Movement No. 10 is a direct modification and refinement of Movement No. 9 — the classic Variable Speed Cone Pulley system — but with a critically important difference: the pulleys are no longer simple straight-sided cones, but instead feature curved, nonlinear profiles. In Movement No. 9, two opposing conical pulleys with linear (straight) tapers are connected by a belt that can be shifted along their length to vary the output speed. While elegant in concept, straight-sided cone pulleys have a geometric limitation: as the belt shifts to different positions along the cone, the rate of speed change is not uniform — and importantly, the belt tends to twist and run unevenly because the linear cone geometry does not perfectly satisfy the geometric condition that the belt must always travel in a single plane. Movement No. 10 addresses this fundamental limitation by replacing the straight cone profiles with carefully calculated curved profiles — typically following a mathematical curve such that at every belt position along the pulley pair, the sum of the effective radii of the two pulleys remains exactly constant. This constant-sum condition ensures that the belt always runs at the same total length, maintaining consistent tension regardless of the belt’s position, and that the belt lies in a true plane at all times, eliminating the twisting tendency. The result is a smoother, more mechanically correct, and more reliable continuously variable transmission than the straight-cone version of No. 9. This principle of nonlinear pulley profiling directly informs the design of modern CVT (continuously variable transmission) systems used in automobiles, motorcycles, and industrial machinery.
10. Is a modification of 9, the pulleys being of different shape.