proceedings - edgeedge.rit.edu/content/p12414/public/msd2 final documents/p12414... · web...

Multidisciplinary Senior Design ConferenceKate Gleason College of Engineering

Rochester Institute of TechnologyRochester, New York 14623

Project Number: P12414

BICYCLE CELL PHONE CHARGER FOR DEVELOPING REGIONS

Brenda LisitanoMechanical Engineering

Zheng(Flora) LiElectrical Engineering

Aaron SieczkarekMechanical Engineering

Daniel TobinMechanical Engineering

Amina PurakIndustrial Engineering

ABSTRACTCommunication over long distances is a common human need and many developing countries or rural areas

lack electricity in homes that could recharge a cell phone. The objective of this project was to create an inexpensive device which transforms kinetic energy from a bicycle to an electric power source capable of charging a cell phone or another small electronic device. The mechanism we created is easy to install, reliable and the materials can be acquired for less than $20.00. The scope of the project included concept discussion, research of currently available products, drawings and design of components combined with production and testing of a working prototype. The design was executed according to an engineering plan. Results of our design and experimentation demonstrated that this device is capable of charging a variety of small electronic devices with no significant increase in work required by the rider.

INTRODUCTION People in countries with inadequate infrastructure have an unmet need for electricity. Only 10% of the rural

population of our target country, Haiti, has access to electricity [1]. The lack of electricity inhibits their ability to communicate, to work in non-daylight hours and to otherwise increase their well-being and productivity. This project focuses on creating electricity and storing power from a bicycle’s rotational energy to provide the energy required for light and communication for customers in rural Haiti.

Several available products satisfy the basic requirement of supplying electrical power from bicycles. However, these products do not have a capacity to store the phone or other device being charged while biking, nor do they utilize a standard USB connection. USB to Phone connectors are available for the most commonly used cell phones for our desired region of Haiti [2]. Other noticeable disadvantages of the benchmark products include the difficulty of installation and alignment, noise generated by the device and significant wear issues. None of the devices benchmarked allowed for easy replacement of key parts. The goal of the device described in this paper is to improve upon currently available devices and address the concerns mentioned above, with only minimal additional cost.

DESIGN PROCESSNeeds- The team was presented with a number of important customer needs. First the underlying premise for this project is to utilize the energy generated by a human pedaling a bicycle to charge the battery in a cell phone. Secondly the rider cannot afford to expend significantly more energy pedaling the bike. Creating an affordable device was another major consideration. Next, the device needed to utilize a standard connector. A preferred design would be lightweight, inexpensive, and one that is easy to install, operate, and maintain. The device should also resist environmental damage caused by weather and road conditions. The total budget for the project was $600 with the requirement that the final design of the device should cost at most $20 per device in a lot of 100. A House of Quality and Functional Decomposition were utilized to determine the most important needs to focus on and their relationships to the other needs and specifications.

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Proceedings of the Multidisciplinary Senior Design Conference

Specifications- Customer needs were translated into the following key specifications.Specification Units Marginal Value Ideal ValueDevice Cost $(US) <40 <20

Range of Bikes Tire size (cm)/(in) 60.6-71.1(cm) 40.6-71.1(cm)Range of Phones % of tested phones >60% >90%

No Increased Effort % increase in VO2 <10% <3%Dust Proof IEC60529 Level 5 6Water Proof IEC60529 Level 4 7

