THE CONCEPTUAL DESIGN

OFAN ELECTRIC BIKE

Edited by

Ilbey KarakurtMurat Cam

Selcuk Oguz ErbilMehmet Kelleci

Ihsan Dogramacı BilkentUniversity

Contents

1 Regenerative Braking System 11.1 Theory of Regenerative Breaking Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Limitations in Usage of Regenerative Braking System . . . . . . . . . . . . . . . . . . . . . . 11.3 Applicability of Regenerative Breaking Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Advantages of Regenerative Breaking Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Introduction and General Overview of Current Electric Bikes 3

3 Motor Systems 63.1 Friction Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.2 Hub Drive Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.3 Mild Drive Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4 Transmission Systems 9

5 The Design 105.1 The Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.1.1 Types of Electric Bike Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105.1.2 Specifying Electric Bike Battery Capacity . . . . . . . . . . . . . . . . . . . . . . . . . 115.1.3 Choosing a Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.2 Motor and Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125.2.1 Motor Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5.3 Frame Material and Fork Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145.3.1 Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145.3.2 Aluminum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155.3.3 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155.3.4 Carbon Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6 Discussion and Conclusion 16

7 Appendix 17

1 Regenerative Braking System

Slowing down a vehicle is actualized with dissipating kinetic energy. In traditional dynamic braking systems,the kinetic energy of the vehicle is dissipated to heat with while hitting the brakes and results in losing theenergy. Whenever the brakes are hit, the kinetic energy of the vehicle is lost without having the advantageof the energy. In newer products such as hybrid cars and electrical bikes regenerative braking systems(RBS)are applied as an alternative. The main idea behind the regeneration is to store the kinetic energy whileslowing down, instead of dissipating it as heat to the environment.

1.1 Theory of Regenerative Breaking Systems

In RBS, there needs to be an electric motor to propel the vehicle. During normal operation motor usesstored electricity to propel the vehicle. When the acceleration pedal is released, motor is rotated in thereversed direction by the momentum of the vehicle. The present momentum of the car rotates the motor inthe reversed direction and while the momentum and kinetic energy of the car decreases the storage of energyis increased. During rotating in the reversed direction motor acts as a electric generator.Energy storage isactualized by conversion of mechanical energy into electrical energy. To achieve it, there needs to be numberof capacitors(according to the mass of the vehicle) that will store the energy for later use, accumulators orbatteries can be used.

While the most popular usage is to store mechanical energy in to electrical energy, in hydraulic regener-ative braking systems when the brake pedal is hit, kinetic energy is used power a reversible pump. As theslowing down process continues, reversible pump sends hydraulic fluid from a low pressure accumulator toa high pressure accumulator. Fluid remains in the space before nitrogen gas occupation, thereafter, driverreleases the brake pedal, fluid comes out from the high pressure accumulator to the low pressure accumulatorso that gives acceleration the vehicle again. In this application energy usage efficiency may reach up to 80percent.

In conclusion regenerative breaking systems are still under development. RBS can be applied in twomethods. One is with electric motors used widely in bicycles and under development for commercial cars,other is with hydraulic pressure which is still not available for any commercial vehicle.

1.2 Limitations in Usage of Regenerative Braking System

Usage of RBS can’t eliminate the traditional dynamic brakes. In the case of instant brake necessitates thedynamic brakes.

Propeller motor may not be connected to both tires. In the case of connecting the motor to one tire,only one RBS can be planted. For a more effective braking, there needs to be a dynamic brake.

Apart from stated reasons, for the usage of RBS, the capacitors, accumulators or batteries that are usedto store energy for later use should not be full. If they are full, motor can not rotate in the reverse direction,therefore, nor storage of energy neither decrement in the kinetic energy and linear momentum is actualized.So that, system should include dynamic brakes for all cases.

Efficiency of regenerative brakes at low speeds is not preferable. Therefore, additional braking is neededfor a complete halt.

For stated requirements, the bike will be designed shall have both RBS and traditional dynamic brakes.RBS will be active for all braking situations, for emergency brakes and complete halt on inclined roadstraditional dynamic brakes will be active.

1.3 Applicability of Regenerative Breaking Systems

RBS can be applied for mild-hybrid(Electric motor for propelling in addition to internal combustion engine)and pure-hybrid(Only electric motor for propelling) commercial cars. And easiest application is on the bikes.To illustrate the easiness of the application of RBS to a bike, following example is given. To add a RBS

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to a traditional bike, all should be done is just to have 2 brushed dc motors will be attached to the placesof dynamic brakes. Dynamic brakes will not be completely removed in the case of needing instant brake.Cables carrying electrical current will be drawn from the motor to wherever that electrical energy is needed.For instance, that energy can be sent to electrical accumulators for later use, or simply just sent to led lightsin front or behind bicycle for illumination.So that, in this system, as the driver hit the brakes, brushed dcmotors will contact the tires and start to rotate, and motors will behave as electric generators. For depictionof the system, please examine figure 1.

