Development of Two Wheel Drive Electric Bikes for Extreme Road and A Long-Range Capabilities

This paper aims to develop the electric bicycle by using a two-wheel drive that has a long range of use. This development is motivated by many extreme roads and the absence of a charging station except in the user’s own house. A folding bicycle type bicycle for adults with 16-inch wheels was used in this study. The two-wheel drive can be adjusted using the driving motor to be more flexible and adapt to road conditions, although the motor power used is small, 350-Watt 24 Volt for one wheel. The battery capacity used is quite large for the range quite far away, which is 24 volts 80 Amps, and the charging time is about 2 hours. The placement of the battery has calculated the center of gravity and balance of the bike. Results show that this electric bicycle can be used for slippery road conditions and slopes of not more than 1A maximum speed of the bicycle can reach up to 30 km/hour, on flat road conditions. Likewise, the bicycle’s range for a full charge is around 220-260 km, with an average speed of 15-16 km/hour. Two drives can be implemented independently, adjusting the running conditions by moving the drive motor selection button. For extreme conditions, it is recommended to use two electric motors.


Introduction
Electric vehicles are a priority for future vehicles with the decreasing reserves of petroleum and fossil energy.Innovation and development of electric vehicles is a necessity and a necessity for the future.The trend of electric vehicles as electric vehicles is also getting stronger in a number of developed and developing countries.Presidential Regulation No. 55 of 2019 concerning the Acceleration of the Battery-based Electric Vehicle Program, has been published in Indonesia.
Electric bike research conducted by Ali Ramadahn et al. [1], Sundhy Pareza [2] and Sunikhita et al. [3] discusses the application of electric bicycles related to environmental issues, smart electric bikes and eco-friendly and energy saving.More technical research, conducted by Benny Setiawan [4], Hendarto Putro et al. [5], Shweta Matey [6], Ram Bansal et al. [7], Hollandra Arif Kusuma et al. [8] related to the calculation of the maximum load that can be driven by a medium power BLDC electric motor with various electric power, such as front, rear and middle drive positions.
The battery is a very important component, especially regarding the determination of the battery capacity or range per one charge, the charging system and how to use it safely.Indah Susanti et al. 2019 [9], conducted an analysis of determining battery capacity and charging for this type of Lead Acid battery.Although for Electrical Vehicles now many have led to two choices of Littium Ion and Lithium Ferro batteries in particular.For more large capacities, users prefer to use the LiFerro type with several advantages for reasons of durability, safety, and battery capacity.The e-bike electric motor drive that will be implemented consists of an electric motor drive with positions on the front and rear wheels.The bicycle that will be used is a folding bicycle with 16 inch wheels for adults with a weight of about 75 kgf.

Torque and Mechanical Power
To calculate the thrust, torque and mechanical power of an electric motor, it is necessary to first find the total mass () that will be driven by the electric motor.The total mass of the bicycle, including the battery, rider, and electric motor is 15 kg + 22.4 kg + 70 kg + (2 x 5 kg) = 117.4kg or 1150.5 N. Then the normal force, static friction force, kinetic friction force and torque are approximate the formula can be described as follows.
Where: N is the normal force at a certain slope angle .If the bicycle is moving on a flat plane then  = . = Where:   is the static friction force,   is the coefficient of static friction Where:   is the kinetic friction force,   is the kinetic coefficient.
From the static and kinetic forces of the wheel radius function, the torque can be approximated by the formulas 2.4 and 2.5.
The torque provided to move the bicycle must be greater than the static and kinetic torque in order to accelerate.Resultant Torque in rolling motion from zero velocity to a certain velocity and constant velocity is determined by the magnitude of the rolling resistance coefficient at the bearing surface.Likewise, it is also affected by tire air pressure.The result of torsion in rolling motion in a flat plane can be shown as follows.
∑ =   (6) Where: T is the resultant torque,   is the rolling resistance force,   is the resistance coefficient,   is the normal force of each wheel at a certain plane angle, which is equal to W  cos(), r is the wheel radius, θ is the angle of inclination of the road surface, I is the moment of inertia and is the rotational acceleration.If the bicycle has been at maximum or constant speed, then equation 2.8 becomes To determine the acceleration can use the equation Where: V is the instantaneous velocity, 0 is the initial velocity,   is the acceleration, S is the instantaneous distance, 0 is the original distance.
If it is assumed that the desired speed is 30 km/h covered over a distance of 40 m, then the acceleration is 0.87 m/s 2 .Acceleration calculations can be carried out for several possible desired speeds from the condition the bicycle starts to move.One important thing that also needs to be considered is the rolling resistance coefficient (  ), where this coefficient affects the thrust resistance.Determination of the rolling resistance coefficient (  ) which is assumed to be a linear function of speed, can use the following equation [16][17].
Where: ƒ0 is the basic coefficient and ƒ is the coefficient determined based on the velocity effect.The values of ƒ0 and ƒ can be obtained from Figure 2 [16] [17].The calculation of electric motor power due to the required torque can use the following equation: Where: P is the mechanical power required to produce a certain resultant driving torque, n is the rotational speed of the drive wheels.

