Luận văn này trình bày quá trình thiết kế và chuyển đổi bộ kit động cơ truyền động giữa cho xe đạp địa hình (MTB) thành xe đạp điện địa hình (e-MTB). Nghiên cứu bao gồm các bước từ khảo sát nhu cầu thị trường, lựa chọn các phương án thiết kế cơ khí và điện tử, đến thử nghiệm và đánh giá hiệu suất. Kết quả đạt được bao gồm thiết kế hộp số, hệ thống tay quay, mạch cảm biến Hall, cảm biến nhiệt, và cải tiến thiết kế mạch điều khiển của VESC Open Source. Dự án kết thúc với các thử nghiệm thực nghiệm để đánh giá khả năng hỗ trợ đạp và điều khiển dòng điện, từ đó đưa ra kết luận và triển vọng phát triển sản phẩm trong tương lai. Mô tả luận văn: Luận văn này là dự án tốt nghiệp của sinh viên Nguyễn Công Hiếu, thuộc ngành Kỹ thuật Cơ điện tử, Đại học Bách Khoa Thành phố Hồ Chí Minh. Mục tiêu của dự án là thiết kế bộ kit chuyển đổi động cơ truyền động giữa để biến một chiếc xe đạp địa hình thông thường thành xe đạp điện địa hình, đáp ứng nhu cầu di chuyển bền vững và thuận tiện cho người dùng trong điều kiện địa hình khó khăn. Nội dung chính của luận văn bao gồm: -Tổng quan và nhu cầu thị trường: Trình bày lý do thị trường cần e-MTB và bộ kit chuyển đổi, cùng với công nghệ điều khiển mô-men và đo lường mô-men cho xe đạp điện. -Thiết kế cơ khí: Bao gồm thiết kế hộp số, hệ thống tay quay, và các bộ phận cơ khí khác. -Thiết kế hệ thống điện tử: Bao gồm thiết kế mạch cảm biến Hall, cảm biến nhiệt, và mạch điều khiển. -Thử nghiệm thực nghiệm: Lắp ráp hệ thống cơ khí và điện tử, đánh giá khả năng hỗ trợ đạp và điều khiển dòng điện. Luận văn kết luận với những kết quả đạt được và những hạn chế còn tồn tại, cùng với những triển vọng phát triển trong tương lai. Dự án này không chỉ cung cấp giải pháp kỹ thuật mà còn đóng góp vào xu hướng phát triển bền vững trong lĩnh vực phương tiện cá nhân.
OVERVIEW
Problem statement
1.1.1 Growing demand for sustainable transportation source
Mobility plays a vital role in the current society that we live in With the growing concern for preserving and sustaining it for future generations, mainly because of the increasing scarcity of natural resources and environmental concerns, protecting the environment poses a significant challenge to society and governments worldwide
Owing to this, some international organizations worldwide are implementing strict criteria for vehicles For instance, In January 2020, the European Union implemented Regulation (EU) 2019/631, setting CO2 emission performance standards for new passenger cars and vans The average CO2 emissions from new passenger cars registered in Europe have decreased by 12% compared to the previous year, and the share of electric vehicles tripled
1.1.2 The best solution for developing sustainable personal transportation
Electric bikes stand out as the most environmentally sustainable mode of transportation due to their reliability, zero emissions, and efficient energy consumption In contrast to conventional petrol-powered vehicles, which contribute significantly to carbon emissions, electric bikes offer a guilt-free alternative that promotes both personal well-being and the health of the planet.
Figure 1.1: Compare the carbon footprints of the different vehicles e-Bikes offer significantly extended travel distances compared to traditional bikes, thanks to the motor's power assistance Research findings indicate that both walking and cycling (with bike riders and pedestrians) possess the potential to reduce car-related CO2 emissions by 8.5 million tonnes annually, equivalent to the energy consumption of 971,309 households over a year In contrast, e-Bikes demonstrate a net emissions reduction capability of 16 million tonnes per year, nearly double the impact and surpassing the energy usage of 1.8 million homes for the same duration
Additionally, e-bikes present another dimension of sustainability They boast a lower carbon footprint than conventional bikes, as they require less food consumption to support pedalling Traditional bikes have a carbon footprint of 21g of CO2 per kilometre, with a significant portion stemming from the additional food needed for cycling and the remainder originating from the manufacturing process [1] The emissions from food production result from various factors, including deforestation for land use, livestock emissions, transportation, fertilizer production, and waste generation
1.1.3 Definition of e-Bikes and e-MTB
An electric bicycle, commonly known as an e-Bikes, is a bicycle equipped with an electric motor that assists the rider in propulsion There are 2 main types of electric bicycles classified according to the electric control signal:
• Pedal-Assist (No Throttle): Motor provides assistance only when the rider is pedalling
• Throttle-Assist (No Pedalling Required): Motor can be activated by a throttle without pedalling and Pedalling is optional
Before mentioning e-MTB, let talk about the mountain bikes (MTB) MTB are a bicycle designed for off-road cycling Mountain bikes share some similarities with other bicycles, but incorporate features designed to enhance durability and performance in rough terrain, which makes them heavier, more complex, and less efficient on smooth surfaces [2]
Therefore, e-MTB are a combination of the ruggedness of MTB and the electric motor of e-Bikes
1.1.4 The development potential of e-MTB and the need for e-MTB conversion kits
Over the years, the sales of e-Bikes have increased rapidly due to the rise in fuel costs, which has led to the growth of the implementation of electric bicycles as a daily means of transport
The electric MTBs market is a small part of the entire e-Bike market (5.77B vs 34.99B) (Figure 1.2 & 1.3) However, while the e-Bikes market already has many giants, especially Chinese companies, the e-MTB market still has opportunities for Vietnamese companies to develop Besides that, although the market share is not large, the estimated Compounded Annual Growth Rate (CAGR) of e-MTB is 12.56% [3] , which is 1.5 times higher than that of e-Bikes (8.16%) [4]
Figure 1.2: Growth Trends & Forecasts of e-MTB market size (2024 - 2029) Figure 1.3: Growth Trends & Forecasts of e-Bikes market size (2024 - 2029)
The advantages of e-MTB include [5]:
• Pedal assistance for longer distances
• Flexibility for different types of riders
However, there are disadvantages of e-MTB like [5]:
And the e-MTB conversion kit can efficiently deal with these three existing disadvantages of e-MTB on the market.
Literature review
At the current time, in May 2024, we have not found any research papers on domestic e-Bikes or e-MTB design However, there are some domestic companies that have been developing their own lines related to e-MTBs, such as:
• The Edge TX product line by Robot Viet Limited Liability Company: mid- drive conversions kit for MTB to e-MTB in prototype process
• The Stella product line by Robot Viet Limited Liability Company (or VierCycle): hub-drive conversions kit for bikes to e-bikes in commercial state
• The MB1 product line by MET EV Company: e-Bikes in prototype process
• In 2021, a group of students from the Maritime University of Raja Ali Haji in Indonesia designed and tested an electric-assisted bicycle with the aim of providing an alternative to traditional fossil fuel powered transportation for residents on a remote island [6] The bicycle included components such as a 24 VDC 10Ah DC power source, a motor driver, a speed controller, a unidirectional freewheel in the front sprocket, a throttle, a 24 VDC 350 Watt brushed DC motor, and no torque sensor The DC motor was mounted on the bicycle frame in an A-shaped arrangement, and the power source was placed on the saddle By using a tachometer sensor and a voltmeter to measure wheel speed, motor voltage, and current consumption, the research group demonstrated a linear relationship between motor input voltage, motor current, and wheel speed Real-world testing showed that users could ride the electric bicycle without pedalling, and the motor temperature increased from 30.6°C to 56.8°C within 21 minutes However, the DC motor eventually burned out, and the research group attributed this to long-term motor usage and resulting overheating
• A research article published in December 2022 summarized the characteristics and capabilities of Mid-drive e-Bikes and delved into the analysis of different motors for various electric bicycle applications [7] The article highlighted the current trend of using permanent magnet synchronous motors (PMSM) powered by AC as the most suitable motor for e-Bikes due to their ability to generate high torque, especially at low speeds The article also provided a Fuzzy control algorithm flowchart for controlling an e-Bikes in the presence of various disturbances such as uneven terrain and gusty winds
• There are many famous and long-standing manufacturers of e-MTB products, the most typical are: BOSCH, YAMAHA, GIANT, TREK, SCOTT, Moreover, there are also several manufacturers of mid-drive conversion kit for bikes to e-Bikes from China, the most typical is BAFANG
• There are also several commercial projects in the process of calling for capital on IndieGoGo since 2020 [8] related to (Figure 1.4)
Figure 1.4: A prototype mid-drive conversion kit to e-Bikes in IndieGoGo
However, the conversion kit for MTB to e-MTB being commercialized on the market comes from only the company CYC-Motor in Taiwan (Researched in 2024 May).
Necessity of product research and development
More than 140 countries, including Vietnam and the biggest polluters – China, the United States, India, and the European Union – have set a net-zero target, covering about 88% of global emissions [9]
The price of an unibody e-MTB is not affordable with almost buyers The average price of the best e-MTB of 2020 at €8,121 and increased to €8,846 for 2021 Moreover, survey participants spent an average of €4,593 on their current e-MTB while planning to spend €4,953 [10]
Vietnam is promoting the economic development of eco-tourism, specifically cycling in forests, lakeside or exploring pristine lands [11] e-Bikes are attracting younger people and are willing to spend a large amount of money to invest in the experience [12]
There is no official distributor of e-MTB in Vietnam, because of price issues and barriers when importing large-capacity batteries manufactured in other countries The price to own a completely imported e-MTB in Vietnam is at least 194 million VND to more than 300 million VND, in 2021 [13]
Without an official distributor and the market is not large enough, domestic maintenance, repair and replacement will certainly be very difficult.
Research and implementation range
This thesis presents the research and design of a conversion kit for MTB into e-MTB, with the following design criteria.
Working in Off-Road condition & Require power
Assists cyclists on off-road terrain, with 10% gradients at speeds of 10-12 mph The weight of the cyclist is 75kg and the weight of the bike is 20kg The average power for the e-MTB effort is about 220 watts (Table 1.1)
• Average speed = 10 -12 Mph and power of biker = 220 watts, which is equal to the average bike speeds [14] and average power consumption of cyclists using MTB without electricity [15] This means that when the power assist mode is turned on, the pedaller’s speed and feeling can remain unchanged even though it is in tough biking conditions
Off-road bike trails present a significant challenge, with slopes reaching 10% and designed for mountain bikes only Due to their difficulty level, these trails are not适合 for children under 11 years old Riders must possess exceptional bike control skills and physical fitness to navigate the demanding terrain, which features tight turns, small rock steps, narrow boardwalk sections, and potentially steep exposed side slopes.
