This website describes a concept for a perpetual motion machine which uses dc motors, airfoils and an alternator in a feedback loop.
It is impossible to create a perpetual motion machine using a single motor and alternator in a feedback loop because all motors and alternators are less than 100% efficient, and the input power needed to operate the motor and alternator is always greater than their output power. In order to create a perpetual motion machine with an alternator and motor in a feedback loop, some type of power amplifier must be inserted into the loop to compensate for the losses in the alternator, motor, bearings and other losses.
Consider how airplanes and helicopters generate lift. Modern airplane wings have lift to drag ratios that are around 20 which means that for 1 lb of thrust, the airplane's wings can generate 20 lbs of lift. For helicopters it appears that that maximum lift to drag ratio is on the order of 6. One can think of the thrust force applied to the wings of an airplane being magnified by the wings (airfoils) moving through air resulting in a lift force that is up to 20x what the thrust force is. A similar phenomenon should also be true for helicopters except that the lift is a linear force and the thrust is a rotational torque.
The following pages describe the perpetual motion machine concept.