A surgical instrument may comprise a chassis configured to be removably coupled with a surgical robotic manipulator and may comprise an elongate flexible shaft coupled to the chassis. The surgical instrument may also comprise a robotic actuation piece coupled to and rotatable relative to the chassis and a manual actuator coupled to and translatable relative to the chassis. A rack gear may be engaged with the manual actuator and with the robotic actuation piece. The rack gear may be movable by the robotic actuation piece and by the manual actuator to control an operation of the elongate flexible shaft.