EVK High Performance Flat Wire Helical Propeller Drive Motor Technology [Electric Drive System Conference]

On June 21, at the 2025 SMM (4th) Electric Drive System Conference & Drive Motor Industry Forum - eVTOL Electric Drive System Forum, jointly hosted by SMM Information & Technology Co., Ltd., Hunan Hongwang New Material Technology Co., Ltd., the People's Government of Louxing District, and the National-level Loudi Economic and Technological Development Zone, Cao Hongfei, Co-founder/General Manager of Anhui EVK Motor Technology Co., Ltd., shared insights on "EVK High-Performance Flat Wire Propeller Drive Motor Technology."

1. Characteristics of Powertrain Motors for Low-Altitude Aircraft

►eVTOL Powertrain Classification:

• Pure Rotor: Single-layer rotor, upper and lower dual-layer rotors;

• Compound Wing;

• Tilt-Rotor Compound Wing.

►Electric Propeller System

Summary:

1. There are various forms of power systems, and none can be said to be an inevitable trend at present.

2. Lift propeller motors are generally external rotor motors; flight path motors are typically internal rotor motors.

3. Motors and propeller systems are directly integrated, with no precedent for integrating motors and electronic controls.

1. Load Characteristics and Technical Requirements of Propeller Motors for Low-Altitude Aircraft

►Technical Requirements and Features of Propeller Motors:

a. According to the load characteristics of the propeller: There is no requirement for constant power field weakening in the drive motor, and the presence or absence of reluctance torque ratio is irrelevant.

b. The motor speed range is narrow; generally, the maximum speed is within 1.4 times the rated speed.

c. Due to the strength of the propeller blades and the requirement that their linear speed must be below the speed of sound, the operating speed of the drive motor is relatively low.

d. The drive motor for low-altitude aircraft is generally directly connected to the propeller, which can improve system reliability, and a shorter axial dimension is typically chosen for the drive motor.

e. Under the premise that the controller frequency of the motor is controllable, increasing the number of pole pairs as much as possible can effectively reduce the thickness of the stator and rotor yokes and decrease the end-winding dimensions of the motor windings. Combined with the relatively low operating speed, motors generally have a higher number of pole pairs, and a permanent magnet concentrated winding scheme is typically chosen.

f. Given the high reliability requirements of propeller motors (especially for manned models), the design of related powertrains generally prioritizes reducing failure rates or providing redundant functions.

►Summary of Characteristics

• Load Characteristics: As the speed increases, the torque index increases. The effective operating speed range of aircraft propeller motors is much narrower than that of automotive motors.

• Efficiency characteristics: The speed range for high efficiency in the propeller system is relatively narrow.

• Motors with this characteristic cannot use field-weakening speed increase to meet high-speed and high-torque requirements, so the back EMF of the motor is generally lower than the working voltage.

• Good solutions must be implemented for PWM losses in the motor!

The weight-torque density of propeller drive motors is crucial, equivalent to the thrust-to-weight ratio of jet engines.

► Selection of Inner and Outer Rotor Structures

♦ Advantages and Disadvantages of Inner Rotors

• Advantages: Simple structure (including bearing support, lead-out wire design, sealing design, etc.); large heat dissipation area on the outer circumference of the stator, allowing for higher electrical load; the rotor is inside the stator, with small moment of inertia, suitable for servo drives; the rotor thickness is generally not sensitive, allowing for more complex magnetic circuit designs.

• Disadvantages: The air gap diameter is relatively small, which is not conducive to increasing torque density; rotor heat dissipation is relatively difficult, and the cost of magnetic steel is relatively high.

♦ Advantages and Disadvantages of Outer Rotors

• Advantages: Large air gap diameter, making it easier to achieve higher torque density; convenient rotor heat dissipation; simple magnetic steel protection, with no concerns about centrifugal stress.

• Disadvantages: Difficult structural design (including sealing design, heat dissipation design); large rotor inertia and centrifugal force, not suitable for very high-speed applications.

It also introduced Shanghai EVK Motor Technology Co., Ltd., also known as EVK.

3. EVK's Concentrated Winding Flat Wire Technology

Flat wire motors are more suitable for electric aircraft

Under the premise that the controller frequency of the motor is controllable, increasing the number of pole pairs as much as possible can effectively reduce the thickness of the stator and rotor yokes and the end dimensions of the motor windings. Therefore, combined with relatively low operating speeds, motors generally have a higher number of pole pairs, and the permanent magnet concentrated winding flat wire solution is typically chosen.

It elaborated on EVK's patented hairpin-type concentrated winding motor.

► Concentrated Winding Flat Wire Motors

In addition, it shared content on how outer rotors + flat wires can balance torque density and cost, EVK's Halbach magnetic steel matrix process, EVK's direct winding cooling technology, an introduction to EVK's propeller motor products and technologies, and EVK's propeller motor production lines.

》Click to view the 2025 SMM (4th) Electric Drive System Conference & Drive Motor Industry Forum Report Special