Above each of the cannons sits a tall ammo silo that holds additional spheres. Each silo holds up to seven spheres, for a total capacity of 14. The silos reload the cannons after they have fired a projectile. They are gravity powered; after a sphere is launched, another one drops down into the cannon to fill its place:

Though the ammo silos are a necessary part of the design, they are quite ugly. This is another example of an engineering trade-off you may encounter when designing your own smart robot—functionality versus cosmetic design. Sometimes it is difficult to make a beautiful robot that also does exactly what you want it to do.