Automatic winding

Automatic winding is not a Rolex invention: John Harwood patented in 1923 a sector rotor that oscillated about 180 degrees, stopped by two lateral springs called bumpers. It was already an enormous conceptual leap. The problem was efficiency: those 180 degrees are not as effective as a complete rotation. The 360-degree rotor, popularized by Rolex with the Perpetual system, solves this limitation and winds in both directions, bidirectional by definition.

The principle is simple: a crescent-shaped rotating mass, called a rotor or oscillating weight, exploits gravity and wrist movement to rotate around the movement's axis. This rotation is transmitted to the mainspring through a train of reduction gears. In bidirectional winding, the spring coils in both directions of the rotor; in unidirectional winding, tension accumulates in only one direction, with theoretically more regular tensioning but utilizing only half the available movement.

The microrotor changes the architecture. Instead of a central rotor covering the entire diameter of the movement, a small-diameter rotor integrated into the plate is used, often in tungsten to compensate for reduced mass with material density. Universal Genève pioneered this with the Microtor in the Fifties. The advantage is direct: less thickness, more movement visibility. The disadvantage is that a smaller mass captures less energy with each oscillation.

Patented systems like IWC's Pellaton use a cam and lever mechanism that transfers the rotor's torque to the barrel with reduced losses and contained wear, contributing to the seven-day power reserves typical of certain manufactures' calibers. Ulysse Nardin's Grinder works on a different principle: a multi-armed frame with flexible transmission multiplies even minimal wrist movements. Urwerk has pushed mechanical logic further with turbine systems that regulate rotor speed through aerodynamic resistance, a solution that also absorbs shocks.

From the bench, I often see automatic movements with worn rotors or a loose transmission system: the spring winds by hand but doesn't hold. The symptom is a power reserve that drops too quickly even with regular use. In these cases, lubrication alone isn't enough: the winding train must be disassembled and inspected piece by piece.