• The weight of the cyclist is about 75kg which is obtained from test methods section 6.1 TCVN 7448:2004 "Electric bicycles - General safety requirements and test methods"
• The weight of the bike is 75kg which is obtained from several previous prototypes
Table 1.1: Constraints for Criteria 1 in summary
Chain Old & Not well-oil
Pedal assistance
The system has to support that the power is equal to the power consumed by the biker times the defined gain coefficient in real time
Lower limit for maximum speed at crankset
Structure of the thesis
The thesis is organized as follows:
Chapter 1: Giving reasons why e-MTB is needed in green mobility and defining the design criteria
Chapter 2: Choose main components/ parts/ modules to design and build a complete e-MTB
Chapter 3: Calculation and mechanical design for transmission elements
Chapter 4: Calculation and electronic design for several modules
Chapter 5: Design controller for the Field Oriented Control (FOC) method and build the concept for pedal assist
Chapter 6: Experimental results and evaluation
Chapter 7: Summary and development orientations.
SELECTION METHODS
Mapping selections
Rotor Position Sensor Torque Sensor
Following design criteria rooted in the interplay among system components, the selection process is bifurcated into two distinct parts: Priority Selections and Secondary
Selections Priority Selections wield significant and direct influence over the system
Conversely, Secondary Selections, while crucial, offer multiple alternatives or can be omitted without compromising the system integrity.
Priority selections
The selection process adheres to a hierarchical order, commencing with options characterized by minimal input arrows and progressing towards options influenced by a greater number of input arrows
2.2.1 Position of actuator & working principal
Motors mounted on e-Bikes are categorized into two primary types: Hub-Drive and Mid-Drive The figures below (Figure 2.3 & 2.4) illustrate these two layout options more explicitly, with the yellow circle representing the motor
Mid-drive e-MTBs dominate the market due to their distinct advantages Table 2.1 highlights the benefits of mid-drive configurations, including increased efficiency and natural handling Mid-drive motors enhance power transfer to the bike's drivetrain, resulting in less energy consumption and longer range They also provide a balanced weight distribution, contributing to a stable and responsive ride In contrast, hub motors offer lower maintenance expenses but sacrifice efficiency and handling due to their location in the wheels.
Table 2.1: Comparison between Mid-drive and Hub-drive
This central placement delivers power directly to the bike's chain and subsequently the rear wheel, which closely mimics the natural pedalling experience
Provide more efficient power distribution, as they leverage the bicycle's gears
Typically offer improved handling and balance because the motor's weight is centralized, resulting in a more natural weight distribution
It is higher cost and complexity Installation and maintenance might be more involved and costly compared to hub drive motors
Figure 2.3: Mid-drive motor e-Bikes Figure 2.4: Hub-drive motor e-Bikes
It is often favoured for off-road and mountain biking, where power and control are essential
Their ability to adapt to different terrains and inclines makes them an excellent choice for adventurous riders
It is integrated into the bicycle's wheel hub, either in the front or rear wheel This design is simple and relatively straightforward, making hub motors an attractive choice for those who want a hassle-free e-Bikes experience
There are fewer moving parts compared to mid-drive motors This can result in lower long-term ownership costs
Hub drive e-bikes are well-suited for urban and city commuting, as they provide consistent power delivery on flat terrain They are also quieter than mid-drive motors, which can be an advantage in residential areas
Hub drive motors lack the gear-shifting capability of mid-drive motors, making them less efficient when tackling steep hills
Since the motor is located in the wheel hub, hub drive e-bikes can exhibit imbalanced weight distribution This may affect handling and control, especially on rough terrain
With Criteria 1: Working in Off-Road condition, easily select mid-drive transmission for this conversion kit
Drawing reference from various mid-drive principal diagrams available on the market, including patents, enables a comprehensive understanding of the design principles and operational mechanisms underlying mid-drive e-Bikes [18] (Figure 2.5)
Figure 2.5: The way to measure torque of the right leg 1: Motor – 2 & 3: Clutch transmission device – 4: Axle – 5: Chainwheel – 6: Torque detection unit – 7: Hosing – 11 & 12: Gears – 41: Hollow tube – 42a & 42b: Cranks
The proposed principle diagram (Figure 2.6) must adhere to the following criteria:
1 The sensor position solely measures the power exerted by the cyclist and does not gauge the total power applied to the vehicle
2 The moments generated by the pedal and the motor, acting on the vehicle (rear wheel), remain independent of each other Specifically:
• The diagram must prevent motor torque from being transmitted to the pedal to ensure safety when only the motor is in operation
• Prevents pedal torque from acting on the motor, thereby ensuring that the pedaller does not expend additional effort to rotate the motor when electric assistance is not engaged
The system will have 2 operating states: Without power assistance (Figure 2.7) and with power assistance (Figure 2.8) The image below (Figure 2.9 &2.10) will more
Crank set clearly describe the torque line (Red line) and how the sensor measures the runner's torque
Due to running in relatively harsh hilly terrain, priority is given to choosing an aluminium protective cover for the battery, with the aim of reducing weight, providing better protection and finally good heat dissipation Like other electric vehicle manufacturers, aluminium is widely used in the construction of battery boxes
There are aluminium protective covers for electric vehicles available on the market and have a bottle design [19] The capacity of the battery depends on the cells we choose to package However, the general configuration of the battery is 10s2p or 10s3p and the rated voltage is 36V
Modern electric bicycles (e-Bikes) predominantly utilize brushless DC (BLDC) motors, a significant advancement over the older brushed motor technology The primary distinction between these two types of motors lies in the method of current direction alternation In brushed motors, mechanical brushes are used to switch the direction of the current flowing to the motor, a process that inherently reduces efficiency
Figure 2.7: The system working without assistance
Figure 2.8: The system working with assistance and leads to wear and tear over time In contrast, BLDC motors achieve this alternation electronically, eliminating the need for brushes and thereby enhancing efficiency and longevity This technological shift has led to the widespread adoption of BLDC motors in e-Bikes over the past decade, solidifying their status as the industry standard due to their superior performance and durability [20] In addition, their electronic commutation not only enhances efficiency and durability but also allows for more precise control compared to traditional brushed motors Consequently, BLDC motors have become the dominant choice in the design and development of contemporary electric bicycles
Calculate power to satisfy Criteria 1 by OMNI Calculator [21] the calculation formula is based on analysis and data collection of millions of people around the world
To achieve the desired power output of 727W, the biker's power contribution must be at most 220W, necessitating a motor power of at least 507W (i.e., `𝑃 𝑚𝑜𝑡𝑜𝑟 ≥ 507𝑊`) This requirement ensures that the motor can compensate for the insufficient power generated by the biker and deliver the desired output.
To meet the proposed capacity requirements, the operating voltage is set at 36V However, considering factors such as domestic availability and the need for a compact design, the Genuine Ryobi RY18LMX40A Electric Motor emerges as a suitable choice This motor, with a rated capacity of approximately 600W, not only aligns with the voltage specification but also offers a reliable and efficient solution that is readily accessible in the domestic market Its compact design further enhances its suitability for the intended application, ensuring both performance and practicality
Figure 2.9: Product drawing from the RYOBI manufacturer Φ Φ Φ Φ
From the manufacturer's motor specifications (Detail specification in section 3.2.1 Calculate the power for the motor and motor selection, max speed at rated torque at the rated voltage 36V:
Max Speed @ Rated Torque (Rpm) = 3230 rpm
2.2.4.1 Compare pros and cons of control methods
Nowadays, there are many control strategies for PMSM drives, including field- oriented control (FOC), direct flux control (DFC), and direct torque control (DTC) [22]
To choose the most suitable control type, we will look at the following set of three main factors: Adaptation with load variation, EV applications, large user community
Table 2.2: Comparison between current control methods
1 1 0.75 very good very good good but not as good as FOC [23]
APPLICATIONS 25% 1 0 0.5 very large just research some practical projects
COMMUNITY 25% 1 0 1 very large none toolbox on Matlab
FOC is the best option over given methods in torque control method for this electric vehicle project
The main idea of vector control is to control not only the magnitude and frequency of the supply voltage but also the phase In other words, the magnitude and angle of the space vector are controlled [24] The steps to implement FOC can be divided into four main steps:
Step1: Measure current already flowing in the motor
Just measure two phases and can interpolate the remaining phase using Kirchhoff's current law (Figure 2.10)
Figure 2.10: How to measure the current of the phases in FOC
Step2: Compare the measured current (vector) with the desired current (vector), and generate error signals
In synchronous motors, the rotor angle is indicative of the rotor flux angle By determining the rotor angle, we can establish the rotor flux angle This fundamental relationship underpins the error signal detection process, as depicted in Figure 2.11.
Figure 2.11: Error between measured current vector and desired current vector
Put i s & Rotor flux axis into new coordinate systems (Figure 2.12 & 2.13) The purpose of this is to convert from sine form to linear form, it is a lot easier to regulate
Figure 2.12: Converting to the fixed coordinate
Figure 2.13: Converting to the synchronous rotation coordinate
The above is an explanation in terms of graphics (Figure 2.14), but in terms of mathematics, we have the operation to convert the coordinate system:
Figure 2.14: States of converting 3-phase to controllable 2-phase in FOC
Forward Clark transformation, converse 3-phase to 2-phase
2 𝑖 𝑐 Forward Park transformation, converse stationary frame to synchronous frame
Step 3: Amplify the error signals to generate correction voltages
To maximize torque and efficiency, the vector 𝑖 𝑑 has to become zero It causes the vector 𝑖 𝑑 will lie on the q axis which is orthogonal with the rotor flux axis (Figure 2.15)
Step 4: Modulate the correction voltages onto the motor terminals (Figure 2.16)
Figure 2.16: States of converting controlled 2-phase to 3-phase in FOC
How much torque we want error(t)
Figure 2.15: Controllers for id and iq
In addition, in FOC there are also many other control techniques, that can operate such as observer, tracking and torque optimization (Figure 2.17)
Figure 2.17: Additional reluctance torque of Toyota/ Prius Hybrid THS II Motor [25]
FOC can also operate in sensor-less mode, which means that without a rotor position sensor, an observer can still predict rotor position for Step 2, yet this is not recommended for high load cases or the initial state of the motor This diagram will illustrate (Figure 2.18) the way for estimating rotor position 𝜃̂
Figure 2.18: Stationary frame state observer for a salient machine [26]
Criterion 3 combined with experimental data and collected from sources on the
Internet [27], the maximum pedalling cadence of a cyclist: n cadence ≤ 130 rpm The transmission ratio of the entire system can be calculated using the formula:
130 = 24.85 Where: 𝑛 𝑚𝑜𝑡𝑜𝑟 : Max Speed @ Rated Torque @ 36V
The gear ratio of the external transmission can be estimated to be about 2.5 to 5 1 , so the gear ratio in the gearbox ranges from 5 to 10 This gear ratio is small to use complex gearboxes such as Harmonic or Cycloidal gearboxes but also quite large to use spur gear gearboxes In addition, there is also a circular motor mechanism and reasonable manufacturing costs, so planetary gears are the right choice
As mentioned in the principal diagram, in section 2.2.1 Position of actuator & working principal, there needs to be a clutch inside the gearbox to prevent the cyclist from pulling the motor when running in unassisted mode
Table 2.3: Comparison between types of clutches in gearbox
W One-way bearing Freewheel Sprag Clutch
CAPACITY 40% 0.75 0.5 1 slip at heavy load broken at heavy load very large
1 0.5 0.5 a lot of choices a few choices more choices than freewheel but hard to buy
Secondary selection
Early e-bikes lacked precision due to cadence-based control, resulting in unpredictable handling To enhance stability and control, torque sensors were incorporated, which measure the force exerted on the pedals This improvement significantly reduced unpredictable behavior during cornering and start/stop scenarios.
