AirTwist - Wind Power Educational Tool Final Report

ME340 - Team 1D Joe Connor, Clayton Hose, Steve Marshall

May 7th, 2008

Abstract

As the demand for alternative energy increases, the demand for engineers to develop those technologies will also increase. For this reason, it is critical that we educate today’s youth about alternative energy. This proposal outlines the design of a wind powered educational tool, AirTwist, to be used by teachers and their students. After researching existing products on the market, it was determined that the final design should have two goals; to be educational and to encourage creativity. These goals will be accomplished by ensuring that AirTwist can be modified by the students. Multiple blade configurations will be possible and emphasis will be placed on encouraging children to create their own blade arrangements. This design feature will encourage creativity while simultaneously teaching children how the number of blades affects the power generated by a wind turbine. To ensure that AirTwist is financially feasible, an economic analysis was performed on competing products. It was found that with a competitive selling price of $30.00, AirTwist will begin making money by the fourth quarter of the first year. After four years of production, AirTwist is projected to have a net present value of $3.95 million. Not only will AirTwist be financially profitable, but it will benefit the field of engineering by encouraging young children to pursue alternative energy.

Table of Contents

Page

Executive Summary 1. Introduction 1-2

1.1 Problem Statement 1 1.2 Educational Importance 1 1.3 Wind Turbine History and Background 1-2 1.4 Project Planning 2

2. Customer Needs and Specifications 3 3. Concept Development 3-6

3.1 External Search 3 3.2 Problem Decomposition 3-4 3.3 Ideation Methods 4 3.4 Description of Design Concepts 5-6 3.5 Concept Selection and Combination 6

4. System Level Design 6-7 5. Detail Design 7-11

5.1 Detail Design Description 7-8 5.2 Calculations of System Performance 8-9 5.3 Material Selection 9 5.4 Component Selection Process and Bill of Materials 10 5.5 Fabrication Processes 10-11 5.6 Construction of alpha prototype 11 5.7 Differences between alpha prototype and mass production unit 12 5.8 Testing of Alpha Prototype 12-13

5.8.1 Test Setup and Initial Testing 12-13 5.8.2 Taguchi Design Array Testing and Results 13 5.8.3 Durability Testing 13

5.9 Economic Analysis 13-14 6. Conclusion 14

Appendix A – References 15-16 Appendix B – Final Design Drawings 16-20

B.1 - Final Design: Housing 16 B.2 - Final Design: Housing Half 1 17 B.3 - Final Design: Housing Half 2 17 B.4 - Final Design: Exploded View 18 B.5 - Final Design: Assembled View 18 B.6 - Final Design: Hub Detailed View 19 B.7 - Final Design: Hub Frontal View 19 B.8 - Final Design: Rear View 20

Appendix C – Dimensioned Drawings 20-24 C.1 - Detailed Drawing: Base 20 C.2 - Detailed Drawing: Blade 21 C.3 - Detailed Drawing: Bottom Housing 21

Table of Contents (continued)

Page

C.4 - Detailed Drawing: Top Housing 22 C.5 - Detailed Drawing: Fin 22

C.6 - Detailed Drawing: Outer Hub (4 pin) 23 C.7 - Detailed Drawing: Inner Hub (4 pin) 23 C.8 - Detailed Drawing: Outer Hub (6 pin) 24 C.9 - Detailed Drawing: Inner Hub (6 pin) 24

Appendix D – Educational and Instructional Manual 25-37 Appendix E – Table, Charts, Patents, and Calculations 38-

E.1 - Gantt Chart 38 E.2 - Original Project Black Box Model 38 E.3 - Quality Function Deployment (QFD) Chart for AirTwist 39 E.4 - Wind Turbine Types and Efficiencies 39 E.5 - Detailed Calculations 40-42 E.6 - Jameco Motor Specifications 42 E.7 - Concept Possibilities Matrix 42 E.8 - Concept Selection Matrix 43 E.9 - AHP (Analytical Hierarchy Process) Matrix for AirTwist 43 E.10 - Axis Oriented Selection Matrix 44 E.11 - Output Selection Matrix 44 E.12 – Drive Type Selection Matrix 45 E.13 – Net Present Value (NPV) Chart for AirTwist 45 E.14 – Educational Toy Survey 45 E.15 – Educational Toy Survey Results 46 E.16 – Competing Wind Powered Educational Toys 47 E.17 – US Patent A 48 E.18 – US Patent B 49 E.19 – US Patent C 50 E.20 – Taguchi Array 51-52 E.21 – Gear Specifications 53 E.22 – Polymer Information Sheet 53 E.23 – Polymer Pricing Sheet 54

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1. Introduction

1.1 Problem Statement

Our team’s goal is to design, construct, and test a table-top wind turbine kit for elementary

school students to learn the basic information of wind power generation. Our design will be easily

assembled and operated by students 10 years of age and older. The windmill will be designed around

the criteria of cost, industrial design, performance, durability, educational value, ease of assembly and

disassembly, safety, compactness, and simplicity.

1.2 Educational Importance

Elementary school kids contain a wealth of creativity and are continually seeking opportunities

to both learn and express themselves. To foster this desire within schools, it is important to provide

teachers with educational toys designed to encourage their student’s imaginations and curiosity. For

many engineers, toys are what originally caused them to pursue the field. They tend to mention Legos

or building blocks as one of the early reasons why they became interested in engineering. For this

reason, it is important that we pay special attention to how and what we teach our youth about. With

the recent demand for development of alternative energies, it is vital that we educate elementary kids

about renewable energy technologies.

One of these emerging technologies is wind power. Although it currently contributes less than

0.5% of the global energy production, wind power is now the fastest growing of the renewable

technologies1. Wind power is a relatively simple concept for elementary school kids to understand.

Wind blows toward the wind turbine which causes the blades to spin which generates energy. For these

reasons, wind power is an excellent starting point to introduce elementary school children to alternative

energy and careers within engineering and science2.

