WizzWall is a very active rotating wheel exhibit.  There are bearing mounted shafts with four flat surfaces that spin when balls drop down.  They can be changed by sliding the disk unit off and on the shafts sticking out of the exhibit.  This is enclosed in plexi and has changeable disks on both sides.  An attention getter for people walking by.   Bottom unit is shown without disks.

Holographic material, Optical illusions, half one color and another so that when spun the color changes, etc. are all things that can go on the disks.  Click HERE for possibilities.