(a) Side View (b) Front Viev

Figure 1: Simple Application of RBS to a Traditional Bike

Most widely application of RBS today is on bikes. Commercial car manufacturers interest in shortdistance transportation. BMW, and Bosch Automotive Technologies do significant work on this system.For instance, as a remarkable step, Audi bought the bicycle manufacturer Ducati to get in to the market,make use of the distribution channels of Ducati. With skilled and experienced engineers, Audi produced afuturistic electric bike.(See figure 2)

Figure 2: An Electric Bike From Audi

In the project of the student working group, the RBS system and its related motor will not be a newdesign. Instead of designing, the manufactured ready to sell products will be bought and used. Sinceapplication of the RBS to a traditional bike is not hard, in this way, project will be completed in a shorter

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time period and will be economically more efficient. RBS systems in bikes comes with the motor kit thatis chosen for the bike. Therefore, more detailed information about the prices and technical specifications ofRBS is given with the motor inspection part of the report.

1.4 Advantages of Regenerative Breaking Systems

With applying RBS there can be up to 25% energy saving which will decrease the user effort. With theenergy savings from RBS, system can reduce the user effort by activating itself while climbing an inclineand can provide comfortable riding on downhills. Apart from road conditions, RBS can provide user ridingwithout pedaling on straight trajectories.

Either internal combustion or electrical engines, the range can a vehicle go is limited. In RBS, sincebraking pedal does not just dissipate kinetic energy as heat to the environment but collecting electricityfrom it for later use, it increases the range of the vehicle.

CO2 emission with electrically supported vehicles are much less than internal combustion motored vehi-cles. Therefore, with these systems environment is not damaged, and it is easy to be stay within the limitsof European Emission Standards.

2 Introduction and General Overview of Current Electric Bikes

There are many electric bikes or in short e-bikes being manufactured and ridden in many countries. Themain and most important components of these bikes are as follows: (1) the electric motor, (2) the chassis,(3) the batteries. Although there are many other parts that are needed the build the bike like seats andtires, the parts listed above are what makes e-bikes differ from normal bikes. The electric motor is whatgives the ability for the bike its ability to reach high speeds and for it to help the rider climb hills with ease.The chassis also differs from normal bikes since weight reduction is important for these bikes. The electricmotor and batteries weigh quite a bit and since the only option to reduce weight via the electric motor andbatteries is to use smaller ones the main option for weight reduction becomes making the chassis lighter.The most intriguing part that sets the e-bikes apart from their normal counterparts are the batteries thatare used to power the electric motor, all the sensors (torque and speed), and the display units. The batteriesare also the heaviest and the most space taking part in the list given above. Another important thing tonote shortly here is that the batteries determine, together with the motor used, the range the e-bike cantravel.

While selecting all the necessary parts that will be used in the assembly of an electric bike one has toconsider its most probable customers and where these people will mainly use them. Currently people aremanufacturing all sorts of e-bikes. Some manufactured e-bikes can reach speeds up to 100 km/h but have ashort range while others average 20 km/h having a much higher range. Mountain bikes, speed bikes usingelectric motors generally use motors with high power output thus reducing the life of the battery. Bikesmade for rural use however have motors having a power output of 200-300 Watts which enable the rider touse the batteries for a longer time.

In this report some e-bikes will be presented representing each class (mountain bike/speed/race bike,and normal purpose bike) first which will give an idea about what kind of designs there are in the marketcurrently. Then each important part will be explained in detail and a design using the selected parts will bepresented in detail giving information about specific dealers/companies supplying the parts and assemblyinformation will also be given briefly.

First 3 different bikes will be represented in as much detail as possible to give an idea about what kindof e-bikes are being manufactured throughout the world.

1-) M55The M55 is one of the most expensive e-bikes money can buy with a price tag of around 40,000 dollars.

The motor used on this e-bike has a power output of 2.2 kW and uses a Rohloff gear hub for transmission.For more information about the Rohloff gear hub.read the detailed explanation of the motor systems. Speeds

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of 40 50 mph can be expected from this motor and drive system duo. When compared to other e-bikes onthis scale such as the Audi Electric Bike, this system is better in terms of performance due to the Rohloffgear hub which is basically a 14 speed gear box compared to the Audis standard bicycle derailleur system.It also uses similar to other high-end bikes a 17 Ah 48V LiPo battery. It has a mainly carbon fiber chassiswith full suspension (front and middle) Also with its lightweight chassis made out of part carbon fiber andpart aluminum for the extra finish it offers both performance and style.

2-) BlacktrailThe blacktrail is currently the most expensive e-bike that is being manufactured with a price-tag of

80,000 dollars. It uses 17-Ah 48V LiFePO4 battery, a clean mobile drive system, and a carbon fiber chassiswith no suspension. It is the result of the collaborative of 3 German companies: PG bikes, Clean Mobile,UB Composites. The clean mobile drive system used on most e-bikes allows the rider and the motor systemto share the same pedal gears which gives a huge advantage in efficiency and performance. Although in thecase of the blacktrail the bike only has a single speed most other bikes use multiple speed gears just like incommon bikes.

The clean mobile system shown in the figure above shows the system on a PG bike like the blacktrail

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giving an idea about the drive system in question and examplifying how the system in question works. Theblacktrail uses many different types of motors depending on the customer however it was announced byPG bikes that the motors can range from a 30 MPH 1.2kW motor to a 65 MPH 3.5kW motor. Anotherimportant aspect of the blacktrail is its choice of material. The blacktrail uses carbon fiber frame and rims.Although people are accustomed to carbon fiber frames the use of carbon fiber rims is becoming more andmore common.

