High Efficiency Exercise Bike Power Generator

MAE 434W

Instructor:

Dr. Sebastian Bawab

Team leader:

Jake Harris

Team Members:

Arlo Bante

Jacob Van Dorn

Michael Padgett

Robert Johnson

Alex Hatfield

Adam Myers

Nick Galotifiore

Advisors:

Dr. Tian-Bing Xu

Dr. Murat Kuzlu

Assistant Advisor:

Evan Bowers

I

Table of Contents:

Table of

contents...............................................................................................................................I

List of Figures.................................................................................................................................II

List of tables...................................................................................................................................III

Abstract …………….....................................................................................................................IV

Introduction ……………...........................................................................................................pg. 1

Background……........................................................................................................................pg. 2

Methods……………………………………………………………………………………….pg. 3

Gears and Transmission.............................................................................................................pg. 3

Mathematics of Gearing.............................................................................................................pg. 5

Direct Current Generator...........................................................................................................pg. 6

Electrical Circuit........................................................................................................................pg. 7

Electrical Math.........................................................................................................................pg. 10

Arduino Circuit…………………....…………………………………………………...…….pg. 11

Results......................................................................................................................................pg. 12

Discussion................................................................................................................................pg. 15

Financial Report.......................................................................................................................pg. 17

Conclusion...............................................................................................................................pg. 18

References................................................................................................................................pg. 19

Appendices...............................................................................................................................pg. 20

II

List of Figures

Figure 1………………………………………………………………………..Gear overview pg 4

Figure 2……………………………………………………………………………Shift Drum pg 5

Figure 3…………………………………………………Ratchet and Star Detent Mechanism pg 5

Figure 4……………………………………………..Speed(Rpm) vs Torque vs Power Curve pg 7

Figure 5…………………………………………………………….Electrical circuit diagram pg 8

Figure 6………………………………………………………………..Estimated Efficiency pg 12

Figure 7…………………………………………………………………….Estimated Power pg 13

Figure 8………………………………………………………………………….Gantt Chart pg 20

Figure 9……………………………………………..Project Budget with Updated Funding pg. 24

Figure 10…………………………………………....Project Budget with Original Funding pg. 24

Figure 11…………………………………………………………….........Work Breakdown pg. 25

III

List of Tables

Table 1……………………………………………………………..Gear Force Calculations pg. 14

Table 2……………………………………………………...……..Gear Stress Calculations pg. 15

Table 3 ………………………………………………………...…………………..Parts

List pg. 23

IV

ABSTRACT

In today’s age of environmental concerns, renewable forms of energy are vital for

reducing pollution and carbon emissions. While most forms of green energy come from the

environment, human energy harvesting is a growing field. As the name suggests, these harvest

energy from human exercise. Exercise bikes are a growing market, and their relative ease of

modification makes them a perfect candidate for adding an energy harvesting system. There are

preexisting bike generators on the market, but many of them are overly pricey or inefficient. The

efficiency of the generator varies with speed of the input, therefore, there is a way to optimize

the efficiency of the bike by aiming for the generator’s peak efficiency speed. Applying the

concept behind motorcycle transmissions, a small, yet versatile, gear transmission was conceived

for correcting small deviations from the optimized gear ratios. To ensure that this mechanism

does not fail, a stress analysis was performed on an initial design concept. Based on some

preliminary design assumptions, a Matlab code was developed to simulate the efficiency and

behavior of the bike during the energy harvesting phase. An arduino controller is utilized to

provide feedback to the user. While an initial wiring diagram was established, the functionality

of this diagram has yet to be tested. Likewise, a system for routing that power was

conceptualized, but there was no opportunity to perform any preliminary testing.

INTRODUCTION

One of Albert Einstein's most memorable quotes was that, “ Energy cannot be created or

destroyed, it can only be changed from one form to another.” This idea formed into the first law

of thermodynamics also referred to as the Law of Conservation of Energy. [1] Taking this law

into account, the human body transforms organic food into fuel to be utilized and stored. This

energy produces mechanical and electrical output. This mechanical output of energy is what this

project is trying to capture by isolating human motion with the use of cardio equipment at a gym

or at home.

According to an article by “Market Watch” [2] the projection market of the fitness

industry has seen a steady growth over the last ten years. As the fitness industry grows, the

global energy cost continues to rise, not only financially but also toward the ecosystem. As

engineers we should always be searching for new innovation. This theme of fusing fitness with

sustainable renewable energy can possibly revolutionize the industry. Therefore, the purpose of

this project is to identify the advantages of harvesting generated electrical power from human

kinetic motion through cardio equipment.

