[ctt956]

I've attached a spreadsheet I made on the characteristics of past game pieces, 1992-2016. It has their shapes, sizes, weights, and other info. A breakdown of the spreadsheet terminology...

For size:
Extra Small: Small enough to hold easily in one hand(1992).
Small: ~6" - ~12" for a sphere, or small in comparison to robot size(2016).
Medium: ~13" - ~30" spheres, not too big when compared to robot size(2014).
Large: ~30" - ~40" spheres, big or bulky when compared to robot size(2015).
Extra large: ~40"+ spheres, as big or bigger than robots(2005).

For abbreviations, CIR = circle, SQ = sqaure, CYL = cylinder, TRI = triangle.

About the "filler" column:
None means the game piece is hollow or empty(just contains ambient air), or is a solid material(like 2016 and 2012).
Air means it's filled with pressurized air(inflated). 1992 is listed as air because tennis balls are filled with pressurized air, but they eventually flatten out.
The rest are self-explanatory.

Some notes:
Weight and size do not scale with each other(a small ball filled with water probably weighs more than a tube full of air).
Spheres are the most common game piece so far.
From 2003 forward, you can see the not-a-sphere, sphere, not-a-sphere, sphere pattern.
Cylinders and flying discs are the least common game pieces.

What hasn't been used as a game piece? Cubes, and star/pointed objects...