US Patent 8235324 Rotorcraft with electrically driven blade control

A helicopter uses multiple redundant harmonic drive motors on the rotor head to actuate the angle of attack of rotor blades at the rotor blade roots, providing collective control that, in combination with a system for providing cyclic control on the rotor blades, eliminates the need for a swashplate, thereby advantageously reducing the weight and maintenance cost of the helicopter, increasing its reliability, and reducing its vulnerability to ballistic attack.