In his youthful notebook in which all the machines designed by Taccola are copied and in the first draft of his Treatise on Architecture, Francesco develops the theme of perpetual motion by proposing various types of mills operating in still water. Even if the subject is never explained in textual form, in his drawings the research focuses on the arrangement of variable-order flywheels or on the development of the water wheel with a view to transforming it into a device that can power itself (fig. 4). Francesco di Giorgio elaborated counterweights of various shapes, sometimes capable of opening, of continuously moving the centre of gravity of the wheel in order to unbalance it and induce its rotation. In his drawings, the overbalanced wheels are imagined as energy generators combined with large operating machines; however, he doesn’t attempt any explanation of how they work.