The effectiveness of an e-bike is heavily influenced by the accuracy of its motor control To ensure optimal performance, the torque sensor monitors the rider's pedaling force and cadence, relaying this data to the controller An algorithm within the controller then calculates the precise motor speed and power, adjusting these parameters to deliver a seamless and responsive riding experience The precision of these measurements and calculations directly impacts the rider's perception of the e-bike's performance.
Table 2.5: Comparison between types of torque sensors
REQUIREMENTS 30% 1 1 1 any metal any metal any
1 0.5 1 no clean/ replace slipring brushes no
CONSUMPTION 10% 0.75 1 1 low very low very low
OTHER not possible/ too complex for some motors/ frames
OTHER only hub-drive; no belt drive; limited dynamic range
As evident from the overview table, the contactless strain gauge sensor is a quite favourable solution for many e-bike applications The main disadvantage is that the rotating part needs additional electronics
The T13 Torque Sensor from Shanghai Moreway International Trade Company Limited was chosen because it is a contactless strain gauge In addition, this sensor has a cadence signal (one phase in clockwise) to calculate the pedal's power, available stock and reasonable price
Table 2.6: Specification of T13 torque sensor
The only criteria for choosing a temperature sensor is that it must be very small because it needs to be placed in the PCB circuit and in the motor stator Therefore, NTC 10k resistant sensor is chosen
Table 2.7: Comparison between types of rotation position sensors
5 Speed signal Forward rotation: 18 pulse/ rotation
Backward rotation: no speed signal output
HALL SENSOR ABI SENSOR SINUSOIDAL
- Relatively high resolution - High resolution and accuracy compared to incremental encoders
- Provides continuous feedback without discrete pulses
- Low resolution compared to other type encoders
- Susceptible to interference from external magnetic
- Limited accuracy and precision, especially at high speed because of a small wrong in any phases
- Requires more space for sensor placement
- Requires more sophisticated signal processing
- Requires accurate design for sensor mounting location
For durable, economic and streamlined design, I choose an option using hall sensor for Rotation position sensor
• Just using the hall sensor for motors at low speed to reduce error caused by phase difference
• Using capacitors for filtering noise
• Type unipolar switching output instead of analog voltage output
• Ease to buy and low cost
• Output rise & fall time ≪ phases circle time
Several well-known brands provide Field-Oriented Control (FOC) controllers for various applications, including motor control, inverters, and other electronic systems Some common examples include:
• Texas Instruments: Texas Instruments offers FOC controllers for electric motor applications, including both direct and indirect control
• Infineon Technologies: Infineon provides FOC controllers for a wide range of applications from electric motors to inverters
• STMicroelectronics: STMicroelectronics offers FOC control solutions for electric motors and various other applications
• NXP Semiconductors: NXP provides FOC controllers for motor and inverter applications
• Microchip Technology: Microchip offers FOC control solutions for diverse applications ranging from electric motors to low-power electronics
Additionally, there are many other companies such as Bosch, Mitsubishi Electric, and Toshiba that also provide FOC controllers for the market However, to easily modify the program to suit the e-MTB application, two common open-source FOC controllers are considered: VESC and SimpleFOC
Table 2.8: Comparison between two popular FOC open sources
EASE TO PROGRAM 25% 0 1 using ChibiOS for running multi-thread framework Arduino
1 0 all firmware is public, user can modify a library on framework
ANALYZING DATA 25% 1 0.5 wiring & wireless wiring
Specialized for EVs, having GPS & log data; Hardware ESC also is public
Specialized for small projects; Hardware ESC have to buy
The VESC Open Source is chosen because it’s more suitable for the e-MTB project Moreover, it just supports NRF51832, NRF52832, and NRF52840 chip Bluetooth, so one of them is used for communication and collecting data
To achieve the highest capacity, INR18650-35E (3500mAh) cells from Samsung or INR18650-35V (3500mAh) cells from EVE are used Both types of cells offer a maximum discharge current of approximately 10A While the price of each EVE cell is two-thirds that of a Samsung cell, their quality is generally comparable The battery configuration consists of two blocks connected in parallel, resulting in a peak current output of 20A Consequently, a Battery Management System (BMS) rated at 10s 20A is selected to accommodate this configuration and ensure optimal performance and safety.
MECHANICAL DESIGN
Working principle
3.1.1 Method to measure torque from both legs
The operating principle of the bottom bracket in this design is to measure the total torque generated by both legs of the rider This is achieved through the integration of torque sensors within the bottom bracket assembly
Figure 3.2: How the system measures the torque of the left leg Figure 3.3: How the system measures the torque of the right leg
3.1.2 Method motor assist the system
The motor in this e-MTB design can operate in two scenarios: either faster than the pedal foot or at the same speed as the pedal foot Due to Criterion 3 , there is no scenario where the motor operates slower than the pedal foot The crankset clutch plays a crucial role in ensuring the safety and functionality of the system Its primary functions are twofold:
• Protection of Pedal Legs: The crankset clutch safeguards the rider's legs from the impact of the motor By engaging or disengaging as needed, it prevents the motor from transmitting excessive force to the pedals, thereby reducing the risk of injury or discomfort to the rider (Figure 3.4)
• Accurate Torque Measurement: The crankset clutch also ensures that the torque sensors only measure the rider's pedaling force, not the motor's torque When the clutch is disengaged, it decouples the motor's torque from the crankset, allowing the sensors to always measure only the rider's input (Figure 3.5)
Figure 3.4: How does the system separate the torque of the motor and the cyclist
Figure 3.5: How does the system assist the cyclist
Motor selection and transmission ratio
3.2.1 Calculate the power for the motor and motor selection
The system efficiency to crankset, not to rear wheel
The required power to satisfy Criterion 1 is calculated using the formula form Omni Calculator [21]
• Resisting force due to gravity
𝐹 𝑔 = 92.701𝑁 Where: 𝑔 = 9.807 𝑚/𝑠 2 : gravitational acceleration 𝑠𝑙𝑜𝑝𝑒 = 10%: slop of hill
𝐹 𝑟 = 23.453𝑁 Where: 𝑔 = 9.807 𝑚/𝑠 2 : gravitational acceleration 𝑠𝑙𝑜𝑝𝑒 = 10%: slop of hill
𝐶 𝑟𝑟 = 0.0253: coefficient at knobby tires & offroad surface
𝐹 𝑎 = 0.5 × 0.408 × 1.225 × (5.556 + 0) 2 = 7.714𝑁 Where: 𝐶 𝑑 × 𝐴 = 0.408: Drag coefficient × Biker ′ s frontal area
𝜌 = 1.225 𝑘𝑔/𝑚 2 : air density at sea level
𝑃 = 716.886𝑊 Where: 𝐹 𝑔 = 92.701𝑁: Resisting force due to gravity
𝑣 = 5.556 𝑚/𝑠: biking speed 𝑙𝑜𝑠𝑠 = 4%: percentage loss in power at chain not well − oil The require power for motor:
0.84 = 591.531𝑊 Where: 𝑃 = 716.886𝑊: Power to satisfy design criteria
𝑃 𝑐𝑦𝑐𝑙𝑖𝑠𝑡 ≤ 220𝑊: Power the cyclist wants to expend
As the previous preliminary calculation in section 2.2.3 Motor selections, the engine selected is Genuine Ryobi RY18LMX40A Electric Motor with specification table (Table 3.1)
Table 3.1: Specification of the motor
As mentioned in section 2.2.5.1 Select gearbox type, according to design Criteria
3, cyclists always receive power support within the cadence range of ≤ 130 𝑟𝑚𝑝 (Because 130 𝑟𝑝𝑚 is the maximum cadence that a typical cyclist can achieve [27])
The optimal gear ratio for an e-bike system is a compromise between torque and speed A higher gear ratio provides more torque, but reduces speed, while a lower gear ratio increases speed at the expense of torque To ensure the rider can feel the power assist, the gear ratio should be chosen so that the crankset produces maximum torque at approximately 130rmp This threshold ensures a balance between torque and speed, allowing the rider to experience the benefits of both without compromising performance.
Desire gear ratio from motor to crankset
130 = 24.85 Where: 𝑛 𝑚𝑜𝑡𝑜𝑟 : Max Speed @ Rated Torque @ 36V
𝑛 𝑐𝑎𝑑𝑒𝑛𝑐𝑒 : Max cadence Relationship between component gears in a planetary gear gearbox
• The number of teeth on sun gear (𝑛 𝑆𝑢𝑛 𝐺𝑒𝑎𝑟 ), planet gear (𝑛𝑃𝑙𝑎𝑛𝑒𝑡 𝐺𝑒𝑎𝑟) and internal ring gear (𝑛 𝑅𝑖𝑛𝑔 𝐺𝑒𝑎𝑟 ) must be divisible by 3 be able to assemble together
• Centre distance between planetary gear and sun gear is equal to centre distance between planetary gear and ring gear
The size of the planetary gear box needs to be approximately the same as the motor diameter to ensure neat assembly:
As in section 2.2.5.2 Clutch in gearbox selection, we use Sprag Clutch with centre distance between sun gear and planetary gear is 28.5mm
Table 3.2: Select transmission ratio for planetary gear box
The reason for eliminating option 1 and other options having 𝑛 𝑆𝑢𝑛 𝐺𝑒𝑎𝑟 ≤ 18 is because of the small dedendum diameter, that is impossible to select key
Where: 𝑥: distance between keyway and dedendum diameter
This means that a pinion design is needed, which is not possible with the main rotating shaft being the rotor of the motor
The reason for eliminating option 3 and other options having 𝑛 𝑆𝑢𝑛 𝐺𝑒𝑎𝑟 ≥ 24 is the transmission ratio is getting smaller and smaller
Select transmission ratio for planetary chain-drive
The selection of chain sprockets is crucial for optimizing performance For MTBs, the BCD 104 sprocket accommodates up to 44 teeth, while the smallest chainring features 9/13 teeth and a 2.54 cm chain pitch for EV applications To achieve a suitable gear ratio, a common gear set utilizes a 9-tooth small sprocket and a 42-tooth big sprocket.