3-) QWC UrbanThis e-bike is rather different from the other two presented above. The main difference is that it does

not offer incredible speeds but it does offer comfort and range. This model is an example of normal bikesthat can be easily used daily for normal use. The range of this model is 120 km with a fully charged Li-ionbattery. It uses Shimano Nexus 7 in terms of gears and excluding the battery it weighs approximately 24kg. The charging time of this model is 35 hours. Unlike most models this model uses two hub-drive motorsto balance the weight distribution and offers better performance.

The three examples given above were given to demonstrate what e-bikes can accomplish. Some e-bikesare made for short distances like the M55 and some like the qwick are made for touring in the city atreasonable speeds. In the following sections detailed information will be provided on different motor systemsand transmission systems widely used in e-bikes.

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3 Motor Systems

3.1 Friction Drive

A Friction-Drive (FD) is an electric bike drive system that spins a roller thats pressed against the bicyclestire. FDs have been around for over 100 years. The main idea is that the roller which is pressed againstthe tire rotates at such an angular speed that the friction between the tire and roller allow them to movetogether making it possible for the roller to rotate the tire. A concern that some manufacturers have aboutan FD is that in wet weather, the roller might slip due to rain making the friction between the tire and theroller smaller than necessary. Although friction drive systems are not that popular and efficient in terms ofperformance they are more practical than the hub-drive or the mid-drive motors. The ease of installation ofsuch systems makes it quite useful for people in a hurry.

There are limitations to how much power that can be put through a friction drive, because accelerationis dependent on the roller keeping a solid contact with a small patch of the tire. Increasing the peak powerof your drive by a little too much may result in the roller simply spinning-out. However moderate speeds (10MPH) can be achieved by using FDs for minimal amounts of cash compared to other drives. Also the rangeon such systems is much more than other drives since the power needed to drive such systems at moderatespeeds is lower compared to other systems. The need for less power makes it possible to a few alternativedesigns with these systems: one could make the batteries smaller reducing overall weight and making iteasier to pedal when necessary, or one could keep the battery constant thus increasing the range of the bike.An example for such a system was found to be as follows:

• $350 (Aus) Eboost drive system, seat post mount with space for one LiPo battery pack

• $60, 170-kV Aeolian RC motor / 22V, 25-MPH

• $140 Phoenix ICE-100 controller

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• $45 LiPo battery 22V / 5-Ah

• $80 power supply and charger for 6S LiPo

• $ 30 Magura throttle and a $125 Cycle Analyst-V2.24

3.2 Hub Drive Motors

The wheel hub motor (also called wheel motor, wheel hub drive, hub motor or in-wheel motor) is an electricmotor that is incorporated into the hub of a wheel and drives it directly. Hub motor electromagnetic fieldsare supplied to the stationary windings of the motor. The outer part of the motor follows, or tries to follow,those fields, turning the attached wheel. In a brushed motor, energy is transferred by brushes contacting therotating shaft of the motor. Energy is transferred in a brushless motor electronically, eliminating physicalcontact between stationary and moving parts. Although brushless motor technology is more expensive, mostare more efficient and longer-lasting than brushed motor systems. Electric motors have their greatest torqueat startup, making them ideal for vehicles as they need the most torque at startup too. The idea of ”revvingup” so common with internal combustion engines is unnecessary with electric motors. Their greatest torqueoccurs as the rotor first begins to turn, which is why electric motors do not require a transmission. A gear-down arrangement may be needed, but unlike in a transmission normally paired with a combustion engine,no shifting is needed for electric motors. Wheel hub motors are increasingly common on electric bikes andelectric scooters in some parts of the world, especially Asia. The hub drives are used by attaching thesemotors to the solid frame of the bike and connecting the motors outer shell to the tire. There are, as withall systems, advantages and disadvantages to these systems. The advantages can be listed as follows:

• Hub motors are produced in massive numbers in China, making them affordable.

• Hub motors are simple to install.

• Hub motors are easy to swap out if blown or worn out.

• Hub motors are easy to upgrade, and re-sell.

• Hub motors are readily available.

• Hub motors have few moving parts.

• Hub motors are fairly reliable.

• Hub motors are fairly stealthy in their appearance and near-silent operation.Disadvantages

• Hub motors are unsprang weight in the wheel.

• Hub motors can snap dropouts.

• Direct-Drive hub motors have drag when unpowered, making the bike feel sluggish to pedal.

• Hub motors are not as efficient as a non-hub.

• Hub motors are not great mountain climbers.

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• Hub motors can be heavy.

• Hub motors make it much harder to change a flat tire.

• Hub motors disrupt the balance of a bike towards the front or back unless there is a motor on each tire.

By examining the lists given above it can be seen that compared to other motors the hub drives get thejob done at low cost and can be implemented to all frames and do not require much maintenance. Also theyare not affected by weather conditions.

Some brand name Hub motors used in the electric bike industry are as follows:• BMC V2, V3, V4: High end geared hub motors. 600w over-volting capacity to 2500 watts. The BMC

is a larger (8lb) geared hub motor, designed to be more efficient and have a better power-to-weight ratiothan a gearless (direct-drive) motor. Price between 378$ - 648$.