Table 1- Priority Device SpecificationsBenchmarks and Reverse Engineering Learning-Significant time was invested in determining the feasibility of and selecting the optimal harvesting method for the project, as well as benchmarking similar products and solutions. In the benchmarking stage several devices were found which addressed certain desired aspects including generating power from a bicycle for a light dynamo as well as hub generators and a roller generator [3]. Reverse engineering the benchmarks informed our design process, and several valuable lessons were learned. The first generation bicycle light generators are very difficult to spin. Therefore, the generator has to be powerful enough to meet the power requirements of charging a cell phone. However, there is a linear correlation between power output and the difficulty in spinning the generator, adding to work on the user. The light generators also utilized a metal roller which over time would eat away at the bike tire causing permanent damage. Designed by Massachusetts Institute of Technology (MIT)/Global Cycling Solutions, our main benchmark was a roller generator. One of the immediate concerns about the Global Cycling Solutions device is that as the device is in use, there is a whirring noise created which has a negative user reaction and leads to the rider believing that they are wasting more energy than in reality. The Global Cycling Solutions benchmark is also just a roller with the understanding that the phone should be stored in the user’s pocket. Brainstorms- During brainstorming, several design possibilities were considered including building a generator with magnets, purely mechanical energy storage devices such as a flywheel as well as harnessing the power of vibration with piezoelectric materials[4]. Analysis conducted on the various solutions included a Pugh Matrix.Feasibility- Calculations were used for the mechanical analysis of the shaft and tube designs. They validate the mechanical design criteria to ensure the final product is robust and will survive normal misuse.Design of Machine Elements Calculations

Symbol Meaning

Units kts Stress Concentration factor torsion n/a

se' Endurance Limit Pa τm Torque N-mka Marin Factor (Surface Treatment) n/a Se Endurance Limit (After k factors) Pakb Marin Factor (Size) n/a D Diameter mkc Marin Factor (Loading) n/a q n/akd Marin Factor (Temperature) n/a Sut Mean Ultimate Tensile Strength Pake Marin Factor (Reliability) n/a n Factor of Safety – Modified Goodmankt Stress Concentration factor bending n/a σm' Midrange Stress Pa

Table 2 Nomenclature for CalculationsShaft Calculations Kf =1+q∗( Kt−1 ) (5)

se '=.5∗sut (1) Kfs=1+q∗( Kts−1 ) (6)

Ka=a∗Su tb (2) τ m=16 τ

π∗Dshaft3 (7)

Se=Ka∗Kb∗Kc∗Kd∗Ke∗s e' (3) σ m' =( ( Kf∗σ m )2+3∗( Kfs∗τm )2 ).5 (8)

σ m=32 Mm

π∗Dshaft3 (4) mod ified goodmann=( Sy

σm' +σa

' ) (9)

Battery Discussion-One of the major decisions for the project in was whether to store the energy harvested from the bike utilizing the internal battery of the desired small electronic device or in an intermediate battery. Lithium-ion

Project P12414

Proceedings of the Multi-Disciplinary Senior Design Conference

batteries are the most commonly used batteries in cell phones and other small electronic devices. They have high specific energy and energy density, long cycle life, no maintenance, no memory effect and many other advantages compare to other kinds of batteries. Normally, lithium-ion batteries are 3.7V for most small electronic devices, and the cell phone has protection circuitry to prevent overcharging [5]. A 5V constant DC input is required for these personal electronics. Based on these factors, the circuitry of our design should be created to provide a constant 5V output and charge the internal battery. Another concern was the price; the charging device needs to be affordable for the intended population so every effort was made to minimize cost. Utilizing an external battery would also have decreased the overall efficiency of the system meaning less energy would be available for charging the desired device. Based on this analysis it was a clear decision to utilize the battery already in the phone to store the energy.

AMPL ANALYSIS AMPL is a linear program that aims to optimize a given objective function either through maximization or minimization. A manufacturing line balancing simulation program was created in order to prepare for the transition from prototyping to mass manufacturing. Given cycle time, a ratio of available hours and market demand, the program calculates the minimum number of work stations required to fulfill demand for our device. The primary assumption is that the manufacturing site will be working with paced lines, which implies a fixed time frame for each station regardless of task completion. Additionally, it is assumed that there is an existing market demand for our product, which was used to calculate cycle time. The sets, groupings of data, within the model are a set of Tasks (T), number of stations (N), and a subset of tasks to establish precedence (PreT{t}). Parameters were the cycle times of 10 minutes, 30 minutes and 60 minutes; the time to complete each task (d[j in T]); and the cost of completing a task in any particular station. The objective function was set up to minimize the total number of work stations that were opened. The primary constraints ensured that every task is assigned to a station (TaskAssignment), that each station produces at or below cycle time (CompletionTime), and that precedence is respected (Precedence).