This process of human kinetic energy collecting isn’t a perfect process due to the ability

of the initial inputted work to overcome the system's friction. This system friction causes the

outputted energy efficiency to always be less than 100 percent. The project, simplistically is a

three step process beginning with a background in how the human body transforms organic food

into energy followed by how the exercise machine takes the kinetic energy and modifies it into a

linear form that then ends by rotating the power generator. Within this process one of the

objectives is to reduce the friction to achieve the most efficient power generated exercise

machine.

BACKGROUND

The human need for electrical energy is very high today, with people researching new

ways to create electrical energy at a very low cost. Several new inventions have been created by

utilizing exercise equipment and harnessing the human energy and turning it into electrical

energy. A gym called Eco Fitness has been able to take different exercise equipment like

exercise bikes, treadmills, ellipticals, etc and transform them to harness human energy and

transfer it to electrical energy. All the energy that is created by the exercise equipment, 74

percent is captured and sent back into the main power grid to be used for the entire building [6].

There have been several different variations of exercise bikes created to convert human energy

into electrical energy. People have created their exercise bike generators by utilizing a fan belt

that connects to the flywheel and generator [5]. Another way is using additional gears and chains

that connect to the generator. What makes this project different from any other exercise bike

generator out there is that this project is utilizing a gearbox that is similar to the gearbox of a

motorcycle. The gearbox was chosen for this project to help maximize efficiency and store as

much power as possible.

METHODS

GEARS AND TRANSMISSION

The purpose of this project is the conversion of biological energy into electrical energy;

thus a bridge between these two forms of energy is necessary. In addition, because this project

revolves around the use of an exercise bike for energy scavenging, some method of variable user

effort is desirable. Out of the several options available, the team decided a mechanical

transmission would fulfill this need as efficiently as possible. Taking inspiration from

motorcycle technology, the team decided to design and build a constant mesh transmission. As

the name suggests, every gear is always in mesh with its mating gear, thus gear changes become

simpler and less complex for the user.

As shown in Figure 1, the transmission is an arrangement of specialized gear sets, one

free-spinning gear and one dog gear. The free-spinning gear is free to rotate relative to its shaft

while the dog gear is fixed in place with splines. The dog gear has extra teeth around the

circumference on both sides of the gear, (parallel to its axis of rotation). As the dog gear slides

up and down the shaft, these extra teeth intermesh with matching grooves cut into adjacent free-

spinning gears. This fixes the free-spinning gear to its shaft, and thus changes the gear ratio

between the input and output shafts. Gear shifts are actuated by a device called the shift drum

detail in Figure 2. This drum has channels cut into its surface in very specific patterns. These

channels cam parts called shift forks back and forth to move the corresponding dog gears and

change gear ratios.

The shift drum is rotated with a ratcheting mechanism. This mechanism pushes and pulls

studs located on the end of the drum, rotating the drum to the appropriate position. Another

device, called a star detent mechanism, assures a positive gear change. The star detent

mechanism is a star shaped camming surface on which a spring loaded roller rests. After the

ratchet mechanism reaches its maximum extension, the shift drum is “in between” two gear sets.

Maximum ratchet extension occurs just after the peak of star point and the spring loaded roller

finishes the movement by camming against the sloped surface of the star detent mechanism. The

star detent mechanism has one point removed to allow the transmission to rest in the neutral

position.

The transmission for this project is designed around a direct drive for third gear. The two

lower to gears increase the amount of effort required by the cyclist while the two higher gears

lessen the effort required. Because the electrical generator is most efficient at a certain rpm, the

transmission needs to maintain an output speed that is constant. The gear ratios cause the

required input speed to change such that the output speed remains constant.

Figure 1: Gearing Diagram

Figure 2: Shift Drum Diagram

Figure 3: Star Detent Mechanism

MATHEMATICS OF GEARING

Equations one through four in the appendix are used to find important values for our

gears. Equations one and two compute the allowable bending and shear stress that the gears can

undergo before damaging itself. The max bending and shear stress for the gears selected are

33,692.51 MPa and 94,252.69 N/m^2 [4]. When comparing the values for bending and shear

stress applied to the gears with the allowable, one can come to the conclusion that the gears will

not exert a bending or shear stress that will be detrimental to the gears. Equation three is for

calculating the needed rpm for the driving gear. The generator optimum is the rpm of the free

spinning gears where the efficiency is at its highest. Using the gear optimum rpm and

multiplying it by the gear ratio calculates the needed velocity for the driving gear to spin to keep

the free spinning gears rpm at a constant 2700 rpm. To calculate torque first the pedal torque and

the flywheel ratio are required. The pedal torque can simply be broken down to human weight

times the radius of the pedal. Once pedal torque is calculated dividing it by the flywheel ratio can

give us the torque produced from the gears.