• MAC Motor: (BMC clone) Very similar to the BMC but not as high quality, so cannot withstand highpower and have the same reliability as the BMC. Price 250$

• Dapu Hub Motor: a new hub motor used on production bikes such as the Neo Jumper and City Com-muter. It is small, wide, and puts out a maximum of 750 watts. Price between 280-350$

• Crystalyte ( HS35 / HT35): A recently released direct drive motor weighing in at 16 pounds. Kit priceapproximately 640$

• Cute Motor: a small planetary geared motor. 5 lbs, and capable of running 800 watts. Around 20MPH top speed on a cute powered E-bike. Price approximately 85 $

• 9-Continents (9C): A gearless brushless motor weighing in around 15 pounds and capable of puttingout serious power when over-volted. A reliable and solid motor

• BionX: A sleek system, but expensive and made from all proprietary components, making it hard toupgrade controller or battery. Comes in 250, 350, and 500 watt configurations. Also comes as a kit withregenerative breaking at a price of 1800$ including all sensors and motor needed as well as the display screen.

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3.3 Mild Drive Motors

Some of the most refined electric bikes on the market are mid drives. Mid drives are not the easiest or thecheapest electric bikes to build, but the performance of these bikes cannot be rivaled by hub drives or FDdrives. The mid-drive allows the use of the bikes transmission as the motors gears, also the position of themotor enables good weight distribution making it better to handle. The efficiency of these motors make it sothat by using less battery power one can go more. As with the hub drive there are benefits and drawbacksto the mid-drive motors as well.

Benefits can be listed as follows:1. Climbs steep hills better than a hub motor.

2. Places the weight of the motor low and centralized in the frame which means a better balanced feel.

3. The motor can use the bikes gears, so the RPMs stay up in its efficient range which implies morerange per battery-Ah.

4. Keeping the motor in its best RPM range means lower peak-amps drawn from the battery.

5. Giving the motor some gears to use also means you can get a broader range of performance from asmaller and lighter motor.

6. Easy to change a flat tire.

7. No broken spokes from hitting a pothole with a heavy hub motor in the wheel.

Drawbacks are :

1. Often more expensive than a simple hub-motor.

2. Some mid-drive motors are noisier than a hub-drive motor

3. Mid-drive kits are more complex to install than a simple hub-drive motor.

4. Shifting a mid-drive electric bike can be hard. With a hub motor bike, the only reason to use gearsis to get the right pedal cadence which usually means just staying in high gear.

5. Mid drives are generally not as well suited for flat land street commuting as hub motor bikes.

6. Mid drives are not as stealthy as most hub motor bikes.

7. Mid drives have more moving parts and therefore tend to be less reliable than most hub motor kitsand require more maintenance when compared to hub-drive motor kits.

8. implementation of regenerative breaking is harder when compared to a hub-drive motor.

4 Transmission Systems

3) Transmission Systems In this section the report will focus on the Rohloff transmission. The Speedhub isan internally geared hub (IGH) with 14 gears spaced evenly at 13.6 % resulting in 526% total gear rangeroughly the same range as a standard MTB 27-speed drive train. By following extremely low tolerancesand keeping the system completely enclosed Rohloff claims to have comparable power loss by friction to an

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externally geared system (derailleurs) and will run virtually forever with minimal servicing (only an annualoil change). The biggest downside to this system is that it is expensive. With a Rohloff equipped bikeyou can ride through anything and not worry about even cleaning the driveline when you are finished. theRohloff is made to last with only routine oil changes (the internal gears are in an oil bath), and there aremany cases of hard core cyclist riding Rohloffs tens of thousands of miles. The Rohloff has a lot of otheradvantages other than just its rugged dependability. It gives you a straight chain line, so chain maintenancebecomes less critical. The Rohloff allows you to shift from a dead stop without any force on the pedals, andto shift while riding you need to let the pressure off the pedals and then shift. All Rohloffs come with aproprietary twist shift gear. The electric bicycle rider is usually familiar with the concept of the twist grip(throttle) so a twist grip shifter should be a welcomed tool as opposed to dual lever shifters on conventionalbikes which can be confusing. There are two ways to use this system: mid-drive or front hub-drive andRohloff at the back wheel.

5 The Design

5.1 The Batteries

5.1.1 Types of Electric Bike Batteries

Electric bike needs a battery to provide power. Battery is a device consisting of one or more electrochemicalcells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal calledcathode, and a negative terminal called anode. Electrolytes allow ions to move between the electrodes andterminals, which allows current to flow out of the battery to perform work. There are different types ofelectric bike batteries to use. Nickel Cadmium (NiCd), Nickel-Metal Hydride (NiMH), Sealed Lead Acid(SLA), Lithium Ion (Li ion), The Nickel Cadmium (NiCd) battery, Lithium Ion Polymer (Li ion polymer)can be ordered as electric bike batteries.