TESTINGUser Added Effort/VO2- Our device aims to minimize added strain on the rider whether physical or psychological. This is measured by VO2 output and vital signs of the users. Each user rode for 7.5 minutes at a speed of 20Km/hr. The test called for the users’ pulse and blood pressure to be measured before and after riding with users alternating riding with or without the device. A 10-minute break was taken before each ride to allow the users to reach baseline conditions. Order of riding was alternated so half of the users would ride with the device first and half without.Electrical Validation- Extensive electrical testing was utilized to verify the device functioned as expected. Different voltage inputs from 1 V to 10 V were applied on the circuit using a DC Power Supply sometimes at steady state and sometimes fluctuating. The outputs from the circuit were recorded. Current flows were tested to ensure levels below the upper limit, so that the voltage regulator is not damaged.Device Durability- According to the customer needs, the device had to resist a wide array of impacts and weather conditions. Different tests were run for each of the conditions given. An impact test was conducted using a weight to simulate the force imparted on the device in a collision. A dust proofing test was conducted using fine sand. The sand was thrown, blown and used to cover the device fully according to IEC60529 testing procedure. The same standard was applied for the waterproof testing [6]. Dustproofing is measured on a scale from level 1 to 6 while waterproofing is measured from level 1 to 7, with the highest value being ideal. User Feedback Testing- This device was exhibited at ImagineRIT, creativity and innovation festival held on the campus of Rochester Institute of Technology. The goal of the exhibition was to introduce the basic concepts of motors, generators and electricity in a fun and exciting way to children (ages 4-11) and their parents. At the event participants were able to talk with the design team and test the device for themselves. For over seven hours more than 200 participants were able to view and utilize the device for a few minutes. Adult participants were asked to rate the aesthetic qualities of the device in a short survey. The device maintained functionality the entire day even though it endured use beyond the expected normal scope. The device was attached to a bike situated on a trainer setup which allows the rider to spin a flywheel with various amounts of resistance to simulate a road.

COST/WORTH ANALYSIS One of the most important needs of this device is that it is available at a reasonable cost to the target customer.

The ideal value for a manufactured batch of 100 units was less than $20 per unit, and the marginal value below $40 per unit, creating a tight monetary constraint. The Functional Requirements listed in the House of Quality (HOQ) are used as the Engineering Metrics in the Cost-Worth Table. The chart ranking the requirements and needs from the HOQ is used as the weighting factor for each engineering metric. All components are rated at a scale of 1, 3 or 9 based on each component’s contributions to the Engineering Metrics. The product of these values and their relative



weight is summed up over all engineering metrics to show a final “Raw Score” per component. Each component is given a “worth” and “cost” rating relative to other components, which are then graphed.

FINAL DESIGNDesign -The final implemented idea is a simple roller generator and phone carrier system situated in highly visible location. Our system evolved into a device with two main components the “box” assembly and the “roller/motor” assembly. One of the advantages to this design is that the box is easily removable via a rubber strap. Theft is deterred as the product requires both components to operate. The box assembly also allows the user to see the phone and shows that the device is indeed charging, while riding the bike. The clear transparent box material also allows the user to see when there is an incoming call and provides visual feedback that the charging device is working correctly. Box Assembly- The box assembly (Fig. 1) is designed to encase the main circuitry of the device as well as the phone being charged. One of the main improvements of our design over the benchmark is that the cell phone is contained within the system. The assembly attaches to the front of the bicycle during use and allows the user to see that the system is functioning. This box assembly also protects the conditioning circuitry from environmental effects such as water.

The circuit board is contained within the box and secured with four 6-32 machine screws to a clear flat piece of acrylic. The circuit components are hand soldered to a circuit board. With only five components and a low production volume project, designed to be manufactured in a low labor cost location, a printed circuit board was not deemed to be cost effective.

The design utilizes a piece of clear plastic to protect the circuitry and separates the phone and the components of device that are designed for user interaction (i.e. the USB port and cable) from the rest of the device. Six 6-32 machine bolts are threaded into the plastic shield and act as standoffs for the circuit board. There is sufficient clearance within the container to house most types of cell phones along with the required USB cable.