1.3 Wind Power History and Background

Wind power for mechanical work dates back as early as 300 BC when

the Persians were said to have used it for grinding grain. This technique

continued to 250 AD when it was introduced to the Romans. However, the

more familiar Dutch windmill, as seen in Figure 1, was not used until the 14th

century. These windmills were primarily used to drain areas of the Rhine River

delta. In 1887, the first windmill was built for producing electricity by Prof

James Blyth of Scotland. However, not until 1931 would the first modern

looking windmill be built in Yalta, USSR. This windmill had an efficiency of 32%

which is comparable to current windmill efficiencies. Another milestone

occurred in 1931 when the first Darrieus rotor wind turbine was created, much

like the one illustrated in Figure 2. As our knowledge base about wind turbines

grow, rotor and blade designs are continually improved upon. One of the most recent developments

occurred in 2007 when a wind belt was invented that does not use a rotor; rather it relies on vibrations

Figure 1 - Dutch Windmill1

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in the wind stream. This new invention can produce power at 1/10 the price per watt of the traditional

wind turbines3.

As seen in the illustrations, wind turbines can be classified into two

basic categories. They are either horizontal axis wind turbines or vertical axis

wind turbines. Horizontal axis turbines have the spinning rotor at the top of

the windmill, and they must be facing the wind such as the Dutch windmill in

Figure 1. Vertical axis turbines do not have to be facing the wind, which is ideal

for areas of turbulent winds. The most common vertical axis turbine is the

Darrieus rotor shown in Figure 2. The Darrieus rotor is composed of two or

three curved blades with the generator placed near the ground. The other type

of vertical axis wind turbine is the Savonius rotor. This wind turbine resembles

a cylinder cut in half and split apart as seen in Figure 3. This style of wind

turbine operates with an efficiency of roughly 15% and is used primarily for

pumping water or grinding grain, applications which require a high torque

but low rotational speed4. One of the benefits of vertical axis turbines is that

unlike horizontal axis turbines, they can be placed low to the ground which is

useful in areas that restrict the height of structures. However vertical axis

turbines tend to produce electricity at only 50% of what the horizontal axis

turbines can produce. This makes them less common in commercial use1.

1.4 Project Planning

This project was split into the following design process steps:

Figure 4 - Design Process Steps

Currently, the design team is in the production ramp-up step. Each of the team members spent

time researching and brainstorming designs. This involved taking surveys about educational toys and

researching existing wind powered toys. These various concepts were then brought together and

compared through decision matrices to determine the best ideas. After developing the best design, the

team built a functioning prototype which was used for further testing and refinement. After refining the

alpha prototype, the team is now ready to begin production of the final product and marketing towards

teachers and students. To breakdown individual tasks throughout the design process, a Gantt chart was

created to assign the team members specific roles, see Appendix E.1. The Gantt chart was designed

with a risk plan in mind such that there was always a week buffer zone before final deadlines. This

ensured that in case there was a problem during the design process, time would be allocated to fix the

mistake.

PlanningConcept

DevelopmentSystem-level

DesignDetailed Design

Test and Refinement

Production Ramp-up

Figure 2 - Darrieus Windmill1

Figure 3 - Savonius Windmill4

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2. Customer Needs and Specifications

To best understand the needs of the customer, our team created a survey which asked

participants about their interaction with educational toys growing up, see Appendix E.14 and E.15.

From these results, we found that there were just as many kids that preferred toys which included

instruction manuals as kids who preferred toys which allowed them to be creative and rely on their

imagination. This is an important consideration, and in order to be effective to as many kids as possible,

our final design must include both instructions for children who desire that style of learning, as well as

an imaginative portion for children who are more free-thinking. The questionnaire also found that kids

tend to enjoy Legos, which focuses on allowing kids to build and create. Our design team felt that this

aspect was equally as important to include in the final design.

Beyond the questionnaire, the design team also created a Quality Function Deployment (QFD)

Chart for our product; see Appendix E.3. This chart compares customer needs to the engineering

specifications and targets. With this information, the design team was able to benchmark our product

against leading competitors on the market.

3. Concept Development

3.1 External Search

After determining the customer needs, an extensive external search was

performed to identify products currently on the market, as well as patents for various

windmill and windmill blade types, see Appendix E.17-E.19. Vertical axis wind turbines

(VAWT)5 and horizontal axis wind turbines (HAWT)6 were both researched and

considered for possible concepts, see Appendix E.101. It was also found to be

quite important to research products currently for sale that will be similar to our

finished product. Various models of both HAWT and VAWT windmills, as seen in

Figures 5 and 6, were found on the market which ranged from $35 to $50, 8” to 12”

in height, and power outputs of 1.7 volts to 10 volts. Some products had features

including variable numbers of blades and energy storage to play music from the

power generated5.6. The construction methods for all of the researched patents7,8,9

as well as the current products were also studied. All specifications, features, and

methods were considered in developing concepts for the design team’s windmill

kit.

3.2 Problem Decomposition

Before beginning the internal search and brainstorming of concepts, the problem needed to be

clarified and broken down into simple sub-problems. Initially a simple black-box model10 was used to

visualize the inputs and outputs of our system in the categories of energy, material, and signal as

attached in Appendix E.2. Next the black-box model was broken into sub-functions in a function

diagram as in Figure 7. This allowed the design team to see how the individual elements of the product

Figure 5 - HAWT windmill on market: WindLab Jr.

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Figure 6 - VAWT windmill on market: Picoturbine

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Wind Energy

interact to create the overall function of the system. This could then be used to focus ideas on making

sure all sub-functions of the problem are met when generating concepts.

3.3 Ideation Methods

To create a list of design ideas and concepts, basic brainstorming methods were used. Each

member of the design team individually came up with a list of ideas. Non-conventional, and perhaps

unrealistic, ideas were encouraged to refine into the best possible idea. The team later met to discuss

the individual ideas generated. A second brainstorming session began as new concepts were built upon

by our previous individual ideas. Once the team felt satisfied with the brainstorming list of ideas, they

were organized into a concept combination chart as shown in Figure 8. This made it easy to visualize the

different ideas, as well as aided in combining the ideas to create finalized concepts for the windmill

product.

