Understand the heart of electric bike – mid-drive motor

Understand the heart of electric bike - mid-drive motor

“E-bike” – a very hot combination of words in recent years, derived from “Electric bike”, i.e. bike with electric assistance, commonly known as electric-assisted bike.

The rated power and speed limits for electric bikes vary from country to country, and according to EU standards, the rated power of the motor must not exceed 250 W.

After the maximum speed of 25 km/h, the aid is automatically turned off.

In this article, we will explore the heart of electric bike – mid-drive motor.

Mid-drive motor is the best solution of front and rear forms, and the motor of an e-bike is placed in the middle of the frame (at the tooth plate).

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    The e-bike wave has swept through Europe, the United States, Japan and South Korea in just a few years, and has gradually become one of the most rapidly developing bike consumer products in developed countries and regions with mature green road traffic.

    With an increasingly large market share and annual sales growth of more than 30%, e-bikes becoming the biggest driving force for the bike industry to sustain its booming development.

    Under the influence of the international epidemic in the past few years, the bike market has shown a rare counter-trend growth in recent years.

    And even the domestic upstream and downstream factories have been working overtime to produce exports, and among them, the rapid growth of electric bikes.

    In the next few years, we can foresee that electric bikes will become a new growth point in the Chinese market.

    Development of the motor structure of the e-bike

    What is an e-bike?

    Electric bike, in a broad sense, is a kind of electric bike, different from pure electric bike or electric car, which still needs to be driven by human pedaling.

    The motor only plays an auxiliary role to assist the bike to do work under rated working conditions, so as to make riding easier and achieve the effect of improving the overall range and reducing the difficulty of riding.

    From the early days of electric-assisted commuter bikes, to today’s electric-assisted mountain bikes, road bikes and Gravel vehicles, the development of electric-assisted systems to date, technically it has been possible to achieve a comprehensive adaptation of models.

    We can see that both ordinary hardtail XC, forest road off-road or road bikes, all have the shadow of electric assistance.

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    Development of the motor structure of the e-bike

    The external expression of electric power is roughly divided into wheel drive (Hub Drive), mid-drive motor (Mid Drive).

    Front-wheel drive motor

    In the early years, due to the design concept and body structure, some commuters and travel vehicles used front wheel drive (such as Panasonic’s single-speed commuter bike in Japan and Xiaomi’s electric folding bike).

    With the drive motor set at the front wheel hub, the motor is integrated into the hub, and the electricity is converted into mechanical energy after power is applied.

    This method is relatively simple and low cost, and is one of the main forms of electric bike conversion on the market.

    Front-wheel drive form

    But it also has many shortcomings.

    The first problem is weight. The front wheel is bigger and heavier. The front wheel will have a greater impact on daily control after adding a few kilograms of weight.

    The second problem is resistance. The wheel motor will increase the resistance of the ride when the battery is dead, combined with the weight affects the riding experience.

    The third problem is adaptability. The front wheel motor requires the manufacturer to prepare the wheel assembly.

    If it is an ordinary commuter bike, if it is a high-end sports bike, the wheel set prepared by the manufacturer is short in both classes and adaptable.

    Rear-wheel drive motor

    The rear wheel motor is more complex than the front wheel motor, and it needs to take into account the transmission system, so the cost is higher, but the rear wheel motor also has some shortcomings that are difficult to overcome.

    Rear-wheel drive motor

    At the same time, the weight problem of the front wheel motor still exists in the rear wheel motor.

    The rear wheel motor driven in some environments easily causes the phenomenon of slippage, and when there is no power, it will still bring greater resistance to riding, the motor is in the gearbox position, long-term vibration or poor working conditions will affect life.

    Mid-drive motor

    Mid-drive motor is the best solution of these three forms, and the motor of an e-bike is placed in the middle of the frame (at the tooth plate).

    According to the installation method, the motor is divided into two types: integrated frame and external.

    According to the structure and shape of the motor, it can be divided into coaxial motor and parallel shaft motor.