Figure 1: Electronics Box Assembly Figure 2: CAD Model of Electronics BoxRoller Assembly- The roller assembly (Fig. 3) contains the generator which is required to convert the kinetic energy of the spinning wheel into electrical energy to be stored in the cell phone battery. The generator is encased in a standard screw cap plastic container and attached to the rubber roller by an aluminum shaft. The design, machining and assembly of the shaft and roller mechanism were completed carefully to ensure alignment with the motor, shaft and tube. This was done to make the device much quieter than the Global Cycling Solutions Benchmark. The assembly is much more robust than the Benchmark with the aluminum tube held securely to the container. This is extremely important as alignment with the shaft and the motor, is required for efficient energy conversion and longevity of the device. Foam cushioning is utilized around the motor to resist rotation while allowing for a minimal amount of flexibility, which dampens vibrations. A spring clip is utilized as the installation connector to attach the assembly to the bicycle. A rubber grip is used to wrap around the bike tube to adapt the clip for various bike tube sizes. In terms of assembly, a key advantage of the designed device is that it can be easily assembled with only a screwdriver, Allen wrench and adjustable wrench or pliers.

Project P12414


Figure 3 Assembly Drawing Figure 4 Motor Housing AssemblyCIRCUIT BOARD DISCUSSION

The circuit (Fig. 5) is a vital portion of the device because it creates additional protection for the electronics in the cell phone. The circuit conditions and regulates the electric power generated by a 12V DC motor. The three capacitors stabilize the non-linear voltage input while a 5V voltage regulator reduces the voltage to a 5V constant output. The power is supplied to small electronic devices via an A-type USB connector, which is standard. An adaptor provided with the device will allow the customer to choose the connector required for their phone or other small electronic devices such as a light, GPS or MP3 player.

C 81 0 u

12V DC motor C 9. 1u

A-type USBConnector

4

1

U 4LM 3 4 0 -5

I N1

O U T2

GN

D3

0

C 71 0 u

Figure 5- Conditioning circuitTESTING RESULTS AND DISCUSSION

The final prototype met all of the required specifications (table 3).

Test Ideal Value Measured ValueIdeal(I) Marginal (M) Fail (F)

Cost Analysis <$20 $15.02 IWaterproof 7 4 MDust Proof 6 6 I

Range of Bikes 60.6-71.1 (cm) 60.96-68358 (cm) MRange of Phones 90% 90% I

Rough Road Stays on and no Damage sustained No damage sustained M

Motor Voltage >7V >7V I

Speed to Charge <20 km/hr. <20 km/hr. (17 km/hr. greatest) I

First Install 1 person 1 tool 1 person 0 tools I

Each Use <5min setup<10 min train

<5min setup<10 min train I

Operating Temperature Change <5 degrees C 4.9 degrees C I

Impact Resistance 15 Lbs. any angle 15 Lbs. any angle IOutput Current >230 mA 402 mA I

Device Size 16x16x16 cm 16x10x12 IAesthetics 75% 4 or better 75% I

V02 <10% Statistically 0% IPhone Charging Yes Yes I

Output Voltage with Input Greater than 6V 5 V 5 V I

Table 3: Overall Results

The device effectively charged a number of phones utilizing rotational energy from a bicycle. The device also works on a variety of bikes although this current version is not adaptable to children’s bikes. The definition of charging was that the device is gaining electrical potential even if it is not as quickly as charging the phone on the grid.User Added Effort/VO2 Results- Our device did not have an effect on the riders, with no significant increase in VO2 exertion. This means that the rider does not to have to exert a noticeable increase in energy to power the device.



