Figure 1. CAD drawing of the final system, showing the wind turbine in place.

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1 Abstract This project aimed to design a portable wind turbine capable of generating 20 watts at 12 volts in a nominally 15 mph wind. The design is a vertical axis wind turbine with two half-cylinder blades and an interchangeable shaft to allow for a hand crank. The drive shaft powers a generator which stores electrical energy by charging a battery while a microcontroller monitors an ammeter to control rpms. The product can power a communication device in remote areas or in power-loss emergencies. Prototype performance isolated areas for improvement in further development and suggested a feasible product. Product Description Figure 1. CAD drawing of the final system, showing the wind turbine in place. The availability of electricity in remote areas is an increasingly important problem. With dependence on electrical systems rising in line with standards of living, and the necessity of electricity for long-distance communication devices like radio, markets exist for a portable, long-lasting source of electricity. Following current trends in environmental conscientiousness, a renewable, clean source of energy is in particular demand.

2 Characteristics and Operation The product proposed by Pinwheel Technologies is a portable, vertical-axis wind turbine capable of producing 20 watts at 12 volts in a nominally 15 mph wind (Figure 1). The product consists of three main subsystems: the turbine shaft, the hub, and the base. Rotation motion of the turbine is transferred to the generator with a drive chain linking the sprockets at a 4.5:1 gear ratio from turbine to generator. Design drivers included portability, effectiveness at power generation, continuous power output, and price. These drivers led to constraints on size, weight, cost, and assembly time. The final product would weigh less than 50 lbs and have the ability to be packaged and carried by a single individual. Set up time would be less than 15 minutes for two people. Electrical energy is stored in a 12 V battery charged by the generator. Additionally, it would be possible to exchange the turbine for a hand crank if low wind interferes with emergency electrical needs. The product would also feature embedded intelligence capable of stopping the turbine in dangerously high winds, in addition to outputting turbine rpms and the generated current to the user. Key Features and Justification Achieving the above characteristics drove all design decisions, and the need to satisfy these requirements led to a number of key design features. The most important feature of the product is its ability to accept multiple inputs with minimal user time and effort required for an input exchange. The design is tailored to generate electricity to power an emergency communication device. Since emergencies may occur under zero wind conditions, the turbine/hand crank interchangeability dramatically increases the product s effectiveness for emergency power. The trade-off is the need for additional work by the user insignificant in a genuine emergency. Additional key features include a turbine braking system, necessary to prevent generator failure, as well as a low assembly time and high portability. Large, nonportable wind turbines with significant assembly time are currently available practical solutions to the problem of remote electricity generation, but they do not address emergency electricity generation or portability. The product is designed to address these concerns, hence the importance of portability and a low assembly time. Design Integration To allow shaft interchangeability, the base of the turbine contains a hollow, central hub capable of accepting various inputs of equal diameter. The hand crank and the turbine shaft are fixed in the hub by an easily removable clevis pin, which is in turn held in place by a cotter pin. Electrical circuitry was designed to switch the generator to a high resistance circuit in order to keep turbine speed below levels dangerous to the generator and operator. This was accomplished with a solid state relay switch activated when a current sensor determines amp production is too high. Assembly time was reduced with a self-contained and portable base-hub system (a 2 ft x 2 ft x 2 ft box), concentrating all

3 assembly time in turbine preparation. The only assembly required for hand crank use is the insertion of the hand crank. Design Relevance The product is a compact, portable and robust wind energy system designed to extract wind energy and convert it to storable, electric energy source. It was designed for use in emergency situations where conventional power has been interrupted, or for use in remote areas such as hiking or camping. A final use for this product would be in thirdworld countries where it would be the only feasible source of power. Based on initial research, there are currently no energy systems available that satisfy design conditions of environmental friendliness, portability, and continuous, renewable operation. Current products may only incorporate one or two of these abilities, but the Pinwheel Technologies product incorporates all three. The products currently on the market that address similar goals are the Sunforce Wind Generator, the Honda EU100i Gas Generator, and batteries. The Sunforce Wind Generator is a wind powered device that converts energy from the wind into electricity. This product is designed for rural areas with a specific focus on farming operations. The Sunforce Wind Generator, however, is designed for permanent use at one location. The Honda EU100i Gas Generator is portable, but can only operate for extended periods of time as long as gasoline is available. In addition, the environmental impact is greater. Finally, while batteries alone are portable, they require frequent replacement if not recharged. The final design improves on existing products with a current demand. Portability and emergency hand crank generation in zero wind conditions provide an edge over currently successful competitors. The device sacrifices some of a battery s portability for the long-term effectiveness of conventional wind generators, taking advantage of the best design traits of currently successful products. Design Process Pinwheel Technologies focused on a step-based design process similar to that suggested by the Gantt chart developed for the group concept selection memo (Figure 2), dividing the full project into smaller sub-projects and assigning these to individuals or intra-team groups. A more group-based, all-inclusive approach was adopted for the initial, conceptual phase of design, but this was abandoned when it became clear that such a strategy though beneficial for major conceptual decisions limited accountability and made consistent progress challenging. The April 15 deadline for prototype demonstration had the greatest impact on the design process. When significant mechanical challenges were identified early on, development of the electrical system was given a lower priority. This decision was based on the irrelevance of any electrical components in the event of a non-functional mechanical system. Mechanical challenges (subprojects) included turbine blade design, effective turbine-shaft attachment, the mechanism of shaft interchangeability, transferring power from the turbine to the generator, base design, and the fabrication of all eventual solutions to these design issues. Electrical challenges included connecting the generator