Axis Orientation

Blade Number

Blade Type

Blade Attachment

Generator Location

Drive Type

Output Base Type

Accessories

Horizontal Axis

3 Twisted Sheet

Snap-in Housing Straight Measurable 4-Leg Stand

Clear Housing

Vertical Axis

2 Airfoil Fixed Base Geared Drive

Measurable and Visual

with switch

Desk Light Stand and Base

Rotating Housing

Variable (2-6)

Sandwich in Hub

Measurable, Visual, and

Audible

Adjustable Height

Twist Lock Adjustable Pitch

Figure 8 - Concept Combination Chart

Pointing Mechanism

Turbine

Shaft PowerGeared

Transmission

T*w

GeneratorElectric Power

Visual Display

Vibration and Drag Forces

StructureDeflection and

Stresses

Velocity and Angle of Wind

Figure 7 – Function Diagram

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3.4 Description of Design Concepts

Concept A, as shown in Figure 9, utilizes a horizontal axis

design with the rotor leading the housing. The output of the motor

will be sent to electrical connectors for connecting a digital multi-

meter. The stand is a four-leg truss that can be separated from the

collar and broken down into four flat sections. The hub is attached

directly to the generator’s shaft by means of a setscrew. The

generator is held inside a plastic housing. The three twisted sheet

blades are secured in the rotor hub. The pitch of the blades cannot

be adjusted. The height of the housing / rotor assembly is adjusted by sliding

the support shaft up and down in a collar at the top of the base. The housing

is attached to a support tube directly under the center of gravity of the

housing / rotor assembly.

Concept B, as shown in Figure 10, utilizes a vertical axis Darrieus rotor

design. The generator is wired to connectors to measure electrical output

and an LED for visual outputs. The base has four legs and supporting trusses.

The generator is positioned vertically under the base and connected directly to

the vertical drive shaft. The four plastic sheet rotor blades are attached

to a vertical shaft. The blades are permanently attached to the base of

the shaft and secured during assembly to the other.

Concept C, as shown in Figure 11, utilizes a horizontal axis

design with the rotor leading the housing. Motor output is sent to

connectors for multi-meter connection to measure output or an LED for

a visual output. The stand uses a square base and tubular support to

hold the housing approximately 12 inches from the base surface. The

drive shaft is attached to gears to increase the speed of the generator

shaft. The housing is of a two-piece split design. The number of airfoil

blades can be changed between 2, 3, and 4. The hub splits into two

pieces and pinches the blades. A fin is attached to the housing to align

the rotor perpendicular to the wind direction.

Concept D, as shown in Figure 12, utilizes a horizontal axis

design with the rotor following the housing. The motor is wired to a

circuit board containing an LED, a speaker, and connectors for visual,

audible, and measurable outputs. The stand uses a square base and

tubular support to hold the housing approximately 14 inches from the

base surface. The motor is located in the base therefore; the drive shaft drives a set of bevel gears,

which changes the direction of the drive shaft down the stand. The housing is a low profile design to

reduce wind turbulence as the wind passes over it. The hub accommodates two twisted plastic sheet

blades. The pitch of the blades can be changed by moving the blades between different sets of

Figure 9 - Concept A

Figure 10 - Concept B

Figure 11 - Concept C

Figure 12 - Concept D

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opposing holes in the hub. The stand allows for the rotation of the housing / rotor assembly

perpendicular to the wind.

3.5 Concept Selection and Combination

To narrow down the concepts to one final idea,

concept scoring matrices were implemented. To create the

scoring matrices, the selection criteria needed weighting.

The analytical hierarchy process (AHP)10 was used to find

these weightings. Each customer need’s importance to the

product was compared against the others in order to create

a weighting for them. This rating was then rounded to even

numbers to create a final weighting for that specific

customer need. See Appendix E.9 for the full AHP Matrix.

The results of the AHP are shown in Figure 13. It was found

that performance, educational value, ease of assembly and

disassembly, and safety are the most important customer

needs with a final weighting of 0.15. It was also found that

low cost and industrial design are the least important customer needs with final weightings of 0.05. The

generated concepts in the concept combination table were each given a score from one to five with one

being the worst and five being the best, in each of the customer needs. This rating was then multiplied

by the customer needs’ respective weighting factor. These new weighted scores were totaled to give

the score for each concept. These could now be compared and ranked to determine which ideas were

best. These selection matrices are attached in Appendices 8.10 – 8.14. Looking at the rankings of the

elements from the concept combination table, the design team created four concepts that incorporated

the best combinations of these elements. Using the same process as before, a selection matrix for

comparing the four concepts was created and is attached in Appendix E.8. After creating the selection

matrix it was found that concept C was the best for the customer needs. Concept B was second best,

followed by concept D and finally concept A. The final concept consisted of a horizontal axis wind

turbine with a variable number of twisted blades that get enclosed in the hub for attachment, a desk

light style stand and base, a geared drive with the motor in the housing, a clear housing that rotates to

always be in the direction of the wind, and both a measurable and visual output with a switch to avoid

power losses for the visual output of lights. With using gears, the design team can increase the RPM of

the generator. This sacrifices torque on the generator, however it is more important to operate the

turbine close to its peak efficiency.

4. System Level Design

We selected concept C with the addition of a few changes. The concept utilizes a horizontal axis

design with the rotor leading the housing. The number of plastic blades can be changed between 1, 2, 3,

4, and 6. Three different blade shapes will be included in the final package to allow students to

experiment with different rotor designs. The hub splits into two pieces and screws back together

sandwiching the blades between the two pieces to secure the blades. The hub is attached to the drive

Total Weight

Final Weight

Low Cost 5 0.0568 0.05

Industrial Design 3.5 0.0398 0.05

Performance 13 0.1477 0.15

Durability 9 0.1023 0.1

Educational Value 12 0.1364 0.15

Ease of A/D 13 0.1477 0.15

Safety 15 0.1705 0.15

Compactness 7.5 0.0852 0.1

Simplicity 10 0.1136 0.1

Figure 13 - AHP Results

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shaft by means of a shaft with protruding flanges, similar to a K’NEX shaft, and matching collar. The

drive shaft is attached to gears to increase the speed of the generator shaft. The generator is secured in

the housing by the two clamshell pieces when assembled. The generator is wired to a switch, which

directs power to either connectors or LEDs for measurable or visual outputs. A fin is attached to the

rear of the housing, which rotates 360 degrees to align the rotor perpendicular to the wind direction.