3.2.3 Technical specification of the transmission
The maximum output power of motor
9.55 = 1626.84𝑊 Where: 𝑣 𝑟𝑎𝑡𝑒𝑑 = 3230 𝑟𝑝𝑚: max Speed @ Rated Torque @ 36V
The maximum torque at shaft I
𝑇 𝑚𝑎𝑥 𝐼 = 4.81 × 5.43 × 0.97 2 × 0.99 × 0.99 2 = 23.85𝑁𝑚 Where: 𝑇 𝑚𝑎𝑥 𝑚𝑜𝑡𝑜𝑟 = 4.81 𝑁𝑚: peak torque of motor
𝜂 𝑏𝑒𝑎𝑖𝑟𝑛𝑔 = 0.99: 𝑎 pair of bearing efficiency The maximum torque at shaft II
𝑇 𝑚𝑎𝑥 𝐼 = 23.85 × 4.67 × 0.93 × 0.99 = 102.55𝑁𝑚 Where: 𝑇 𝑚𝑎𝑥 𝐼 = 23.85 𝑁𝑚: peak torque at sharf I
Chain drive design
Use software Autodesk Inventor 2024 to design, change and test values until the design passes the durability test on software
• [Tab Design] Roller Chain Sprocket1: 𝑧 = 9
• [Tab Design] Roller Chain Sprocket2: 𝑧 = 42
• [Tab Design] Number of Chain Links: 𝑘 = 1
• Other parameters are left as default
Figure 3.6: Tab Design of Chain Design in Autodesk Inventor
• [Tab Calculation] Required service life: 𝐿 ℎ = 1000 ℎ𝑟
• [Tab Calculation] Application: Slight shocks
• Other parameters are left as default
Figure 3.7: Tab Calculation of Chain Design in Autodesk Inventor
Then return to the calculation tab Choose the right type of chain, the standard chain on bicycles has a chain pitch of 12.7mm (1/2 inch) and the red dot is in the blue area of the chain, it satisfies the design requirements
Figure 3.8: Tab Selection Chain of Chain Design in Autodesk Inventor
After choosing the appropriate type of chain, click calculate to check the design again If there are no red flags, the design is fine and export the results
Chain : ISO 606:2004 - Short-pitch transmission precision roller chains
Number of Chain Strands k 1.000 ul
Minimum width between inner plates b1 7.750 mm
Maximum pin body diameter d2 4.450 mm
Maximum inner plate depth h2 11.810 mm
Maximum outer or intermediate plate depth h3 10.920 mm
Maximum width over bearing pins b 17.000 mm
Maximum inner plate width t1 1.500 mm
Maximum outer or intermediate plate width t2 1.500 mm
Maximum tension in chain span FTmax 1285.532 N Static safety factor SS > SSmin 13.846 ul > 7.000 ul Dynamic safety factor SD > SDmin 6.923 ul > 5.000 ul
Design power PD < PR 0.805 kW
Chain power rating PR 1.306 kW
Chain service life for specified elongation th > Lh 3105 hr Chain link plates service life thL > Lh 1448 hr Roller and bushing service life thr > Lh 33000 hr
Gearbox design
Number of teeth of the ring gear: 𝑧 1 = 93
Number of teeth of the sun gear: 𝑧 2 = 21
Number of teeth of the planet gear: 𝑧 3 = 36
Rate speed of the motor: 𝑛 𝑚𝑜𝑡𝑜𝑟 = 3230 𝑟𝑝𝑚
Peak torque of the motor: 𝑇 𝑚𝑎𝑥 𝑚𝑜𝑡𝑜𝑟 = 4.81 𝑁𝑚
Use software Autodesk Inventor 2024 to design, change and test values until the design passes the durability test on software
3.4.1 Transmission gears: sun gear and planetary gear
• [Tab Design] Design Output: Module
• [Tab Design] Design Gear Ratio: 36/21; Don’t tick Internal
• [Tab Design] Facewidth:13mm (Gear 1); 12mm (Gear 2)
• Other parameters are left as default
Figure 3.10: Tab Design of Gear Design (Sun + Planet gears) in Autodesk Inventor
Figure 3.9: Working principle of the planetary gearbox with fixing the ring gear
• [Tab Calculation] Type of Strength Calculation: Check Calculation
• [Tab Calculation] Material Values: EN C45 Heat treatment
• Other parameters are left as default
Figure 3.11: Tab Calculation of Gear Design (Sun + Planet gears) in Autodesk
Durability testing will sometimes produce incorrect results, we need to re-select the appropriate material or increase the Facewidth If try and error still does not work, you must increase the module or increase the number of teeth As long as there are no red error messages, the design is satisfied:
Number of Teeth z 21 ul 36 ul
Unit Correction x 0.0000 ul 0.0000 ul Pitch Diameter d 21.000 mm 36.000 mm Outside Diameter da 23.000 mm 38.000 mm Root Diameter df 18.500 mm 33.500 mm
Normal Force Fn 162.160 N Circumferential Speed v 3.552 mps
Factor of Safety from Pitting SH 1.225 ul 1.230 ul Factor of Safety from Tooth Breakage SF 1.352 ul 1.311 ul Static Safety in Contact SHst 1.925 ul 2.020 ul Static Safety in Bending SFst 2.570 ul 2.549 ul
3.4.2 Transmission gears: planetary gear and ring gear
• [Tab Design] Design Output: Module
• [Tab Design] Design Gear Ratio: 93/36; Tick Internal
• [Tab Design] Facewidth:12mm (Gear 1); 13mm (Gear 2)
Figure 3.12: Tab Design of Gear Design (Ring + Planet gears) in Autodesk Inventor
• [Tab Calculation] Type of Strength Calculation: Check Calculation
• [Tab Calculation] Material: EN C45 Heat treatment
• Other parameters are left as default
Figure 3.13: Tab Calculation of Gear Design (Ring + Planet gears) in Autodesk
Durability testing will sometimes produce incorrect results, we need to re-select the appropriate material or increase the Facewidth If try and error still does not work, you must increase the module or increase the number of teeth As long as there are no red error messages, the design is satisfied:
EN C45 Heat Treatment Type of model Component Component
Number of Teeth z 36 ul 93 ul
Unit Correction x 0.0000 ul 0.0000 ul Pitch Diameter d 36.000 mm 93.000 mm Outside Diameter da 38.000 mm 91.000 mm Root Diameter df 33.500 mm 95.500 mm
Factor of Safety from Pitting SH 1.340 ul 1.340 ul
Factor of Safety from Tooth Breakage SF 4.907 ul 4.920 ul
Static Safety in Contact SHst 3.170 ul 3.170 ul
Static Safety in Bending SFst 9.614 ul 8.195 ul
After calculating and preliminary estimating the shaft size, including 4 cylinders:
The distance between the supports /load:
Analyse the force applied to the shaft, where:
• 𝐹 𝑟 = 𝐹 𝑝 × 𝑘 𝑥 = 1477.28 𝑁: Force acting on the shaft [28]
• 𝑀 = 23.85 𝑁𝑚: Input moment of chain − drive
Figure 3.14: Arrange the distance on the shaft
Using the axis design feature in Autodesk Inventor 2024, first enter 4 cylinders into the Tab Design
Figure 3.16: Analyzing the force acting on the shaft
Figure 3.15: Tab Design of Shaft Design in Autodesk Inventor
Then declare Support points, declare Load points and enter load values in Tab
Calculation Note that the software automatically calculates the reaction forces at the supports, however, the reaction moment must be added so that the software can calculate
Figure 3.17: Tab Calculation of Shaft Design in Autodesk Inventor
After exporting the results on the software, we have the following charts
Figure 3.18: Shear Force Graph, YZ Plane
Figure 3.19: Shear Force Graph, XZ Plane
Figure 3.20: Bending Moment Graph, YZ Plane
Figure 3.21: Bending Moment Graph, XZ Plane
Figure 3.22: Ideal Diameter of Shaft
3.4.4.1 Key selection for chain sprocket assembly
Using Autodesk Inventor 2024 for selecting keys Choose 2 keys 5x5x12mm for shafts with a diameter of 17mm
• Other parameters are left as default
Figure 3.23: Tab Design of Key (Chain Sprocket) in Autodesk Inventor
Figure 3.24: Tab Calculation of Key (Chain Sprocket) in Autodesk Inventor
After choosing the appropriate key, the results are summarized:
Number of Keys N 2.000 ul Application Factor Ka 1.000 ul Fatigue-Life Factor Kf 1.000 ul Wear-Life Factor Kw 1.000 ul Load Distribution Factor Km 0.600 ul Desired Safety Sv 1.000 ul Key
Material Surface-hardened steel Allowable Pressure p A 600.000 MPa
Allowable Stress in Shear τ A 275.000 MPa
Material Surface-hardened steel Allowable
3.4.4.2 Key selection for clutch assembly
Choose 1 keys 5x5x10mm for shafts with a diameter of 17mm
• [Tab Calculation] Type of Strength
• Other parameters are left as default
Figure 3.26: Tab Calculation of Key (Chain Clutch) in Autodesk Inventor
After choosing the appropriate key, the results are summarized:
Figure 3.25: Tab Design of Key (Chain Clutch) in Autodesk Inventor
Application Factor Ka 1.000 ul Fatigue-Life Factor Kf 1.000 ul Wear-Life Factor Kw 1.000 ul Load Distribution Factor Km 1.000 ul Desired Safety Sv 1.000 ul Key
Allowable Stress in Shear τ A 275.000 MPa
Bearing 4204 was selected to minimize output shaft runout, supported by a comprehensive 3D design Autodesk Inventor 2024 validation confirmed the effectiveness of the selection.
• [Tab Calculation] Radial load: 3484.69N Shear force at bearing in section 3.4.3 Shaft design
• [Tab Calculation] Key Material: Surface-hardened steel
• [Tab Calculation] Shaft Material: Surface-hardened steel
• [Tab Calculation] Hub Material: Surface-hardened steel
• Other parameters are left as default
Figure 3.27: Tab Calculation of Bearing Selection in Autodesk Inventor
Adjusted rating life Lna 17284 hr Calculated static safety factor s0c 3.58712 ul Power lost by friction Pz 1.95412 W Necessary minimum load Fmin 125 N
Over-revolving factor kn 0.000 ul
Life adjustment factor for reliability a1 1.00 ul
Crankset design
Following the selection 2.2.6.2 Clutch in crankset, additional requirements are considered to ensure the appropriateness of the chosen bearing type
• The maximum torque exerted on one pedal is calculated based on the weight of the cyclist and the pedal radius For an 82 kg individual with a pedal radius of 160 mm, the maximum torque is determined to be 129 Nm [29]
• It is recommended that the inner diameter of the selected bearing exceeds
40 mm to accommodate the mounting diameter of the torque sensor, which is 40 mm This ensures that the bearing's inner ring provides sufficient clearance for the sensor installation
The CSK45-PP one-way bearing is selected for its superior torque handling capacity, surpassing the maximum torque requirement of 325 Nm Its inner diameter exceeds 40 mm, seamlessly accommodating the torque sensor's mounting diameter specifications, ensuring compatibility.
