Four Advantages of Slotless BLDC Motor and Slotted BLDC Motor Comparison

In the early period of slotless BLDC motor design, its power density was lower than that of an equivalent slotted motor. In the past 10 years, bldc motor are increasingly replacing brushed DC motors, especially in high-speed (above 12,000 rpm) and long lifespan applications.


In fact, brushless dc motors don’t have all the advantages. Brushed DC motors provide simple control and no cogging, while the complex structure of brushless DC motors means higher costs-conventional brushless DC motors have a slotted design, that is, the coils are wound in slots around the stator.


Four advantages of slotless bldc motor and slotted bldc motor comparison.


  1. The volume of the slotless BLDC motor can be smaller.

In slotted brushless DC motors, the presence of stator teeth makes the overall size of the motor unable to be minimized. In addition, as the size of the motor shrinks, the winding process has gradually become difficult. In comparison, the slotless brushless DC motor has oblique or axial windings fixed on the cylindrical stator core, making it easier to reduce the size.



  1. Slotless BLDC motors are cheaper.

The slotless design also has cost advantages because it reduces complexity and makes the stator core easier to manufacture.


  1. Slotless BLDC motor with high power density.

Although both designs can run at high speeds, slotted and slotless designs have different characteristics at high speeds.


In order to obtain mechanical stability under high-speed operation (from 40,000 to 60,000 rpm), usually slotless rotors have a two-pole permanent magnet design. In addition, due to the existence of the large air gap, when the motor is running at high speed, the loss of the stator core is limited to an acceptable range. This means that the slotless BLDC motor benefits from the slotless stator structure, the core loss is relatively small, so it has a high power density.


In the early period of slotless BLDC motor design, its power density was lower than the equivalent slotted motor. However, the emergence of high-energy permanent magnets and their alternative magnetization devices have narrowed the performance gap. Slotted brushless DC motors cannot use high-energy magnets because the thicker teeth required to increase the magnetic load of the motor have the effect of reducing the area of the slot, thereby reducing the electrical load of the motor.


  1. Slotless BLDC motor has better overload.

Slotted brushless DC motors can provide higher torque than slotless designs because the slotted design can handle higher temperatures, allowing more torque to be produced. However, due to the saturation of the magnetic circuit during overload operation, the torque of the motor will be reduced, and the toothless design in the slotless design has no magnetic saturation, thus providing better overload.



Although slotless BLDC motors have many advantages over standard BLDC, in practical applications, slotless BLDC motors are not always the best choice. For example, slotless BLDC motors provide low inductance, which brings challenges to motion control. If pulse width modulation (PWM) control is used, low inductance will result in higher motor losses. Control devices with higher switching frequencies (80 to 100 kHz) or series-compensated inductance can be used to alleviate the problem of low inductance.



In fact, different brushless DC motor technologies are suitable for different applications. Slotted brushless DC motors are suitable for applications that require a large number of poles, such as electric vehicles or household appliances, and the final size is not a problem. They are also preferred in harsh environments because the slotted design coils are easier to protect and are mechanically fixed by the stator teeth. For applications that require high speed and small size, such as in medical equipment or portable industrial tools, a slotless BLDC motor is a better choice, and it can provide the best solution.


Honest Automation has more than 13 years in the industrial motor automation equipment industry. Products include motor production line, stator winder, rotor winding machine, etc. Motor manufacturing equipment is widely used in automobiles, household appliances, office equipment, new energy vehicles and  electric tool industry.


We have many successful cases of fully automatic bldc motor production line. Many of our cooperating brands are well-known international group companies.