How to choose a mid drive ebike motor?
Under the influence of the international epidemic, the bicycle market has shown a rare growth trend in recent years, with domestic upstream and downstream factories working overtime to produce and export. Among them, electric powered bicycles are growing rapidly. In the foreseeable future, electric powered bicycles are bound to become a new growth point in the domestic bicycle industry.
Electrically assisted bicycles, in broad terms, are a type of electrically assisted bicycles, which are different from pure electric bicycles or electric vehicles, and still require manual stepping and driving. The electric motor only serves as an auxiliary function. It performs auxiliary work on the bicycle under rated operating conditions, making riding easier, improving overall endurance and reducing riding difficulty.
From the earliest electric powered commuter vehicles to today’s electric powered mountain bikes, road vehicles, and Gravel vehicles, the development of electric power systems has been able to achieve comprehensive adaptation of vehicle models in technology. We can see that whether it is a common hard tail XC, a heavier taste of off-road forest vehicles, or road vehicles, there is the shadow of electric power. I have also experienced different development stages and forms of electric power products in my long-term cycling experience. Here is a simple sharing.
The external manifestations of electric power assistance are generally divided into wheel drive and mid drive.
In the early years, due to the design concept and body structure, some commuter and travel vehicles used the form of front wheel drive (such as Panasonic’s single speed commuter car and Xiaomi’s electric powered folding bicycle in Japan). A drive motor was set at the front wheel flower drum, and the motor was integrated into the flower drum. After being powered on, the electric energy was converted into mechanical energy. This way is relatively simple in structure and low in cost, It is also one of the main forms of refitting electric powered bicycles on the market.
However, there are many problems with front wheel drive. The first problem is weight. The front wheel is relatively large and heavy. Adding a few kilograms of weight to the front wheel will have a significant impact on daily handling; The second problem is resistance. When the battery runs out of power, the wheel motor will increase the resistance during riding, and combined with its own weight, it will affect the riding experience; The third issue is adaptability. The manufacturer needs to prepare a wheel set for the front wheel motor. If it is a common commuter vehicle, it is not a big problem.
However, if it is a high-end sports bicycle, the wheel set prepared by the manufacturer has shortcomings both in terms of grade and adaptability; In addition, the dead weight and driving force of the front wheel motor can increase the pressure on the front brake, exacerbating brake losses, and in severe cases, may cause some safety issues; Wheel motors also do not have an advantage in energy consumption. Therefore, it is reasonable that this driving form has not been widely promoted in sports bicycles.
Compared to the front wheel motor, the structure of the rear wheel motor is more complex, and it is also necessary to consider the matching of the transmission system, such as the tower base flywheel, which leads to higher costs. However, the rear wheel motor also has some shortcomings that are difficult to overcome. The first is its integrity, which makes it difficult to find a rear wheel motor on the market that can be used for retrofitting and matching brand wheel rims.
Therefore, it is still necessary to prepare a wheel set by the manufacturer, which is very inconvenient for the adaptability of different models, “It also has an impact on the later upgrade of the wheel set, and the weight problems of the front wheel motor still exist on the rear wheel motor. The rear wheel motor drive is prone to slipping in certain environments, and when there is no power, it still brings significant riding resistance. The motor is located in the wheel set position, which can affect its life in long-term vibration or harsh working conditions.”.
Of these three forms, the central motor is undoubtedly the optimal solution. Although the central motor also has a large weight, placing it in the five way section of the frame does not affect the balance weight of the front and rear wheels, and can also reduce the center of gravity. At the same time, the central motor often uses clutch transmission gears inside, which can automatically cut off the connection between the motor and the transmission system when not stepping on or when the battery is dead, so it does not cause additional resistance.
Compared to wheel motors, electric powered bicycles with a central motor system can freely change their wheel sets without affecting later upgrades. It can be said that the central motor represents the technical direction of electric power assisted systems in sports bicycles, and is the antidote to the structural problems of sports electric power assisted bicycles. Therefore, it is also a strategic focus for major brands to compete for research.
There are many brands in the market that make mid set motors, but the famous ones are still several industry leaders such as Bosch, YAMAHA, etc. They almost monopolize the high-end market, and the price is naturally very high-end. Shimano, Giant and other bicycle brands also entered the mid set motor market a few years ago, seizing a part of the mid end market. Domestic brands such as Bafang, Qingke, Newark, NECO, CHOOCH, etc. also follow closely, and launched various motor systems, Gradually filling the market gap.
For consumers, what brand of electric power assistance they choose today is not actually “selecting a car”, but rather selecting an electric power assistance system. Due to appearance constraints, mid mounted motors often require deep binding to the chassis, and there is currently no uniform appearance specification or international standard, so it is difficult to evaluate different motor systems on the same track.
Therefore, I also hope that domestic motor manufacturers can first unite internally to determine an internal “national standard” for the appearance of the industry, which will make it easier for vehicle manufacturers to design frames and provide more imagination for upstream and downstream component manufacturers. At the same time, it can also force major foreign brands to consider unified standards.