Sealed Lead Acid: One of the first types of electric bike batteries is the sealed lead acid design. Thesebatteries are very cheap and easy to recycle. They also don’t require a lot of maintenance. However, theseelectric bike batteries are very sensitive to abuse. They also have a limited lifespan, so they will eventuallydie. These batteries are also one of the heaviest designs

Nickel Metal: One of the next types of batteries is the nickel metal hydride variety. These electricbike batteries are lightweight and can be charged faster than some other types. These batteries also have areduced toxicity so they are easier to dispose of safely. The main disadvantage of these electric bike batteriesis that cold weather causes them to perform poorly. It will be also had to discharge them periodically.

Lithium Ion: There are also lithium ion batteries that bike can use to power . These electric bikebatteries are very lightweight and require no maintenance. They also have a longer lifespan. However, theseelectric bike batteries are more expensive. You will also have to be careful when charging and dischargingthese batteries or the cells may become damaged.

Nickel Cadmium: One of the next types of electric bike batteries is the nickel cadmium variety. Thesebatteries usually last longer than other types. They also have more capacity. The main problem with theseelectric bike batteries is that the cadmium is very harmful and difficult to recycle. They are also expensive.

Lithium Polymer: One of the final types of electric bike batteries is the lithium polymer design. Thesebatteries are safer to use when compared to lithium ion batteries. They are also one of the lightest electricbike batteries that can be bought. However, they are also the most expensive. Also, these batteries haveonly been tested in the laboratory instead of real world applications.

When buying an electric bike today there are only two common types of battery chemistry. Lead acid,

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which is the older, heavier, dirtier and cheaper option; and lithium ion, which is the newer, lighter, far longerlasting and efficient, and more expensive option. The vast majority of new electric bicycles are equippedwith lithium ion batteries. Lead acid batteries typically fail after 100 to 300 charges, and during this timetheir max capacity falls very quickly. Lithium ion cells last far longer on the other hand, usually lasting tobetween 700 to over 1000 charges before dropping below it half capacity. They have next to no memoryeffect, meaning that people can partially charge them without issue and their natural discharge over timedoesnt create the problems which are experienced with older chemistry types such as lead acid. They areextremely light in comparison to other batteries which is ideal for electric bikes, and they also carry a largecharge so people can travel further on a single charge. The biggest drawback with the technology is that it isexpensive and is likely the most costly component of any electricbike. The cost is not so important for thisconceptual design therefore the most common and efficient Lithium ion batteries will be used the reasonswill be explained next part.

Lithium ron Phosphate (LiFePO4) Battery: The lithium iron phosphate (LiFePO4)battery, alsocalled LFP battery. LiFePO4 batteries have lower energy density than the more common LiCoO2 designfound in consumer electronics, but offers longer lifetimes, better power density and are inherently safer.The LiFePO4 battery uses a lithium ion derived chemistry and shares many advantages and disadvantageswith other Lithium-ion battery chemistries. However, there are significant differences.LFP chemistry offersa longer cycle life than other lithium ion approaches. Like nickel based rechargeable batteries and unlikeother lithium ion batteries, LiFePO4 batteries have a very constant discharge voltage. Voltage stays duringdischarge until the battery is exhausted. This allows the battery to deliver virtually full power until it isdischarged. And it can greatly simplify or even eliminate the need for voltage regulation circuitry. And, alongwith the good safety characteristics of LFP batteries, this makes LFP a good potential replacement for lead-acid batteries in many applications. The use of phosphates avoids cobalt’s cost and environmental damage,particularly concerns about cobalt entering the environment through improper disposal. LiFePO4has highercurrent or peak-power ratings than LiCoO2. The energy density of a new LFP battery is some 14% lowerthan that of a new LiCoO2 battery. Also, many brands of LFPs, as well as cells within a given brand ofLFP batteries, have a lower discharge rate than lead-acid or LiCoO2. Since discharge rate is a percentageof battery capacity a higher rate can be achieved by using a larger battery if low current batteries mustbe used. Better yet, a high current LFP cell which will have a higher discharge rate than a lead acid orLiCoO2 battery of the same capacity can be used.LiFePO4 cells experience a slower rate of capacity lossgreater calendar-life than lithium-ion battery chemistries such as LiCoO2 cobalt or LiMn2O4 manganesespinel lithium-ion polymer batteries or lithium-ion batteries. After one year on the shelf, a LiFePO4 celltypically has approximately the same energy density as a LiCoO2 Li-ion cell, because of LFP’s slower declineof energy density. Thereafter, LiFePO4 likely has a higher density.

5.1.2 Specifying Electric Bike Battery Capacity

When choosing electric bike battery or browsing the battery capacity on an ebike The first thing whenthinking of purchasing, there are generally two figures provided which describe the capacity; Voltage (V),and Amp hours (Ah). Both of these contribute to the overall capacity of the battery, so higher voltage ora greater number of amp hours, translates to larger capacity and a greater distance traveling on a singlecharge. In fact the best way to get a feel for the capacity of a battery is to multiply the two numbers togetherwhich will give the Watt hours (Wh). For example:

Battery A: 24V * 10Ah = 240Wh

Battery B: 36V * 8Ah = 288WhSo Battery B has a total of 288 watt hours, providing it with a larger capacity that will take further

on a single charge than Battery A. Its impossible to exactly say what distance a batterys full charge willactually cover, theres too many variables such as hill conditions, amount of pedaling, outside temperature,

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total weight, wind etc. As a very rough guide, a 36V 10Ah battery powering a 250W motor and riddenunder standard conditions will cover 50-60km. That includes light pedaling and few hills. In tough and hillyconditions that distance can easily half. Ebike battery capacity is not the only important aspect, its alsoworth paying attention to voltage options.

