After FK animation, a joint chain may flip to an undesired position when you enable the IK solver (Key > IK/FK Keys > Enable IK Solver).
Joint flipping is a normal result of the spline IK solver’s calculations and occurs when the orientation of a joint is more than 90 degrees from its rotation value of 0. A joint’s rotation value is 0 when its Rotate X, Y, and Z values are 0, relative to its parent joint’s rotation values. Flipping is most pronounced when a joint nears 180 degrees rotation.
Note: If your joint chain suffers from flipping, use the rotate plane solver instead of the single chain solver. The rotate plane solver was introduced with the pole vector to control the flipping of IK chains that you sometimes get with the single chain solver. It is not recommended to use a single chain solver for a 2 bone chain.
To undo the joint flipping and prevent it from occurring when you turn on
Enable IK Solver, do the following:
- In the
Animation menu set, turn off
Key > IK/FK Keys > Enable IK Solver.
This returns the joint chain to the position it had before flipping.
- Select the IK handle, then select Skeleton >
Set Preferred Angle from the Rigging menu set.
- Turn
Key > IK/FK Keys > Enable IK Solver back on.
- Select
Key > IK/FK Keys > Set IK/FK Key.
Continue using IK as desired.