IK constraint unwanted rotation on IK chain

Dear people,

I have a problem with the IK constraint tag on my chain.
each time i activate it, my whole chain rotates around its y-axis (aaprox. 30 degrees).

I found out that my Bone M2 is the cause. It has a fixed rotation axis that is 20 deg off normal.I attached my comments on my rig setup, so you can follow my problem.

it is mandatory that M2 ca only rotate around an angle that is 20deg off the world-z or local y axis of the parent bone. Actually its a “universal joint”-issue i have and how to properly rig it.

Can anyone explain to me where this bug might come from?
or eldse tell me how to properly setup an IK chain for this specific purpose?

pls look at my attached jpg.

Thanks anyone
cheers eL

Hi @eL_Be

Please post the file, that is the best way to get help around here. This allows someone to really get in there and look at all the details. There are a lot of details to getting an IK chain to work right, but once you get it, it’s easy to do…

Randy

Hi Randy.

please find the blend file attached.
You might want to start by switching the IK Constraint on Bone “M2b” on and off, and you will see
immediatly what my problem is.

It is really important to keep the 20 degree tilted rotation axis angle between the two cylinders M1.Geo and M2.Geo, as I need to transfer the data to real world sensors.

Hope you can help me out.
maybe my setup is too complicated.

cheers eL
Kardan_IK_v08.blend (941.0 KB)
Kardan_IK_v08.blend (941.2 KB)
Kardan_IK_v08.zip (237.7 KB)