With an external actuator, the object being moved is mounted to the nut external to the motor assembly, and the screw rotates providing the motion along the length of the screw.
By contrast, in a non-captive actuator, the screw passes completely through the motor assembly, with the nut housed inside the motor and the payload or moving object attached to the motor itself. As the screw rotates, the motor, load, and nut travel along the screw, while the screw ends are typically fixed to the surrounding equipment.
Because the screw can pass through the motor, this configuration often allows for a longer overall screw length. It is also well suited for external linear guide bearings, which are almost always required in non-captive applications. These guides add stiffness and help prevent deflection, reducing premature wear on the nut, screw, and internal motor bearings.
A less common non-captive arrangement attaches the device or payload to the end of the screw rather than to the motor assembly. In this configuration, the screw translates through the motor as the internal nut rotates. Because the screw itself provides limited stiffness, this approach is suitable only for very light loads and requires external linear guidance to prevent deflection. The design must also provide clearance for the screw to protrude from the opposite side of the motor.
