of the knee bone (thigh bone, not the shin bone) and extrude it outward from the knee. Make sure this bone is "connected" to the parent. Call this bone IKKneePoleArm.L. Then extrude again (from this new bone) and call the second one IKKneePoleHandle.L. Disable Deform for both of these.

  • Setup normal IK using IKKneePoleHandle.L as the pole target for the leg.

  • Go into the bone settings and turn off inherit rotations for IKKneePoleArm.L. This will keep the feedback problem (mostly) at bay.

  • Completely hide IKKneeHandle.L. You only need to rotate IKKneePoleArm.L around its orbit axis to aim the knee. You can also disable the other axes (in pose mode).

  • You can also attach a sphere object to the pole arm, so that it appears to be a sphere that orbits the knee. Then you can grab the sphere and push/pull it around and the system will convert that into rotations.

The only issue I've found with this so far is that some adjustments seem to lag behind by one frame by a small fraction. So if you type in values, you have to press enter twice (only if you are cursed as a perfectionist).

If there is a better solution anyone knows of, I'm definitely interested. Thanks!


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