The housing is attached to the stand at the housing / rotor assembly’s center of gravity. When fully

assembled, the housing sits 12 inches off of the base surface.

5. Detail Design

5.1 Detail Design Description

The design will have an

adjustable number of blades

between 1, 2, 3, 4, and 6 blades.

The hub will separate into two

pieces and be fastened together

with threaded pins and thumb

nuts to secure the blades in

position. The blades will be

tapered and measure six inches

in length. The total rotor

diameter will measure about 15

inches. The hub will be attached

to the drive shaft by a shaft with

protruding extensions fitting into

a matching collar fitted inside the

outer hub. Gears with a 2:1 ratio

will be utilized to increase the speed of the generator shaft and provide educational value. Ribs in the

interior of the clear housing will be used to secure the generator and provide structural support for the

housing. The housing will be a two-piece top and bottom design assembled with screws. The centerline

Figure 15 - Final Design Exploded View

Figure 14 - Final Design Assembled View

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of the housing will be 12 inches from the base surface. A fin will be located at the rear of the housing to

orient the rotor perpendicular to the wind by rotating the housing and stand in the base. The blades,

hub, housing, fin, and gears will all be made of polystyrene. The generator will be wired to a switch to

manually select the power output mode. Connectors will be located at the bottom rear of the housing

to allow for measuring power output. LEDs will be placed in the clear housing for visual power output.

All electrical connects will be color-coded for easy assembly. The steel stand will sit in a tube attached

to the steel base. All screws will be 2-56 and of the same length for ease of assembly.

5.2 Calculations of System Performance

To determine the performance of the design team’s wind turbine system, the actual efficiency

of the motor needed to be determined. By finding the input power and output power of the generator

through the use of the specified data provided by the Jameco website15 , the motor manufacturer, and

attached in Appendix E.6, a plot of the generator’s efficiency could be made. The plot for power input

was produced using the equation Power=Torque*ω. The torque in this equation14 was found using the

equation Tin=Kt*Ia+Tloss. Ia in this equation is the armature current which was found by the equation

Ia=Ke*ω/(RL+Ra), where RL+Ra was found to be 17 ohms.14 Kt is the torque constant and it is found by

using the data on the Jameco website and taking torque/current. The output torque was found by using

the equation Tout=Kt*Ia.14 The power was then found by again multiplying the torque by ω. Once this

data was found, the efficiency could be found by taking the power input/power output. The results are

plotted in Figure 17 and the governing equations are attached in Appendix E.5. Also, the design team

ran tests to create experimental efficiency data as well. This was achieved by attaching a power drill to

the generator and recording power outputs across a 10 ohm resistor at various speeds. This data is

attached in Appendix E.5. The data was plotted so an equation could be found for the values. The

equation found was Power=2*10-7*ω1.9. In addition to these tests, a drop test was also performed to

find different power inputs to the system. This was done by attaching a .625in radius wheel to the shaft

of the motor, and attaching weights to a string and dropping them to find the power inputs. Using the

equation previously found, the design team could use data points for the same speeds of the drop tests

to find the efficiency. This data is shown in Appendix E.5 and the results are in Figure 16.

0

0.1

0.2

0.3

0.4

0.5

0

2

4

6

8

10

0 2000 4000 6000 8000

Po

we

r (W

atts

)

Speed (RPM)

Power and Efficiency

Power Input

Power Output

Efficiency

Test Efficiency

Figure 16 - Jameco motor 238473 power and efficiency

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From analyzing this graph it was found that the maximum efficiency that one can get from this

generator would be about 42%. Also, the design team needed to find the maximum efficiency of the

rotor. By analyzing the graph attached in Appendix E.4, a three blade wind turbine can achieve a

maximum efficiency of 48%. To achieve this number, a tip speed ratio of 6 to 9 must be met. Through

calculations attached in Appendix E.5 for tip speeds with the wind speed of 7 miles per hour which was

tested, it was determined that the rotor must be spinning at 1008.3 RPM to 1512.5 RPM to be in this

range. When testing the design, the design team found that their rotor was spinning around 700 RPM.

To achieve the best efficiency, 2:1 gearing will be used to increase the generator speed to 1400 RPM.

When looking at Figure 17 for 1400 RPM, an efficiency of about 22% can be expected. To find the power

output expected, the maximum amount of power achievable for a circular cross section of wind was

found. This power was 1.777 Watts. It was assumed that there are 25% mechanical losses in the

generator, which left the power at 1.333 Watts. Finally, using the efficiency of 22% found for a rotor

speed of 1400 RPM, it was found that the power the design team can expect from the wind turbine is

0.293 Watts.

5.3 Material Selection

An important consideration for the design team was the selection of materials for AirTwist.

Proper materials help to ensure a low production cost and appropriate structural properties. Figure 17

describes the materials which will be used for each part of the mass production unit. Parts omitted from

this table include the motor, gears, shaft, LED’s, resistors, wire, electrical connectors, and fasteners

which will all be bought from outside manufacturers. Polystyrene (PS) plastic was chosen because of its

low cost and good structural properties18. The housing portion of the product will be made of clear

Polystyrene plastic so that students can observe the inner workings of the wind turbine18. Steel was

used for the base and support pole to provide strength, but most importantly weight. The final design

must be heavy enough so that when the fan is turned on, the wind turbine does not slide away from the

fan.

Part Description Material

Outer nose-cone Polystyrene Plastic

Inner nose-cone Polystyrene Plastic

Blades Polystyrene Plastic

Motor and Gears Housing Clear Polystyrene Plastic

Rear Fin Polystyrene Plastic

Support Pole 1020 Steel

Base 1020 Steel

2:1 Gears Polystyrene Plastic

Figure 17 - Material selection of custom-made parts for mass production

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5.4 Component Selection Process and Bill of Materials

After going through the

final design, an inventory of each

of the components of the design

was taken. When deciding how

each of these components were

going to be acquired, as in

whether the team would

manufacture them, injection

mold them, or simply purchase

them, the cost of these

procedures was taken into

account as shown in Figure 18. It

was determined that the plastic

parts such as the nose cone, the

blades, and the gears would be

best to use injection molding.

