Electric Scooter Power System Design: Optimization Path from Motor Selection to Transmission Efficiency

Keywords: electric scooter, power system, wheel hub motor, mid mounted motor, transmission efficiency

abstract

The power system is the core of electric scooters, directly affecting their performance and user experience. This article analyzes the technical selection and optimization strategies of motor types, drive control, and transmission structures.

1.1 Comparison and Selection of Motor Types

Hub Motor:

Structural features: The motor is directly integrated into the interior of the wheel, without additional transmission components, and has a compact structure (such as the 300W brushless wheel hub motor used in the No. 9 E22 scooter).

Efficiency analysis: The peak efficiency is 85% -90%, but the efficiency decreases at high speeds (due to increased magnetic resistance losses), making it suitable for short distance commuting (range of 20-30km).

Mid Drive Motor:

Structural features: The motor is located below the pedal and drives the rear wheels through a chain or belt (such as the Xiaomi Pro 2, which uses a 250W mid mounted motor and belt drive).

Efficiency advantage: Peak efficiency of 92% -95%, supporting torque vector control, and improving climbing ability by 30% (suitable for mountainous terrain).

1.2 Drive Control Technology

FOC (Field Oriented Control):

Implemented through TI C2000 series DSP, the current loop response time is less than 100 μ s, the speed fluctuation is less than 1%, and the low-speed climbing stability is improved.

Improve energy recovery efficiency by 20% (such as converting kinetic energy into electrical energy during braking, extending range by 5km).

Square wave control (Six Step):

Low cost (the cost of the driver chip is only one-third of the FOC solution), but with large torque ripple (increased noise by 5dB), suitable for low-end models.

1.3 Transmission System Optimization

Belt drive:

Using Gates carbon fiber belt, the transmission efficiency is 96%, and the service life is over 5000km, but it needs to be tensioned regularly (it is easy to slip when the tension fluctuates by more than 10%).

Gear transmission:

The planetary gear reduction ratio is 5:1, and the torque is amplified to 15N · m, but the noise increases by 8dB (helical gears need to be used to reduce meshing impact).

1.4 Power Performance Test

Acceleration performance: 0-25km/h acceleration time<5s (mid motor model), wheel motor model requires 6-8 seconds.

Climbing ability: The mid motor model supports a 15 ° slope, while the wheel motor model only supports a 10 ° slope (requires a high-power motor, but with an additional weight of 1.5kg).

1.5 Lightweight and Heat Dissipation Design

Motor housing material: Made of 7075 aluminum alloy (density 2.8g/cm 3), which is 20% lighter than traditional 6061 aluminum alloy.

Heat dissipation structure: Heat dissipation fins are added to the stator core of the motor (with a 30% increase in surface area), combined with graphene coating, reducing the thermal resistance to 0.1K/W.

conclusion

Mid mounted motors are suitable for high-performance requirements, while wheel hub motors are suitable for lightweight design. Through FOC control and transmission optimization, power, efficiency, and cost can be balanced.