A rotary transfer mechanism is disclosed for a motor, pump, or other downhole tool that accommodates the eccentric motion of a rotor without the need for a flex shaft, articulating joint or CV joint. In one configuration, the rotor is coupled to the drive shaft at a radial offset from the drive shaft axis. The orbiting motion of the rotor, rather than rotation of the rotor about its own axis, generates a torque on the drive shaft, by applying a tangential force to the drive shaft at the location of the radial offset. The radial offset may be set equal to the orbital radius so that no radial movement or flex is required at the drive shaft to accommodate the eccentric rotor movement.