Fixing IK/FK hand orient in post

[MarcoVJ]

Hi! This is my first post here. I’m not sure I used the correct tag—sorry about that (and also for my English ).

I’ve been searching and reading threads about this issue but couldn’t find a complete fix. While the rotation matches at the neutral pose, when you reset controls or switch spaces the IK still flips or rotates incorrectly. So I used @Andy’s script as a starting point to figure out where the problem begins:

Unable to mirror IK hand rotation on EPIC_arm component

This POST script seems to do the trick. I modified a script from another thread that @chrislesage made that aligns the IK controls to the FK hand controls. But I had to match the rotation the the wrist guide instead of the FK hand, otherwise the hand would flip 180. Then I added a snippet that zeros out the transforms by transferring them to the offset parent matrix, instead of adding an npo node. It’d probably be better to move this function someplace else but I’m still learning this stuff. I…

The thing is, changing controls to match rotations isn’t best practice—you end up with extra rotation values, mismatched spaces, and so on. That’s why I went for a root‑level fix. It appears the actual root group isn’t aligned with the guide’s rotation (not sure if it’s a node or transform issue). I adjusted the script to work with that group: it aligns the FK control’s rotation and updates the parentConstraint so spaces work correctly.

Here’s the script:

import maya.cmds as cmds
import pymel.core as pm
import mgear.shifter.custom_step as cstp

"""
Based in @Andy script from mGear forums
http://forum.mgear-framework.com/t/unable-to-mirror-ik-hand-rotation-on-epic-arm-component/3514/3 
"""

class CustomShifterStep(cstp.customShifterMainStep):
    """Custom Step description
    """

    def setup(self):
        self.name = "HandIKAlign"

    def run(self):
        for side in 'LR':
            self.fix_ik_hand_orientation(side)

    def zero_OPM(self, obj):
        joints = obj
        aux = pm.group(em=True)
        for jnt in joints:
            aux.setMatrix(jnt.getMatrix(ws=True), ws=True)
            pm.parent(aux, jnt.getParent())

            aux.matrix >> jnt.offsetParentMatrix

            pm.xform(jnt, t=[0, 0, 0], ro=[0, 0, 0], s=[1, 1, 1])
            if pm.objectType(jnt, isType='joint'):
                jnt.jointOrient.set([0, 0, 0])
            aux.matrix // jnt.offsetParentMatrix
        pm.delete(aux)

    def fix_ik_hand_orientation(self, side):

        handRef = pm.PyNode('arm_{}0_fk2_ctl'.format(side))  # locate FK hand control
        ikCns = pm.PyNode('arm_{}0_ik_cns'.format(side))  # locate ik_cns group root
        ikCtrl = pm.PyNode('arm_{}0_ik_ctl'.format(side))  # locate IK hand control
        guideRef = pm.PyNode('clavicle_{}0_tip|arm_{}0_root'.format(side, side))  # locate arm guide root
        handChildren = ikCtrl.getChildren(type='transform')
        cnsNode = pm.PyNode('arm_{}0_ik_cns_parentConstraint1'.format(side))  # get parentConstraint node
        cnsTargets = cmds.parentConstraint(str(cnsNode), q=True, tl=True)  # get parentConstraint targets
        cmds.setAttr(str(ikCns) + '.rotateX', lock=0)  # unlock ik_cns group rotation attributes
        cmds.setAttr(str(ikCns) + '.rotateY', lock=0)
        cmds.setAttr(str(ikCns) + '.rotateZ', lock=0)
        cmds.matchTransform(str(ikCns), str(handRef), rot=True)  # match ik_cns group rot to FK_hand_ctl

        # adding rot offset to ik_cns group

        xRot = cmds.getAttr(str(ikCns) + '.rotateX')

        if guideRef + ".mirrorIK":
            if side == "L":
                cmds.setAttr(str(ikCns) + '.rotateX', xRot + 90)
            else:
                cmds.setAttr(str(ikCns) + '.rotateX', xRot + -90)
        else:
            cmds.setAttr(str(ikCns) + '.rotateX', xRot + 90)

        for eachTarget in cnsTargets:
            cmds.parentConstraint(eachTarget, str(cnsNode), edit=True, maintainOffset=True)

        obj = [ikCns, ikCtrl]

        # reset ik_hand_ctl rot
        cmds.setAttr(str(ikCtrl) + '.rotateX', 0)
        cmds.setAttr(str(ikCtrl) + '.rotateY', 0)
        cmds.setAttr(str(ikCtrl) + '.rotateZ', 0)

        # locking ik_cns group rot attributes
        cmds.setAttr(str(ikCns) + '.rotateX', lock=1)
        cmds.setAttr(str(ikCns) + '.rotateY', lock=1)
        cmds.setAttr(str(ikCns) + '.rotateZ', lock=1)

        return

I’d prefer to implement this in the build process itself, but at least it works as a post‑build solution. I’ve tested it with EPIC templates and it works fine there, though I haven’t confirmed it works with every rig.

Cheers!

EDIT: Forgot to mention that I’m not used to PyMel, so the code is a bit mixed with cmds.