I found the following rig the Blend file on sketchfab and tweaked while following DanPro advanced rigging tutorials.
Then I noted that I have a strange issue with the rig, and I'm curious as for why it happens and how tweak it.
When legs are in IK mode the bones follow the Torso Z transformation, nearly as if it was an FK bone. I.e. The leg translation isn't isolated anymore, it actually follow the Z transformation of the Pivot/Torso. As for the rotation it seems to be conditioned by the both FK, IK.
The IK bones are linked to the root bones and have no constraints, also, the body has no shape keys.
Practically speaking it is a nice feature. A full IK including the Z is useful for walk/run cycles, while this ‘in between’ feature offers more convincing poses. .... If I could only understand its rigging.
Also, I note the field 'Pivot Slide'/Jaz Properties condition the Pivot/Torso Z transformation but I don't understand exactly how it is conditioned by the Drivers and if is relevant to the IK Z transformation.
Any suggestion, input would be highly appreciated, and plenty of thanks in advance!