    Mid-drive motor-1

    Although the mid-drive motor also has a larger weight, placed in the five-way part of the frame will not affect the front and rear wheel counterweight, can try to maintain the balance of the bike’s front and rear weight, and will not affect the action of the shock absorber.

    The motor is also less likely to hit the road, but can also play a role in reducing the center of gravity.

    At the same time, the mid-drive motor often uses clutch drive gears inside, which can automatically cut off the connection between the motor and the drivetrain when not pedaling or when the battery is dead, so it will not cause additional resistance.

    Compared to the former motor forms, electric bikes with mid-drive motor systems are free to change wheel sets, and later upgrades are not affected.

    It can be said that the mid-drive motor represents the technical direction of the electric auxiliary system in sports bikes, and is the antidote to the structural problems of sports electric auxiliary bikes, so it is also a strategic place for major brands to compete for research.

    Mid-motor

    There are many brands doing mid motor on the market, but the famous ones are still, such as Bosch, YAMAHA, etc.

    They almost monopolize the high-end market, and the price is naturally very high-end. Shimano, Giant and other bike brands also entered the mid-drive motor market a few years ago, grabbing a share of the mid-drive motor market.

    Chinese brands such as Bafang, Light Passenger, Sheng, New Zealand, NECO, CHOOCH, etc. also follow suit.

    Chinese brands such as Bafang, Lightbus, Tongsheng, Nuxink, NECO, CHOOCH, etc. have also followed suit and launched various motor systems to gradually fill the market gap.

    How to choose the right mid-drive motor system?

    Before choosing the right e-bike, choosing the electric power system is also a very important thing.

    Restricted by appearance, the mid-drive motor often needs to be deeply attached to the frame.

    There are still no uniform appearance specifications or international standards, so it is difficult to evaluate different motor systems at the same starting point.

    Therefore, it is necessary to determine an internal industry “national standard” to regulate appearance.

    This will make it easier for manufacturers to design the frame, as upstream and downstream component manufacturers also have more imagination.

    How to choose the right motor system

    However, excluding external factors such as frame drive wheelsets, how to evaluate a mid-drive motor system is very simple.

    Whether it is a traditional bike or an electric bike, parameters and configurations are secondary, the core issue is always – whether it is good to ride, in this context, the comparison between the mid-drive motor has meaning.

    A good mid-drive motor riding system needs to be fast, accurate, ruthless, provincial, and also low-level.

    ① Fast -The power response speed should be fast, and many cars like to set the throttle to be mild.

    The bicycle, especially the sports bicycle, is about a foot to the bike, that is, to step on it, and the sports bicycle with electric power addition should be so.

    If there is a stampede delay, it will have a great impact on the rhythm of the ride.

    The response speed of Bosch’s mid-drive motor can reach 50 milliseconds, and some Chinese mid-drive motors are even faster.

    ② Accurate – The power output of the mid-drive motor should be accurate, not stepping on it, and not a step on the “takeoff”, the output change between different gears should be linear, and finally achieve the effect of how much to step on how much, to achieve the unity of rider and the bike.

    ③ Practical – Thoughtorque is big. This point in the mid-drive motor has an inherent advantage, through the combination of internal clutch gear to achieve the effect of torque amplification.

    Whether it is flat road riding or climbing, load conditions can get higher torque.

    Shimano

    ④ Energy-saving – Energy consumption to be low, improve the range by no more than two points, open source and cut costs.

    Using a larger battery pack, this is one way, but limited by the current level of technology, the battery energy density is almost fixed, and the bike can not be equipped with an exaggeratedly large battery, so it is necessary to work on the energy consumption level of the mid-drive motor.

    Low presence refers to the need to be quiet and smooth when riding.

    It is best to make people forget that they are riding an electric bike, riding when there is no power, there can be no sense of drag.

    And most importantly, the mid-drive motor should be leathery and durable enough, dust and water resistance should be good, and do not let riders worry about it in post-maintenance.

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