What differentiates a servo motor from a DC motor in a closed-loop system?

• A. A servo motor includes internal feedback and a controller with closed-loop positioning.
• B. A DC motor has internal feedback; servo does not.
• C. A servo motor runs only on AC.
• D. A DC motor is used only for high-precision positioning.

Answer: (B)

In a closed-loop setup, the key idea is using feedback to precisely control where the system ends up. A servo motor is built to do this directly: it includes the motor, a position sensor (like an encoder or resolver), and a built-in controller that constantly compares the commanded position with the actual position and adjusts the motor to reduce any error. This integrated feedback loop provides precise, repeatable positioning without needing extra components.

A DC motor by itself is just the motor that converts electrical power into rotation. It doesn't come with internal feedback or an embedded controller for positioning. If you want closed-loop position control, you’d add external feedback and a separate controller around the motor. The motor itself doesn't provide the automatic correction that a servo package does.

So, the distinguishing feature is the built-in feedback and integrated control in a servo motor, enabling closed-loop position control, whereas a plain DC motor lacks that inherent feedback.