"The simplest design consists of a pair of contra-rotating drums mounted on collinear input and output shafts. A pair of cords or belts wrapped around the drums

"The simplest design consists of a pair of contra-rotating drums mounted on collinear input and output shafts. A pair of cords or belts wrapped around the drums connect two arms mounted on the input shaft and output shaft." From http://www.meccano.us/differential_analyzers/robinson_da/torque_amplifiers.pdf http://www.meccano.us/differential_analyzers/robinson_da/tor....