An actuator, comprising: a motor assembly, comprising: a motor housing, comprising: a cover, and a base; an electric motor, within the motor housing, comprising: an external stator, and an internal rotor; and a hollow output shaft that is connected coaxially with the internal rotor such that rotation of the internal rotor causes a corresponding rotation of the hollow output shaft; a drive coupling assembly connected to the base of the motor housing, the drive coupling assembly, comprising a drive coupling housing containing a drive coupling, wherein the drive coupling engages the hollow output shaft such that rotation of the hollow output shaft causes a corresponding rotation of the drive coupling; and an actuator shaft that engages the drive coupling such that rotation of the drive coupling by the hollow output shaft causes the actuator shaft to move; characterised in that the electric motor is located on one side of the base inside the motor housing and the drive coupling assembly is located on the other side of the base external to the motor housing; the connection between the drive coupling assembly and the motor housing is releasable so that the motor housing can be removed from and reattached to the drive coupling assembly; and the actuator shaft (14, 114) extends through the hollow output shaft (30, 130) and the internal rotor (12, 112), wherein rotation of the drive coupling (13, 113) causes the actuator shaft (14, 114) to move axially. a motor assembly, comprising: a motor housing, comprising: a cover, and a base; an electric motor, within the motor housing, comprising: an external stator, and an internal rotor; and a hollow output shaft that is connected coaxially with the internal rotor such that rotation of the internal rotor causes a corresponding rotation of the hollow output shaft; a drive coupling assembly connected to the base of the motor housing, the drive coupling assembly, comprising a drive coupling housing containing a drive coupling, wherein the drive coupling engages the hollow output shaft such that rotation of the hollow output shaft causes a corresponding rotation of the drive coupling; and an actuator shaft that engages the drive coupling such that rotation of the drive coupling by the hollow output shaft causes the actuator shaft to move; a motor housing, comprising: a cover, and a base; a cover, and a base; an electric motor, within the motor housing, comprising: an external stator, and an internal rotor; and a hollow output shaft that is connected coaxially with the internal rotor such that rotation of the internal rotor causes a corresponding rotation of the hollow output shaft; an external stator, and an internal rotor; and a hollow output shaft that is connected coaxially with the internal rotor such that rotation of the internal rotor causes a corresponding rotation of the hollow output shaft; a drive coupling assembly connected to the base of the motor housing, the drive coupling assembly, comprising a drive coupling housing containing a drive coupling, wherein the drive coupling engages the hollow output shaft such that rotation of the hollow output shaft causes a corresponding rotation of the drive coupling; and an actuator shaft that engages the drive coupling such that rotation of the drive coupling by the hollow output shaft causes the actuator shaft to move; the electric motor is located on one side of the base inside the motor housing and the drive coupling assembly is located on the other side of the base external to the motor housing; the connection between the drive coupling assembly and the motor housing is releasable so that the motor housing can be removed from and reattached to the drive coupling assembly; and the actuator shaft (14, 114) extends through the hollow output shaft (30, 130) and the internal rotor (12, 112), wherein rotation of the drive coupling (13, 113) causes the actuator shaft (14, 114) to move axially.