Slotless High Speed BLDC Motor Overview

When brushless DC motors became available on the market, they were a great alternative to brush-commutated motors.Brushed DC motors had limited operational lives, were energy inefficient, generated electrical inference, and tended to be noisy, making them ill-suited for some industrial and medical applications.

Slotless Brushless DC Motor Applications

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Because of dramatic reductions in cost and size, BLDC motors have gained broad appeal across various industries. However, really fast motors need to have small diameter rotors to minimize the rotating mass. So, despite the advantages of BLDC motors, manufacturers needed to overcome the speed limitations of small diameter motors.

The result was the creation of the slotless BLDC motor.

Traditional BLDC Motor Construction Custom versus Slotless BLDC Motor Construction

Slotted BLDC Motors

BLDC motors use electronic commutation—magnets, Hall-effect sensors and electronic motor controllers—instead of brushes and commutators. The rotor comprises a steel shaft, with a ring of permanent magnets around the shaft. The amount of torque available increases as the magnet’s flux density increases.

Traditional slotted BLDC motors have stators with a stack of steel laminations that are fused together.  The spaces, or slots, in the lamination stack are shaped to allow coils to be wound around them. Manufacturers then wind copper coils into each of the slots to complete the stator assembly, and create an electromagnetic field.

Laminated material near the copper windings complete the magnetic circuit’s return path. Brushless slotted motors are made more powerful through the use of high energy product rare earth magnets.

Slotless BLDC Motors

Instead of winding copper wires through lamination slots, slotless BLDC motor manufacturers wind them into a cylindrical shape and protect them with high-temperature-resistant resin to maintain their shape. This configuration negates the need for a slotted stator lamination stack. This eliminates cogging and reduces vibrations, noise, and eddy current-related damping losses. Since a slotless wound stator takes up less space than a slotted lamination stack, the rotor can have a larger diameter, increasing torque.

The absence of teeth in a slotless motor reduces the winding inductance and decreases the damping for fast motor response.

Higher power is achieved in motors by narrowing the air gap between the stator and the armature.  In slotted BLDC motors this gap is inherently wide due to the lamination geometry.   In slotless BLDC motors, the only limit to decreasing the air gap is the precision of the manufacturing. Sinotech’s quality custom slotless BLDC motor maximizes the electromagnetic field strength for the greatest power output.

Benefits of Slotless BLDC Motors

  • The lack of stator teeth eliminates cogging
  • Quieter operation
  • Smoother and improved performance thanks to low loss lamination materials
  • Reduced damping-related losses
  • Reduced inductance for faster dynamic response
  • Minimal vibration
  • Increased lifespan
  • Smoother high-speed operation
  • Speed capabilities of up to 100,000+ rpm
  • Power-to-weight ratios facilitate the design of lightweight hand tools
  • Insulation for temperatures of up to 200°C
  • The use of power dense magnets reduces the impact of core losses at high-speed operations
  • Beneficial for various applications, including those in the medical, automotive, aerospace and robotics industries

Slotless BLDC Motor Customization

Sinotech’s slotless BLDC motors feature a modular design that makes it simple to customize the motor components to meet performance needs. For example, engineers can integrate spur gearheads into the motors for higher-torque alternatives. You can also add components such as optical encoders, rotor position indicators, and differential line drivers.

When comparing slotted and slotless BLDC motors, it’s important to keep in mind that one is not better than the other. They are simply better for certain applications. When you bring your ideas to Sinotech, our engineers will help you determine which type of BLDC motor is best for your needs. Our specialists then scout the best factories in the Pacific Rim, inspect them to ensure they’re capable of handling your project, and perform audits during production to ensure the quality of your custom design. The processes we developed over the last two decades are designed to reduce costs, minimize risks and deliver the highest quality custom motor components on the market. Contact Sinotech today to learn more.


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