Many of the standard parts such

as threaded rods, nuts, shafts,

switches, and lights will be

bought from McMaster. Finally,

the non plastic parts that have

somewhat irregular shapes such

as the fin on the back of the

windmill as well as the base for the windmill could be manufactured by the company. After performing

a cost analysis for these components, it was found that the cost to produce one wind turbine would be

$12.42.

5.5 Fabrication Processes

For mass production of AirTwist, the following

plastic pieces will be molded: outer hub, inner hub,

blades, housing, and rear fin. The support pole will be

cut from stock steel pipe and the base will be made

from a die cast. These pieces will be placed on the

assembly line along with the parts purchased from

outside vendors, which include the motor, gears, shaft,

LED’s, wire, and electrical connectors.

First, the motor, gears, shaft, and LED’s will be mounted into the housing shell. The wires will

then be connected from the motor to the LED’s which will be wired in parallel, as shown in Figure 19.

The upper half of the housing shell will then be placed on top and screwed into place. Next, the tail fin

Component / Category Quantity How Acquired Cost

Nose Cone 4 Injection Molded $0.30

Blades 18 Injection Molded $1.20

Threaded Rods 10 Purchased $0.40

Thumb Nuts 6 Purchased $0.33

Housing 1 Injection Molded $0.61

Gear Shaft 1 Purchased $0.42

LED Lights 4 Purchased $0.40

2:1 Gears 1 Injection Molded $0.40

Electrical Switch 1 Purchased $0.40

Motor 1 Purchased $3.54

Fin 1 Injection Molded $1.09

Base 1 Manufactured $0.65

Support Shaft 4 Purchased $0.40

Support Pole 1 Purchased $0.10

Wires 4 Purchased $0.20

Output Terminals 2 Purchased $0.25

Labor ---- Hired $0.64

Packaging / Marketing 1 Purchased/Printed $0.40

Shipping ---- Hired $0.25

Development Cost ---- Hired $0.44

Total Cost $12.42

Figure 18 - Component Process Table

Figure 19 - Wiring Schematic

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will be screwed onto the bottom of the housing unit. Lastly, the completed motor unit and remaining

parts will be placed into the packaging. The rest of the parts will be assembled by the students when

they put together the wind turbine in their classroom.

5.6 Construction of alpha prototype

Construction of the alpha prototype began

with the rapid prototyping of the outer hubs as

shown in Figure 20, the inner hubs as shown in

Figure 21, and the inner ribs for holding the

generator. Once this was completed a racquetball

container was cut in half to serve as the clear plastic

housing to hold the inner ribs as shown in Figure

22. Threaded rods were cut to size and glued into

the outer hub as shown in Figure 19. The base was

made out of steel with a hole was cut in it, and

tapped for threading a stand into the base. A PVC

shaft was fit over the base, as shown in Figure 23,

and a cap was purchased to fit on top of the PVC

shaft. This cap was cut and glued to fit the clear

plastic housing. The blades were made out of bass

wood, and different designs and sizes were cut and

glued to balsa wood supports for attachment like in

Figure 24. These supports were cut at angles for proper pitch, and had holes

were drilled in them for connection over the threaded rods. A clear plastic

piece was cut and glued onto the back of the housing, as were two smaller

plastic pieces to hold the large tail fin which too was cut out of plastic. These

two pieces as well as the tail fin had holes drilled in them to hold them

together with screws. The assembly of all of these pieces is shown in Figure

25. The gears were attached to the shaft of the generator as well as the shaft

attached to the nose cone. Another gear is used as a washer to hold this shaft

in place. Two K’NEX pieces are used as a locking mechanism for connecting

the nose cone and hub to the shaft. The parts that need to be assembled by

the consumer include screwing the stand into the base, attaching the blades to

the nose cone and hub, and securing them with thumb nuts. The thumb nuts ensure that the blades are

unable to fly out when the rotor is spinning. Placing the PVC shaft over the stand and placing the

housing on top of the PVC shaft must be done as well. The tail fin needs to be attached through the use

of two screws and two thumb nuts. The nose cone and hub also need to be attached to the shaft simply

by pressing these assembled pieces on to the shaft. Once assembled the final product appears as in

Figure 26.

Figure 20 - Outer Hub Figure 21 - Inner Hub

Figure 22 - Motor Housing Figure 23 - Base, Stand, and Shaft

Figure 24 - Blades Figure 25 - Tail Fin

Figure 26 - Final Assembly

12

5.7 Differences between alpha prototype and mass production unit

There were a few differences between the alpha prototype model and the mass production

version of AirTwist. The first difference is with the assembly of the motor housing. For the alpha

prototype, a pre-made clear, plastic tube was bought and a rib structure was rapid prototyped to fit

within the tube. This was done because the design team desired to have the motor housing made out of

a clear material so that the students could observe the inner components of the wind turbine. However,

the mass production design called for a two piece clear motor housing (resembling that of a handheld

drill) which was too expensive to make for the alpha prototype. This difference is demonstrated in

Figure 27 and 28.

Figure 27 - Mass Production Housing Figure 28 - Alpha Prototype Housing Rib Cage

Another difference between these two units is the construction of the rear fin. The alpha

prototype model is made out of balsa wood and dowel rods. However, this material is very fragile and is

not well suited for mass production. Therefore, the mass production unit will have a fin made out of

molded plastic. The nose-cone of the mass production model will also be made out of molded plastic,

unlike the alpha prototype which has a nose-cone made from a Rapid Prototype machine. The other

difference is that the support pole of the alpha prototype is made from a PVC pipe. For large scale

production, this piece would be made from steel.

5.8 Testing of Alpha Prototype

5.8.1 Test Setup and Initial Testing

To test the alpha prototype of the wind turbine the design team prepared a box fan and an

anemometer. This was used to measure the precise wind speed of the fan. The wind turbine was

placed in front of the fan, and the switch was set so that the current was sent through the electric leads.

A multimeter was used to measure the current and the voltage across a 10 ohm resistor that was

produced by the generator. Using the equation power=voltage*current, the output power could be

determined. The initial testing of the alpha prototype with the rapid prototyped and molded blades was

unsuccessful. The wide base and narrow tip of the blade did not provide enough torque to spin the

geared generator. As a secondary test, a rough blade design was constructed out of balsa wood and the

13

turbine rotated at 700 RPM. This second test showed the geared turbine would spin at the design speed

of 1000RPM if properly designed.

