A Guide to Slotless Brushless DC Motors

While all electric motors convert electricity into mechanical energy that can be used to drive connected devices and systems, the exact design and configuration can vary between individual units to suit different applications. For example, a motor may utilize direct current (DC) or alternating current (AC) electricity, employ brushes (brushed motors) or active electronic control elements (brushless motors) for commutation, and feature slotted or slotless stators. Below, we provide an overview of slotless brushless DC (SBLDC) motors, highlighting what they are, their key advantages, and their typical industrial applications.

What Is A Slotless Brushless DC Motor?

Slotless brushless DC motors are a unique type of motor that combines elements from slotless, brushless, and DC motor technologies; DC motors turn DC electricity into mechanical energy, brushless motors remove the mechanical brush-commutator mechanism that reduces performance reliability over time in brushed motors, and slotless motors eliminate the slots in the stator element that cause cogging torque in slotted motors. The resulting design consists of a permanent magnet rotor and a wire-wound stator. The stator windings are positioned inside stacked steel rings (i.e., the stator lamination) that do not have conventional teeth to support them. Instead, epoxy resin is used to encapsulate the windings, which creates a self-supporting winding structure; it sits within the air gap between the stator lamination and rotor. 

Key Advantages of Slotless Brushless DC Motors

Slotless brushless DC motors offer a number of advantages over other types of motors, including:

  • No cogging torque: the rotors do not have a preferred position, and the shafts rotate smoothly at any speed
  • Smoother operation: the reduced torque ripple enables smooth torque during acceleration, deceleration, and running
  • Better high-speed performance: the stator coils are not surrounded by laminated iron, resulting in lower electrical time constant and, consequently, better performance at high speeds
  • Quieter operation: the slotless stator design increases the uniformity of winding distribution achieved and decreases the amount of lamination material needed, reducing electrical noise
  • Higher efficiency: the lack of teeth in the stator lamination allows the stator windings to be placed more evenly and compactly, which, combined with reduced core loss, results in greater efficiency with the same speed and torque output
  • Easier cooling requirements: the heat produced by the motor can be easily removed through the frame without significant transfer through the bearings
  • Smaller envelope: the integration of high-energy magnets reduces the overall size of the envelope needed

For more information on these advantages, check out this blog post, “Why Choose Slotless Brushless DC Motors?”.

Typical Applications of Slotless Brushless DC Motors

Due to the numerous benefits they provide, slotless brushless DC motors find application in many industries. Additionally, their modular design enables motor manufacturers to tailor them to meet nearly any industrial customer’s requirements and restrictions. Some examples of typical industrial applications include: 

  • In aerospace applications, slotless brushless DC motors are used in control systems to ensure pilots receive smooth feedback. 
  • In general industrial equipment applications, slotless brushless DC motors are utilized for handheld production tools to eliminate cogging and resulting vibrations that can cause ergonomic problems. They are also found in other types of industrial equipment, such as material handling systems (e.g., robots), processing systems (e.g., feeders and benders), and measurement and testing systems (e.g., scanners). 
  • In medical applications, slotless brushless DC motors are integrated into manual and automated medical and surgical tools that feature robotic grippers and claws. They are also suitable for use in miniature respirators and pumps as well as imaging and test devices. 
  • In military applications, slotless brushless DC motors are incorporated into microclimate cooling systems within military helicopters, which help pilots maintain normal body temperature conditions in extreme environments.

Slotless Brushless DC Motors at Elinco International JPC

At Elinco International JPC, we’ve designed and manufactured high-performance precision electric motors since around the beginning of World War II. Both of our sister companies—Japanese Products Corporation (JPC) and Elinco International, Inc.—specialize in brushless DC motors. After recognizing the inherent advantages of this motor technology in the early 1980s, we developed a new type that offered unique performance—the slotless brushless DC motor. 

Advantages of Our Slotless Brushless DC Motors

Our patented design features a rotor with permanent magnets affixed to it and stator windings inside of a laminated stator ring without teeth (i.e., slotless). Compared to other motor designs, it allows for more peripheral space for the stator winding, more magnet surface area, and more air gap flux. Other key advantages include: 

  • The use of powerful rare earth magnets provides a higher torque-to-motor weight ratio, allowing for a smaller overall package. 
  • The elimination of stator teeth enables more copper winding to be integrated and, consequently, allows for more power density, resulting in more torque. It also stops torque cogging and reduces audible noise during operation. 
  • The customizability of the motor design offers broad flexibility, allowing customers to adapt their equipment to their specifications. We have options for embedded magnets (which simplify manufacturing operations, eliminate the need for a rotor speed, and improve part-to-part rotor balance consistency) and surface mount magnets (for enhanced performance). We also sell our products in framed, frameless, and integrated variations. Additionally, regardless of the customer’s power density, noise, weight, cost, vibration, or efficiency requirements and restrictions, we will optimize the magnetic design to ensure their success. 

Our Slotless Brushless DC Motors

We maintain a range of slotless brushless DC motors to meet different customer needs. See the table below for some of the key specifications of each model.

Model Frame
(in mm)
(in V)
(in mN·m)
Rated Speed
(in rpm)
Rated Power
(in W)
Peak Current
(in A)
SL1628-12-270 16 x 28 12 1.6 22,000 3.7 1.4
SL1640-24-300 16 x 40 24 4 25,000 10 1.9
SL1656-24-300 16 x 56 24 9 25,000 24 4
SL27113-320-430 27 x 113 320 460 32,000 1,500 17
SL2844-24-170 28 x 44 24 24 14,000 37 6.3
SL2866-24-170 28 x 66 24 54 14,000 79 12.8
SL34124-320-430 34 x 124 320 450 35,500 1,700 17
SL39119-320-460 39 x 119 320 460 35,000 2,000 22
SL45125-320-390 45 x 125 320 550 31,150 2,300 27
SL49120-48-240 49 x 120 48 705 24,000 500 34
SL49180-320-330 49 x 180 320 300 32,000 1,000 12
SL4990-110-130 49 x 90 110 140 13,000 200 7.6

We also manufacture and distribute many other types of brushless DC motors, including our closed-loop, FHD, FYD, VH inner rotor, and VH outer rotor series. Visit our brushless DC motor catalog for more information on all of our brushless DC motor offerings.

Elinco International JPC: Your Partner for Quality Slotless Brushless DC Motors 

Looking for slotless brushless DC motors for your next project? Elinco International JPC is the perfect partner! We are experts in the design and manufacture of custom slotless BLDC motors. We’ve produced tens of thousands of slotless brushless DC motors for customers in a diverse set of industries, including aerospace, general industrial, medical, and military. Our extensive motor fabrication experience, combined with our flexible SBLDC design, enables us to develop and deliver a solution tailored to your specifications. Whatever your issues (speed, power, weight, size, noise, etc.), we will optimize your equipment to provide the performance you need. 

To learn more about slotless brushless DC motors or our product offerings, contact us today.