When adding IK - the arm moves a tiny amount

Question

When I add the IK constraint to the arm, and then the pole target, it moves a bit so it is no longer perfectly on top of the other counterparts. It looks like it rotates around 1,5°. At first I thought I'd made a mistake, but then I checked your Luna_rig file and found a similar thing happens there (but only 0.9°). Maybe it doesn't matter and it's OCD?

Maybe you mentioned something about this when going over IK in a previous course or exercise, but I have a memory like a goldfish!

Answer 1 · 2024-11-27T12:14:53Z

replied November 27, 2024 12:14pm

When you add a pole target blender points the bone's x axis towards the pole targets head. Then you use rotation to roll the bone back into position. Most riggers just use even 90 or -90. This of course leaves a few degrees that it can be off depending on the original position of the x axis. If your OCD is bothered by this you can make the adjustment in the rotation to be more exact.

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Answer 2 · 2024-11-27T15:25:02Z

replied November 27, 2024 3:25pm

Thanks, I was able to dial it in so they overlapped almost exactly by using the value 1.5°.

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Answer 3 · 2024-11-27T22:54:10Z

Wayne Dixon replied November 27, 2024 10:54pm

Hi Markus.
If the pole target is directly in-line with the leg chain and perfectly straight - you won't have any mode shifting (That's what I call it when the rig moves when you jump between edit mode and pose mode)
A lot of the time though, there will be a tiny bit of shift when the leg is at an outward slope (like it is in Luna).
If it's a small shift, don't worry about it, but if it's a large jump, you can adjust the pole vector angle to reduce it.

Hope that makes sense.

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