Electric Bikes Motor Types: Mid Drive VS Rear Hub

Introduction

Motors are an important component of electric bikes, because they supply energy to the bike by converting electrical energy into mechanical energy. Earlier electric motors used brushes to vary the path of current flowing into the motor. The recurrent action made electric motors less efficient and more prone to deteriorate over time. For more than 10 years now, electric bikes have been using brushless DC motors, and as the name denotes, they do not have brushes in their operation. For brushless DC motors, electric energy is converted into mechanical energy with the use of permanent magnets and electromagnets.

Inside the brushless DC motor, there is the stator, which is the stationary electrical device, and the rotor, which is the rotating electrical device. The stator consists of wires coiled round an assembly of separate electromagnets arrayed in such a system that they form a hollow tube, with the individual electromagnets having one pole facing the direction of the centre of the tube. This is the stationary component of the brushless DC motor. The rotor, on the other hand, consists of an assembly of permanent magnets inside the hollow tube, with the poles facing the direction of the stator poles. The rotor is the rotatory component of the brushless DC motor. All the bikes offered by DJ Bikes have a brushless DC motor.

Operating mechanism

The purpose of this configuration of the motor components is to cause rotatory motion of the motor shaft due to the rotatory movement of the rotor. When the motor controller pulls electric current to the stator’s electromagnets from the battery, they repel and attract the rotor’s electromagnets, thereby causing the rotor to rotate. The stator is connected to a shaft.

There are two major types of motors on electric bikes: mid-drive motor and hub motor. For the mid-drive motor, the shaft rotates to produce torque, and by a small chainring joined to the shaft, power is supplied to the pedals which assists you to pedal the bike. On the other hand, for hub motors, the shaft is the axle, and thus does not rotate. The rotatory action is caused by the rotor, which causes the complete motor to rotate to produce torque, by rotating either the front or rear wheel.

Overview: Types of Motors

There are four types of motors that are used on (or have been used) on electric bikes. They are listed below:

Mid-drive Motors

Mid-drive motors are located in the middle of the frame of the bike, typically positioned at the bottom bracket. The electric motor produces a torque that rotates the shaft (connected to the stator), which is connected to a small chainring. With this type of motor, no extra source of power is needed, as the motor complements the energy you exert on the pedals within the chain drive of the bike. Typically, embedded within the motor pack is a gear reduction technology. To protect the small chainring from fracture when the bike is not in gear, most mid-drive structures comprise of gear sensors which cut off power to the motor. The DJ Mid Drive Fat Bike uses a powerful Bafang rated watt 48V 750W “mid-drive motor.”

DJ Mid-drive Fat Bike with the direct-drive motor at the centre of the bike frame

Direct-drive Hub Motors

In direct-drive hub motors, the shaft of the motor is the rear axle, in a stationary position, while the motor (i.e. the hub) rotates about the shaft, and thereby creates acceleration. These are the least complicated of all electric bike motors. Typically, direct-drive motors have a larger diameter compared to geared hub motors, which produces increased torque. These motors have the unique ability of moving forward and backward with even efficiency. During the braking process (which includes slowing down or coming to a complete stop), direct-drive electric bikes can also produce electric energy. This process is called regenerative braking. During the braking process, energy flows to the battery from the wheels, instead of being dissipated as heat. This “saved” energy is now used when the bike becomes operational, or increases its speed.

Geared Hub Motors

Geared hub motors are similar in operation to direct-drive hub motors, with the exception of anmelectric motor that rotates within the hub at a considerably higher speed. The hub rotates at the lower speed, due to the shaft of the motor connected to a series of orbital gears that are connected to the hub. This system creates additional torque but lower speeds. Typically, geared hub motors have a smaller diameter than direct-drive motors, because a larger motor is not required to produce the equivalent quantity of torque, however, the orbital gears make the hubs larger. These motors also comprise of a “freewheel”, which removes the possibility of regenerative braking, but will cruise smoothly rather than produce a slight drag when they are not under power. Electric bikes with geared hub motors perform in a similar fashion with conventional bicycles. The majority of the bikes offered by DJ Bikes are Geared Hub Motors.

