A rotary actuator assembly comprising: an output member configured to selectively rotate about a rotary output axis relative to a structure and configured to impart motion to a driven object; a first sub-actuator having a first stator and a first rotor; said first stator fixed to said structure and said first rotor configured to selectively rotate about a first sub-axis of rotation relative to said first stator; a second sub-actuator having a second stator and a second rotor; said second rotor configured to selectively rotate about a second sub-axis of rotation relative to said second stator; said second stator rotationally coupled to said first rotor such that said second stator rotates about said first sub-axis of rotation relative to said first stator with rotation of said first rotor about said first sub-axis of rotation relative to said first stator; said second rotor rotationally coupled to said output member; at least one controller (90, 91A, 91B) configured to drive said first sub-actuator and said second sub-actuator to selectively control rotation of said output member about said rotary output axis within an output angular range of rotary motion about said rotary output axis; said controller configured in a normal mode to drive said first sub-actuator and said second sub-actuator to selectively control said rotation of said output member about said rotary output axis within said output angular range of rotary motion as a function of a sum of rotation of said first rotor and said second rotor about the first sub-axis of rotation and said second sub-axis of rotation, respectively, relative to said structure; and said controller configured in a failure mode to drive one of said first sub-actuator or said second sub-actuator to selectively control said rotation of said output member about said rotary output axis within said output angular range of rotary motion with an operational failure of said other of said first sub-actuator or said second sub-actuator. an output member configured to selectively rotate about a rotary output axis relative to a structure and configured to impart motion to a driven object; a first sub-actuator having a first stator and a first rotor; said first stator fixed to said structure and said first rotor configured to selectively rotate about a first sub-axis of rotation relative to said first stator; a second sub-actuator having a second stator and a second rotor; said second rotor configured to selectively rotate about a second sub-axis of rotation relative to said second stator; said second stator rotationally coupled to said first rotor such that said second stator rotates about said first sub-axis of rotation relative to said first stator with rotation of said first rotor about said first sub-axis of rotation relative to said first stator; said second rotor rotationally coupled to said output member; at least one controller (90, 91A, 91B) configured to drive said first sub-actuator and said second sub-actuator to selectively control rotation of said output member about said rotary output axis within an output angular range of rotary motion about said rotary output axis; said controller configured in a normal mode to drive said first sub-actuator and said second sub-actuator to selectively control said rotation of said output member about said rotary output axis within said output angular range of rotary motion as a function of a sum of rotation of said first rotor and said second rotor about the first sub-axis of rotation and said second sub-axis of rotation, respectively, relative to said structure; and said controller configured in a failure mode to drive one of said first sub-actuator or said second sub-actuator to selectively control said rotation of said output member about said rotary output axis within said output angular range of rotary motion with an operational failure of said other of said first sub-actuator or said second sub-actuator.