Note:This is my very first rig so this may be crap
Here is my tank rig its also my first its very simple to use its an m1 abrams(i might do a challenger). You can turn the turret around, Set the position of the cannon and move the main section around.
(sorry about the fraps thing)
Its also come with a little animation to demonstrate the features.
Download:https://www.dropbox.com/s/ecxe0ts4w4yz3d1/Tank%20rig.mani
It might be the first tank rig ever (correct me if im wrong)