Holder motor design
Using the ANSYS toolbox embedded in Autodesk Fusion 360 to test the durability of the motor mounts under chain tension loading conditions and ensure their structural integrity and reliability in operation First apply a force equivalent to the chain tension created on the shaft: 𝐹 𝑟 = 1477.28 𝑁
Figure 3.28: Put the force the chain system exerts on the shaft in Autodesk Fusion
Primarily, 6061 aluminum is selected because it is easy to process, with a lower melting point compared to other materials, which simplifies manufacturing and allows for more precise fabrication of parts Additionally, 6061 aluminum is widely used and readily available in the production industry, making it a cost-effective and reliable choice
Figure 3.29: Define the material for objects being analyzed
Based on the analysis, it is evident that the safety factor exceeds 8 for the entire structure, indicating a substantial margin of safety (Figure 3.31) Additionally, the maximum displacement observed is only 0.05mm, suggesting minimal deformation under load (Figure 3.30) Therefore, it can be concluded that designing the system using two aluminum panels of the specified size and shape is sufficient to meet the structural requirements
Figure 3.30: Displacement of the Motor after solving in Autodesk Fusion
Figure 3.31: Safety factor of the Motor after solving in Autodesk Fusion
ELECTRICAL – ELECTRONIC DESIGN
Controller hardware module
The e-MTB project has made hardware modifications to the open-source VESC platform, which is known for its ability to control BLDC motors These modifications were made to meet the specific requirements of the project and optimize the functionality and performance of the electronic control system within the e-MTB.
Figure 4.1: Reference schematic design of Open source VESC
The project entails the design and customization of several hardware blocks to align with the unique demands of electric mountain biking:
• Adapt the MCU Block: Incorporate additional IO pins for monitoring the cyclist's power output
• Integrate the Display Block: Establish communication with the display screen
• Integrate the Power Supply Block: Enable system activation and deactivation based on signals from the screen
• Integrate the Torque & Speed Block: Manage power distribution and filter noise signals from the Torque and Speed sensors
• The remaining hardware components remain largely unaltered
The final schematic version and 3D image of this project are illustrated in Figure 4.2 and Figure 4.3 respectively Note that the hardware circuit design of controller is consulted and supported by VIEROBOT company
Figure 4.2: General schematic of the controller hardware
Figure 4.3: 3D images of the controller hardware
Hall effect sensors module
4.1.1 Position arrangement for hall effect sensors
The position of the hall effect sensors must be ordered to be 120° apart in phase, the formula to determine the position of these sensors is (Figure 4.4):
Where: 𝐴𝑛𝑔𝑙𝑒 is the angle between two sequential phases 𝑃𝑎𝑖𝑟 𝑝𝑜𝑙𝑒𝑠 = 3 is pair poles in rotor
Figure 4.4: Hall effect sensors arrangement
Choose A3144EUA hall effect sensor because it satisfies the requirements in part 2.2.9 Rotor position sensor selection.
3= 1000 𝑚𝑠 Where: 𝑅𝑖𝑠𝑒 𝑡𝑖𝑚𝑒 = 2𝜇𝑠: Output Rise Time (Max) 𝐹𝑎𝑙𝑙 𝑡𝑖𝑚𝑒 = 2𝜇𝑠: Output Fall Time (Max) 𝑀𝑎𝑥 𝑠𝑝𝑒𝑒𝑑 = 3230 𝑟𝑝𝑚: Max speed of motor 𝑃𝑜𝑙𝑒𝑠 𝑝𝑎𝑖𝑟 = 3: Number of poles pair in motor
Table 4.1: Specifications of the A3144EUA hall effect sensor
In my power supply block, just having 3.3V, 5V, 12V so I choose supply voltage
V CC = 5 V The Hall sensor acts like a switch to the ground Therefore, a pull-up resistor is needed for the output signal I choose 𝑅 = 4.7𝑘Ω (Figure 4.5)
Figure 4.5: Prototype schematic of the hall effect sensors module
Figure 4.6: Hall effect sensors module signal at the prototype version
After conducting an examination, it was observed that the Hall signal exhibited significant noise, particularly in phase B (as indicated by the red line representing Hall
2 in Figure 4.6) Consequently, capacitor C103 was introduced to mitigate the phenomenon of voltage drop (Figure 4.7) Following this adjustment and subsequent re- experimentation, the results demonstrated a notable reduction in noise (Figure 4.8)
Figure 4.7: Final schematic of the hall effect sensors module
Figure 4.8: Hall effect sensors module signal at the final version
Temperature sensors
The NTC thermistors used to measured temperature of MOSFETs (Controller hardware module) and motor (Hall effect sensors module) have resistor between 8.21 𝑘Ω at 30°𝐶 and 0.517 𝑘Ω at 125°𝐶
Figure 4.9: Reference design for NTC sensors
The schematic is designed based on the left design reference (Figure 4.9) and capacitor 104 to filter the signal (Figure 4.10) With this design, the system will be better protected if there is a short circuit at the resistor
Besides that, 𝑉 𝑟𝑒𝑓 = 3.3𝑉 (ESC) or 5𝑉 (Motor) and 𝑉 𝑜𝑢𝑡 ≤ 3.3𝑉 (ADC reference voltages):
Figure 4.10: Wiring diagram of temperature sensors inside of the ESC (left side) and motor (right side)
Bluetooth module
The NRF52832 module operates at 3.3V, while the output pin of the Controller hardware module supplies 5V Consequently, it becomes necessary to incorporate the AMS117 module to regulate the voltage from 5V to 3.3V, ensuring stability (Figure 4.11) Moreover, retrofitting the ESC with a 3.3V output presents additional challenges, particularly due to its integration post the installation of the Controller hardware module
Figure 4.11: Schematic of the Bluetooth module
CONTROL – ALGORITHM DESIGN
Current reference generator
Based on design Criterion 2, the final goal is: The power of the servo motor is equal to K times the power the bike is consuming (with K being a constant)
However, instead of having to collect cadence data to calculate the pedal's power, in fact, using only the torque signal to control the flow ensures Criteria 2
We want to assist, it means 𝑷 𝒄𝒚𝒄𝒍𝒊𝒔𝒕 proportion to 𝑷 𝒎𝒐𝒕𝒐𝒓 :
𝑷 𝒄𝒚𝒄𝒍𝒊𝒔𝒕 ~𝑷 𝒎𝒐𝒕𝒐𝒓 ⟺ 𝑷 𝒎𝒐𝒕𝒐𝒓 = 𝑮 × 𝑷 𝒄𝒚𝒄𝒍𝒊𝒔𝒕 (𝟓 𝟏) Where: 𝑷 𝒄𝒚𝒄𝒍𝒊𝒔𝒕 is the power of the cyclist
𝑷 𝒎𝒐𝒕𝒐𝒓 is the the power of motor
𝑮 is the gain coefficient, user define
Where: 𝑻𝒐𝒓𝒒𝒖𝒆 (𝑵𝒎) is the torque created by the cyclist
Where: 𝑻𝒐𝒓𝒒𝒖𝒆𝒎𝒐𝒕𝒐𝒓@𝒄𝒓𝒂𝒏𝒌𝒔𝒆𝒕 (𝑵𝒎) is the torque created by the motor 𝑺𝒑𝒆𝒆𝒅𝒎𝒐𝒕𝒐𝒓@𝒄𝒓𝒂𝒏𝒌𝒔𝒆𝒕(𝑹𝑷𝑴) is the speed motor at crankset
Therefore, the speed of the motor automatically equal proportional to the cyclist’s cadence: 𝑺𝒑𝒆𝒆𝒅𝒎𝒐𝒕𝒐𝒓@𝒄𝒓𝒂𝒏𝒌𝒔𝒆𝒕 = 𝑪𝒂𝒅𝒆𝒏𝒄𝒆 𝒄𝒚𝒄𝒍𝒊𝒔𝒕 (𝟓 𝟒)
The output torque is also nearly proportional with current input: 𝑻𝒐𝒓𝒒𝒖𝒆𝒎𝒐𝒕𝒐𝒓@𝒄𝒓𝒂𝒏𝒌𝒔𝒆𝒕 ≈ 𝑲 𝑰 × 𝑪𝒖𝒓𝒓𝒆𝒏𝒕 × 𝒖(𝟓 𝟓),
Where: 𝐊 𝑻 : torque constant of motor 𝐮: transmisstion ratio
𝑲 𝑰 × 𝒖× 𝑻𝒐𝒓𝒒𝒖𝒆 𝒄𝒚𝒄𝒍𝒊𝒔𝒕 Where: 𝑲 𝑰 is the torque constant by the motor
𝑮 is the assistant gain coefficient
If the current vector is at 90° (electrical) with respect to the rotor flux axis, the motor will exhibit maximum torque per ampere As mentioned previously on the operating principle of FOC in section 2.2.4.2 Working principle of FOC, to control the motor torque most effectively:
𝐾 𝐼 × 𝑢× 𝑇𝑜𝑟𝑞𝑢𝑒 𝑐𝑦𝑐𝑙𝑖𝑠𝑡 Where: 𝐾 𝐼 = 0.077: The torque constant of the motor
𝐺 is the assistant gain coefficient This e-MTBs is designed with 3 power modes:
• ECO: Motor power = 1/2 × Cyclist’s power
• TOUR: Motor power = 1 × Cyclist’s power
• SPORT: Motor power = 2 × Cyclist’s power
Current controller
For this analysis, the motor electrical characteristics are assumed to be isotropic with respect to the 𝑞 and 𝑑 axes It is assumed that the torque and flux regulators have the same starting value of 𝐾 𝑃 and the same 𝐾 𝐼 value The closed loop system in which the motor phase is modelled using the resistor-inductance equivalent circuit in the
Figure 5.3: The current control system is divided into two blocks
Since block B consists of computational conversion and mainly motor and is locked, the transfer function is expected to have the form of the armature transfer function
Figure 5.4: Block diagram after prediction and reduction
By inserting 𝐾 𝑃 /𝐾 𝐼 = 𝐿/𝑅, it is possible to perform pole-zero cancellation shown below
Figure 5.5: Pole suppression plan in current control
Transfer function after reducing blocks
Using VESC software with detect parameter function (Figure 5.6)
Figure 5.6: Transfer function prediction results in VESC Tool
Typically, the 𝜔 𝐶 = 1500 𝑟𝑎𝑑/𝑠 (closed loop system bandwidth) is set, which is equivalent to 𝑇 𝐶 = 0.00067 𝑠 (time constant) [30] However, design time constant:
𝑇 𝐶 = 0.001(𝑠) is round the number up to get the better sensitivity to the measurement noise instead of the dynamic response
EXPERIMENTAL RESULTS AND EVALUATION
Mechanical processing and assembly
The experimental mechanical section utilizes an earlier actuator model to assess the effectiveness of the control algorithm From a kinematic perspective, there is no difference between the Version 1 and the Version 2 mechanical models
3D printing is an integral part of the mechanical manufacturing Therefore, before sending elements for machining, they need to be printed for a final check (Figure 6.1)
Figure 6.1: Some images about components of the gearbox are 3D printed
After 3D printing and testing to ensure the mechanical system functions correctly, proceed with mechanical processing and assembly (Figure 6.2)
Figure 6.2: Some images after machining and assembly the gearbox
Experimental results indicate that the system functions effectively, but there are two main issues, both addressed in the upgraded Version 2:
• The bearing assembly tolerances are not accurate
• The ring gear is kept from slipping using a cup-point set screw When tightened with significant force, the ring gear deforms into an oval shape
Table 6.1: Compare upgrades in two gearbox versions
Electrical discharge machining → Machining gears using
Shaping method EDM machining does not guarantee the required tolerances
A cup-point set screw → Three pins
A cup-point set screw distorts the shape of the ring gear, causing it to deform
One-row bearing → Two-rows bearing
Changing the bearing type not only helps the gearbox handle the load better but also helps it avoid vibration
None → Oil seals + Waterproof sealant Oil seals are employed at the spindle positions, while water- resistant sealants are utilized at the flanges
The original crankset was fabricated from a laser-cut 4mm aluminum sheet and combined with a freewheel (Figure 6.3)
Figure 6.3: The prototype version of the crankset
Then, instead of using cut-out aluminum sheets, the crankset arm is milled and treated with sandblasting and black anodizing to enhance its aesthetic appeal and durability (Figure 6.4)
Figure 6.4: Version 1 of the crankset with changing to block aluminium
However, a serious problem occurred when the freewheel tooth broke (Figure 6.5) Therefore, in Version 2, the freewheel must be replaced with a one-way bearing to provide better load-bearing capacity and reduce vibration
Figure 6.5: Freewheel damage when going off-road for over 60km
Figure 6.6: The crankset version 2 has replaced the freewheel with the bearing
Table 6.2: Compare upgrades in two crankset versions
Freewheel no teeth → One-way direction bearing
The bearing can withstand loads better and exhibits reduced vibration
The mechanical system version 1 (Figure 6.7) has been fully assembled, providing a foundation for the development of the mechanical system version 2 (Figure 6.8)
The motor holder pieces are machined using the V-bending method with 3mm steel sheets Upon assembling the entire system, the next steps involve circuit design and control algorithm implementation In Version 1, employing 3mm iron sheets and V- bending for motor holder fabrication resulted in significant assembly errors due to machining inaccuracies
