A computer-assisted system includes an instrument manipulator assembly including a preload assembly and a motor, an insertion assembly configured to control a position of the instrument manipulator assembly, and a motor controller coupled to the preload assembly. The motor controller is configured to actuate the preload assembly to control an amount of preload applied by the preload assembly to the motor and actuate the preload assembly to apply a low preload in response to detecting that a sterile adapter is mounted to the instrument manipulator assembly.