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So I've been working on a complex rig for a long time. So long I would prefer not to admit the actual time I've put into it. However, I cannot design a pole target setup for IK that I can be happy with. And I've built several versions of it. Probably around 10 at this point.

My latest attempt is a system where the pole target orbits the joint when the user spins a gizmo on the joint, and it follows the limb when posing without exploding pretty well. However, it still runs into strange angle problems when the limb is placed into specific poses, such that 12-4'o clock angles have a different resolution that other angles, and certain rare poses still make the whole thing flip.

What I want is a very simple gizmo that attaches to the elbow/knee that can be twisted to rotate the pole target. Something that falls in line with the animation controls of everything else. The one I've managed to set up with a bunch of extra bones and complex constraints is imitating something about as complex as our solar system, just to have my elbows pointing in the right directions. Is there not an easier way?

For example, is it possible to just use a dial? Can I tell Blender to just give me a driver-modifiable value that I can feed a value to? One that is capable of animating and such? Basically I want to remove the concept of the "pole target coordinate" altogether and just use an angle. Is that possible? I considered just setting up a static object as a pole target and driving the angle value, but this seems a bit hacky, and I'm assuming it will have other issues I haven't considered. Has anyone found a solution to this?

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You can try this setup:

A simple Shoulder-UpperArm-ForeArm-Hand IK chain, limited to two bones (UpperArm and Forearm, not extending to shoulder), of course hand is not child of forearm.

Add a Rotor bone, child of shoulder.

Add a bone going from shoulder to hand, child of rotor, add a stretch to constraint (target: hand).

Add a pole bone, child of "Stretch to hand" bone, set it as pole of the IK and trim the pole angle as needed.

Now rotating the rotor bone in one single axis (lock the other 2 in Euler mode) will make the elbow rotate as expected.

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  • $\begingroup$ I was doing something similar, but did not know the stretch to constraint could be used for this purpose. I was using copy position at 50% to find the center point between your stretch bone. I will try this setup. Thanks! $\endgroup$
    – Robert
    Commented Feb 25, 2023 at 19:39

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