Table 6.3: Compare other upgrades in two versions
Steel sheet (3mm), laser - cutting & V -bending machining methods
→ Aluminium sheet (5mm), laser -cutting & milling machining methods The product boasts enhanced aesthetics and improved positioning
Figure 6.7: Several images after whole assembly
Figure 6.8: Several render image of mechanical system Version 2
Moreover, the assembly process also necessitates the enhancement of water resistance for certain components
• ESC: An additional layer of moisture-resistant silicone coating is sprayed onto the components to augment their water resistance (Figure 6.9)
• Torque sensor: An additional layer of shrink film is applied to certain components to provide protection against water ingress (Figure 6.10)
Figure 6.9: Moisture damage, particularly those subjected to significant loads and high temperatures
Figure 6.10: A layer of nylon is applied to the torque sensor to enhance its durability and resistance to moisture
Electronic processing and assembly
With the support of the VIEROBOT company in designing PCB circuits and SMT soldering, a controller board version has been developed for my e-MTB project (Figure 6.11 & 6.12)
Figure 6.12: The PCB circuit after processing
Following the design and overseas ordering of the PCB, it was mounted onto the motor stator The appropriate face angle of the hall effect sensors was then selected, after which glue was poured to insulate them
Figure 6.13: Mounting the PCB into the stator of the motor
The face angle of the hall effect sensor with the rotor is crucial for proper operation Several incorrect configurations have been identified, including:
• Non-parallel sides: When the two sides of the sensor are not parallel, electrical signals may exhibit significant timing differences between high and low pulse levels, leading to signal noise and potential feedback issues (Figure 6.14)
• Wide gap between sides: A wide gap between the sides of the sensor can result in noisy signals and occasional failure to provide feedback (Figure 6.15)
• Hall sensor surface not aligned with magnetic field lines: If the sensor is not positioned correctly along the arc-shaped magnetic field lines, it may fail to detect changes in magnet poles despite being near the rotor
To verify the functionality of the hall sensor, use the "hall_analyze_[current for measure] " command in the VESC tool This command assists in diagnosing whether the hall sensor is operating properly Figure 6.16 exemplifies a usable sensor signal.
Figure 6.14: Sensor signal when they are placed in the wrong face angle
Figure 6.15: Sensor signal when they are far the rotor
Figure 6.16: The usable signal of hall effect sensors
The installation of the temperature sensor is relatively straightforward, with minimal potential for errors It does not necessitate high accuracy, as its primary function is to act as a limit switch to deactivate the motor or ESC (Figure 6.17) in case of overheating An additional layer of shrink film is applied to certain components to provide protection against water ingress (Figure 6.18)
Figure 6.17: Some temperature sensor installation locations
Figure 6.18: Reading the temperature signal
The Bluetooth module was added later to facilitate the logging of bike data, resulting in space constraints within the controller box Despite its simplicity in terms of hardware, the programming of this module presents challenges due to its complexity
Figure 6.19: Some images about installation the Bluetooth module
The linear error observed in measuring pedalling speed may be attributed to suboptimal programming techniques
𝜔 𝑒𝑀𝑇𝐵 ≈ 1.2 ∗ 𝜔 𝑠𝑡𝑒𝑝𝑝𝑒𝑟 Where: 𝜔 𝑒𝑀𝑇𝐵 is cadence speed read by the eMTB
To investigate this, experimental tests were conducted wherein a stepper motor was set to rotate at a constant speed, and the corresponding values obtained from the e- MTB were recorded (Figure 6.20) To rectify this error, a scaling adjustment is necessary to synchronize the cadence speed of the bicycle with the speed specified for the stepper motor
Figure 6.20: The experimental setup for recalibrating the cadence speed
Acknowledging the relative simplicity of the battery-making process, a detailed report on this aspect will be omitted Nonetheless, it's crucial to highlight the significant role the battery plays in the functionality of this e-MTB
Moreover, prior to storing battery cells, it is imperative to balance them to ensure optimal performance (Figure 6.22) Occasionally, the Battery Management System (BMS) may fail to effectively manage the battery, or individual battery cells may become damaged, necessitating the need for rebalancing (Figure 6.23)
Figure 6.22: Balance the battery cells before packaging the battery
Figure 6.23: Balance the battery cells after packaging the battery
Control
The bicycle was positioned on a roller for experimentation purposes The objective of the test was to measure the time constant (𝑇 𝑐 ) by applying a step input (Figure 6.24)
Figure 6.24: Preparation for the current control experiment
Using unit-step inputs, excluding the initial 0A to 8A transition due to the motor not being completely at rest during startup, the smallest measurable settling time observed was 0.029 seconds
The observed settling time deviates from the desired time due to hardware limitations, specifically the fluctuating sampling time (0.02-0.108 seconds), which exceeds the designed settling time Despite this, the system response remains satisfactory, with zero steady-state error and no overshoot.
Figure 6.25:Experiment result with the step inputs (8A to 19A, each step 1A)
An additional experiment was conducted with varying step control currents (0-10A) under identical conditions as the braking motor setup Analysis revealed that the controller maintained stable currents, as intended, with 𝑖 𝑞 at 10A and 𝑖 𝑑 at 0A throughout the experiment.
Figure 6.26: Experiment result with the step input (0A to 10A, one step 10A)
6.3.2 Switch from sensors to sensorless mode in FOC
Since the rotor position sensor at high speeds has a high error and it is not always possible to make it constructively, such applications require the use of sensorless control systems
Measure the no-load motor speed in both sensor (Figure 6.26) and sensorless (Figure 6.27) modes
Figure 6.27: Motor speed work no load at sensor mode
Figure 6.28: Motor speed work no load at sensorless mode
It is evident that in sensorless mode, the motor speed can be higher and more stable, as the installation of hall effect sensors inherently introduces positional errors (Figure 6.29 & 6.30) Therefore, I have established a threshold to transition from sensor to sensorless mode, thereby leveraging the startup benefits of the Hall sensor and the advantages of high-speed operation (during which the required torque is small and stable) (Figure 6.31)
Figure 6.29: Motor speed work on the heavy load at sensorless mode
Figure 6.30: Motor speed work on the heavy load at sensor mode
Figure 6.31: The motor operates under heavy load in sensor mode when the ERPM is below 5000, and transitions to sensorless mode when the ERPM exceeds 5000
With the default observer algorithm in VESC open source, a minor fluctuation is noticed when transitioning between modes This fluctuation can be significantly reduced by refining the precision of the hall sensor settings.
Before experimenting with the VESC tool via mobile, it's imperative to configure the motor settings Additionally, utilize the phone to log bike data along with GPS information The battery's rated voltage of 36V and maximum discharge current of 20A (equating to a power output around 700W), set the maximum power for the motor to 750W and set the continuous current to 30A to ensure the overall device operates within safe temperature limits (Figure 6.32) Concurrently, mode driving is mode TOUR, assist's power will be expected to equal with biker's
Figure 6.32: Setup motor before the pedal-assist experiment
After recording data on the phone, connect it to the computer and utilize the Log Analysis tab in the VESC tool to read and analyse the collected data (Figure 6.33)
Figure 6.33: Logging data at Tour Mode (Blue line: Power of motor; Red line: Measured Torque; Purple Line: Cadence)
To conduct a detailed analysis, extract a brief period from the dataset, specifically from 92.993 seconds to 99.315 seconds of Tour Mode data Initially, identify the peaks in both the cyclist's power and the motor's power to measure the delay time Subsequently, employ the power integration method to calculate the work done by both the pedal and the engine within this time frame
Direct measurement of the motor’s assistance power is not feasible Consequently, it is necessary to measure the total engine power consumption, encompassing both output power and wasted power To address this, the cross-correlation method is employed to determine the similarity between the two graphs This approach focuses solely on comparing correlation rather than gain
• The cross-correlation between Power of Cyclist and Power of Motor in the extract period: 66.97%
• The cross-correlation between Power of Cyclist and Power of Motor in whole time: 70.71%
If we calculate the total work done by the engine and the pedal during the period quoted above, then:
Assuming that the engine efficiency remains constant at max speed and rated torque (Table 3.1) is 72.1%
The measured results exhibit a significant deviation from the calculated results, whereas the desired assistance value is 1.
LOG DATA IN PERIOD FROM 92.993 TO 99.315 SECOND FOR ANALYZING
Power of Cyclist Power of Motor
CONCLUSIONS AND OUTLOOKS
Conclusions
• Reasons for the market need for e-MTBs, particularly e-MTB conversion kits
• Exploration of torque control technologies for e-Bikes
• Proposal and analysis of feasible options, selecting appropriate solutions for a complete conversion kit from MTB to e-MTB
Regarding the mechanical: Two complete versions have been designed (The gearbox, the crankset, the chain transmission):
• Version 1 has been put into practical use, accumulating a total travel distance of 1000 km
(Figure 7.1) and continues to operate stably
• Version 2 is an upgraded iteration of Version 1, featuring enhancements in water resistance, heat dissipation, load-bearing capacity, safety factors, and aesthetics However, due to lack of funding, it remains in the design document stage and has not been implemented
Regarding the electrical: A complete electrical system
(Controller hardware, hall effect sensor module, Bluetooth module, temperature sensors) has been designed, with a working duration similar to that of Version 1, exceeding 1000 km
Regarding control and algorithms: The system can control the engine's power with a correlation with 70% with the control signal
• Assembly of the mechanical and electrical system
• Experimental evaluation of the current controller
• Experimental evaluation of pedal assist capabilities
Regarding the Mechanical: Version 1 has encountered issues such as noise, overheating, lack of water resistance, and significant mechanical processing errors
Figure 7.1: Total distance traveled under assistive mode
However, Version 2 has been designed to address these problems and is anticipated to be deployed and tested soon
Regarding the Electrical: Currently, the electrical system experiences a phenomenon where the chip fails if the power source is hot-plugged into the wire connected to the screen Research indicates that the issue arises from sparks generated by the high voltage source
Regarding Control and Algorithms: The power a pedal assist results have revealed control errors.
