Proceedings of the Multi-Disciplinary Senior Design Conference Page 3
Project Number: P12414
Copyright © 2012 Rochester Institute of Technology
Proceedings of the Multidisciplinary Senior Design Conference Page 3
Bicycle Cell phone Charger for Developing regions
Brenda LisitanoMechanical Engineering / Zheng(Flora) Li
Electrical Engineering
Aaron Sieczkarek
Mechanical Engineering / Daniel Tobin
Mechanical Engineering / Amina Purak
Industrial Engineering
Abstract
Communication 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 process
Needs- 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.
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 / 6
Water Proof / IEC60529 Level / 4 / 7
Table 1- Priority Device Specifications
Benchmarks 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.
Project P12414
Proceedings of the Multidisciplinary Senior Design Conference Page 3
Design of Machine Elements Calculations
Project P12414
Proceedings of the Multidisciplinary Senior Design Conference Page 3
Symbol / Meaning / Units / kts / Stress Concentration factor torsion / n/ase' / Endurance Limit / Pa / τm / Torque / N-m
ka / Marin Factor (Surface Treatment) / n/a / Se / Endurance Limit (After k factors) / Pa
kb / Marin Factor (Size) / n/a / D / Diameter / m
kc / Marin Factor (Loading) / n/a / q / n/a
kd / Marin Factor (Temperature) / n/a / Sut / Mean Ultimate Tensile Strength / Pa
ke / Marin Factor (Reliability) / n/a / n / Factor of Safety – Modified Goodman
kt / Stress Concentration factor bending / n/a / σm' / Midrange Stress / Pa
Table 2 Nomenclature for Calculations
Project P12414
Proceedings of the Multidisciplinary Senior Design Conference Page 3
Shaft Calculations / Kf=1+q*Kt-1 (5)se'=.5*sut (1) / Kfs=1+q*Kts-1 (6)
Ka=a*Sutb (2) / τm=16τπ*Dshaft3 (7)
Se=Ka*Kb*Kc*Kd*Ke*se' (3) / σm'=Kf*σm2+3*Kfs*τm2.5 (8)
σm=32Mmπ*Dshaft3 (4) / modified goodman n=Syσm'+σa' (9)
Project P12414
Proceedings of the Multidisciplinary Senior Design Conference Page 3
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 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).
Testing
User 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 DESIGN
Design -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.