Which is better, the mid-drive motor or the hub motor? Pros and cons?
What is hub motor?
The hub motor, as its name implies, integrates the motor into the hub. After the power is turned on, the motor converts electrical energy into mechanical energy, which drives the wheels to rotate and drives the vehicle forward.
Generally, designers will install the hub motor on the rear wheels, especially for sports models. Because the rear triangle is more stable and reliable in structural strength than the front fork, the transmission of torque cadence signals and routing will also be more convenient (prerequisites) You want to buy an electric bicycle instead of an electric donkey). In the market, there are still some exquisite small wheel diameter city cars. In order to take into account the internal gear hub and the overall shape of the vehicle, it is ok to choose a front wheel hub solution. In order to pursue more powerful power, some brands have installed motors on the front and rear wheels with a rated power of up to 1000W. This type of product has already been included in the ranks of electric motorcycles.
With its mature design and relatively low price, in-wheel motors occupy most of the power-assisted bicycles. But because the motor is integrated on the wheel, it will break the front and rear weight balance of the vehicle, and at the same time, it will be greatly affected by bumps when off-road in the mountain. For full suspension models, the rear wheel motor will also increase the unsprung mass. To cope with greater inertial impact, the sports car models of the big brands usually use the center motor.
What is a geared hub motor?
There are two types of in-wheel motors: toothed motors are also called gear motors (usually planetary gear designs) and gearless motors are also called direct-drive motors.
The planetary gear plays a similar role in the motor. It can reduce the speed and amplify the output torque, so that the compact and lightweight motor can also have a strong power output. The figure above shows the internal structure of a geared motor.
Early geared hub motors were limited in accuracy and materials, and they encountered frictional resistance, noise, and wear problems. With the development of industrial technology, most of the motors with gear hubs are now very well made, so you don't need to worry about this.
When the power system is off, the vehicle is coasting, or when we step on it with human power, the resistance of a geared motor is smaller than a gearless motor. It may sound a bit difficult to understand. This is because a clutch device is usually designed inside the geared motor. The pedaling force is directly applied to the rear wheels through the clutch device. Too much extra resistance.
What is a gearless hub motor?
After understanding the geared hub motor, let's introduce the gearless hub motor.
As shown in the figure above, the internal structure of the gearless hub motor is relatively traditional. There is no complicated planetary reduction gear. It directly relies on electromagnetic conversion to generate mechanical energy to drive the vehicle.
Gearless hub motors may not have a clutch device inside (such motors are also called direct drive), so magnetic resistance needs to be overcome when riding without power, but because of this, the hub motor of this structure can achieve kinetic energy recovery. That is, when downhill, the kinetic energy is converted into electrical energy and stored in the battery.
Not all toothless direct-drive wheel motors can achieve kinetic energy recovery. Although this sounds like a great idea, it actually costs more to implement and increases the complexity of the entire electric power assistance system. The little amount of electricity recovered is obviously worthless.
What is a center motor?
As mentioned above, in order to achieve better sports performance, high-end mountain-assisted bicycles usually use a mid-motor solution. The mid-mounted motor, as the name suggests, is a motor placed in the middle of the frame (at the crankset). According to the installation method, the center motor is divided into two types: integrated frame and integrated. According to the structure and shape of the motor, it can be divided into a coaxial central motor and a parallel axis central motor.
The advantage of the center-mounted motor is that it can maintain the balance of the front and rear weights of the vehicle as much as possible without affecting the shock absorber action. The road impact that the motor bears is also smaller. The super-high integration can reduce unnecessary exposure of the line pipe, so In terms of off-road handling, stability, and passability, it is better than models with wheel motors. At the same time, players can also freely choose wheel sets and transmissions, and the daily disassembly and maintenance of the hub is simpler.
Of course, this is not to say that the mid-mounted motor will definitely be better than the wheel motor. Any brand product has a grade level. When comparing, it also needs to comprehensively evaluate multiple dimensions such as performance, price, and use. Everyone needs to take a reasonable look when choosing. . In fact, the mid-mounted motor is not perfect. Because the driving force needs to be transmitted to the rear wheels through the chainring and chain, compared with the hub motor, it will aggravate the wear of the chainring and chain, and it requires a little stepping when changing speed. Be gentle to avoid the terrible clatter of chains and flywheels.
What is a coaxial center motor?
The same for the center motor, there is another coaxial structure. The coaxial center-mounted motor is circular on the outside. The power output shaft of the motor and the crankshaft axis of the human step are located on the same axis line. There is also a series of speed-reducing gears and clutch devices inside, which reduces the high speed of the motor to our The pedaling frequency is approaching, and at the same time, the boosting torque is amplified to help us combat steep slopes.