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Happy’s Tech Talk #39: PCBs Replace Motor Windings

The age of electric vehicles has arrived. If we can improve energy storage, lower the price tag of batteries, andmake them work at lower temperatures, EVs may become our favorite mode of transportation. Certainly, the motors are going through a massive change. Figure 1 shows a typical EV motor.  

In a prior column¹, I discussed my former employer, Foxconn, and its goals of providing 25% of all the required components of future EVs. This was formulated by Terry Goa, Foxconn chair, whom I met in 1982 while working for Hewlett-Packard Taiwan. Back then, he only made plastic knobs for television sets, but he was a major contributor to Sampo Corporation, Taiwan’s major appliance manufacturer. I was part of the government’s program to bring electronics manufacturing and computer technology to Taiwan.

EV Motors
Thanks to Edison and Tesla, electric motors have been around for a long time. With the boom in electric vehicles, electric motors will eventually be able to take on many forms with improved performance and weight reduction. Figure 2 shows the weight of the iron core stator and the copper windings. The electric motor has always been bulky. The focus on miniaturization has led to the need for smaller and more efficient electric motors to create an interaction of the copper windings and the magnets for torque and speed. This is essential for the future of EVs and robots.

PCB Stators
For the last 100 years, electric motors and their iron core and windings have used radial flux to drive the moving iron stator. However, the printed circuit and rare earth magnets axial flux motor (AFM) (shown in Figure 3) are usable, and they allow many innovations for the traditional electric motor, particularly in efficiency, size, weight, and precision.

The PCB or Pancake Motor Design
Figure 4 shows a typical new generation axial flux pancake motor. Engineers use these motors in applications where compact, lightweight design and high reliability are required, such as portable products, medical equipment, and aerospace/defense devices. They are:

• Up to 70% lighter than conventional options
• Achieve efficiencies greater than 90%
• Require 20% of the raw materials (notably copper)
• Acoustically quieter by up to 30 dB
• Printed circuit motors have the armature and commutator printed on a PCB, reducing the number of components and resulting in smaller, lightweight motors
• The motors have lower armature inductance and a smaller time constant
• The motors quickly develop full-load torque

Design
AFMs can use single or dual rotors or stators. They are common in high-power applications, although they require a housing with accompanying iron losses. Single stator/dual rotor designs can dispense with the yoke, saving weight and increasing efficiency. In the latter, the rotors and their iron plates that close the flux move in the same direction/speed as the magnetic field.

You can stack some AFMs to provide higher power output in a modular fashion. YASA's 37 kg stackable 750R motor delivers 800Nm and >5kW/kg with an axial length of 98 mm (3.9 in). Figure 5 shows an optimized coil pattern for axial-flux from software like COMSOL Multiphysics electric machine modeling, which supports axial, radial flux, and transverse flux motors. Software is also available for axial flux motor designs from 4W to 20 kilowatts by ECM PCB Stator Inc.

Aviation
The Rolls-Royce Spirit of Innovation (holder of the current world speed record for an electric aircraft) uses three axial flux motors. Mercedes-Benz subsidiary, YASA, makes AFMs for this plane. YASA’s goal is to build aircraft motors that deliver 50 kW/kg, to allow for the substantial weight reductions required for electric-powered flight. A triple-stacked 200kW YASA 750R axial flux motor powers the 7.3 m (24 ft) aircraft, driving a 2,400 RPM, three-blade propeller. The 750 volt, 216 kWh battery has 6,480 cells, with cork insulation and active cool flux motor ng. Battery output power is continuous at 500 hp (373 kW), reaching 750 kW (1,010 hp) at maximum power. The design aims to achieve the highest energy density for an aircraft, enabling a 170 nautical mile range. (310 km).5

Summary
Printed circuits continue to grow and expand into new markets and products. Axial flux PCB motors will grow in the $200 billion electric motor market. The extremely light weight and increased power allow electric motors to be part of many new applications, particularly in robotics and aerospace. Who knows? Soon, we may even see the efficient air taxi.

References

1. “Happy’s Tech Talk #17: Can You Build EVs Like PCs?” by Happy Holden, PCB007 Magazine, February 2023.
2. “CES 2024: Magna puts multiple innovations in a new, more efficient 800V e-motor,” by Chris Clonts, SAE Automotive Engineering, Jan. 10, 2024.
3. ECM brochure.
4. “Axial Flux Motor Topology Signals Next Generation of Electric Motors,” by Rehana Begg, Machine Design, Jan. 22, 2024.
5. “Axial flux motors,” by Nick Flaherty, eMobility-engineering.com.
6. “PCB Stator Technology Replaces Bulky Copper Windings,” by Rehana Begg, Machine Design, May 23, 2023.

Happy Holden has worked in printed circuit technology since 1970 with Hewlett-Packard, NanYa Westwood, Merix, Foxconn, and Gentex. He is currently a contributing technical editor with I-Connect007, and the author of Automation and Advanced Procedures in PCB Fabrication, and 24 Essential Skills for Engineers. 

This column originally appeared in the May 2025 issue of PCB007 Magazine.