Sticking with the no-nonsense explanation, voltage can be thought of as the ability for the battery toprovide energy over the shortest period of time possible. Basically, it affects the max power which the batteryis capable of providing. Batteries and motors work their hardest during hill climbs, and an electric bike witha 24V battery may not climb as fast or as well as an identical electric bike with a 36V battery. What iscrucial here is to match the battery to the motor. A powerful electric motor will require a relatively highervoltage battery to perform at its best, while on the flip side a weak electric motor with a high voltage, highcapacity battery, is not getting any performance advantage from the higher voltage although the capacity isobviously better.

5.1.3 Choosing a Battery

As covered in the electric bike motor section of this guide the maximum legal motor size is 250 watts providedpeople want to be able to ride your bike on the road and have it treated as a regular bicycle under law.From personal experience when riding up hills, a 36V battery will outperform a 24V battery slightly. Thereare 48V batteries available but they are costly for the added capacity and are basically overkill for a 250watt motor. If you decide to purchase an ebike which is overpowered and illegal for road and bike pathriding, then this might be the best choice and of course it adds to the total range you can expect on asingle charge. One of the big reasons most manufacturers do not exceed 36V is because human skin usuallydoes not conduct electricity below about 40V which makes these batteries extremely safe. When it comesto deciding on how much capacity people want, bear in mind that larger capacity e bike batteries are moreexpensive and if people only planning on taking short trips without too many hills, you may find a smallerbattery to be totally adequate. That said, if its within budget a larger capacity battery is always betterthan one with smaller capacity.

5.2 Motor and Transmission

In our design we will be targeting people living in the cities with lots of hills that people cannot normallyride with a bike. As mentioned above there are 3 different motor types. The motor that will be used in thisdesign will be a hub-drive motor due to the following reasons; first when compared to FDs the hub-drivemotor gives better performance, second when compared to mid-drive motors the give less power however theyare easier to maintain and run, third they give moderate ranges when compared to the other two motors,fourth the batteries used with these motors are smaller than mid-drive motors making the bike weigh less,sixth all sorts of maintenance and repair operations are easier and can be done by virtually anyone. SeveralHub-drives will be presented below after all the parts required in the design have been presented here.

The second important part in the design of the motor and transmission is the transmission system. Themost common transmission system used in normal bikes is generally a 27-speed chain driven transmissionwith twist grip shifters on the handlebar. However using a 27-speed chain driven transmission is not thetrend of today due to it being not extremely reliable, requiring frequent maintenance when compared tothe new transmission systems. The transmission system that will be used will be a Rohloff speedhub. Asexplained above this system has gears inside the hub in an oil bath which makes a total of 14 different speedconfigurations which has ratios that rival the 27-speed transmissions. However to use the Rohloff speedhubthis device needs to be mounted on the rear tire, and the hub-drive motor has to be mounted on to thefront-tire. Since the two devices are of the same approximate weight, the weight distribution of the bike isquite good. Also since the Rohloff uses traditional twist grip shifters most users will feel comfortable withthe device. The approximate price for such a system is 1220 $.

The other important devices are the sensors that will be used within the system. The sensors that wewill want to see in our design will be torque sensors since the targeted customers are people who will not

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race but will climb hills, introducing the need for a torque sensor so that the electric motor can adjust itselfto the riders characteristics.

Also another thing to consider is the regenerating breaking option. This sort of breaking as mentionedabove gives the rider the change to slowly recharge the batteries while moving which in turn increases therange of the bike. To enable regenerating breaking E-brakes will have to be used. These brakes have a 3-pinconnection which is connected to the controller of the system. When the brakes are touched slightly theregenerating breaking option is turned on, however if the rider pulls on the brakes hard then the regeneratingbreaking option will not be enabled and the mechanical brakes will do all the work. Apart from rechargingthe battery the regenerating braking system is sort of a control system which makes it possible for the biketo maintain its speed without actually using the mechanical brakes.

To combine all the information given above I will compare some products that can be used in the designand will come up with a preliminary design combining the given products.

5.2.1 Motor Comparison

1) BionX P250 DL/RL: These kits made by BionX offer a 250 Watt power output motor. The kits comefully equipped on the front rim making assembly a much easier process. The kit also includes the battery,charger, holder. The DL version has the battery holder mounted below the saddle while the RL versionmakes it possible to mount the battery on top of the rear wheel. The battery used for this motor which isalso supplied with this kit is a Li-ion 48V 6.6Ah battery with 39 cells. The range of this bike is approximately80 Km. And most importantly the torque output of this motor has nominal/maximum values of 9/40 Nm.Also another important aspect of this kit is that by purchasing E-brakes and connecting it to the controllerof this kit one can achieve regenerating breaking. This kit satisfies all the requirements of the project. Theprice for such units is approximately 1600 EUR.