Calculation of Torque and Mechanical Power
Based on the above formulation, namely the equations 2.8, 2.10, 2.12, and 2.13, under conditions of 20 psi tire pressure and 16-inch wheel radius (0.203 m) then the results can be obtained a, μ_r, T, as shown in the following table.vo−v1 is power when V 0 to V 1 ; P V1−a=0 is the power when a = 0 P ave is average power based on maximum velocity If tables 1 and 2 are observed that every increase in speed, the power also increases.From the results that the maximum average power requirement to reach a velocity of 30 km/hour, is 308 watts.Power requirements are very large when the bike is accelerating.Meanwhile, if the speed is constant or there is no acceleration, the power required is relatively low, namely a maximum of 96.2 watts.
The analysis above is based on flat road conditions and asphalt roads (hard roads).If the road conditions are sloping, using equations 2.8, 2.10, 2.12, 2.13 and 2.14, the maximum capability, torque, power and recommended speed are shown in the following table.Note: using two-wheel drive (two electric motor drives) The implementation of a two-wheel drive e-bike on an inclined surface of up to 15 o requires a power requirement of between 461.3 watts to 476.0 watts, so it is recommended that electric bicycles use the option of two wheel drive, front and rear.

Electric Motor Determination
Brushless DC (BLDC) motors are the most commonly used motors for medium speed electric vehicles.This motor no longer uses a brush.If in a brushed DC motor, the coil acts as a rotor, in a BLDC motor, a permanent magnet acts as a rotor.The advantages of BLDC motors are good torque, high efficiency, have good resistance in long use, can work optimally in all rpm rotation ranges.But the weakness of the BLDC motor is that it requires a controller, limited top speed, and low power weight ratio.With the torque and power requirements for medium speed and road conditions with a maximum slope of 15 degrees, the motor specifications were chosen as shown in table 4 below.If the motor uses two drives, it means that the total torque and power of the electric motor are doubled, with the same maximum speed i.e. 400 -440 rpm.Utilization of two electric motors is used when heavy loads and incline conditions.
Based on the above calculations, it is recommended that the use of an electric bicycle for flat and constant speed roads is sufficient to use only 1 electric motor drive with rear wheel drive.Based on the power calculation above, if the bicycle is applied to a maximum speed with an acceleration of 0.87 m/s 2 , and a maximum speed of 30 km/hour, then an electric bicycle is safer to use two drives.If the acceleration is 0.6 m/s 2 and the maximum speed to be achieved is 25 km/h, then it is enough just to drive an electric motor.Meanwhile, if using two electric motor drives and on some road slope conditions it is estimated to use 2 electric motor drives with the maximum achievable speed as shown in Table 3.For heavy field conditions and inclined planes, the recommended maximum power is 500 Watt, with two drives electric motor is applied.

Determining Battery Capacity
The LiFePO4 battery is the choice for use on this electric bicycle with a fairly large capacity specification, i.e. operating voltage 3.2 Volts, charging voltage 3.65 volts and max continuous current 80 Ah.The operating capacity of the battery is very stable, and is much higher in many usage ranges from 100% to at least 20%.Details of specifications and battery capacity with voltage adjusting the voltage and power of the electric motor can be seen in table 5 below.A fully charged battery will reach 3.65V at the end of the bulk charge and absorption stages and be held in voltage until a disconnection current is reached (usually between 3-5% battery capacity).The charger will enter the float stage from 3.26-3.54V.

Battery Usage Time
The electrical energy stored in a battery can be recharged when the stored energy has been completely absorbed by the BLDC electric motor load.Battery discharging time can use the equation.Consumption of electric power on electric bicycles can be done by calculating the use of batteries for BLDC electric motors with an average velocity of 15 to 30 km/hour with a voltage of 24 volts with the assumption that the value of the electric current is proportional to the value of the bicycle's velocity.

Test Confirm Design and Performance
From the calculations and design concepts at the design stage, it is continued with the manufacture of a two-wheel drive e-bike prototype as shown in the following figure

Figure 1 .
Figure 1.Virtual Design of 3D E-Bike Two Wheel Drive

Figure 2 .
Figure 2. Supplementary coefficients ƒ0 and ƒ  for use in Equation2.13[16][17] of battery capacity and motor current when working is, t battery consumption = 80 Ah 14.6 A then  i = 5.48 hours.Battery de-efficiency 20% = 4.384 hours, so the effective mileage at 30 km/hour is 131.5 km.The mileage is close to 200 km if the average speed of the V1 is between 15 km and 20 km.

Figure 3 .
Figure 3. Prototype of two-wheel drive e-bike The results of the prototype performance test as a confirmation test include maximum speed, ability on sloping roads and battery consumption and range of use.The speed of two-wheel drive in the performance test can reach 30 km/hour as can be seen in the following figure.

Figure 4 .
Figure 4. Velocity test on a flat roadThe mileage test of the two-wheel e-bike was tested on the highway using the Reliev Application to measure the travel distance, maximum speed and average speed, including measuring battery capacity.

Figure 5 .
Figure 5. Performance Test: mileage, maximum velocity, average velocity and battery consumption

Table 1 .
Torque Requirements per several final velocity levelsThe power required at each level of speed increase can be seen in table 2 below.

Table 2 .
Drive power requirements per several final velocity levels

Table 3 .
Velocity, torque and maximum power at some angles of road slope

Table 4 .
Specifications of the Electric Motor used

Table 6 .
Calculation of electric bicycle usage and mileage, with an electric motor BLDC 350Watt 24V, 14.6 A, max velocity 30 km/h.