Brushless DC Motor Design

Brushless dc motor design

Brushless Motor Torque

Portescap offers mainly two types of brushless DC motor technologies: slotted and slotless. Both of these brushless DC motors have permanent magnet rotors with 2 or 4 pole pairs. Slotted brushless DC motors have coils inserted in the slots of the stator. Due to these slots, the rotor has preferred equilibrium positions when the motor is unenergized. This resistant torque is called cogging or detent torque. Slotless brushless DC motors have a self-supporting cylindrical coil, creating no detent torque thus the rotor does not have preferred equilibrium positions. Both of these brushless DC motor technologies feature high efficiency, high speed, and hall sensors/sensorless options.

Conventional DC motors use a stationary magnet with a rotating armature, combining the commutation segments and brushes to provide automatic commutation. In comparison, the brushless DC motor design is a reversed design: the permanent magnet is rotating whereas the windings are part of the stator. These can be energized without a commutator-and-brush system. Even while operating at extremely high speeds, brushless DC motors achieve a long, trouble-free life, as there is no mechanical commutation. The commutation of the brushless DC motor is made electronically and can be done either by looking at the back-EMF of the motor or by using a position sensor.

BLDC Motor Design

During the brushless DC motor design phase, Portescap engineers aim to optimize the brushless motor torque. Motor torque is the amount of rotational force that a motor generates during operation. The key components involved in producing torque are the magnet, the winding and the flux path. The higher the number of pole pairs in the magnet, the higher the amount of brushless motor torque for the same dissipated power. Copper content of the winding contributes to the power provided by the motor while flux path guides all of the magnetic field in the usable channel, minimizing losses. Striking the right balance is important while creating a motor with maximum brushless motor torque that does not draw a tremendous amount of power. Understanding the complete motor design allows Portescap engineers to pack the most power possible into the smallest motor package.

Portescap’s Ultra EC platform offers 3 families of motors to help you address a wide range of requirements for brushless motor torque and speed. The patented U coil provides outstanding performance, including minimal iron losses, increased efficiency and cooler operation. The key to the outstanding performance of these mini brushless motors is this new coil, designed by Portescap in Switzerland. This unique coil design allows two-pole motors, for example, to deliver 30 % more brushless motor torque compared to the same size motor using a conventional coil design, while substantially lowering iron losses.

DC Brushless Special Features

Most of our BLDC products can be customized or modified with special features that include:

  • Special shafts (longer or shorter, larger or smaller diameters, cross holes, axial holes, cannulated, special materials and coatings)
  • Special construction for non-medical applications (aluminum housing/end bellws, steel gearhead components, steel bearings)
  • Special windings (higher voltage, different speeds)
  • Special lead terminations (no connections, special connectors, integral connectors, special colors)
  • Special mounting features
  • Alternate lam materials
  • Alternate magnet materials
  • Sterilizable option
  • Encoder options


Composition and Variations of Brushless DC (BLDC) motors

Permanent magnet brushless DC motor designEssentially linear torque/speed curve (neglecting iron losses), with torque proportional to current and speed proportional to voltageEase of speed and position control
Brushless DesignLife is not limited by brush wear but only by wear in ball bearingsVery long life, high reliability, insensitive to environment. No arcing, dust free. Reduced audible and electrical noise
Autoclavable versionSuitable sealing and optimized designWithstand autoclaving and sterilization cycles. Sealing prevents contamination
Static winding attached to motor housingImproved heat dissipationOverload capability

Slotted vs. Slotless BLDC Motor Technologies

Ability to withstand harsh environment / Autoclavability+++
Torque / Power ratio+++
High speed capability+++
Battery life+++
Detent torque-+

Feedback options

Versions without hall sensorTypically used in spindle applicationsCost effective. Less sensitive to environment. Only three connecting wires
Versions with hall sensorsTypically used in applications where speed or load variation are neededVery simple commutation circuitry
Versions with encoder or resolverTypically used in incremental motionVery precise speed and position control
Version with integrated electronicHall sensors and commande circuitry are integrated to the motorPlug and play configuration
Can be driven like a brush DC motor

BLDC Slotted Motors - Additional Information

Brushless DC slotted - Rear end bell and PCB

Brushless DC slotted - Laminations stack

Brushless DC slotted - PCB

Brushless DC slotted - Rotor

Brushless DC slotted - Molded stator