[Lab] Model escalator...

[Adrian Jones]

Anyone out there in 'makerland' got any ideas for me. 
For an art project, my partner, Lise, needs me to build a pair of small
model escalators that run against a projected backdrop. 
Each escalator will have a small figurine, one ascending while the other
descends.
Rough estimates are that each elevator should be about 18-20" long with a
6-8" elevation. For each I've been thinking about using a stepper motor
driving a loop of toothed belt. The belt has one or more small triangular
balsa steps glued to it. The stepper will move in one direction (ascend),
stop and then reverse direction (descend) to end up at the same point, while
the other does the opposite. This cycle then repeats. 

                       
          /|    /|    /|
         / |   / |   / |   <-->  
   ___==/==+==/==+==/==+===============___
  /   \                               /   \\
 |  A  |                             |  B  ||
  \___/                               \___// 
     ==================================== 


Imagine pulley A elevated so that hypotenuse of triangur 'step' is
horizontal... Get it?

Thoughts, suggestions... 
 

Many thanks, 

.... Adrian