Leonardo da Vinci designed gear trains to transfer power with toothed wheels.
A gear train is a set of meshing gears that transmits rotation from one shaft to another. By changing the sizes and numbers of teeth, it can increase torque, alter speed, or change the direction of motion. Leonardo drew many gear arrangements while studying clocks, mills, lifting devices, vehicles, and other machines.
Gears were not Leonardo’s invention; toothed mechanisms had been used for centuries. His notebooks are valuable because they show unusually systematic attention to mechanical advantage, interlocking teeth, and the conversion of motion. He often combined gears with cranks, screws, pulleys, and springs.
A gear train is not one single Leonardo invention or a particular named machine. It is a mechanical system used across many of his designs. Modern transmissions still rely on the same basic principles, although modern gears are manufactured to far tighter tolerances and commonly use specialized alloys, lubrication, and computer-designed tooth profiles.