Multiple problems: Rigged arm & hand with elbow corrective shape key I have multiple Problems. :/


Trying to create a corrective shape key driver for the elbow, I managed to create the shape key itself without a problem. assigning it to a driver I realized, that the value of the driver always remained 0. Even when moving the FK_bone, thus deforming the forearm successfully, the value did not change, so neither did the shape of the elbow. Please help me with that.
Upon trying to figure it out myself, I played around with the roll of the different bones (left arm and left hand) in edit mode. I did this trying to make sense out of why the value did not change on the driver. As a result I can now not move the forearm along the global or the local z-Axis. Please help with this one too.


I am trying to teach myself Blender while I have a full schedule, plus this is my first Character created in this programme, so please excuse obvious mistakes or an unclean file. 

Thank you for your help :)

Here is the file:


P.S. His right arm is unrotated or rolled. His right arm is the maximum movement I would like the shape key to have as value 1.
ORG-forearm.L is not rotating anymore simply because its rotation values are locked (picture n. 1)



In your actual setup the rotation of this bone on his local Z axis has a negative value, so you can get your corrective shape key work with a negative expression (multiplied by 0.5 for having maximum effect roughly at full rotation; picure n. 2).