DIRECT CURRENT GENERATOR

There are really only two types of generator, direct current generator and alternating

current alternator. The similarities between the generator and alternator is that both have rotating

magnetic fields that induces electricity current (I) with the copper winding. A generator that has

a large magnetic field and a lot of copper winding will produce more current. A DC generator

will be used in this project since the power that is being produced will be stored in a battery. The

kinetic energy from the person is transformed into a rotational energy for the generator. This

rotational energy will start spinning the rotor coils inducing the electromotive force (emf) or

voltage (V). Power is measured in voltage, current (ampere) and resistance. Voltage is the

driving force that pushes current (ampere) through the electrical wire. In plumbing voltage can

be expressed as the water pressure and current is compared to the rate of water flow within the

pipes. Depending on the types of electrical conductor being used, there will be a resistance to the

flow of electricity. Resistance is measured in ohms. A conductor that has one volt that pushes

one ampere to flow has one ohm of resistance. The two major considerations with every

generator is the relationship between the torque and revolutions per minute. This is very

important when using kinetic energy to rotate a DC generator. The generator needed in this

project should have the ability to have a very high rpm input. The higher the revolution per

minute into the shaft of the generator is directly proportional to the power generated in

electricity. The power curve depicts in figure 4

shows the relationship between the rotational

speed into the generator to how much power is

being produced. As you can see that about 3700

rpm the power and torque curve cross. The

torque falls as the power increases. This is where

the generator should be operating to produce the

most efficient energy.

ELECTRICAL CIRCUIT

The purpose of this project is to convert human kinetic energy into a practical and

sustainable source of renewable energy. The kinetic energy is conveyed from the cyclist into the

gearing system and ultimately spins the direct current generator which induces the electrical

charge that can be harvested and stored.

The project’s electrical circuit is designed to regulate voltages/current for components

safely. This parallel circuit consists of an Arduino loop and the primary battery loop. The line in

the diagram is the electrical wire which is made of american wire gauge (AWG) 18 copper. The

reason for this is that the DC generator has a maximum flow current of 14 amps. AWG 18 wire

is rated up to 1 amp per 500 feet according to the, “American Society for Testing and Materials”,

which is well below the safety factor. The circuit starts by producing the electrical current at the

DC generator. Once the current leaves the battery it is divided into separate loops. One of the

loops to use to power the rpm sensor and the other loop that is not shown in the diagram is

powering the Arduino circuit board. Both loop begin at the DC DC buck converter. The system

can be easily adjusted to

accommodate the addition

of a DC to AC inverter.

The motor is 350

Watt, 14 amp permanent

magnet at its optimal rpm

of 2700. The electricity

initially flows through a 14

amp glass fuse to protect

the motor from exceeding

manufacturing RPM parameters. The second component is the diode, which is an electronic

component that only allows current to flow in one direction. This is accomplished by using type

N-P semiconductor. The word semiconductor indicates the partial mixture of insulator and

conductor. The semiconductor is made of silicon on one side and germanium on the other which

have four valence electrons, out of a maximum of eight electrons. The silicon and germanium are

mixed with other materials to add characteristics to make one side little more positive charged or

little more negative charge then the opposite. The composition is different for every application.

This unbalance allows the current to flow through the diode easier in one direction sense its

acting like a conductor and harder in the other direction since it acts as an insulator.

A charge controller is placed in line to regulate the voltage into the battery in case of a

fluctuation in the voltage from the motor. This is done with a microprocessor that reads the

incoming voltage and compares it to input voltage parameters. The regulator will adjust the

voltage when required. Within the charger controller is a limit switch or battery management

system (BMS) is a device that uses an actuator which will open the circuit once the battery is

fully charged. This protects the battery from overcharging and becoming a fire hazard. Once the

electricity flow is stopped an internal circuit loop allows the current back into the neutral wire

and completes the loop back to the battery.

