A robotic assembly is configured to support, insert, retract, and actuate a surgical instrument mounted to the robotic assembly. The robotic assembly includes an instrument holder base member, a motor housing moveably mounted to the instrument holder base member, a carriage drive mechanism operable to translate the motor housing along the instrument holder base member, a plurality of drive motors, and a plurality of output drive couplings driven by the drive motors. One or more of the drive motors includes one or more magnetic flux shields to inhibit magnetic interference with an adjacent drive motor and/or with an adjacent motor orientation sensor.