Outlooks
Regarding the Electrical Component: Anti-spark ICs are required to enhance system protection
Regarding Control and Algorithms: The power a pedal assist results have revealed high control errors
The significant deviation in power assistance control may be attributed to several factors:
• Using a constant efficiency to calculate output power is inaccurate, as motor output is not a linear function with input power
• The MCU has not been optimized, leading to system lag during both torque signal reading and the control process, since the MCU serves as both the controller and the motor driver
• The power tracking controller is a proportional (P) controller, which simply multiplies the torque value by a gain to obtain the control current value
• There might be a ramp program at the falling edge of the control signal or a deeply embedded filter in the open-source code causing the system to experience delays
To address these control issues, the following solutions can be implemented in sequence:
• Approach 1: Inspect the open-source code for any functions causing delays at the falling edge of the power graph (requires programming skills)
• Approach 2: Streamline the program to improve system performance (requires programming skills)
• Approach 3: Integrate a PID controller instead of the P controller to enhance motor power control (requires programming skills)
• Separate the hardware into distinct controller and driver parts, each with its own MCU (requires electrical hardware skills)
• Design a mechanism to independently measure the engine's output power for control purposes (requires mechanical skills).
[1] J Anable, I Philips and T Chatterton, "E-bikes and their capability to reduce car CO2 emissions," ELSEVIER, vol 116, pp 11-23, February 2022
[2] G Heil, "singletracks," 3 January 2018 [Online] Available: https://www.singletracks.com/uncategorized/beer-definition-mountain-biking/ [Accessed 3 May 2024]
[3] "Mordor Intelligence," [Online] Available: https://www.mordorintelligence.com/industry-reports/e-mountain-bike-market
[4] "E-bike Market SIZE & SHARE ANALYSIS - GROWTH TRENDS &
FORECASTS UP TO 2029 Source: https://www.mordorintelligence.com/industry-reports/e-bike-market," [Online] Available: https://www.mordorintelligence.com/industry-reports/e-bike-market
[5] B Gloross, "LEMMON," 29 November 2023 [Online] Available: https://www.lemmofuture.com/blogs/news/e-bike-vs-normal-bike-mountainbike- entscheidung [Accessed 03 May 2024]
[6] Hollanda Arief Kusuma, Ibnu Kahfi Bachtiar, Tonny Suhendra, Unai Sunardi, Septia Refly, Eka Suswaini, Anton Hekso Yunianto and Agus Salim,
"Experimental Study of Pedelec E-Bike Using Modified Mid Drive," in E3S Web of Conferences 324, MaCiFIC 2021, 2021
[7] C Contò and N Bianchi, "E-Bike Motor Drive: A Review of Configurations and Capabilities," Energies 2023, 2022
[8] "IndieGoGo," Lightest ebike kit: YOUR BIKE WITH SUPERPOWERS, 23 April
2020 [Online] Available: https://www.indiegogo.com/projects/lightest-ebike-kit- your-bike-with-superpowers#/ [Accessed 03 May 2024]
[9] "United Nations," [Online] Available: https://shorturl.at/djAPU [Accessed 03 May 2024]
[10] "The most exciting findings of the biggest eMTB reader survey 2020," 21 November 2020 [Online] Available: https://ebike-mtb.com/en/emtb-reader- survey-2020-findings/ [Accessed 05 May 2024]
Promoting cycling tourism requires official recognition and support from the government The Huế Province People's Committee issued Decision No 1300/QĐ-UBND on June 24, 2021, approving the Cycling Tourism Development Plan in the Huế Province This plan aims to establish cycling routes and rest stops and develop community-based tourism activities Furthermore, the province has collaborated with the Vietnam Cycling Federation to organize cycling events, attracting domestic and international cyclists to the region.
[12] K Duy, "Xe điện thu hút người trẻ sử dụng - Báo Mới," 29 March 2024 [Online] Available: https://baomoi.com/xe-dien-thu-hut-nguoi-tre-su-dung-c48691416.epi [Accessed 03 May 2024]
[13] T Nhạn, "Xe đạp trợ lực điện giá hàng trăm triệu đồng về Việt Nam - VN Express,"
28 April 2021 [Online] Available: https://vnexpress.net/xe-dap-tro-luc-dien-gia- hang-tram-trieu-dong-ve-viet-nam-4269465.html [Accessed 03 May 2024]
[14] M Rogers, "Average Bike Speed Of Various Bikes: The Definitive Guide - Informed Cyclist," 02 June 2023 [Online] Available: https://shorturl.at/djl08 [Accessed 03 May 2024]
[15] F Overton, "THE DIFFERENCE BETWEEN ROAD AND MOUNTAIN BIKE POWER OUTPUT - FASCAT," 31 July 2021 [Online] Available: https://fascatcoaching.com/blogs/training-tips/mountain-bike-power [Accessed
[16] "Trail Grades - Sport Ireland Outdoors," [Online] Available: https://www.sportireland.ie/outdoors/trail-grades
[17] "Electric Bike Motors Explained: Mid-Drive vs Hub - EVOLO ELECTRIC BICYCLES," [Online] Available: https://shorturl.at/krAI5 [Accessed 04 May 2024]
[18] S.-Y Lee, S.-M Lin, X.-Y Tian, W.-Y Cai and B.-S Zeng, "CRANK TREADING TORQUE DETECTION DEVICE FOR ELECTRIC BICYCLE" Unitedd States Patent US 10167049 B2, 1 January 2019
[19] "Battery eBikes - AliExpress," [Online] Available: https://shorturl.at/ejluV
[20] D ROE, "Everything You Want to Know About E-Bike Motors, Explained - Bicycling," 15 April 2022 [Online] Available: https://www.bicycling.com/bikes- gear/a25836248/electric-bike-motor/ [Accessed 04 May 2024]
[21] "Cycling Wattage Calculator - OMNI CALCULATOR," [Online] Available: https://www.omnicalculator.com/sports/cycling-wattage [Accessed 04 May 2024]
[22] K Kakouche, A Oubelaid, S Mezani, D Rekioua and T Rekioua, "Different Control Techniques of Permanent Magnet Synchronous Motor with Fuzzy Logic for Electric Vehicles: Analysis, Modelling, and Comparison," Energies 2023, vol
[23] M S Merzoug and F Naceri, "Comparison of Field-Oriented Control and," World
Academy of Science, Engineering and Technology, vol 2, p 9, 2008
[24] D o E T.-P d 101, Open Loop Low Speed Control for PMSM in High Dynamic Application, 2010
[25] TOYOTA MOTOR CORPORATION - Kazuaki Shingo; Kaoru Kubo; Toshiaki Katsu; Yuji Hata , "Development of Electric Motors for the TOYOTA Hybrid Vehice "PRIUS""
[26] TEXAS INSTRUMENTS - Dave wilson Sr Industrial Systems Engineer
[27] Z Nehr, "WHAT IS THE BEST CYCLING CADENCE? - Mottiv," 04 September
2022 [Online] Available: https://www.mymottiv.com/blog/what-is-the-best- cycling-cadence [Accessed 04 May 2024]
[28] C Trịnh and U V Lê, "TÍNH TOÁN THIẾT KẾ HỆ DẪN ĐỘNG CƠ KHÍ - TẬP MỘT," Nhà xuất bản giáo dục, pp Page 87-88
[29] "Human strength - Roy Mech," [Online] Available: https://shorturl.at/dfuTU [Accessed 08 May 2024]
[30] "USER MANUAL UM1052 - Page 38/178," [Online] Available: https://www.st.com/resource/en/user_manual/um1052-stm32f-pmsm-singledual- foc-sdk-v43-stmicroelectronics.pdf
(MOUNTAIN BIKE) TO e-MTB (ELECTRIC MOUNTAIN BIKE)
- Typically easier to install and integrate into various systems.
- Widely available and come in various sizes and designs Disadvantages:
- Not perform well at very high speed compared to other clutch mechanisms
- Simple and reliable structure, easy to maintain
- Robust and capable of handling significant loads
- Susceptible to wear and tear
- Limited performance at high speeds
Type of gearbox Clutch in Crankset
Option 1: One-way bearing Option 2: Freewheel Option 3: Sparg
- Handle higher loads and torque compared to one-way bearings and freewheel clutches.
- Provide a firm engagement without backlash.
- Typically more durable and can last longer under demanding conditions.
- More expensive due to their complex design and higher manufacturing costs.
- High torque density in a small package.
- Capable of handling high torque and shock loads due to the multiple gears & shafts sharing the load.
- Noisier than some other types of gearboxes, especially at high speeds.
- Complex, high manufacturing and maintenance costs.
- Very high torque in a compact size.
- Long lifespan due to the rolling contact mechanism, which reduces wear.
- Higher friction losses compared to the planetary gearbox.
Option 1: Planetary Option 2: Cycloidal & harmonic Option 3: Spur gear
- Simple design, which makes them easy to manufacture and maintains.
- Less expensive due to the straightforward design.
- Load is concentrated on a few teeth at any given time, which can lead to increased wear and stress.
- Less capable of handling shock loads compared to planetary and cycloidal gearboxes.
- Cost-Effective for high volume.
- The bending process is quick.
- The process produces minimal waste compared to subtractive methods like milling.
- Achieving tight tolerances can be challenging, and the process is less precise compared to milling.
- Very tight tolerances and intricate details, ideal for precision components.
- Capable of producing highly complex shapes and 3D contours, suitable for customized and intricate parts.
- Provides precise control of torque and speed for high-performance applications.
- Ensures smooth motor operation with low torque ripple.
- Operate motors efficiently across a wide range of speeds.
- Implement and requires significant computational resources.
- Needs accurate motor parameters and careful tuning of control loops.
- Highly versatile and adaptable to a wide range of applications.
- Advanced control and tuning options for precise motor control.
- Large and active community with ample resources and support.
- Extensive safety features and telemetry data.
- Complex to set up and configure for beginners.
- Overkill for simple applications where advanced features are not needed.
- Easy to use, ideal for beginners and quick prototyping.
- Arduino compatibility simplifies integration with existing projects.
- Modular and flexible, can be adapted to various hardware setups.
- Focused on accessibility and simplicity.
- Less advanced control features compared to VESC.
- Limited telemetry and safety features.
- Might not be suitable for high-power or highly demanding applications.
- Simpler control strategy due to the direct regulation of flux.
- Can potentially achieve high efficiency by maintaining optimal flux levels.
- Less commonly used and studied compared to FOC and DTC.
- May not provide the same level of torque control precision as FOC.
- Simpler control algorithm compared to FOC.
- Excellent dynamic performance with rapid torque response.
- Less sensitive to parameter variations and can be more robust in certain conditions.
- Higher torque ripple compared to FOC.