2) Crystalyte HT2425: This motor is a hub motor by crystalayte which allow disc brakes to bemounted on to the bike unlike other hub drives. The T in the model name stands for Torque version of theseries which as the name implies puts more emphasis on the torque output of the motor rather than the topspeed. This model weighs approximately 5.7 kg and can be mounted on the front wheel of the bike. Thesemodels have different configurations that can be chosen from such as sensorless and sensored models. For ourdesign we will be using sensored models which will include the torques sensor mentioned before. Also thismotor gives the option to use regenerative braking by using E-brakes that are connected to the controllerunit. The reliability of this unit is quite good it has only one moving part which is the center bearing andsince the motors can produce up to 2000 Watts without problem, normal riding conditions at around 250Watts will not produce any burnouts. There are however drawbacks to this motor. The brand crystalyteis known for its dragging pedaling. Although many modifications were made by the company in the newermodels, when compared to other motors it is harder to pedal freely. Unlike the BionX motor kit this doesnot come with a controller and a suitable controller must be chosen. There are many controllers one canchoose but the brand recommended Crystalyte analog controller will be used which is approximately 130EUR. Also since the torque model will be used on the front wheel a torque arm needs to be installed which isapproximately 25$. Also the pedal assist system module will need to be purchased in order for the controllerto be able to adjust the speed of the motor while free pedaling which costs approximately 15$. Also theE-brake system will need to be purchased and installed which costs around 50$. And finally to accelerate ordecelerate we will need a throttle that will be attached to the handlebar which is approximately 20$.

3) BMC Geared-Hub Motor: The BMC geared-hub motors are approximately 8 pounds in weightand are able to get e-bikes up to speeds of 30 MPH. The version we will be interested in will be the V2 modelwhich is designed especially for hill-climbing. The V2 motor is a high-torque motor which is internally gearedmaking this a better solution for the hub-drive motors. It is quiet and small which makes it hard for anyoneto notice the motor. It uses a planetary gear reduction technique which makes it run more efficiently thanits direct-drive counterparts like the crystalyte motor above. This motor also has a one-way clutch making

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free pedaling easy when the motor is not in use. In terms of durability this motor rivals the crystalyte motorsince it is built for above 1500 Watt power output but is generally run at around 200-300 Watts makingburnouts near-impossible. Also when compared these motors are better at hill-climbing. The battery ofchoice for these motors is 48V LiPo batteries running at 10-Ah. The controller also needs to be chosen forthis motor since it does not come as a kit. Crystalyte analog controllers will be used which is approximately130 EUR. The same extra accessories mentioned in the crystalyte motor will also be used here.

Conclusion: When the above motors are compared it is logical to select the BionX kit and combine itwith a Rohloff speedhub. The logic behind is the following, first the BionX kit comes fully equipped withtorque sensors, display unit, motor, battery making the assembly very easy. Second the Rohloff speedhubenables people to make use of high-end gear technology while using the common twist grip shifts. Thirdmaintenance is less of an issue since the BionX motor is specifically designed with city touring in mind. Alsofor the inexperienced E-bike use it would be easier to disassemble this kit for regular maintenance. Anotherthing to note is that this kit allows for regenerating breaking making it ideal for city touring by increasingthe range of the e-bike. Another issue with the maintenance that should be considered is that since theshifting is done inside the Rohloff speedhub there will be only one chain connected to the pedals making iteasier to replace and maintain. The total cost for the system mentioned above will be 7240 TL includingshipment fees. Also by adding the torque sensor, torque arm, twist grip shift, controller(if needed), E-brakes,and throttle the total amount adds up to 8000 TL ( torque sensor + torque arm+ twist grip shift+ controller+ E-brakes + throttle).

5.3 Frame Material and Fork Material

Different materials are used for manufacturing the frame of a bicycle. Most commons are steel, aluminum,titanium and carbon fiber. All of the materials have specific advantages and disadvantages as explainedbelow (It is considered that the measure of the frame is same for all materials).

5.3.1 Steel

Important material properties of steel (SAE 4130) are given below.

Young’s Modulus(E) 205 GPaDensity (ρ) 7850 kg/m3

Tensile Strength σT 731 MpaYield Strength σY 460 Mpa

[6] Advantages:

• Steel frame is stiff and strong; therefore, it can be affected from accidents less.

• Steel frame is cheaper than others ($1200-$3000 [3]).

• Steel frame is relatively easy to repair.

• Manufacturing a frame is easy from steel.

Disadvantages:• Because of the high density, steel frame is the heaviest one in the 4 options.

• Steel frame doesnt absorb shock well enough. It causes to feel roads roughness if there is no suspensionon the frame.

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• If steel frame isnt maintained, it would be rusted.

Fork of bicycle can be made of steel and it shows the properties of the frame.

5.3.2 Aluminum

Important material properties of aluminum (6061 (T6)) are given below.

Young’s Modulus(E) 69 GPaDensity (ρ) 2700 kg/m3

Tensile Strength (σT ) 310 MpaYield Strength (σY ) 275 Mpa

[6]Advantages:

• Manufacturing an aluminum frame is easy.

• Aluminum absorbs shock well.

• As the density of aluminum is less, the frame made of aluminum is light.

• Aluminum frame is repairable.

• Aluminum frame is also cheap ($2000-$3000 [3]).

Disadvantages:

• It is more open to get damage compared to steel Aluminum forks are stiff and light and can be shapedeasily for better aero dynamism.