Both batteries are lithium ion batteries which are capable of fast charging and for

repeated cycling. The lithium ion batteries are made up of four components. A cathode which is

a lithium compound at the positive terminal, and anode that is almost always made of graphite on

the negative terminal. The battery is filled with electrolyte fluid that generally contains lithium

salts. The cathode and anode is divided by the porous separator that allows the ions to pass free

from the anode and cathode.

After the battery it was decided to install a digital multimeter. The multimeter is able to

measure the voltage, current, power and produced energy and store this data. This can come in

handy for detection how much power is being produced by the cyclist. Also installed on the

battery is an easy to read battery level indicator.

The buck converters are used as direct DC to DC steps down voltage controllers. Two of

the buck converters are used to obtain the necessary voltage that is needed at the Arduino and the

RPM sensor. Arduino have internal fuse but are very difficult to change, therefore each Arduino

has its own individual fuse to protect it from overheat due to possible fluctuating currents which

is not shown in the diagram. This is also a safe factor, since having excess current going into the

Arduino circuit board could possibly damage or destroy it. .

The last component in the primary battery loop is a DC to AC inverter. This is also not on

the diagram. This electronic device converts the direct current from the battery into alternating

current. Direct current travel only in one direction where alternating current continually reverses

its direction. There are many benefits to AC power over DC power since most appliances require

120 volts AC power to run.

ELECTRICAL MATH

Once torque and the RPMs are found using the mechanical equations, the amount of

power output can be calculated using the equations 5 through 12 in the appendix. The force and

velocity found are plugged into the power equation and simplified. It is known that 1hp is

equivalent to 30,000 pounds per minute. The amount of horsepower is now able to be calculated

and can be transferred into Watts. The percentage of efficiency can finally be found by using

equation 13 in the appendix.

The reason these equations are important is because we are working on making this

exercise bike with high efficiency. A person can generate about 700W in very short bursts

(seconds), 200-300W in medium bursts (minutes), and can produce on average around 75-100W

in one hour of pedaling [5]. Efficiency will be lost as energy is being transferred from human to

mechanical to electrical energy. More efficiency will be lost as power will have to be converted

from DC to AC in order to be used in the main power grid of a building. Using the gear ratios,

the goal is to maximize the efficiency so that the max amount of power output remains. The

more efficient the exercise bike is, the more power it will be able to store.

ARDUINO CIRCUIT

For this project the utilization of the Arduino Uno (rev3) logical board will be used as the

main logic board for communicating to the 16-pin LCD display in order to track and produce

relevant information to the rider. There was discussion of using a Raspberry Pi4 as the main

logic board, but given the more expensive price point and the current lack of channels to

purchase quickly form this late in the game it was decided that we will be sticking with the

Arduino Uno Rev3. The components will be powered by a singular 12V lithium-ion battery

which will be recharged from the bike system itself. In order to maintain a safe and efficient

system there will be voltage regulators placed on both the Arduino (7-12V) and LCD (3-5V)

screen in order to not overburden the components and cause damage to them. This relevant

information will include and is not limited to, amount of calories burned, power generated from

calories burned, time elapsed during the workout, and RPM produced by the rider. The

introductory circuitry for this has already been mapped and is included in (Appendix A8.1). The

pinouts as well are described in detail for both the logic board and the LCD screen (Appendix 7)

This will be changing due to the need for sensors to read both power output and RPM of the

bike. The DC current monitor has already been purchased through Amazon because no local or

vendors on ODU’s approved vendor list had the equipment that was needed, and will be donated

at the end of the project to the university along with the Arduino logic board by Alex Hatfield.. It

is, however, important to note that both the diagram and code may change based on the final

location of the display. For example, as stated in (Appendix A8.1), the D2-D5 PWM pinouts

used for translating code from the logic board to the LCD are dependent on the orientation of

both components, which will change the code.

Because of the physical nature of Arduino coding and the questions still remaining in

terms of mounting, creation of final code has been challenging. This is why the exact logic board

and LCD display have been shipped to Alex Hatfield, in order to begin the troubleshooting

process for the code from home. Testing was done on the initial bits of code, but without the

proper sensors, full and complete testing is impossible. The up to date code can be found in

Appendix 9. Without the application of the sensors you can see the code working functionally

via equations encoded into the sensor library.

The sensors that are required are being delivered

directly to Alex Hatfield on 6/30/2020. This

should make the coding process much less

susceptible to error and arrive at a competent

display of the data discussed earlier when it

comes time for final assembly of the bike.

