IK rig behaving weirdly and I can't seem to fix it

I’m trying to establish a workflow to create a game character base model from MBLab addon (the Github version).

But after several updates to both Blender and the addon, I noticed that the character rig no longer behaves the same way as it did before.

The most problematic symptom for me is that it became almost impossible to use IK helper nodes to pose the character in a certain way.

And I’m not sure if it’s related, but I also noticed that the newer (problematic) version’s character shifts its pose when I switch between Pose and Rest positions.

I had spent a day to investigate the problem myself, but my limited experience with Blender has been preventing me from making much progress.

Could anyone check those test case Blender files and see why After.blend shows such symptoms described above, unlike Before.blend? (Please ignore meshes and other stuffs, because they were modified to reduce file size.)

Thanks in advance!

Before.blend (2.5 MB)
After.blend (2.9 MB)


I am also new to Blender but maybe this will help you,
there is something wrong with the polevectors for the legs (see snapshot)
if you move this bones the legs will come to the desired Pose,

but as i said Iam also not familar with blender , and in snapshot b Iam missing a Pole target, like IK_control_kn_R IK_control_kn_L ???

good luck


Thanks for the answer! However, I’m unsure if I understood you correctly. Do you mean there’s something wrong with how those control bones (i.e. ‘IK_control_kn_L/R’) are constructed in After.blend?

To be clear, those IK constraints in both of the Blend files I attached lack pole targets. And I’m aware that I’m supposed to move those control bones to pose the character’s knee positions.

My problem is, for some reason, it only works in Before.blend as expected. And when I try to move those bones in After.blend, the legs tend to move erratically so I can’t really pose them in the included animation.

Also, the character slightly shifts its position when I switch between the rest and pose positions. It may or may not be relevant to the problem with the IK bones, but it also only happens with After.blend.

Your model (in both files) uses overlapping IK chains. In the current, 2.82 Blender release, there is a bug with overlapping IK chains that can create "random"ish behavior ( https://developer.blender.org/T73051 ).

I don’t understand why you’re using those overlapping IK the way you are. If your goal is to create, e.g., an upper arm tweak bone, you can create non-overlapping IK instead by duplicating the upper arm bone (1 copy parented to clavicle in 2-bone IK chain with no constraint, duplicate parented to original with 1-bone IK constraint.)

You could also try downloading a daily build or something and seeing how that affects your files, as it’s my understanding that the bug fix is live, just not yet in a stable build.

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