DJ Super Bike with a Jiabo 48V 500W Brushless Rear Geared Hub Motor

Friction Motors

Friction-driven motor electric bikes are not as common as the hub and mid-drive systems, however, they have the advantage of a cheaper design for users who want to transform a conventional bike with marginal effort. A bolt-on motor drives a small wheel linked to the tire. The location of this kit is usually below the chainstays, above the seat trays, or attached to the fork’s brake mount. The wheel of the motor rotates the tire, thus causing forward motion. As the name implies, the action of the motor causes increased wear on the tire, however, these kits can be substituted easily between bikes.

Summary

Comparison between Mid-drive motors and Hub Motors

Mid-drive motors: Advantages

They perform more efficiently on hills, because the bike can climb at low speeds
Due to their centred position on the bike, they offer a more stable ride
They are more suitable for electric mountain bikes
It is easier to change tires, as there is no wiring between the hub and the frame

Mid-drive motors: Disadvantages

An increased wear of the chain due to the addition of the mid-drive motor to the chain leads to frequent replacement of the chains
Due to increased mechanical components and a higher gear reduction, it is a more expensive bike

Hub motors: Advantages

Due to the fact that hub motors function outside the chain drive of the bike, their chain does not wear out like mid-drive motors
They are inexpensive compared to mid-drive motors, because manufacturers are not required to modify the bike’s frame to accommodate a custom motor, and can also be manufactured in large quantities
As no mechanical component is used during transmission, they are more reliable and long-lasting
They require slight, and in most cases, no maintenance
They can still be ridden if the chain is broken, as the hub motor is attached directly to the bike’s wheel and not dependent of the electric bike
They are easier to ride

Hub motors: Disadvantages

They are heavier compared to mid-drive motors because their motors and batteries are bigger, due to more electric power required
It is more difficult to change tires, because you have to remove all the cables associated the hub motor

Comparison between Direct-drive Hub motors and Geared Hub motors

Direct-drive Hub motors: Advantages

As a result of regenerative braking, direct-drive hub motors have the advantage of a reduced brake wear
Typically, they are more quiet than geared hub motors
Compared to geared hub motors, direct-drive hub motors perform better at high speeds

Direct-drive Hub motors: Disadvantages

Compared to geared hub motors, they are larger and weigh more, due to additional magnetic material needed to produce a torque of low speed
They produce a drag during pedaling

Geared Hub motors: Advantages

They are more suitable for low speeds and elevated torque applications
With the same torque rating of a direct-drive hub motor, the weight of a gear hub motor is considerably lighter
They can cruise smoothly with very little drag
They are smaller and less bulky, therefore a preferred choice for commuters

Geared Hub motors: Disadvantages

Compared with direct-drive hub motors, geared hub motors experience difficulty in attaining the same speed

Conclusion

What type of motor should you be looking for when buying an electric bike? It really depends on your needs.

The bikes manufactured by DJ Bikes has either the Mid-drive or the Hub Motors installed. See below the summary of the motor types in the array of DJ Bikes.

S/No	Name	Type of Motor
1	DJ Mountain Bike	Bafang Brushless Rear Geared Hub Motor
2	DJ City Bike	Bafang Brushless Rear Geared Hub Motor
3	DJ Fat Bike	Bafang Brushless Rear Geared Hub Motor
4	DJ Mid Drive Fat Bike	Bafang Brushless Rear Middle-Drive Motor
5	DJ Folding Bike	Bafang Brushless Rear Geared Hub Motor
6	DJ Folding Bike Step Thru	Bafang Brushless Rear Geared Hub Motor
7	DJ Super Bike	Jiabo Brushless Rear Geared Hub Motor
8	DJ Super Bike Step Thru	Jiabo Brushless Rear Geared Hub Motor