Help needed with basic magnet function.

I have an animation of a teddy bear who I want to hold and manipulate some colored balls in a simple way. 

I have tried to follow exactly the instructions here:

https://youtu.be/ivt3zQ0zni0

I've tried to get the green ball and the arm to operate essentially exactly identically to the coffee mug in the example, but regardless of what I do the magnets just don't seem to do anything at all.

I'm attaching some screen shots of my rigging set up. Any help spotting what I've done wrong would be very appreciated.