However, excluding external factors such as frame drive wheel sets, how to evaluate a central motor system is very simple. Whether it’s a traditional bicycle or an electric powered bicycle, the parameters and configuration are secondary, and the core issue is always whether it’s easy to ride. In this context, the comparison between central motors makes sense.
According to my experience, a good mid-mounted motor system needs to be fast, accurate, ruthless, and economical, as well as achieve a low sense of presence.
Fast – The power response speed should be fast, unlike many cars, which prefer to adjust the accelerator to be “lazy”. Bicycles, especially sports bicycles, focus on stepping on and walking from foot to foot. This is especially true for sports bicycles with electric power assistance. If there is a delay in stepping on, it will have a significant impact on the rhythm of riding. The response speed of Bosch central motors can reach 50 milliseconds, Some domestic mid mounted motors have even faster response times.
Accurate – The output power of the central motor should be accurate, and it cannot be stepped on, nor can it “take off” immediately. The output change between different gears should be linear, ultimately achieving the effect of stepping on as much as possible, achieving the integration of people and vehicles.
Harsh – The torque should be large, which is the inherent advantage of the center mounted motor. Through the internal clutch gear combination, the torque amplification effect can be achieved, and higher torque can be obtained regardless of whether it is riding on flat roads, climbing, or under load conditions.
Economy – Low energy consumption, improving battery life is nothing more than two points, opening up sources and reducing costs. Using a larger battery pack is an option, but due to the current technological level, the battery energy density is almost fixed, and bicycles cannot be equipped with exaggerated batteries. Therefore, efforts should be made to improve the energy consumption level of the central 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 electrically assisted vehicle. When riding without power, there should be no drag and tear. Most importantly, the central motor should be sturdy and durable enough, with good dust and water resistance, and should not cause car owners to worry about later maintenance.
Taking the recently tested Newark SP20 mid mounted motor system as an example, the SP20 has a dynamic monitoring system consisting of a built-in torque sensor and two speed sensors, which can accurately capture stepping movements within milliseconds. Through Newark’s self-developed algorithm for analysis, the assistance compensation command is output to the motor, without empty stepping or a long power response process, achieving rapid response without delay when stepping or walking, It’s more handy when starting uphill – fast.
At the same time, the command signal controls the motor in a sine wave manner through FOC (Field Oriented Control) and SPWM (Sine Wave Pulse Width Modulation) technologies to achieve accurate and smooth control of the motor torque output. The control algorithm of Newark SP20 can also combine real-time data from various sensors to match the output of the motor with the force of stepping, correct the output power, and compensate and smooth real road conditions and stepping scenes to achieve accurate assistance.
The motor with the rated power of 250W and the peak power of 500W in the SP20 system adopts the outer rotor structure, which has more stages than the traditional inner rotor motor. The reduction mechanism is used to amplify the torque, which can produce greater torque under the condition of low speed. It can not only meet the requirements of flat road cruising, but also easily cope with long-distance climbing.
In terms of energy consumption, the SP20 system uses a higher strength hollow spindle, combined with a lightweight design, which reduces the weight of the central motor and reduces the load of the entire vehicle. At the same time, it also reduces the frictional resistance of the central shaft drive, improving conversion efficiency, and can achieve a limit range of nearly 100 kilometers after being paired with a 36V lithium battery, making it unnecessary to worry about power issues during short and medium distance trips – saving energy.
In addition, the durability of the SP20 mid drive ebike motor has also been optimized. It is stably linked to the frame through a three point fixing method, ensuring stable operation of the motor, reducing excessive vibration of the motor system during bumps, and effectively suppressing noise. The motor adopts a semi wrapped design to maximize heat dissipation and reduce the risk of failure caused by overheating of the motor.
The packaging process also pays more attention to durability, adopting a waterproof and dustproof design. The motor and shell are assembled using a sealing process, the circuit board is treated with waterproof paint, the spindle is paired with waterproof grease and sealing rings, and the wiring harness interface uses a waterproof plug. In theory, maintenance free effect – low presence can be achieved.
If you want to choose an electric powered bicycle equipped with a mid drive ebike motor, you can try my simple judgment method of “fast, accurate, tough, economical, and low presence” to identify the increasingly diverse electric powered products nowadays.
Although the attention of domestic consumers to electric powered bicycles remains mostly at the “taste level”, it cannot be ignored that more and more domestic manufacturers in China are beginning to participate in the research and development of electric powered products.
Therefore, as participants in bicycle sports and consumers of related products, it is necessary for us to deepen our understanding of electric powered bicycles. I also believe that E-Bike/Piedelec, an electric powered bicycle, should not be just a “toy” for international tycoon players. With technological progress and lower costs, electric powered bicycles will eventually enter more and more families.
Greensky Power Co., Ltd. is a professional manufacturer engaged in the research, development, production, OEM motor, sale of mid drive ebike motor.
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