Rider AgeResting HR (Beats/min) Resting BP

HR (Beats/min) BP

HR (Beats/min) BP

With V02 (mL/min/kg)

W/o V02 (mL/min/kg) % Difference

Male User 22 92 120/90 134 140/88 150 142/98 21.85 24.46 -11.94Male User 23 76 124/84 112 148/88 116 144/96 22.11 22.89 -3.57Female User 23 88 122/76 120 122/74 132 140/82 20.45 22.50 -10.00Female User 21 76 122/72 128 140/74 144 136/78 25.26 28.42 -12.50Female User 22 100 120/78 120 132/88 140 130/90 18.00 21.00 -16.67

Control Device in Use Without Device Results

Table 3 VO2 Test ResultsELECTRICAL TEST RESULTSDC Voltage Test-The soldered circuit board was tested with a set of voltage inputs from a DC Power Supply. As a result, the output voltage stays at 5V when the input voltage is above 6V. This outcome agrees with the simulation. The circuit board will regulate the voltage to 5V DC to provide the appropriate voltage.Nonlinear Voltage Input -Detailed are the results of testing the soldered circuit board with a nonlinear positive voltage input which is created by a function generator. This assessment tests the circuit board for 10 second duration. The blue line is the input voltage, and the green line is the output voltage. From Fig. 6, we can see that the output voltage cuts off at 5V when the input voltage gets to around 6V. The output voltage is constant when the input voltage is in the range of 6V to 10V. This outcome agrees with the simulation. According to the simulation, the circuit maintains 5V output when the motor’s output is between 6V to 12V.

Figure 6 Nonlinear Voltage ImputThe power output test was difficult to test with the current setup as current cannot be recorded in real time. Each phone has a different required amperage and voltage needed to charge the battery. The phones utilized were also quite old and had not been used consistently. Due to budgetary constraints new phones and new batteries were not utilized. Instead we assumed that the phones available were representative of what might be available to the target population and could be used for the tests. However, this might have impacted the results of the tests.

DEVICE DURABILITY RESULTSEnvironmental Test Results-The device passed all environmental tests. For example in the dustproof test, no sand was able to get into the device reaching the ideal criteria. For the impact test the extreme case was tested first and it was assumed that if passed, the device would also pass lesser conditions. The result was that the device resisted any damage from the impact of an approx. 15 pound steel rod from various directions. The only environmental test that the device did not pass ideally was the waterproofing test. The ideal case was the ability to be submerged under 1 meter of water for 30 minutes without any water penetration. Unfortunately there was a small leak through the lid of the phone box and the top of the shaft of the motor housing. The device did however easily pass the marginal test for waterproofing which was the simulation of a heavy rainstorm using a water hose with a flow rate of approx.12 gal/min. There was no water penetration from this and the device fully functioned after the test as well.

USER FEEDBACK TESTING-Aesthetics Results- From a survey pool of 69 participants 75% rated this design as attractive or very attractive. This value exceeded our ideal specification of 70% approval.

Project P12414


Figure 7 Aesthetic Survey Results

COST WORTH RESULTSFigure 8 shows that the ‘ideal’ price of each component would lie on the yellow line, indicating that there is

complete balance between how much ‘worth’ that component contributes to the specifications and how much it costs in terms of overall cost. The red and black curves are 10% confidence intervals, between which values are still reasonably priced. Any items that fall above the red 10% curve are expensive for their relative worth; any items that fall below the black 10% are cheap for their relative worth. In our case, the Clear Plastic Box and the 2oz Single-Wall White Jar are well priced in terms of the value they bring to the project. The ¼”-20x1/2” machine screws with nuts from Home Depot, however, are expensive for their individual contribution.

0.00% 2.00% 4.00% 6.00% 8.00% 10.00% 12.00% 14.00% 16.00% 18.00% 20.00%0.00%2.00%4.00%6.00%8.00%

10.00%12.00%14.00%16.00%18.00%20.00%

Kolpin Re-placement Straps for

Rhino Grips

1/4"-20x1/2" machine screws

with nuts

Clear Plastic Box 24 oz with lid

Cost-Worth Diagram(Based on "Total Part Cost" as divisor)

Relative Worth

Rela

tive

Cost

Figure 8- Cost-Worth Diagram

AMPL RESULTS Table 4 shows the results of the linear program as run through the publically available NEOS server. The

longest manufacturing process is set at 9 minutes; therefore cycle times below 9 minutes are currently infeasible. Fitting the acrylic electronics covering requires the most time creating a bottleneck. If lower cycle times are expected, it is recommended that assembly processes be re-evaluated and divided into more components and re-timed.

