a complete mechanical drive system, for example that which transmits power from an engine to the rotor system of a helicopter

wheelwork consisting of a connected set of rotating gears by which force is transmitted or motion or torque is changed; "the fool got his tie caught in the geartrain"

Complete system required to rotate the driving wheels, including the engine, clutch/torque converter, transmission and drive shaft.

Lower and central body as it relates to football playing strength.