4 and the battery, determining requirements for imbedded intelligence, microcontroller programming, circuit design, and circuit construction. W5 W6 W7 W8 W9 210 W11 W12 W13 W14 W15 W16 2/12 2/19 2/26 3/4 3/11 3/18 3/25 4/1 4/18 4/15 4/22 4/29 Indiv. EG. Trade Study* Group Concept Development Bill of Materials Turbine Design Circuit Design Transmission/Housing Design Platform Design Virtual Model Development* Prototype Development* Draft Design Documentation*- ----Prototype Testing*--- --Design Review Prep.-- CDR* --Final Design Documentation*-- PDR* PDR* PDR* PDR* PDR* PDR* PDR* PDR* PDR* Figure 2. Gantt chart tailored to design process. An * denotes an associated hard deadline. Resource Allocation Table 1, below, provides a summary of human capital allocation at Pinwheel Technologies. Tasks were assigned based on each employee s assessment of his or her interests and capabilities. Table 1. General areas of responsibilities for each employee. Employee Specialty/Expertise Responsibilities Heather Manufacturing, turbine shapes Budget for bill of materials, CNC, base design, turbine blade geometry, blade offset dimension Michael Microcontroller programming Embedded intelligence, circuit design, hand crank design, shaft dimensions Domenic Manufacturing, CAM CAM programming for CNC, base design, wind turbine stability (tipping), Matt CAD, drawing, machinist CAD modeling, sketches, lathe, saw, drill, and mill work, turbine dimensions Joey Editing, web publishing Web site maintenance, document compilation, TTS collection, hub design All Mechanical Engineering Final group consensus for all design decisions, brainstorming solutions for major conceptual questions, formulate PDRs Following these trends, employees were assigned to urgent projects that appeared after conceptual decisions had been made.

5 Key Steps and Decision Points The major design decisions taken by the group were the selection of a vertical rather than a horizontal axis, turbine shape, and shaft interchangeability. All of these decisions were made before the group concept selection memo was due prior to spring break. Determination of turbine shape and size led to a group decision to use a 55 gallon drum for ease of manufacturing, which was ordered before spring break. Previous vertical axis wind turbines, most notably the Savonius, worked effectively with blades made from 55 gallon drums. Once modeling began and parts were ordered, the amount and scope of remaining work became more evident. The group was behind schedule. To pull back, the steps between receiving parts and finalizing the prototype were organized and divided among group members. Each group member was assigned to one primary task and one secondary task, according to Table 2 below. Table 2. Accountability breakdown for final assembly. Assignment Employees Base (CNC, dimensioning, assembly) Domenic, Heather Shafts (attachments, keyways, flats, holes) Matt, Joey Turbine (braces, flanges, holes, sanding) Heather, Domenic, Matt Hand crank (procurement, welding, design) Joey, Michael Embedded intelligence (circuit design, programming) Michael, Joey In this manner, every subsystem had an accountable group member in addition to a supporting group member. Individual accountability was the central emphasis in the physical completion of the prototype. d. Options Considered Initial concept sketches were submitted by each group member along with key features of each concept. The main design decision was vertical axis over horizontal axis. While horizontal axis wind turbines have relatively few design variations, the vertical axis wind turbine had a larger number of options to consider. The different designs considered are shown below (Table 3). Table 3. Wind turbine design considerations. Considered Feature Key Features Technical Challenges This design would be extremely lightweight, and easily portable. The blades would allow the wind to come from any direction and still turn the turbine. Construction of efficient turbine blades would be difficult.

6 This design would minimize the drag force acting against the direction of rotation on the turbine blades, and also would not need to be adjusted if the wind direction changes. Building the hood that blocks the wind from one half of the turbine blades would be difficult, along with connecting the hood to the main shaft. This horizontal axis turbine would fold onto itself, allowing for ease in portability. Attaching and detaching the drive system from the shaft requires a high level of alignment accuracy. This design is compact and would be easily portable, It also works in all wind directions. Difficult to manufacture cups of large surface area due to weight and attachment concerns. Torque may be minimal. This horizontal axis turbine would utilize current turbine technology, and most likely be very efficient. Also, the hinged blades would allow for ease in portability. Creating the hinged blades could be a problem if there is not a way to lock them into place when in use. Also, the turbine would have to be adjusted if the wind direction changed.