- May produce more switching noise due to the frequent changes in voltage vectors.
- While robust, it may not provide as smooth control as FOC in steady-state conditions.
- Not affected by electromagnetic interference.
- Very precise and sensitive measurements
- More expensive than electrical strain gauges.
- Do not require physical contact with the rotating components
- Less susceptible to mechanical wear and environmental factors Disadvantages:
- May have limitations in terms of the range of torque that can be accurately measured.
- May have limitations in terms of the range of torque that can be accurately measured.
Option 4: Optical Option 5: Magnetic field strength
- No physical contact means less wear and tear, leading to longer sensor life.
- Less prone to mechanical failure due to the absence of physical connections.
- Susceptible to electromagnetic interference (EMI) which can affect accuracy.
- Less expensive than contactless systems.
- Slip rings are subject to mechanical wear and can degrade over time.
- Requires regular maintenance to ensure accurate readings and longevity.
Option 1: Contactless strain gauge Option 2: Slipring strain gauge Option 3: Indirect strain gauge
- Can be placed in areas where direct strain measurement is not possible.
- Often less expensive than direct measurement systems.
- Less accurate than direct measurement methods due to the indirect nature.
- Susceptible to errors from external influences.
Weight One-way bearing Freewheel Sprag
EVALUATION TABLE: CLUTCH IN GEARBOX
Weight One-way bearing Freewheel Sprag
EVALUATION TABLE: CLUTCH IN CRANKSET
EVALUATION TABLE: CONTROL TORQUE METHOD
EVALUATION TABLE: TYPE OF TORQUE SENSOR
Contactless strain gauge Slipring strain gauge Indirect strain gauge Optical Magnetic field strength
Ease to Program Deep Embedded
EVALUATION TABLE: TYPE OF GEARBOX
Cycloidal/harmonic gearbox Spur gear
Working principle is designed Machining planetary gearbox Gearbox' Clutch: Sprag 30Nm Crankset' Clutch: Oneway Bearing CSK45PP Motor Holder Machining: Milling Aluminum Battery Case: Aluminum Bottle FOC control & Controller Hardware: VESC Motor Ryobi RY18LMX40A Bluetooth Module NRF52832 Rotor Position Sensor: Hall effect sensor A3144EUA Display SW102
Full Name Signature Date Amount Volume Scale
DESIGN CONVERSION MID-DRIVE MOTOR KIT FOR MTB (MOUNTAIN BIKE) TO e-MTB (ELECTRIC MOUNTAIN BIKE)
L Thanh Nhat Sheet: 01 Total sheet: 07
- Working in Off-Road conditions.
- The type is pedal assist e-MTB.
- Select mechanical solutions that are suitable for the Off-road conditions.
- Select electronics and electrical equipment to ensure the stable operation, efficiency.
- Select control algorithm options suitable for torque control.
Too large to implement into theBottom bracket
Full Name Signature Date Amount Volume Scale
Ultra Low-Profile Hex Socket Head Screw Screws M5x10
Screw M4x10 Button Head Hex Drive Screws
Cup-Point Set Screw Screws M2.5x5 1
SKF Company Supplier Misumi Company Supplier
Cup-Point Set Screw Screws M5x6
Motor Left Holder Steel 3mm sheet, EDM & V-Bend Machining
Alloy Steel Socket Head Screws Screws M6x20
Motor Right Holder Steel 3mm sheet, EDM & V-Bend Machining
Screw M4x80 Alloy Steel Socket Head Screws
Bearing 6003RS SKF Company Supplier
Ring Gear Steel C45 Heat Treatment
Inner Retaining Ring ∅22 Misumi Company Supplier
One-way Clutch Vierobot Company Supplier
Inner Retaining Ring ∅35 Misumi Company Supplier
Bearing 6202RS SKF Company Supplier
Sun Sear Steel C45 Heat Treatment
Outer Retaining Ring ∅15 Misumi Company Supplier
Ultra Low-Profile Hex Socket Head Screw Screws M5x10 1
1 The standard applied in the design is TCVN 1992:2009
2 The Housing Gearbox and The Motor Front Housing need a waterproof-silicone layer before assembling
3 The bearings are lubricated with the lithium grease
4 The inner gearbox are filled 2/3 space with the lubricant grease oil
DESIGN CONVERSION MID-DRIVE MOTOR KIT FOR MTB (MOUNTAIN BIKE) TO e-MTB (ELECTRIC MOUNTAIN BIKE)
Full Name Signature Date Amount Volume Scale
DESIGN CONVERSION MID-DRIVE MOTOR KIT FOR MTB (MOUNTAIN BIKE) TO e-MTB (ELECTRIC MOUNTAIN BIKE)
Ultra Low-Profile Hex Socket Head Screw Screws M5x10 6
Cup-Point Set Screw Screws M5x6
Hex Socket Head Screw Screws M5x25
Cup-Point Set Screw Screws M3x6 1
Spring Loaded Rotary Load Shaft Seal 1 Wiper Lip
Ultra Low-Profile Hex Socket Head Screw Screws M5x10 Aluminum 5mm Sheet, EDM
1 The standard applied in the design is TCVN 1992:2009
2 The Housing Gearbox and The Motor Front Housing need a waterproof-silicone layer before assembling
3 The taper pin ∅3x20mm is reference direction for The Heatsink and The Motor Front Housing assembly
4 The bearings are lubricated with the lithium grease
5 The inner gearbox are filled 2/3 space with the lubricant grease oil
SKF Company Supplier SKF Company Supplier
Misumi Company Supplier Misumi Company Supplier Misumi Company Supplier
Hex Socket Head Screw Screws M5x70
Ultra Low-Profile Hex Socket Head Screw Screws M5x25
Full Name Signature Date Amount Volume Scale
DESIGN CONVERSION MID-DRIVE MOTOR KIT FOR MTB (MOUNTAIN BIKE) TO e-MTB (ELECTRIC MOUNTAIN BIKE)
DISP_TX DISP_RX CAN_H CAN_L
HEAD_LIGHT TAIL_LIGHT BREAK_LIGHT
VIN VOUT SYS_EN CURR_SENS
CURR_A CURR_B CURR_C CURR_FILTER
BRAKE THROTTLE DISP_UART_RX
VOLT_SENS VOLT1 DISP_UART_TX
SPI1_SCK SPI1_MOSI SPI1_MISO
HALL & TEMP Connector IO Connector CAN Connector TAIL_LIGHT Connector
Voltage supply (0-60V) Needs external decoupling caps to avoid high voltage transients of the battery wiring while switching the FETs
Also critical for EMI/RF compliance
Connect signal ground and power ground in one place only
PWR_FLAG PWR_FLAG PWR_FLAG
PWR_FLAG PWR_FLAG PWR_FLAG PWR_FLAG PWR_FLAG
ESC-HARDWARE is divided into internal blocks on board:
ESC-HARDWARE has eleven external connectors on board:
HALL EFFECT SENSOR MODULE (External Module) BLUETOOTH MODULE (External Module) Two external modules combine with ESC-HARDWARE
- HALL EFFECT SENSOR MODULE: Placed in the motor and has a suitable mounting position
- BLUETOOTH MODULE: Placed anywhere ensuring waterproof conditions
Components available on the market combine with ESC-HARDWARE:
- FRONT LIGHT (Many different types)
- REAR LIGHT (Many different types)
INPUT_FLAG OUTPUT_FLAG BIDIRECTIONAL_FLAG PASSIVE_FLAG
PA0 (ADC123_INO/WKUP) PA1 (ADC123_IN1) PA2 (ADC123_IN2) PA3 (ADC123_IN3) PA4 (ADC123_IN4) PA5 (ADC123_IN5) PA6 (ADC123_IN6) PA7 (ADC123_IN7) PA8
PA9 (OTG_FS_VBUS) PA10
PB0 (ADC12_IN8) PB1 (ADC12_IN9) PB5
PB7 PB8 PB9 PB10 PB11 PB12 PB13 (OTG_HS_VBUS) PB14
PC0 (ADC12_IN10) PC1 (ADC12_IN11) PC2 (ADC12_IN12) PC3 (ADC12_IN13) PC4 (ADC12_IN14) PC5 (ADC12_IN15)
PC11 PC10 PC9 PC8 PC7 PC6
PC14-OSC32_IN PC15-OSC32_OUT
PH0-OSC_IN PH1-OSC_IN
PA13(JTMS-SWDIO) PA14(JTMS-SWCLK)
PA15(JTDI) PB13(JTDO/TRACESWO)
VOLT1 VOLT2 VOLT3 ADC_TEMP CURR_SENS
TORQUE_IN THROTTLE EN_GATE nFAULT CAN_RX CAN_TX SCL SDA DC_CAL L1 L2 L3
SENS1 SENS2 SENS3 VOLT_SENS MOTOR_TEMP
DISP_UART_RX TORQUE_SPEED2 CURR_FILTER
DISP_UART_TX SPEED_SENS
SWDIO SWCLK DBG_LED_R DBG_LED_G
Bypass, place next to VDD pins
Bottom MOSFETs Temperature Sensor Top MOSFETs Temperature Sensor
FILTER BLOCK NTC TEMP BLOCK
Use channel B of Op-Amp in Torque Measure
DISP_TX -BATT DISP_KP DISP_PWR
Display Power Supply Power Key Output
Full Name Signature Date Amount Volume Scale
DESIGN CONVERSION MID-DRIVE MOTOR KIT FOR MTB (MOUNTAIN BIKE) TO e-MTB (ELECTRIC MOUNTAIN BIKE)
ON/OFF MC74VHC1GT66
ON/OFF MC74VHC1GT66
ON/OFF MC74VHC1GT66
RT_CLK is the clock input, COMP is the voltage comparator, VSENSE is the voltage sense, PWRGD is the power good, OCTW is the output driver, FAULT is the fault indicator, DTC is the diagnostic output, M_PWM is the main PWM output, M_OC is the main overcurrent output, GAIN is the gain setting, OC_ADJ is the overcurrent adjust, DC_CAL is the duty cycle calibration, GVDD is the gate drive supply, CP1 and CP2 are the compensation capacitors, EN_GATE is the enable gate, INH_A, B, C are the inhibit inputs, INL_A, B, C are the inhibit latches, DVDD is the digital supply, REF is the reference voltage, SO1 and SO2 are the status outputs, AVDD is the analog supply, and AGND is the analog ground.
SS_TR EN_BUCK PVDD2 PVDD2 BST_BK PH PH BIAS BST_A GH_A SH_A GL_A SL_A BST_B GH_B SH_B GL_B SL_B BST_C GH_C SH_C GL_C SL_C SN1 SP1 SN2 SP2 PVDD1
Dead-time adj Required 6PWMs Disable Cur Protect
MCU must sense the voltage at each phase
3.3V regulator for the logic MCU
Time constant(T) Determined by Cts & Rts
Inrush current protection Anti-spark when power is plugged
Full Name Signature Date Amount Volume Scale
DESIGN CONVERSION MID-DRIVE MOTOR KIT FOR MTB (MOUNTAIN BIKE) TO e-MTB (ELECTRIC MOUNTAIN BIKE)