A surgical assembly for use with and selective connection to a robotic arm, the surgical assembly comprising: an electromechanical instrument including: a housing portion supporting a driven member therein; and a shaft having a proximal end supported by the housing portion and a distal end having an end effector operably coupled to the driven member; and an instrument drive unit including: an outer shell configured to be selectively coupled to a robotic arm; and an inner hub rotatably disposed within the outer shell and configured to be non-rotatably coupled to the housing portion of the electromechanical instrument; characterized in that the instrument drive unit further comprises: a first motor (M1-M4) disposed within the outer shell and configured to be operably coupled to the driven member of the electromechanical instrument; and a second motor disposed within the outer shell and including: an outer stator fixedly coupled to the outer shell; and an inner rotor rotatably disposed within the outer stator, the inner rotor having an inner surface that defines a longitudinal channel having the inner hub non-rotatably disposed therein, wherein actuation of the second motor rotates the inner hub to effect rotation of the electromechanical instrument along a longitudinal axis thereof. an electromechanical instrument including: a housing portion supporting a driven member therein; and a shaft having a proximal end supported by the housing portion and a distal end having an end effector operably coupled to the driven member; and an instrument drive unit including: an outer shell configured to be selectively coupled to a robotic arm; and an inner hub rotatably disposed within the outer shell and configured to be non-rotatably coupled to the housing portion of the electromechanical instrument; a housing portion supporting a driven member therein; and a shaft having a proximal end supported by the housing portion and a distal end having an end effector operably coupled to the driven member; and an instrument drive unit including: an outer shell configured to be selectively coupled to a robotic arm; and an inner hub rotatably disposed within the outer shell and configured to be non-rotatably coupled to the housing portion of the electromechanical instrument; an outer shell configured to be selectively coupled to a robotic arm; and an inner hub rotatably disposed within the outer shell and configured to be non-rotatably coupled to the housing portion of the electromechanical instrument; a first motor (M1-M4) disposed within the outer shell and configured to be operably coupled to the driven member of the electromechanical instrument; and a second motor disposed within the outer shell and including: an outer stator fixedly coupled to the outer shell; and an inner rotor rotatably disposed within the outer stator, the inner rotor having an inner surface that defines a longitudinal channel having the inner hub non-rotatably disposed therein, wherein actuation of the second motor rotates the inner hub to effect rotation of the electromechanical instrument along a longitudinal axis thereof. an outer stator fixedly coupled to the outer shell; and an inner rotor rotatably disposed within the outer stator, the inner rotor having an inner surface that defines a longitudinal channel having the inner hub non-rotatably disposed therein, wherein actuation of the second motor rotates the inner hub to effect rotation of the electromechanical instrument along a longitudinal axis thereof.