7 This vertical axis turbine would be compact, especially with the detachable blades, allowing for ease of portability and simplicity. The turbine might not extract enough energy from the wind with the small blades, and reattaching the disassembled blades could be difficult. e. Solutions Selected One of the first design decisions was the selection of the vertical axis turbine over the horizontal axis turbine. Advantages included the ability to seamlessly adapt to changing wind direction and the lower precision required for more robust blades. The performance of lift-based blades is associated with their air foil shape. Performance is also related to shape with drag-based blades, but the relationship is not as sensitive. Determining the final shape of the blades for the drag-based design was based on calculations of the surface area required to generate 20 watts of power at typical vertical axis turbine efficiencies. The cup shape was too small, and the paddle shape required a hood. Two overlapping half cylinder shapes would not require a hood. Such shapes have been produced by cutting a 55 gallon drum in half in previous wind turbine designs, and, given this proven record of effectiveness and ease of assembly, the group decided to order a 55 gallon drum before spring break. Blade type determination framed the problem for blade attachment. Options examined for attaching two half cylindrical blades to a vertical shaft included bolting through the shaft and bracing the shaft at the top and bottom. Bracing the shaft requires less machining overall, eliminates line contacts between the shaft and the blades, and allows for an efficiency-increasing overlap between the blades. These advantages led the group to opt for bracing (Figure 3). Figure 3. Bracing attachment of the turbine blades to the shaft.

8 Strengths and Weaknesses The product s strengths lie with its versatility. By having an interchangeable shaft, the product can be adapted to different situations where a wind turbine design would not be feasible. The product is also portable, allowing for ease of set-up and transportation to optimum environments for usage. Another strength of this design is its provision for circumstances in which the turbine blades might be hazardously spinning. The system s ability to allow for the turbine to free spin preserves the integrity of the electronic components as well as the turbine blades themselves. One significant weakness of the product is that it does not generate enough energy to power more then just small electronic devices. This results from its smaller size compared to non-portable turbines. The bulkiness of the turbine compared to competing technologies like the gas generator may seem to belie its ability to generate power, unfortunately the efficiency of the turbine is low due to its drag-based design. Also, the turbine, while portable, is not necessarily transported easily so much as transported more easily than permanent wind turbines. The decisions made from trade study findings impacted the dimensions of the design as well as the geometry. Blade design decisions were influenced by the height and width trade study. Height was determined to be the largest contributor to the power and was maximized in the chosen design. The offset and radius of curvature of the blades were optimized based on the power and efficiency that could be derived from their features. Another trade study examined the relationship between the driveshaft and the hub, leading to the decision to select the lightest possible hub that will not fail under gale force (90 mph) winds. The drive shaft was also examined in a trade study, which helped to determine the appropriate material and height of the turbine to reduce the amount of curvature that would be seen by the driveshaft. The final trade study examined the forces needed to stabilize the entire system under maximize force from the wind. This helped to design the size of the product base and the amount of weight distribution most effective in resisting tipping forces. f. Feasibility The key design feature explored with the prototype was performance. Portability became a secondary consideration. The group decided it would be more feasible to design portability into a functional design than vice versa. The prototype did not perform to specification (20 watts at 12 volts), but it did highlight areas for improvement. The torque provided by the wind turbine was underestimated, and the 4.5:1 gear ratio from turbine to generator was not high enough. A higher gear ratio would improve rpms from current levels (tested average of 311 rpm in mph winds) to required levels of 600 rpm necessary for 20 W production. The torque produced by the turbine was underestimated possibly because its rotational inertia was not accounted for and more analysis is needed to determine what gear ratio would provide 600 rpms. The final product would have a transmission. To improve portability, lighter materials could be used. The prototype was limited by manufacturing methods and suppliers. Consequently, heavy materials like steel were used for the turbine and generator shafts. The turbine itself could have been lighter,

9 perhaps made with aluminum or a thinner plastic. Further analysis could determine a turbine blade/shaft interface that is easier to disassemble than the current interface, which was designed to ensure against prototype failure and requires 28 bolts. Other considerations include product safety and ease of use. A chain guard around the drive chain would enhance safety, as would eliminating metal corners from the base. The clevis pin connection between the shaft and the hub demonstrated easy interchangeability, but it could be improved to allow for easier alignment (currently the user must align the holes). g. Conclusion The group learned important manufacturing processes and the true extent of the work necessary to develop a concept from an idea to a prototype. Results from prototype testing were positive and, though 20 watts at 12 volts was not achieved, areas for additional analysis and improvement were isolated. Weight could be reduced, attachments could be simplified, and rpms could be increased with the addition of a transmission and higher gear ratios. Implementing these improvements could lead to a marketable product.