Arm Orientation Selection

This set-up allows the animator to control which axis the arm should follow when the torso bends. I did this by using four locators that have an orient constrain influence at the locator at the top of the arm. When the torso joints rotate, the parented locators will rotate accordingly (or not as the case may be). The upp. arm joint will then follow the locator with the weight value of 1.

I also set up an orient attribute on the upp arm - in a rig this would have been set up on the controller - so the animator can dial in the orient axis they wish to follow. Useful for rotating the body whilst maintaining the arms orientation.