As electric vehicles and e-mobility solutions continue to advance, hub motors serve as the core drive units directly powering the wheels. Their performance directly determines the competitiveness of the end product.

A detailed teardown of a high-performance hub motor reveals that the real determinant of performance lies not in its housing or magnetic design, but in the accuracy and consistency of its coil winding process.

 

 

There’s a saying in the motor industry: “Seventy percent of motor performance comes from design, and thirty percent from manufacturing.”

Among that thirty percent, the coil winding process alone accounts for two-thirds of the impact.

In this article, we take a closer look at hub motor manufacturing to analyze the common challenges and critical factors in the coil winding process that ultimately define motor performance and reliability.

 

Hub Motor

 

The coil structure in hub motors differs fundamentally from that of conventional motors.

Due to strict installation space constraints, a hub motor must achieve maximum electromagnetic conversion efficiency within a limited annular area. This unique design requires the coils to adapt precisely to specialized slot geometries and to be wound with exceptional accuracy in confined spaces—while simultaneously meeting multiple performance demands, including insulation, heat dissipation, and mechanical strength.

 

The precision requirements for hub motor coil manufacturing are significantly higher than those of traditional motors. At the same time, hub motors demand a higher slot fill factor to maximize power density and efficiency. These demanding conditions are the key reasons why hub motor coil production is far more challenging than that of standard motors.

 

 

Core Challenges in Coil Manufacturing

 

(1) The Balance Between Precision, Efficiency, and Cost

 

In the field of hub motor coil manufacturing, companies often face a persistent challenge: achieving the right balance between precision, efficiency, and cost.

High-precision winding typically requires advanced equipment and higher investment, which can reduce overall production efficiency. On the other hand, prioritizing speed and output may lead to quality fluctuations, while excessive cost control often compromises product consistency.

As a result, many manufacturers are forced to find a delicate balance among these three critical factors.

 

(2) Hidden Risks in Coil Insulation During Winding

 

Hub motors operate in complex environments that demand exceptional insulation reliability. However, during high-precision winding, even microscopic damage to the wire’s insulation layer often goes undetected in production — only to become a critical failure point during later operation.

 

Industry failure analyses show that a significant proportion of hub motor malfunctions are directly related to insulation degradation or damage within the coil. Most of these issues originate in the winding process itself, typically caused by improper tension control, localized stress concentration at tooling contact points, or excessive mechanical friction during wire placement.

 

(3) Spatial Challenges Under High Slot Fill Requirements

 

As hub motors evolve toward higher power density, achieving a high coil slot fill factor has become a critical bottleneck for performance improvement.

However, the unique annular structure of hub motors imposes severe spatial constraints on coil winding. The available winding space is extremely limited—especially on the inner side of the stator—where the usable area is significantly smaller than that of the outer ring.

This structural characteristic makes precise wire placement and compact layering far more challenging, directly affecting the motor’s electromagnetic efficiency and manufacturability.

 

(4) Process Adaptation Challenges Brought by New Materials

 

In recent years, emerging technologies such as hairpin windings and high-thermal-conductivity insulation materials have been increasingly adopted in high-end hub motors. While these innovations enhance performance, they also introduce new manufacturing challenges.

 

Flat wires, for instance, improve slot fill factor and power density but have high rigidity and are prone to corner damage, placing greater demands on winding equipment precision and process control.

Similarly, high-thermal-conductivity insulation materials offer superior heat dissipation but typically exhibit lower mechanical strength and flexibility compared to conventional materials. As a result, issues such as delamination and cracking are more likely to occur during automated winding, requiring careful parameter optimization and tooling design.

 

Core Challenges Behind Hub Motor Coil Manufacturing

 

Examining the core challenges of hub motor coil production, the key pain points can be summarized as follows:

 

1. Geometric Constraints of the Annular Structure

The ring-shaped architecture of hub motors fundamentally dictates the unique requirements of coil manufacturing. Unlike conventional radial motors, the stator in a hub motor is distributed in a circular ring, with winding paths fanning out across the annular slots. This creates significant differences in the arc lengths between the inner and outer rings.

 

These geometric characteristics can lead to: large differences in conductor lengths between inner and outer coils, resistance imbalance, difficulties in tension control during winding, inner coils that are too loose, outer coils that are overly tight, uneven slot fill distribution, and inner coil fill factors that are typically lower than those of the outer coils.

 

2. Insufficient Process-Equipment Matching

Most commercially available winding machines struggle to meet the specialized requirements of hub motors. The main reasons include:

 

General-purpose winding machines lack adaptability to the annular geometry of hub motors.

 

Existing winding processes are not optimized for the narrow slot designs unique to hub motors.

 

Specialized winding equipment for flat wires, irregular-shaped conductors, and other new wire types is scarce.

Insufficient Material-Process Synergy: Hub motor coil manufacturing involves the interdisciplinary integration of electromagnetic design, materials science, and mechanical engineering.

However, current industry practices show a lack of comprehensive research and optimization in material-process synergy. This gap limits the ability to exploit the potential of advanced materials and winding techniques fully, ultimately constraining coil performance, reliability, and manufacturability.

 

Although the challenges in hub motor coil assembly primarily reflect the manufacturing industry’s transition from “capable of production” to “excellence in execution”, they carry far-reaching implications.

As market competition shifts from product features to performance and reliability, the intricate process details hidden within the product will ultimately determine a company’s market position and long-term viability.

 

For many years, Honest Automation has been dedicated to the research and application of intelligent motor assembly systems. We have successfully provided numerous motor manufacturers with end-to-end solutions, covering stator assembly, rotor assembly, and complete motor testing.

 

We understand that behind every high-performance motor lies countless meticulously controlled process details. Every technological breakthrough stems from a deep understanding of industry pain points and relentless exploration of innovative solutions.

 

 

Facing the technological wave in hub motor winding manufacturing, Honest Automation is eager to collaborate with industry peers to explore pathways for process optimization. We offer professional motor assembly process evaluation services and welcome discussions on industry insights, jointly advancing motor manufacturing sector toward higher precision, greater efficiency, and enhanced reliability.

 

Suppose you are seeking breakthroughs in hub motor or other motor assembly processes. In that case, we invite you to connect with our technical team for professional process assessments or to schedule a technical consultation. Let the experts handle the specialized challenges.