Rigs of the Trade # 04 - Part 3/6 ❅ Pelvis Region Rig with Helper Bones [ Intermediate ]

We address a critical Organic Rigging topic: the complex Joint between the Hips and Thigh Bones on a humanoid character.
I'm using a Helper Bones solution instead of a Corrective Shape Keys one; also favoring Transformation Bone Constraint instead of Drivers.
Blender 3.2.1
Academic Work (references):
skinning.org/direct-methods.pdf
www.researchgate.net/profile/...

[@edmatrariel]

I made a helper bone for the character's knee with constrain in calf bone and child of the thigh bone, but when the thigh bone is rotated the helper bone returns to the starting position. Just when the calf bone is rotated run everything ok. Note: Target and owner is in local position. Thanks

[@pxy-gnomes9781]

Hi; It's a bit difficult for me to visualize what's going on. Because there are few communications options here in UA-cam comments section, if you are in Discord's channel Blender Community or Blender Discord, you can find me there to get more in-depth.
However, maybe you can solve it by developing over these ideas:
A problem is that I do not know which Bone Constraints you used. I assume the Transformation Bone Constraint; but then there is the Parenting to the Thigh Bone (Connected or Disconnected/Offset)… ? Or, instead, is it a Child Of Bone Constraint? Child Of Bone Constraint doesn't give you as much Location Options as Copy Location Bone Constraint. And Direct Parenting, whether Connected or Disconnected/Offset, will make the Child Bone Inherit, by default, all Transforms: and then you lose control over the Bone, furthermore you get probably unwilling Bone Rotations on all XYZ Axes, which are problematic because of the Skinning Algorithm.
For the Transformation Bone Constraint on the Helper Bone, you must make sure you analyze the Rotation Angle of the Shin, Target Bone, using Map From: probably Min from 0° to Max somehwere about (+ or -) 170° (the Knee bending fully as the Shin touches the back of the Thigh).
I think the problem is the Parenting and/or the Location Constraints you've made, because the Location of those Helper Bone are highly dependent on the IK Chain Bone Locations; it's very tricky to set up a correct Addition of Constraints for Locations in Blender. I recommend you Parent Offset the Helper Bone to a stable, Master Bone, like a Hips/Torso/Spine Bone; and that you use the method of stacking Copy Location Bone Constraint + Transformation Bone Constraint that I've presented just at the end of the whole tutorial (for fixing the Volume Loss on the back of the Thigh Bone as it Rotates forwards; Leg's front bending).
Hope this helps; ¡Good Luck!

[@edmatrariel]

@@pxy-gnomes9781 Your answer was enlightening and helped me a lot. The problem was caused by the inversion of the bone axis after the mirror. This problem occurred because I applied this technique in auto rig pro, where I can't control the bone axis freely. But in a common skeleton this problem does not occur. I'm not a rigger and I always use rigify or ARP for my characters. They are great but in the customization part, sometimes they bring problems. I love the videos on the channel about custom bones, because believe me, I searched a lot and only found it well explained here.