In some cases, it is important to have a piece of equipment or machinery in physical form to show a judge or jury the significance of altering said equipment.  The overall size of this model was determined by its length.  It needed to be as big as possible, while still allowing it to sit comfortably on a table top.  The specific scale selected enabled us to purchase available toy tires, rather than spend the labor cost to make them.  Since this was made for courtroom demonstration purposes only, we could have used painted plastic for the conveyor belt.  Instead, we opted for the more authentic feel of rubber and cut up a bicycle inner tube.  This is not a toy, but was admittedly quite fun to make.