RESULTS

Matlab Code

Figure 6. Estimated efficiency based on constant torque and increasing rpm.

Figure 7. Estimated power generated in kW to rpm

Gear Analysis was completed using the AGMA Stress Analysis Method in Excel. Several

design parameters were assumed; gear face width, shaft center distance, and pedal radius among

several others. Using an Excel spreadsheet allowed for live updates of the code, so that gear

ratios can be selected for easily manufacturable gears. As shown in the below tables, these gears

will not be exposed to excessive stresses. Therefore, the gears can be simple cast gears instead of

precision machined pieces. The shaft calculations were completed using the Modified Goodman

Distortion Energy Theory Criterion (DE-Goodman Criterion). Moments and torsion at the step

shoulders and keyways were generated and input into a MATLAB code to calculate step

diameters at each location. The AutoCAD drawing was then updated to reflect the changing shaft

diameters. Modifying the original drawing proved more difficult than starting from the

beginning.

Once the gear and shaft designs were finalized, all the other components that make the

transmission mechanism were drawn. Certain gears had to be modified with dog clutch teeth and

shift collars so that the transmission could function properly. The shift drum mechanism is

especially complex because three camming channels needed to be located and phased precisely

to prevent multiple simultaneous gear engagements. Autodesk Fusion 360 does not support

wrapping a sketch around a cylinder, so a separate file was created to unroll a pipe of the

appropriate diameter and create the channel sketches. Once the channels were cut and the pipe

was re-rolled, the center was extruded and the whole component was imported into the original

drawing. A v-belt pulley and a chain drive sprocket were also added to the drawing to support

power transfer into and out of the gearbox. To appropriately design these two components, the

Machinery’s Handbook 12th edition was consulted [9],[10].

The gears and shift forks were cast using 3D printed parts and the transmission housing

was cast using wooden prototypes. The molds were created by placing the 3D printed gears into

a special sand, called Green Sand, and compacting the sand tightly into a wooden flask. To

prevent unwanted sticking of the sand to the parts, baby powder was liberally applied. Once the

sand was compacted, the flask was flipped over and the top of the part was covered again in baby

powder and sand. Once the molds were ready, the 3D printed gears were carefully removed from

the sand, leaving a mold to pour into. While preparing the mold, the furnace was heated up to

1500 oF. Scrap aluminum was thrown into the furnace and allowed to melt. Once fully liquid, salt

was added to act as a degassing agent and the resultant dross was removed. The molten

aluminum was left in the furnace for another two minutes to reach optimal pour temperature,

approximately 1450 oF. Then the aluminum was removed from the furnace and quickly poured

into the molds previously created. After 20 minutes to freeze, the newly made gears were pulled

from the sand molds, cleaned off, and finished with machining.

Table 1

Teeth Pitch Diameter (in) User

Set Ratio Gear A Gear B Gear A Gear B RPM

1st 1.285 14.00 18.00 1.40 1.80 77.10

2nd 1.134 15.00 17.00 1.50 1.70 68.04

3rd 1.000 16.00 16.00 1.60 1.60 60.00

4th 0.882 17.00 15.00 1.70 1.50 52.91

5th 0.778 18.00 14.00 1.80 1.40 46.69

Shaft Velocity (rpm) Torque (lbf·ft) Power (hp)

F_t (lbf) F_r (lbf) F (lbf)

