When I was rigging my robot for the jan/feb challenge my problem was that when I moved the arm the entire shoulder (and the spikes) would bend down too. Also when I would turn the neck the face plate would twist because there would some joints in the neck and some in the head, so they were all affecting the same surface. I solved it by reducing the influence, that's why I thought it could solve your problem too.
Sorry it didn't work.
There can not be Good without Evil, so then it must be good to be Evil sometimes.
:tup: