No Flip Shoulder Setup
Maya Rigging: Extas
The following is a method for creating a no flip shoulder setup. This is a troublesome area but once broken down it’s quite simple to manually build the no flip shoulder in about 10 mins.
The basic idea is to distribute the twist through the shoulder without using rotational values as they are unreliable due to gimbal. Instead we can use a aim type setup (quaternion) using ik.
We’ll have 3 chains to drive this setup
1. Regular arm setup: Clavicle > Shoulder > Elbow (driver chain, often the ik fk switch arm)
2. A no flip shoulder joint (and elbow) (using Ik with a zero’d pole vector)
3. The twist joints driven by spline ik (using advanced twist with the up vector assigned to the No Flip Shoulder)
1. The driver joint chain is the regular arm, usually the arm that switches between IK and FK options.
2. The no flip shoulder is a joint placed on top of the shoulder. We use the ik in a way so that it doesn’t flip no matter what axis it’s pointed.
3. The twist is a spline ik chain with multiple joints to distribute the twist. We use the advanced twist controls to drive the shoulder. But if setup in the usual way the twist will flip at the north and south poles. So we use the up axis of the no flip shoulder to designate the up axis. The no flip will move with the shoulder so we’ll never hit the poles up or down.