Input Output Gear A Gear B Gear A Gear A&B

Gear A&B

Gear A&B

3469.50 2700.00 4.71 3.67 3.11 29.60 10.78 31.50

3061.80 2700.00 4.16 3.67 2.42 26.13 9.51 27.80

2700.00 2700.00 3.67 3.67 1.88 23.04 8.39 24.52

2380.95 2700.00 3.23 3.67 1.47 20.32 7.39 21.62

2101.17 2700.00 2.85 3.67 1.14 17.93 6.53 19.08

Table 2

Lewis Form Factor V (ft/min) K_v K_o K_s K_m

Gear A Gear B Gear A & B

Gear A & B

Gear A & B

Gear A & B

Gear A & B

0.277 0.309 1272.04 1.15114 1.00 0.98120 1.11646

0.290 0.303 1201.99 1.14732 1.00 0.98240 1.11458

0.296 0.296 1130.97 1.14332 1.00 0.98294 1.11290

0.303 0.290 1059.96 1.13916 1.00 0.98356 1.11142

0.309 0.277 989.91 1.13489 1.00 0.98407 1.11013

K_B J C_f I C_p sigma_b sigma_c sigma_b allow

Gear A & B

Gear A & B

Gear A & B

Gear A & B

Gear A & B

Gear A Gear A

1.00 0.23 1.00 0.09037 2200.73 454.63 53454.63 33692.51

1.00 0.25 1.00 0.08539 2200.73 393.74 49827.72

1.00 0.27 1.00 0.08035 2200.73 341.51 46594.98 sigma_c allow

1.00 0.29 1.00 0.07530 2200.73 296.70 43746.84

1.00 0.28 1.00 0.07033 2200.73 285.73 41247.23 94252.69

DISCUSSION

The purpose of this project is to harness the unused kinetic energy of exercisers and

convert that energy into electrical power. This will be accomplished by harvesting the rotational

motion of a stationary bike to power an electrical generator. Because the generator is most

efficient at a higher speed than can be produced by the cyclist, a large total gear reduction is

necessary, on the order of 45 to 1. This can be accomplished in one stage, flywheel to

transmission; or several, pedal to flywheel to transmission. This limits the amount of torque

experienced by the transmission, and thus the quality of the gears required to withstand these

loads. Lower quality gears yield reduced manufacturing time and costs. Though the exact shaft

stresses have yet to be calculated, because the gears have such small forces the shaft should not

experience too much stress. This will allow for thinner shafts, again reducing manufacturing

costs.

The Matlab code found in A.2 produced Fig 6 and Fig 7. In Fig 6, a rough approximation

of a rpm-power efficiency map was utilized to generate the efficiency of the bike at each gear

transmission ratio at a variable user rpm [8]. The approximation was determined by interpolating

multiple points on the efficiency map. From the graph, the gear ratios shift the peak efficiency

along the user rpm. As one gear transmission starts to lose efficiency, the next can take over. If

the gear ratio has an rpm that is too high, it runs the risk of damaging the generator. This is

represented by the lines cutting off at a certain point. In Fig. 7, the efficiency estimation was

used to determine the theoretical power output of the system at increasing rpms. An important

thing to note is that the Matlab code assumes a constant user torque. This assumption will lead to

some skewing. From the graph, it is clear that the initial inefficiency of the lower user rpm

results in noticeable differences in the output power. As the gear ratios approach peak efficiency,

it is hard to tell them apart. This is from the slow drop off of the efficiency at higher user rpms.

These lines again end as the generator rpm approaches speeds that could damage the generator.

For the second half of the project, there are two routes that the project could go. If the

school opens up and access to the lab is granted, a physical project can be completed. If not, the

project will continue as an online paper-based project. For either version of the project, a shaft

stress analysis will have to be completed in the same vein as the gear stress analysis, as well as

producing an arduino program for the bike to run. For a physical design, the arduino program can

be tested with a completed bike, but for a paper based project, the arduino program will have to

be tested via home tests. While home tests can help refine the program, they will not yield as

accurate results as in person tests. For a paper based project, the preliminary Matlab code will

likely have to be greatly expanded to provide more detailed and precise results. For a physical

design, the Matlab code will likely only be used as a reference for theoretical results, which

could be compared to experimental results.

FINANCIAL REPORT

This report is based on the original funding for the project which was $2,000 given to the

project by the mechanical engineering department. Additional funds are available on a by need

basis from Dr. Xu’s lab fund. These funds are to be used on this project and another project that

parallels the exercise bike. The original funding was broken down in the parts list below. The

additional funding will be used to purchase a more modern bike and to account for any

miscellaneous cost associated with fabrication, labs, and labor. Due to the situation surrounding

COVID-19 some smaller parts have been bought by group members to expedite the process and

allow the group to continue working towards its final goal. Both the parts list and budget

graphics can be found in the appendix section (Appendix A3.1, Appendix A4.1).

CONCLUSION

The goal of this project was to convert biologically produced energy into usable electrical

energy in an efficient manner. To do this the team would design a mechanical device which

would be connected to a traditional recumbent exercise bike. This device consists of a flywheel

attached to the existing pedal assembly of the exercise bike that is connected to an electric

generator via a gear box which would allow the generator to spin at its ideal rpm to produce the

maximum amount of power for the exercise. This gearbox is modeled off a motorcycle

transmission and allows for an easy step up of rpm based on the rider's desired resistance. From

the electric generator energy flows into a lithium ion battery for storage and into another battery

set up which powers the arduino and LED display. This display allows the rider to easily view

key metrics such as, calories burned and energy produced from the workout. This semester the

team is primarily focused on prototype manufacture. The gears and several other components

were 3-D printed through the university for use as master moulds for sand casting techniques. By

doing this the team was able to produce suitable gears without the use of the university machine

shop. The cast pieces will be machined and finished in the coming weeks for final assembly and

demonstration.

