Inside leg measurement , hat size and weekly booze consumption....

I believe that the Weapon provides a stop to prevent the axle rotating ...the wheels torque reaction is transfered thru the weapon and onto the ground thus allowing drive.... reverse the motors and the weapon / axle performs an overhead arc.

http://www.makezine.com/blog/archive/2006/12/cotton_reel_tan.htmlhttp://www.makezine.com/blog/archive..._reel_tan.html