5.8.2 Taguchi Design Array Testing and Results

In order to determine the best blade design a Taguchi design array was developed and tests

were run to collect data for analysis. See Appendix E.20 for the full results of the Taguchi array. The

Taguchi testing varied parameters of blade length, mid-blade width, and edge angle to optimize the

blade rotation speed/power output. The test results lead to the conclusion that a rectangular blade

with a length of 5 inches and a width of 3 inches was the best design for power optimization. After the

Taguchi testing was completed, testing for the optimum number of blades was done. Tests for 2, 3, 4

and 6 blade configurations were completed. From this test, it was concluded that 4 of the rectangular

blades produced the most power. As construction of the production modeled continued from the alpha

prototype, the power output slightly decreased with added features. Testing was again done with

various blade designs left over from the Taguchi testing and the number of blades to ensure the selected

blade design and number was optimized. Although the power had decreased, the origin test results

were verified. Tests were completed with a single blade and two different blade shapes on the hub in

an attempt to get more power out of the wind turbine. These final tests produced positive results. Two

rectangular blades and two wide tip/narrow base blades produced more power than previously tested

configurations. With these results, the test day configuration was set to the two and two design.

5.8.3 Durability Testing

Along with performance testing, durability testing of the wind turbine was done as well. The

design team allowed the turbine to spin for an extended period of time at the same speed and observed

that the performance of the turbine had not diminished. Also repeated assemblies and disassemblies of

the windmill took place and wear on any of the components was not observed.

5.9 Economic Analysis

To ensure that the proposed design will be able to sustain itself, the team performed a net

present value (NPV) analysis to predict the long-term financial profitability of the project10. Assuming a

manufacturing rate of 100,000 items per year

at an interest rate of 10%, it was found that the

product would be profitable during the fourth

quarter of the first year. By analyzing four

years of production, the projected net present

value was found to be $3.95 million. Figure 29

shows a listing of similar wind powered

educational toys and their market price (see

Appendix E.16 for pictures of products). This

analysis is based on production costs of one item to be $12.42 (found from Figure 13 during the

Similar Wind Powered Educational Toys

Product Price

Loopwing Wind Power Generator Set11 $46.49

Solar Wind Turbine12 $39.00

WindLab Jr.6 $35.00

Wind Power Science Kit13 $47.95

Figure 29 - Price Comparison

14

component selection process) and the selling value to be $30.00, thus competing with similar products

on the market. See Appendix E.13 for the detailed NPV chart.

6. Conclusion

Upon completion of the AirTwist educational wind turbine, the design team was very satisfied

with the results. The team feels that this product is a viable product for further development and

eventual production. When focusing on the customer needs, the most important categories were safety

and educational value. The design team addressed these areas by designing a secure locking system for

the blades that rotates slower from gearing. For the educational value, AirTwist allows the user to

switch between multiple blade and height combinations. Because of these design elements, AirTwist

could be an educational product sold to either children or teachers to assist in demonstrations in the

classroom. By allowing students to experiment with different features of the wind turbine, AirTwist

would provide teachers with multiple opportunities to teach their students about factors affecting the

design of wind turbines.

When looking back on the entire project, there are a few areas of the design which could be

improved upon. The blades are sometimes difficult to attach, as they must first be laid onto the hub,

and then all of the blades need to be simultaneously lined up with the nose cone. At times this can be

difficult. A possible improvement would be to redesign the connecting portion of the blade into the

hubs. The design team also feels that different blade shapes could be looked into. These include curved

and twisted blades, as all blades were flat. The addition of blades that have rounded edges would also

increase the safety of the final product. Finally the output device could be switched from a single

Christmas light to a series of lights, possibly LED’s, which turn on in succession based on the power

generated.

Overall, there were many valuable topics learned upon completion of the project. Along with

learning the history and basic information about wind power generation and wind turbines, the design

team learned a great deal about the production of a design, as well as the testing and refinement of that

design. Perhaps most importantly, valuable experience was gained in proposal and report writing.

Expressing design ideas and results in a well documented report was a skill that had been used very little

in course work until this project, but will prove to be valuable in the future when working on other

projects.

However, there were aspects of the project which did not turn out to be as beneficial as they

were time-intensive. Seeing errors made on previous proposals and reports was extremely insightful,

but much of the time spent on preparing the next report was used mostly on fixing the errors of the past

reports. For the final paper, changing one thing from a previous report could mean major changes to

the entire report, resulting in a very time consuming process. Yet overall, this project was a valuable

lesson in understanding the design process and the skills needed to effectively portray and express a

design. Through many mistakes and set-backs, the team was able to fully understand what is associated

with producing a successful product and will be able to take these skills with them on future projects.

15

Appendix A - References

1 Dodge, Darrell. “Illustrated History of Wind Power Development.” TelosNet. 2006. 28 March 2008.

<http://www.telosnet.com/wind/>.

2 “Renewable Energy Education.” Wisconsin K-12 Energy Education Program. 2001. 5 April 2008

<http://www.uwsp .edu/cnr/wcee/keep/Renewable%5FEnergy%5FEducation/>.

3 Ward, Logan. “Windbelt, Cheap Generator Alternative, Set to Power Third World.” Popular Mechanics. November 2007. 10 April 2008 <http://www.popularmechanics.com/technology/ industry/ 4224763.html?series=37>.

4 "Savonius Wind Turbines.” Renewable Energy United Kingdom. 2008. 20 April 2008

<http://www.reuk.co.uk/Savonius-Wind-Turbines.htm>.

5 "Awesome Energy Science Fair Projects." Picoturbine Windmill Kit. 6 April 2008 <http://www.super-science-fair-projects.com/energy-science-fair-projects.html>.

6 "Windlab Jr. Wind Turbine Educational Kit." Sundance Solar. 6 April 2008 <http://store.sundancesolar.com/wijrwitukit.html>.

7 Lin, Chen-Hsiung. "Toy Windmill." Google Patents. 26 Oct. 1999. 6 April 2008

<http://www.google.com/patents?id=WVYWAAAAEBAJ&pg=PA1&lpg=PA1&dq=United+States+ Patent+5971828&source=web&ots=SsPnqNPf9M&sig=pca8wAlJ4l_tuEj0_9Gfd5vdFew&hl=en#P PA1,M1>.