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[9] “Belts and Pulleys - Machine Tool Drives” in Machinery’s Handbook, E. Oberg and F.D.

Jones, Eds., 12th Ed. New York, NY, USA: The Industrial Press, 1943, Ch. 28, pp. 822 - 844.

[10] “Transmission Chain and Chain Drive” in Machinery’s Handbook, E. Oberg and F.D. Jones,

Eds., 12th Ed. New York, NY, USA: The Industrial Press, 1943, Ch. 30, pp. 850-881.

APPENDICES

Appendix 1. Gantt Chart:

Appendix 2. Matlab Code:

clear

clc

flyR=45;

transR=[1.285 1.134 1.000 .882 .778];

pedalT=165; %lbf ft

rpmax=2700/.75;

rpmlimit=120;

n=zeros(5,rpmlimit*2);

motorType=1; %1:IM, 2:IPM, 3:SPM

length=[1 1 1 1 1]*rpmlimit;

ls=zeros(5);

Pgen=zeros(5,rpmlimit*2);

for i=1:5

for rpm=1:rpmlimit*2

t=pedalT*transR(i)/flyR;

v=rpm*flyR/(transR(i)*2);

hp=v*t/5252;

P=hp/.7457;

if(v>rpmax)

length(i)=rpm;

break;

end

n(i,rpm)=efficiency(v,motorType);

if(n(i,rpm)<.7)

ls(i)=rpm;

end

Pgen(i,rpm)=n(i,rpm)*P;

end

end

plot((ls(1):length(1)-1)/2,n(1,ls(1):length(1)-1),'r',(ls(2):length(2)-1)/2,n(2,ls(2):length(2)-1),'m',(ls(3):length(3)-1)/2,n(3,ls(3):length(3)-1),'g',

(ls(4):length(4)-1)/2,n(4,ls(4):length(4)-1),'b',(ls(5):length(5)-1)/2,n(5,ls(5):length(5)-1),'k')

grid on

xlabel('User rpm')

ylabel('Estimated Efficiency')

legend(['gear ratio: ', num2str(transR(1))],['gear ratio: ', num2str(transR(2))],['gear ratio: ', num2str(transR(3))],['gear ratio: ', num2str(transR(4))],

['gear ratio: ', num2str(transR(5))] )

figure

plot((1:length(1)-1)/2,Pgen(1,1:length(1)-1),'r',(1:length(2)-1)/2,Pgen(2,1:length(2)-1),'m',(1:length(3)-1)/2,Pgen(3,1:length(3)-1),'g',(1:length(4)-

1)/2,Pgen(4,1:length(4)-1),'b',(1:length(5)-1)/2,Pgen(5,1:length(5)-1),'k')

grid on

xlabel('User rpm')

ylabel('Estimated Power Generated (kW)')

legend(['gear ratio: ', num2str(transR(1))],['gear ratio: ', num2str(transR(2))],['gear ratio: ', num2str(transR(3))],['gear ratio: ', num2str(transR(4))],

['gear ratio: ', num2str(transR(5))] )

function n=efficiency(rpm,motor)

switch(motor)

case 1 %Inductance motor

if(rpm<1500)

n=rpm*.9/1500;

elseif(rpm<2400)

n=.9+.02*(rpm-1500)/(2400-1500);

elseif(rpm<5000)

n=.92-.01*(rpm-2400)/(5000-2400);

else

n=.91-.02*(rpm-5000)/(12000-5000);

end

end

end

Appendix 3. Parts list:

Part Price Quantity TotalBafang 750W BBS02 Mid Drive Motor Kit & Battery 799 1 79936V/48V SW900 LCD Display - 36V 54.99 1 54.99e-Bike Speed Controller Bag 14.99 2 29.98Half Twist Throttle for 24V 36V 48V 19.99 1 19.99Universal Laser Cut Torque Arm 9.99 2 19.98Geared Front Rear Conversion Kit - Rear 36V 303.18 1 303.18Geared Front Rear Conversion Kit - Front 36V 259.08 1 259.08Direct Drive Front Rear Conversion Kit - Rear 48V 347.28 1 347.28Direct Drive Front Rear Conversion Kit - Front 48V 286.64 1 286.64Exercise bike 542.32 1 542.32

