Studies for the design of a mechanical perpetual wheel
The main drawing on this sheet reproduces a perpetual wheel peripherally overbalanced with the percussion of spheres. The circumference is divided into 32 sections, within which are spheres free to move: following the direction of rotation, the spheres fall until they impact the lower wall delimiting the section. The percussion should prompt the motion that favours continuous rotation. To increase the overbalance of the wheel, Leonardo introduces hollow spokes connecting each couple of opposing sections, so as to form a hydraulic circuit in which the liquid always flows towards the direction of rotation. In this way, when the compartments pass from the active phase of descent to the passive phase of ascent, the spheres, due to gravity, descend towards the lower walls of the sections, pushing the liquid up through the ducts until it fills the void left by the spheres; these, in turn, enter the active phase of rotation and descend towards the bottom. Thus the weight of the liquid is added to that of the sphere, producing a greater moment than that of the opposite side.
Also of considerable interest are the two smaller drawings of perpetual wheels—which integrate the design of the main wheel—in which Leonardo proposes solutions studied at the beginning of the 1490s. The central device seems to combine the peripheral sphere percussion system with the radial one found in the studies on folio 473r of Codex Atlanticus. The other wheel, on the other hand, offers an overbalanced system with rotating arms mounted on the circumference and along the spokes, a configuration previously studied in folio 212 of Codex Arundel. Leonardo plans to use these “rotating appendages” as actuators for butterfly valves, which he plans to insert into the hollow spokes in the main wheel to allow the liquid to flow across into the other section.
The reverse of this sheet contains a very accurate study of a compartmentalised wheel similar to the previous one, but divided into eight sections. There is also a reference to the articulated arm wheel extensively studied in folios 147v-148r of Codex Madrid I and 89v-90r of Forster II, both dating back to the first half of the 1490s. Folio 778r also contains studies of siphons and architectural structures that could later be added to the perpetual wheels, which can be dated to the beginning of the 1490s, when Leonardo devoted himself to this type of study.