Demand For 1 New Part (minutes)

10 30 60

Stations Needed 8 3 2 Table 4- Stations required as given by product demand

Given a demand of parts in the form of 1 part needed in X minutes, table 2 indicates the required number of stations. For a demand of 1 part per 10 minutes, 8 stations are required; for a demand of 1 part per 30 minutes, three stations are required; finally, for a demand of 1 part per 60 minutes, 2 stations are required.

CONCLUSIONS AND RECOMMENDATIONS Our device shows promise for a system that can be manufactured and utilized in Haiti. Overall, the device

satisfies the customer needs and meets the project requirements. With minimal additional cost, we were able to incorporate design innovations that resulted in a superior product to the benchmarked devices. We believe that our



primary customer is satisfied with the outcome of the design project and that the end consumer will realize the value offered by this design. This project was successful in many respects however there are several improvements that could be made. These changes include the following: an improved motor-shaft connection, increased grip of the spring clip design and increased aesthetic appeal. Other factors that could be evaluated include reducing the number of parts and decreased complexity of design.

Further projects could be conducted based on the work done for this design. Recommendations include decreasing the number of tools required for manufacturing so the product could be easily built in Haiti. Designing for manufacturing would improve the device and allow for broader implementation. If future analysis requires cycle times below 9 minutes, the data model for the AMPL analysis will need to be revaluated and the manufacturing process times of individual steps reduced below 9 minutes. The overall design could also be reduced in complexity based on the Cost-worth analysis. The majority of components fall on the low end of the cost-worth spectrum; this clustering allows for future improvements through the reduction of the total number of components, there is also potential improvement in finding cheaper alternatives to the ¼”-20x1/2” screws that are currently in use. Changes could also potentially be made to have the device engage only when the user desires, such as when going down a hill, making the device capture only wasted energy. Potentially utilizing an AC Motor and testing of additional motors would allow for a more efficient conversion of energy. It is also recommended that future team members for this project have experience with design for manufacturing and a mechanical engineering student who has taken systems modeling. This class gives the background for modeling the motor output and circuitry with a dynamic model which is expected to further confirm the current analysis and design. Future generations of this project could also encompass design for environment components. These would include an environmental impact assessment that will be used for material selection. A Life Cycle Analysis of the final prototype will help show the biggest areas of improvements in terms of reducing environmental impact through the materials, manufacturing, use and disposal of this device. This project was very much a learning experience and if this team were to repeat the project several things would be done differently.

We recommend that future teams approach the project with a spirit of innovation, interest, commitment to work and a desire design projects for developing countries.

REFERENCES [1] Verner, D., Egset, W., 2007, Social Resilience and State Fragility in Haiti, World Bank, Washington, D.C., Executive Summary, pp. xv[2] Tison, Marc. "Reseau cellulaire Digicel en Haiti." La Presse. La Presse, 08 Oct 2010. Web. 8 Jan 2012. <http://affaires.lapresse.ca/economie/international/201010/08/01-4330651-reseau-cellulaire-digicel-en-haiti-22-millions-dabonnes-en-quatre-ans.php>.[3]Battery Operated Devices and Systems - from Portable Electronics to Industrial Products. (2009). n.p [4] "Piezoelectric Energy Harvesting Kit." PIEZO SYSTEMS, INC.. PIEZO SYSTEMS, INC., 15 Jan 2012. Web. 15 Jan 2012. <http://www.piezo.com/prodproto4EHkit.html>.[5] Kiwia, Bernard. "Bicycle Phone Charger: Design with the Other 90%." Smithsonian Cooper-Hewitt, National Design Museum. Smithsonian Cooper-Hewitt, 28 Sept. 2010. Web. 18 May 2012. <http://www.designother90.org/cities/solutions/bicycle-phone-charger>.[6] "Waterproofing Standards Demystified Adventure Insider Magazine." Adventure Insider. Adventure Insider Magazine, 28 Sept. 2010. Web. 25 Jan 2012.

ACKNOWLEDGMENTSWe would like to thank several people including:Mrs. Sarah Brownell R Community BikesMr. Gerry Garavuso

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