A high density actuator, comprising: a housing assembly composed of: a first housing element containing a motor stator; and a second housing element containing a gear reduction mechanism in the form of a circular spline positioned inside the second housing element; a rotational core (32, 34) being composed of: a motor rotor; a transmission input in the form of a wave generator operatively connected to the motor rotor; a transmission output in the form of a flex spline connected to the transmission input, the transmission output being positioned at the center of the gear reduction mechanism; a torque transfer output operatively connected to the actuator transmission output; characterized in that the motor rotor is configured to rotate freely around a center shaft via conical roller bearings positioned between the center shaft and the first housing element; and in that the torque transfer output is furthermore operatively connected to the center shaft, which passes through the transmission output, rotational core (32, 34) and second housing element; wherein the center shaft ensures proper radial and axial alignment between the housing assembly and the torque transfer output. a housing assembly composed of: a first housing element containing a motor stator; and a second housing element containing a gear reduction mechanism in the form of a circular spline positioned inside the second housing element; a rotational core (32, 34) being composed of: a motor rotor; a transmission input in the form of a wave generator operatively connected to the motor rotor; a transmission output in the form of a flex spline connected to the transmission input, the transmission output being positioned at the center of the gear reduction mechanism; a torque transfer output operatively connected to the actuator transmission output; characterized in that the motor rotor is configured to rotate freely around a center shaft via conical roller bearings positioned between the center shaft and the first housing element; and in that the torque transfer output is furthermore operatively connected to the center shaft, which passes through the transmission output, rotational core (32, 34) and second housing element; a first housing element containing a motor stator; and a second housing element containing a gear reduction mechanism in the form of a circular spline positioned inside the second housing element; a rotational core (32, 34) being composed of: a motor rotor; a transmission input in the form of a wave generator operatively connected to the motor rotor; a motor rotor; a transmission input in the form of a wave generator operatively connected to the motor rotor; a transmission output in the form of a flex spline connected to the transmission input, the transmission output being positioned at the center of the gear reduction mechanism; a torque transfer output operatively connected to the actuator transmission output; characterized in that the motor rotor is configured to rotate freely around a center shaft via conical roller bearings positioned between the center shaft and the first housing element; and in that the torque transfer output is furthermore operatively connected to the center shaft, which passes through the transmission output, rotational core (32, 34) and second housing element; wherein the center shaft ensures proper radial and axial alignment between the housing assembly and the torque transfer output.