Abstract: A variable displacement pump/motor characterized by a housing, a rotary shaft assembly disposed of within the housing, a plurality of hinged vanes engaged with the rotary shaft assembly, and an offset rotor assembly engaged with the vanes and having its own axis of rotation. The output of the pump or motor is changed by varying the axis of rotation of the rotor relative the axis of rotation of the rotary shaft assembly. A pair of counter rotating eccentrics are used to smoothly vary the axis of rotation of the rotor along a plane which is common to the axis of rotation of the rotor and the axis of rotation of the shaft assembly. The output of the pump/motor can be varied smoothly between a maximum in a first direction, to zero, to a maximum in a an opposite direction, and back again.