25-Slot 5-Phase Stator with 0.5mm Lamination 177mm OD 120mm ID 25mm Stack

The Story Behind the 25-Slot 5-Phase Permanent Magnet Synchronous Motor Stator

In 2009, Rakesh Dhawan embarked on a mission to revolutionize direct-drive electric bicycle motors. He recognized a critical challenge in the industry—cogging torque, the unwanted resistance that creates a jerky and inefficient ride. Determined to find a solution, he meticulously designed this 25-slot, 5-phase stator, optimizing the geometry to achieve an extremely low cogging torque.

His approach was groundbreaking. By leveraging a 5-phase configuration and carefully selecting M350-50A laminations with 0.5mm thickness, he minimized magnetic losses while maintaining high efficiency. The stator’s 177mm outer diameter and 120mm inner diameter were engineered to seamlessly integrate into outer-rotor direct-drive motors, providing smooth and powerful performance.

Envisioned initially for electric bicycles, this stator’s design has since proven versatile, extending its applications to high-efficiency industrial motors, e-mobility solutions, and renewable energy systems. Today, it remains a testament to Rakesh Dhawan’s ingenuity and pursuit of perfection in electric motor design.

The earliest version of this motor in action can be seen here: https://lnkd.in/eddbMGys. It demonstrates extraordinarily low cogging torque and implements field weakening and phase advance algorithms in the motor controls.

Animated view of the 25mm lamination stack.

Animated View of the Winding

Details of the Individual Poles