A surgical instrument for treating tissue, the instrument including a housing and a shaft with an articulating portion and an end effector. The surgical instrument including a first casing connected to and rotatable with the proximal end of said shaft with an internal frame housed within the first casing and a plurality of posts supported by the internal frame and connected on their distal ends to at least one drive wire, and connected on their proximal ends to a threaded shaft; and a second casing connected to the first casing and rotatable therewith, said second casing housing the threaded shafts. The surgical instrument includes a first electric motor driving a first gear interfacing with the threaded shafts such that a first pair of the plurality of threaded shafts rotate in the same direction and cause the articulating portion to articulate in a first plane.