Driving sheave 1, over which the hand chain runs, is the carrier and rotates about axis A on stud shaft 8 of block 2. Eccentric a of sheave 1 is connected by a turning pair to planet gears 3 and 5. Gears 3 and 5 are rigidly attached together and mesh with internal gear 6, rigidly attached to block 2, and internal gear 7 which is rigidly attached to hoisting chain sheave 4. The speeds n₁ and n₄ of driving sheave 1 and hoisting sheave 4 (in rpm) are related by the equation n₄=n₁(z₇z₃-z₅z₆)/(z₇z₃) where z₃, z₅, z₆ and z₇ are the numbers of teeth of gears 3, 5, 6 and 7, which are selected so that the difference z₇z₃-z₅z₆ is very small. When sheave 1 rotates, sheave 4 rotates at a much lower speed, hoisting the required load with a large mechanical advantage.
$2958$CxG,MH$