8 McCabe, Francis J. "Windmill Structures and Systems." Google Patents. 23 Jan. 1998. 6 April 2008 <http://www.google.com/patents?id=YC4FAAAAEBAJ&dq=windmill+airfoil+blade>.

9 Steven, Goldberg B. "Vertical Axis Wind Turbine with a Twisted Blade Configuration." Google Patents. 11 Apr. 1995. 6 April 2008 <http://www.google.com/patents?id= aKciAAAAEBAJ&dq=hawt+windmill>.

10 Ulrich, Karl T., and Steven D. Eppinger. Product Design and Development Fourth Edition. New York, NY: McGraw-Hill, 2008.

11 “Wind Power Kit.” Popgadget. 5 April 2008 < http://www.popgadget.net/2007/09/ wind_power_kit.php>.

12 “Solar Wind Turbine.” The Green Shop. 6 April 2008 <http://www.greenshop.co.uk/acatalog/

index.html>.

13 “Wind Powered Science Kit.” Discover This: Educational Science Kits and Toys. 2008. 28 March 2008

<http://www.discoverthis.com/wind-power-science-kit.html>.

14 Hau, Erich. Wind Turbines. Springer, 2005.

16

15 "Jameco Electronics." 15 April 2008 <www.jameco.com>.

16 "Wind Energy Manual." Iowa Energy Center. 2008. 7 April 2008 <http://www.energy.iastate.edu/

Renewable/ind/wem/windpower.htm >.

17 United States Plastic Corporation. 2008. 28 April 2008 <http://www.usplastic.com/catalog/

default.asp?utm_source=google&gclid=CPzCjbeEkJMCFSJ3lgodXVX6gw>.

18 Callister, Jr., William D. Materials Science and Engineering an Introduction. 7th ed. New York, NY:

John Wiley & Sons Inc., 2007.

19 Dieter, George, and Linda C. Schmidt. Engineering Design (Engineering). New York: McGraw-Hill

Science/Engineering/Math, 2008.

Appendix B – Final Design Drawings

B.1 - Final Design: Housing

17

B.2 - Final Design: Housing Half 1

B.3 - Final Design: Housing Half 2

18

B.4 - Final Design:Exploded View

B.5 - Final Design: Assembled View

19

B.6 - Final Design: Hub Detailed View

B.7 - Final Design: Hub Frontal View

20

B.8 - Final Design: Rear View

Appendix C – Dimensioned Drawings

C.1 - Dimensioned Drawing: Base

21

C.2 - Dimensioned Drawing: Blade

C.3 - Dimensioned Drawing: Bottom Housing

22

C.4 - Dimensioned Drawing: Top Housing

C.5 - Dimensioned Drawing: Fin

23

C.6 - Dimensioned Drawing: Outer Hub (4 pin)

C.7 - Dimensioned Drawing: Inner Hub (4 pin)

24

C.8 - Dimensioned Drawing: Outer Hub (6 pin)

C.9 - Dimensioned Drawing: Inner Hub (6 pin)

25

Appendix D – Educational and Instructional Manual

26

Page

History of Windmills…………………………….……………………………. 2-3

Part List…………………….………………………………………………………… 4

Instructions for students.…………….…….…..………………………… 5-10

Instructions for teacher…………………………..………………………..11-12

Table of Contents Table of Contents

27

So you want to learn about wind power! First, we need to understand the

history of wind turbines and how they have changed over the years.

A BRIEF HISTORY

Wind power for mechanical work dates back as early as 300 BC when

the Persians were said to have used it for grinding grain. This technique

continued until 250 AD when it was introduced to the Romans. The more familiar

Dutch windmill, as seen in Figure 1, was not used until the 14th century. Dutch

windmills were primarily used to drain areas of the Rhine River delta. In 1887,

the first windmill was built for producing electricity by Prof James Blyth of

Scotland. Not until 1931 however would the first modern looking windmill be built

in Yalta, USSR. This windmill had an efficiency of 32% which is comparable to

current windmill efficiencies. Another milestone occurred in 1931 when the first

Darrieus rotor wind turbine was created, much like the one illustrated in Figure

2. As the years go by, sleeker designs of blades and rotors continue to be

developed and improved upon. One of the most recent developments occurred in

2007 when a wind belt was invented that does not use a rotor; rather it relies on

the current from vibrations in the wind. This new invention can produce power at

1/10 the price per watt of the traditional wind turbines.

VERTICAL VS. HORIZONTAL

So why do Figure 1 and 2 look different and are they both called windmills? As a matter of fact

they are. These figures represent two different kinds of wind turbines, horizontal and vertical axis

turbines. Horizontal axis turbines have the spinning rotor at the top of the windmill, and they must be

facing the wind such as the Dutch windmill in Figure 1. Many windmills that you have probably seen look

like this and most likely had a tailfin on them. This tailfin is used to direct the wind turbine into the wind

to produce the most energy. When it is time to build AirTwist, you will have the chance to attach the

tailfin to your windmill.

Vertical axis turbines however, do not have to be facing into the wind which is ideal for areas of

turbulent winds. Turbulent wind simply means that the wind is unpredictable and blows in many directions.

The most common vertical axis turbine is the Darrieus rotor as shown in Figure 2. Unlike horizontal axis

turbines, the vertical axis turbines can be placed low to the ground which is useful in areas that restrict

the height of structures. For horizontal axis turbines, the higher they are built, the faster the wind blows.

The faster the wind blows the more energy the turbine can produce. Although vertical axis turbines sound

more advantageous, they tend to produce electricity at only 50% of what the horizontal axis turbines can

History of Windmills History of Windmills

Figure 2 - Dutch Windmill

Figure 3 - Darrieus Windmill

28

produce. This makes them less common than horizontal axis turbines which you and I are most common

with.

BLADE DESIGN

So why are there so many

different styles of wind turbines?

Over the years, various blade designs

and configurations have been

experimented on wind turbines. As

people began to understand the

principles behind how wind power

worked, newer designs became more

efficient and could generate more

power. Today it’s your turn to

experiment and learn the same

things that other wind turbine

builders have learned in the past.

