A robotic actuator assembly configured to selectively perform at least two actions in response to control motions applied by a drive assembly within a robotic system, wherein said robotic actuator assembly comprises: a tool mounting portion configured to be attached to said drive assembly; an end effector, comprising: a staple cartridge; an anvil selectively movable relative to said staple cartridge between an open position and a closed position in response to a closure control motion, and a firing portion selectively movable between a starting position and a finishing position in response to a firing control motion, wherein the firing portion is a sled mounted on a helical screw thread and configured to cut and staple tissue clamped within the end effector; a closure tube, wherein axial movement of the closure tube reversibly moves the anvil between the open position and the closed position; a closure drive nut in threading engagement with an internal thread of the closure tube; an elongate shaft assembly, comprising: a proximal end portion operably supported by said mounting portion; and a distal end portion operably interfacing with said end effector to apply at least one of said control motions to said end effector; a transmission, movable between a first position and a second position, and operably supported by said mounting portion, and shifting drive assembly configured to move the transmission between the first position and the second position wherein said transmission is configured to operably interface with a rotatable drive element of said drive assembly to receive a rotary output motion from said drive assembly when said mounting portion is attached to said drive assembly, wherein the rotatable drive element is a drive sleeve with a driven gear that is in meshing engagement with a drive gear on a drive shaft transmitting the rotary output motion from said drive assembly; wherein said rotary output motion causes the closure control motion to be applied to said end effector through said elongate shaft assembly when said transmission is in said first position, wherein the closure drive nut is rotated by the closure control motion, and wherein said rotary output motion causes the firing control motion to be applied to said end effector through said elongate shaft assembly when said transmission is in said second position, wherein the firing control motion causes rotation of the helical screw thread. a tool mounting portion configured to be attached to said drive assembly; an end effector, comprising: a staple cartridge; an anvil selectively movable relative to said staple cartridge between an open position and a closed position in response to a closure control motion, and a firing portion selectively movable between a starting position and a finishing position in response to a firing control motion, wherein the firing portion is a sled mounted on a helical screw thread and configured to cut and staple tissue clamped within the end effector; a staple cartridge; an anvil selectively movable relative to said staple cartridge between an open position and a closed position in response to a closure control motion, and a firing portion selectively movable between a starting position and a finishing position in response to a firing control motion, wherein the firing portion is a sled mounted on a helical screw thread and configured to cut and staple tissue clamped within the end effector; a closure tube, wherein axial movement of the closure tube reversibly moves the anvil between the open position and the closed position; a closure drive nut in threading engagement with an internal thread of the closure tube; an elongate shaft assembly, comprising: a proximal end portion operably supported by said mounting portion; and a distal end portion operably interfacing with said end effector to apply at least one of said control motions to said end effector; a proximal end portion operably supported by said mounting portion; and a distal end portion operably interfacing with said end effector to apply at least one of said control motions to said end effector; a transmission, movable between a first position and a second position, and operably supported by said mounting portion, and shifting drive assembly configured to move the transmission between the first position and the second position wherein said transmission is configured to operably interface with a rotatable drive element of said drive assembly to receive a rotary output motion from said drive assembly when said mounting portion is attached to said drive assembly, wherein the rotatable drive element is a drive sleeve with a driven gear that is in meshing engagement with a drive gear on a drive shaft transmitting the rotary output motion from said drive assembly; wherein said rotary output motion causes the closure control motion to be applied to said end effector through said elongate shaft assembly when said transmission is in said first position, wherein the closure drive nut is rotated by the closure control motion, and wherein said rotary output motion causes the firing control motion to be applied to said end effector through said elongate shaft assembly when said transmission is in said second position, wherein the firing control motion causes rotation of the helical screw thread.