5.3.3 Titanium

Important material properties of titanium (Ti-6Al-4V Solution treated and aged) are given below.

Young’s Modulus(E) 105 GPaDensity (ρ) 4428.78 kg/m3

Tensile Strength (σT ) 1050 MpaYield Strength (σY ) 827.4 Mpa

[6]Advantages:

• Titanium frame lasts for a very long time.

• It is light (approximately half weight of the steel and two times of the aluminum frames) also.

• It is also stiff and much stronger than steel frame.

Disadvantages:• Titanium frame is the most expensive metal frame ($3000 - $4000 [3]).

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• Manufacturing a titanium frame is hard. To manufacture frame, expensive titanium welding tools.

It is hard to manufacture titanium fork because of difficulties of manufacturing of titanium. Titaniumframes generally.

5.3.4 Carbon Fiber

Important material properties of steel (SAE 4130) are given below.

Young’s Modulus(E) - GPaDensity (ρ) 1780 - 2000 kg/m3

Tensile Strength (σT ) - MpaYield Strength (σY ) - Mpa

[6]Carbon fiber frame can be the lightest, the stiffest and the most durable according to the intensity of

matrix. Depending on stress analysis, a part of a frame can be more intense in carbon fiber matrix (wherestress is higher e.g at joining points) that makes the part stiffer, stronger. Carbon fiber is the lightest optionaccording to the comparison of density values. As carbon fiber is not a metal there is no risk of being rusted.Also, carbon fiber frames are very durable. However, like titanium frames, carbon fiber frames are expensivetoo (approximately $5000 [3]). Moreover, carbon fiber frames arent repairable as a carbon fiber bar is aproduct of following knit of fibers. Carbon fiber can be also considered as the best choice of manufacturinga fork because of the natural ability of absorbing shock. However, it is not suggested heavy cyclers becausethe fork weights less than 1 lb. which cannot be carry the load.

In conclusion, it is demanded that the frame should be strong, stiff, durable and light (cost isnt a concernin conceptual design phase). Carbon fiber frame meets the demand depending on the material comparisonabove. Additionally, for fork, to appeal everyone aluminum is the best choice.

6 Discussion and Conclusion

By considering the given information above, it is seen that the frame should be light, durable, stiff and strong,also considering that the budget is not an issue at this stage the most appropriate material for the frameis chosen as carbon fiber. However, the fork of the bike cannot be made out of carbon fiber because if thefork is made from carbon fiber it cannot bear the weight above approximately 90 kg. Due to this limitationthe fork will be made out of aluminum. The total approximate cost for the frame and fork is approximately5500-6000$. This value is an approximate value which does not include labor cost, mold cost, and materialcost specifically, it is an approximate value found by comparing different frame structures readily available.As mentioned before to satisfy the requirements of the system in question hub-drive motor at the front wheelcombined with a Rohloff speedhub gear box at the rear wheel will be used. The transmission from the pedalswill be done by using a regular chain. The choice of chain comes from the facts that it is easy to maintain,it is readily available, and since we will only have one chain connected to two gears breakdown of the chainwill be near impossible assuming it is changed annually and is serviced monthly/weekly depending on usage.The hub-drive motor will be bought as a kit combining the hub-drive motor, the display unit, torque sensor,and battery and the Rohloff will be directly bought from the company for a total cost of approximately 8000TL ( approximations are done to account for the change in Dolar/TL rate). The motor will give out 200-300Watt power using a 48V battery. The recharger will also come with the kit itself. The E-brakes, twist gripshift, torque arm will cost approximately 150 EUR. The twist grip shift will be chosen from shimano and thetorque sensor will come from crystalyte. The controller unit comes together with the kit as well. The saddlewill be made out of leather and will have springs at the back for comfort, it will be Velo Plush costing 60 TL.There will also be suspensions at the front to account for the added weight of the hub-motor. The breakswill be disc brakes will be Avd Elixir R with an approximate value of 1500 TL for front and back. The

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handlebar will be delta epoch carbon and will be approximately 150 TL. Pedals will be Shimano PD-M530MTB locked at a price of 180 TL.

References

[1] http://citybikes.com/articles/road-bike-materials-pg57.htm

[2] http://bigshark.com/articles/which-frame-material-is-the-best-pg531.htm#.

[3] http://www.rodbikes.com/articles/material-world.html

[4] http://www.rei.com/learn/expert-advice/bike-frame-materials.html

[5] http://talu.com/materials.php

[6] SolidWorks

[7] http://www.electricbike.com/bionx/

[8] http://newwheel.net/electric-bike-basics/

[9] http://www.electricbike.com/hub-motor-conversion-front-or-rear-wheel-drive/

[10] http://lyen.com/

[11] http://electric-bikes.com/betterbikes/bmc.html

[12] http://www.jozztek.com/shop/controllers/191-crystalyte-analog-system-controller-.html

[13] http://www.elektrofahrrad-einfach.de/products/bionx/BionX-P-250-DL.html

[14] http://ridebionx.com/

[15] deltabisiklet.com

7 Appendix

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Figure 3: Proposed E-Bike Design

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Figure 4: Proposed Design in Nature

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Figure 5: CAD drawing vs. Original Product

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