Brushless motors are a more efficient and longer-lasting evolution from brushed DC motors which used to be a standard. Since the phase-out of a brushed commutator for more advanced electronic servo systems, they have been widely adopted for many applications. In general, they deliver better reliably for lower maintenance, and reduced weight and heat. While they have become a standard “workhorse” component in all types of electrical equipment, they are not a one-size-fits-all motor.
Obviously, there are large brushless motors for placements like elevator drives, lifts, and industrial pumps, and small brushless motors for applications like small fans and hand tools, but their size and shape are not the only factors to consider. One of the main attributes of a brushless motor is whether it incorporates sensors or is sensor-free.
Each type offers unique advantages and limitations. Although an OEM, engineer, mechanic, or hobbyist may know their application calls for precision engineered brushless motors, they may not know whether sensored or sensorless amounts to a better choice. So what is the difference and which one is best?
How Motors Work With And Without Sensors
The main differentiator between sensored and sensorless brushless motors is the presence or lack of position sensors. In the sensored variety, the positional sensors, or Hall effect sensors, will detect the position of the rotor during the motor’s initial start-up. When this feedback is sent to the motor’s controller, the drive pattern will sync with the position of the rotor.
Sensorless brushless motors lack these sensors and instead operate with the use of a sensorless brushless motor controller or a brushless electronic speed controller. The drive pattern is established as the motor speeds up and an electromotive force is generated between the motor’s permanent magnets and its stator coils. This then creates a back electromotive force, which generates a frequency that’s directly proportional to the motor’s speed. The controller then recognizes and uses the frequency to adjust the drive pattern.
Do Sensors Amount To Better Performance?
Since sensored motors can start up faster and control motion with greater accuracy than sensorless brushless motors, one might conclude that the addition of sensors amounts to a better motor, but it is not that simple.
In some cases, the addition of positional sensors provides many advantages. By creating a closed-loop system between the rotor and the controller, a sensored motor’s degree of motion control is very responsive and accurate. This means that it’s possible to get a level of positioning and actuation that makes these motors useful in robotics and stepper and servo systems. However, there are many limitations in how and where sensored brushless motors can be used.
The operation of a sensored brushless motor is completely reliant on the proper function of the sensors. If they are not operational, or if something interferes with their performance, such as dirt, dust, moisture, or vibration, the motor will not work. The quick start-up and closed-loop operation of these motors make them most useful for short duty cycles and low speeds. If that type of performance is necessary for an application, then sensored brushless motors are the better choice.
Brushless motors without sensors will perform best where start-up accuracy is not as critical as continuous motion and efficiency over longer, high-speed duty cycles. Since these motors lack sensors and the resulting vulnerabilities, they are more robust. They are applied to many high-power, high-speed systems, such as pumps, fans, mixers, and other equipment designed to run continuously.
How To Get The Best Type Of Brushless Motor
Whether sensored or sensorless, brushless motors should always be paired with a compatible controller. This component will have a substantial impact on how well the motor runs. Other factors that affect whether a brushless motor will deliver the best possible operation include its design, insulation, housing, and overall assembly. Sourcing a high-performance motor from a manufacturer that offers support, design services, and customization is a great way to ensure a brushless motor will be the best fit for a specific application.