Final answer:
In order to drive his robot, Ed should attach a gear to the DC motor's output shaft, which is the component that connects the motor's internal rotary motion to external parts like gears.
Step-by-step explanation:
Ed, an engineer, should attach a gear to the output shaft of the DC motor in order to drive the robot. The output shaft is the part of the motor that translates the motor's internal rotational movement into a form that can be utilized by external components, such as gears. While the commutator and armature are involved in the electrical operation of the motor, and the stator is a stationary part, it is the output shaft that extends outside the motor's casing and to which mechanical components like gears can be affixed to drive the robot's wheels or other moving parts.
The DC motor operates by converting direct current electrical power into mechanical rotation. The armature rotates within the magnetic field created by the stator. As electricity flows through the armature, it generates a magnetic field that interacts with the stator's field, causing the armature, and therefore the output shaft, to turn. The commutator and brushes work together to ensure the current in the armature windings is switched at the right moments to maintain continuous rotation.