Total 2662.44

Donated or Bought with Outside Funds Price Quantity Total3D Printed gears ~100 1 ~100Arduino with Sensors 120 1 120Motor 50 1 50Casting of Gears 25 1 25

Appendix 4. Budget:

Appendix 5: Work Breakdown

WBS Description Responsible Deliverables

Exercise Bike Project Jake

1.0 Mechanical Systems Michael/Adam

1.1 Flywheel Arlo Design and modify the flywheel on the

bike

1.1.1 Gearing Adam/Michael/Nick Develop gears to install on the flywheel

1.1.2 Motors/Generators Arlo/Robert Design and find a way to connect generator

to bike

1.2 Housing Adam/Nick Design for bike housing

1.3 Bike Robert Design and modify bike that is chosen

2.0 Electrical Systems Arlo/Robert

2.1 Battery Arlo/Robert Design and attach battery to exercise

bike

2.2 Coding Jake/Alex Coding for exercise bike

2.3 Microcontroller Alex/Jake Create and develop a microcontroller

3.0 Budget Jacob Work on making a budget for all

expenses for project

Appendix 6:

σ all=(St /SF)×[Y N / (KT × K R)]……………………………………………....….Equation 1

σ c, all=(Sc/ SH)׿…………………………………..…..Equation 2

Velocity=Gear Optimum×Gear Ratio………………………………………….....Equation 3

Torque=(Human Weight × Pedal Radius)/ Flywheel Ratio………………...…...Equation 4

Power=Force× Velocity……………………………………………..……………..Equation 5

Velocity=DistanceTime …………………………………………………….………………Equation 6

Force=TorqueRadius…………………………………………………………..…………….Equation 7

Power=( TorqueRadius

)× (2(π)(Radius )(RPM ))…………………………….……………..Equation 8

Power=(Torque)×(2(π )RPM )…………………………………………...…………Equation 9

Hp=((Torque)×(2(π ) RPM ))

33000……………………………………………..……………Equation

10

Hp=Torque(RPM )5252

……………………………………………………..………….…Equation 11

Phorsepower=PWatts

746………………………………………………………………..Equation 12

η=Pout

P¿×100………………………………………………...……………………..Equation 13

Appendix 7:

Descriptions of Pinouts in use:

● LED:

○ LED+/-:

■ These are the power and grounding pinouts respectively for the LCD backlight

display

○ DB7-DB4:

■ These are the digital input pinouts that will take the information from the logic

board

○ E:

■ The “Enable” pinout is used to send data based on a low or high voltage being

sent to it(i.e 0=sends instructions, 1=resests loop)

○ R/W:

■ “Read or Write” pinout, based on a given voltage this pinout either reads

instructions or writes them(0=Write, 1=Read)

○ VO:

■ This pinout controls the contrast of the lighting on the LCD display, which is

controlled by the amount of resistance given (normally connected to a potentiometer,

which is a knob that controls resistance)

○ VDD:

■ Voltage input

○ VSS:

■ Ground input

● Arduino uno (Rev3)

○ D2-D5:

■ Digital output/input pinouts, used to communicated to the LCD screen

○ D11 PWM/MOSI

■ This digital output has the capability to send a pulsing signal(PWM- Pulse Width

Modulation), which when connected to the E pinout on the LCD screen will control if it

sends instruction or respects.

○ D12/MISO

■ THis pinout (MISO meaning Master In Slave Out) , similarly to the D11 pinout

will control the Register pinout on the LCD screen on when to go to the command

registry or the data registry.

○ GND:

■ Ground input

○ 5V:

■ Voltage input

Appendix 8: Arduino Diagram

Appendix 9: Code version 1.4.2

Appendix 10: Separation of Work for Final Paper

Arlo Bante:● Introduction ● Electrical Circuit● Direct Current Generator

Jacob Van Dorn:● Budget● Conclusion

Michael Padgett:● Transmission design● Gear stress calculations● Shaft stress calculations (started, have not finished yet)● Discussion

Robert Johnson:● Background section● Electrical calculations● Gantt Chart and Work Breakdown structure

Alex Hatfield:● Arduino Coding section

Adam Myers:● Mathematics of Gears section

Jake Harris:● Abstract● Results● Discussion

Nick Galotifiore:● Transmission Build● Gear Casting● Visual Aid