Electric scooter hub motor: How a motor-wheel is made, piece by piece

The motor in an electric scooter is almost always housed within the wheel; it's called a hub motor or wheel motor. It doesn't have a chain, belt, or gearbox. Its unique feature is that it's built "inside out": the part that holds the windings remains fixed, secured to the axle, while the outer casing, lined with magnets, rotates along with the tire. Understanding this construction helps you choose a motor, install it correctly, and diagnose any unusual noises or malfunctions.

An outrunner motor

In a conventional electric motor, such as that found in a drill, the rotating part is in the center, and the stationary part surrounds it. Hub motors reverse these roles: we are talking about a motor with an external rotor. The stator is in the center, and the rotor forms the casing that surrounds it.

This architecture offers two key advantages for an electric scooter. First, the motor directly drives the wheel: there are no transmission components to maintain, adjust, or break. Second, the magnets are placed on a large diameter, which provides a significant leverage and a lot of torque from a standstill, without the need for a gearbox. This is also why hub motors have a large number of poles, as explained in our guide on Kv, Kt, and motor poles.

The stator: the fixed core

The stator is a stack of thin sheets of magnetic steel, cut into a star shape. Each arm of the star is called a tooth; around each tooth is wound a layer of coated copper wire. The teeth are connected in three groups, which represent the three phases of the motor.

The stator is fitted and secured to the shaft, which is itself held in place within the scooter's frame by nuts. Therefore, it never moves. Instead, it is the magnetic field created by the current flowing through its windings that "rotates," controlled by the controller, and which pulls the magnets along with it.

The way these windings are made (number of turns, wire gauge) determines the motor's characteristics: whether it prioritizes speed or torque. This is the difference between our High Speed and High Torque versions.

The bell and its magnets

The bell is a steel or aluminum tube closed by two flanges. Permanent magnets, typically made of neodymium, are glued to its inner surface, arranged alternately with north and south poles. Between the surface of the magnets and the teeth of the stator, there is only a very small air gap: the air gap. The thinner and more uniform this air gap is, the more efficient the motor is, but the more precise the manufacturing process must be.

The magnets operate under high stress: they are attracted to the stator, shaken by road vibrations, and heated by the motor. A magnet that comes loose will rub against the air gap and produce a characteristic scraping noise; at that point, you should stop riding. The width of these magnets is often used to identify the motor; see our guide on motor sizes 60, 70, 75, 80.

Flat tires, bearings, and hollow axles

Each side of the bell housing is closed by a flange, which is a type of screwed cover. In the center of each flange is a ball bearing that rotates around the axle. These two bearings support the entire weight of the rider and absorb the impacts. A worn bearing can be identified by a rumbling noise that increases with speed, or by lateral play in the wheel.

On one side, the axle is hollow, at least: this is where all the motor wires exit. The passage is narrow, and this is a critical point. The cable emerges from the axle right next to the arm, where it is subjected to vibrations and suspension movement. A pinched, crushed, or chafed cable will eventually become damaged, leading to jerks or complete failures.

The flat surfaces on the axle, these two flat faces machined at its ends, prevent it from rotating within the arms. If the nuts are not tightened properly, the motor's torque can cause the axle to rotate, which can twist and tear the wires: this is a common failure that we see regularly in the workshop.

The wires that come out of the motor

The three phases:

These are the thick cables, one for each winding group. They carry all the current from the motor, often much more than what comes from the battery. Their cross-section depends on the motor: our motors from the MHS, MHT, XHS, and XHT ranges have 10 mm² phases, while our SHS60 and SHT60 models have 4 mm² phases. At the end, there are connectors that must be up to the task: for these ranges, they are 8 mm AMASS bullet connectors. An undersized connector will overheat, blacken, and eventually cause disconnections.

Hall sensors

A thinner cable, often with five wires, connects three small sensors located between the stator teeth. These sensors detect the passage of magnets and indicate the position of the rotor to the controller, enabling smooth and jerk-free starts. Two wires power the sensors, while three transmit their signals.

The temperature sensor

Many high-performance motors incorporate a sensor embedded within the windings. Connected to the controller, it allows the controller to reduce power before the motor is damaged. The reasons for this overheating are detailed in our guide explaining why an electric motor overheats.

Integrated rim or half-rim

The rim is the component that holds the tire. Two types of construction exist:

• The integrated rim is part of the bell. This applies to our SHS60, SHT60, W50, and W60 motors, which feature a 6.5-inch integrated tubeless rim. Advantage: a simple, airless assembly. Disadvantage: you cannot change the rim without changing the bell.
• Split rims consist of two halves bolted together on either side of the hub. They are separated to mount the tire, which avoids the need to struggle with a tire lever. This applies to our MHS and MHT models, which are supplied with 6.5-inch split rims, and to our XHS and XHT models, which offer an optional CNC-machined aluminum rim.

All of our motors are listed in the electric scooter motors category.