In the field of motor drives, sensored motors and sensorless motors are the two most common types. While their performance may appear similar at medium to high speeds, at low speeds they behave quite differently. For applications such as electric vehicles, robotics, drones, and industrial automation, low-speed performance often determines smooth startup and precise control. Understanding these differences is therefore critical.
Basic Difference Between Sensored and Sensorless Motors
Sensored motors: These are equipped with Hall sensors or encoders that directly detect rotor position and feed signals back to the controller.
Sensorless motors: These estimate rotor position indirectly by monitoring back electromotive force (Back-EMF).
This fundamental difference in rotor position detection is the key reason behind their distinct low-speed characteristics.
Low-Speed Operating Characteristics
1.Sensored Motors: Smooth Startup and Strong Torque
Even at zero or very low speed, Hall sensors can accurately provide rotor position information. The controller can therefore switch phases precisely.
With timely feedback, the motor delivers consistent torque at low speeds, preventing jitter and loss of synchrony.
This makes sensored motors ideal for frequent start-stop operations and low-speed, high-torque requirements such as electric vehicle launches and servo positioning systems.
2.Sensorless Motors: Startup Jitter and Instability
Since sensorless motors rely on Back-EMF detection, at low speeds the signal is too weak to be reliable.
This results in imprecise commutation, leading to jitter, delayed response, or even startup failure.
Once the motor accelerates and Back-EMF becomes stronger, it can transition into stable operation.
Application-Level Differences
Electric Vehicles & E-Scooters
Sensored motors provide smoother and more responsive low-speed acceleration, whereas sensorless motors may exhibit jitter during startup, affecting ride comfort.
Robotics & Industrial Control
Precision at low speeds is essential for robotic joints and CNC equipment, where sensored motors outperform sensorless alternatives.
Drones & High-Speed Fans
Since these applications operate mostly at medium or high speeds, where Back-EMF is reliable, sensorless motors are often preferred for their simplicity and lower cost.
Can Sensorless Low-Speed Issues Be Improved?
With advancements in control algorithms, some techniques (such as model-based estimation and hybrid control strategies) can improve the low-speed performance of sensorless motors. However, compared to motors with built-in sensors, their response is still less precise and stable.
Conclusion
In summary, sensored motors clearly outperform sensorless motors at low speeds. They offer smoother startup, stronger torque, and higher precision. Sensorless motors, on the other hand, suffer from jitter and unstable response at low speed, though the performance gap narrows at medium to high speeds.
For applications where low-speed control is critical—such as electric vehicles, servo systems, and robotics—sensored motors are the more reliable choice. In cost-sensitive scenarios where low-speed precision is less important, sensorless motors remain a practical and economical option.