Rig IK arm with hand rotation control

In this IK setup, the hand is forced to rotate as the arm moves:

 

In this rig however, the hand maintains its own rotation. The nub is still there for the IK goal, but the hand is an additional piece of geometry linked to the goal.

If you rotate the goal the hand will also rotate.

 

If you want the rotation of the hand to be completely divorced from the goal:

Under Hierarchy/Link Info turn OFF rotation.

The “hand” box is linked to the nub right after the IK goal.

Moving the IK goal, the hand now stays straight and can be controlled on its own better. (Make sure to move the pivot of hand at the “wrist” and then align that pivot to the nub’s pivot point.)

RIG a two part (twisty) Upper Arm

The upper arm is a ball and socket joint. It is difficult to animate because of the contradictory pulls on the mesh.

This solution deploys a 2-bone upper arm

The TOP bone of the upper arm is restricted to moving the arm Up/Down and Forward/Back.

[the top bone on the arm here is actually the clavicle]

The LOWER part of the upper arm is restricted to “twisting”