The connecting rod and crank system is used to transform rotary motion into direct reciprocating motion. A crank fixed to a connecting rod at one end is applied to a wheel. The connecting rod is a system composed of two poles joined by pivots. The last pole of the connecting rod is fixed so that it can turn in only one direction and, when it is pulled and pushed by the attached crank, it moves as a result.

The wedge is a pyramid-shaped object that is placed in groove or between two surfaces to separate them. The energy derived from a blow applied to the head of a wedge is distributed toward the surfaces. It is used to distribute energy in different directions. The basic idea of the wedge is the inclined plane.

Every type of gear depends on the idea of the axle and the wheel. An axle that rests on or passes through a circular hole will stay in place but will still turn. Leonardo also studied the effects of wear and tear on axles when different materials are used.

To apply a brake to a gear mechanism, Leonardo often uses a lever that interlocks with teeth cut out of a wheel so that the wheel is blocked. However, by doing it this way the wheel is still free to rotate in the opposite direction; a small spring can be added to the stop lever (pawl) to return it to its position. This kind of stop is often used for blocking system and for loading leaf springs.

The flywheel accumulates kinetic energy; Leonardo calls it “auxiliary motion”. At first, a large amount of energy is required to start turning the wheel or the weight attached to it, but once it is in motion the weight itself creates its own energy and it is difficult to slow down the system. The flywheel was to prove fundamental to Watt’s steam engine and to feedback systems.

The various kinds of articulated mechanical joints are essential for building robots and automata. Codex Madrid I shows several types. The basis of these joints is the use of the pivot or axle: each pivot has a degree of free rotation. The surprise lies in the innovative notion of using the ball and socket joint, which imitates the joints in the human skeleton and allows for considerable freedom of movement.

A cam is a device created with a wheel which has an irregular rim or with pegs that will make the desired shape. The rim of the irregular wheel pushes or moves a lever and makes it perform a movement that follows its shape. In this case, the wheel rim moves a lever, raising the hammer, which is then made to drop with a bang at each turn of the cam.

Leonardo drew many types of chains. The chain is an assembly of metal elements connected to each other by pins. Compared to a pulley, the chain can be grasped between the teeth of a gear and is in any case much stronger. It is a mistake to think that here we have proof that Leonardo had thought of a bicycle with pedals and a chain because in fact he only drew vertical chain systems for the purpose of lifting weights or containers.

First of all, Leonardo makes a serious study of the use of bearings to reduce wear and tear. If balls or cylindrical objects are placed between two rotating surfaces they greatlyy reduce the effects of wear and tear that would tend to slow the mechanism. Leonardo studied various shapes and materials for different uses.

Leonardo analyses the screw in terms of mathematics and geometry, describing it as an inclined plane coiled around an axis. In these terms, the “nut” slides and moves upwards on the screw’s plane; when the nut’s progress is blocked the “plane” moves. Part of the screw can be used to engage a toothed wheel and it is then known as an “endless screw”.

A spring is a long piece of flexible metal, coiled several times in a spiral around an axle. If the axle is rotated, the metal band behaves like an accumulator for “flexible” energy which, when released, returns the axle to its starting position. The principle characteristic of the spring is that the accumulated flexible energy is greatest at the first moment of release and very weak at the end. Spiral springs release rotary energy; springs of a different shape release energy in the opposite direction from that in which it was accumulated.

The main property of a pendulum is that (in simplified terms) the time of oscillation is proportional to the length of the cord and independent of the weight and amplitude of the swing. Leonardo studied the effects of the pendulum and used it to provide power in a large number of gadgets, not just those for measuring time, but also in mills and mechanisms.