Figure 3 shows some of the things

they learned. This graph represents

a few blade designs and

configurations that are currently used today and describes the relationship between tip speed ratio and

efficiency. Tip speed ratio is the ratio of the speed of the tip of the blade and the speed of the wind.

Efficiency refers to how well the wind turbine generates power. The higher the efficiency, the better the

wind turbine.

Have you ever seen a wind turbine in real life? How many blades did it have? Many current wind

turbines typically have three blades, which means they have a three-bladed rotor. From looking at Figure

3, why do you think that the designers choose to use three blades?

You may have noticed in the graph that the three-bladed rotor has the highest efficiency

compared to all the other windmill designs. This is why so many current windmills have three blades.

However to achieve that efficiency, designers must make sure that the tip speed ratio falls between 5 and

9. If the windmill has a different tip speed ratio, then perhaps another design would be better. Rather

than just talk about what may happen, let’s start building a windmill. AirTwist is unique and will allow us

to change the number of blades and the actual blade shape to see what happens to the power we

generate.

Figure 4 - Tip speed ratio vs. Efficiency of common Wind Turbines

29

Part List Part List

P

Metal Base Support Pole Green PVC Pipe (x4)

4-pin Inner Hub Motor Housing 4-pin Outer Hub

6-pin Inner Hub 6-pin Outer Hub Tail Fin

Blade – Type A (x6) Blade – Type B (x6) Blade – Type C (x6)

Thumb Nut (x6)

Multimeter and cables

Included in This Package:

NOT Included in This Package:

Box Fan

Blade Balancer for one

blade rotor design

10 ohm Resistor

Screws and Nuts (x2)

30

The following instructions will show you how to put together your AirTwist Wind Turbine. For your

first experiment, we will be making a three-bladed rotor with blade type A. The wind turbine will stand 10

inches off the ground.

Now that you have read the safety warning, it’s time to start building! Follow the steps below and

soon you will be generating power!!

1) ASSEMBLE THE SUPPORT STAND

Take the metal base and screw in the support pole. Make sure that the AirTwist logo is facing

towards the support pole.

Next, slide the green PVC pipe overtop of the support pole. For your first experiment, use the

green PVC pipe labeled 10”.

SAFETY WARNING: AirTwist includes moving parts which may be very dangerous if not properly handled. When AirTwist is set up in front of a fan, move everything away from the blades, especially fingers!! If you must adjust something on AirTwist, turn the fan off and wait for the blades to stop rotating before touching the wind turbine.

Instructions Instructions

31

2) ATTACH THE MOTOR HOUSING

Located on the bottom of the motor housing is a yellow cap. Slide this cap onto the top of the

green PVC pipe.

3) INSERT THE TAILFIN

Slide the tailfin into the groove located on the back of the motor housing. The tailfin has two sets

of holes located on it which line up with holes on the back of the motor housing. Align the tailfin

in the following direction.

Next, slide the two screws through the holes and tighten them with their corresponding nuts on

the other side.

This tailfin will ensure that your wind turbine is always directed into the wind.

32

4) CHOOSE YOUR BLADE SHAPE

AirTwist includes three different blade shapes, labeled A, B, and C. Find the six blades labeled

with the letter A. Blades with the letter B and C on them can be put back in the box for now.

5) CHOOSE THE NUMBER OF BLADES

For your first experiment, we will only be using three of the blades labeled A. You can put the

remaining three blades back in the box.

6) ATTACH THE BLADES TO THE HUB

For a wind turbine with three blades, we will need to use the 6-pin hubs. Find both the inner and

outer hub labeled 6-pin. Slide three of the type A blades into the slots of the 6-pin inner hub

(green hub) so that they are evenly spaced. When placing the blades in the grooves, make sure

that the green side is touching the green hub and the yellow side is touching the yellow hub.

Next, slide the 6-pin outer hub (yellow hub) through the holes of the 6-pin inner hub (green hub),

making sure that the arrow on the outside of the hubs line up. Notice that the yellow side of the

blade is facing the yellow hub.

33

To fasten the two hubs together, take three thumb nuts and tighten them onto the screws of the

slots with blades in them.

When complete, you will have formed the rotor for the wind turbine.

7) ATTACH THE ROTOR TO THE MOTOR HOUSING

With your finished rotor, slide the hub onto the shaft sticking out of the motor housing. Press

firmly until the hub is securely attached to the shaft.

8) PICK YOUR POWER OUTPUT

AirTwist allows you to switch between two different power output settings. By flipping the switch

on the motor housing towards the picture of a light bulb, AirTwist will light up a single light to

visually show you the power being generated. The more power generated, the brighter the light

will get. If the switch is flipped towards “1,2,3”, AirTwist will allow you to read out your generated

power through a multimeter (which your teacher will provide).

34

For this experiment, flip the switch towards “1,2,3”. Obtain the multimeter and a 10 ohm resistor

from your teacher. Plug in the cables to their matching ports on the wind turbine. The red cable

goes to the red port and the black cable goes to the black port. Set the multimeter down on the

table behind the wind turbine.

Ask your teacher to set up the multimeter so that it will read the power in miliwatts. Your

teacher will also assist you in attaching the 10 ohm resistor to the cables of the multimeter.

9) PREPARE FOR TESTING

You are almost ready to test your wind turbine. First we need to get our wind source. Ask your

teacher to set up a box fan on the floor or a test table. Place your assembled wind turbine 3 feet

away from the fan. Next, make sure that any loose objects are cleaned up around the wind

turbine.

10) START MAKING POWER!

After making sure everyone is standing away from the wind turbine, turn on the fan! The

multimeter will display the power generated in miliwatts. After you record the power generated,

turn off the fan and wait for the rotor to stop spinning. Switch the output to the light bulb to

see what happens. Remember, only touch the wind turbine when the fan is turned off and the

rotor has stopped spinning.

11) COMPARE YOUR RESULTS

Now that you have successfully gotten the wind turbine to generate power, it’s time to compare

different blade shapes and different number of blades. Using the remaining blades left in the

box, experiment with different shapes and different amounts of blades. Try using 1, 2, 4, and 6

blades on the rotor.

35

** To make the 2 and 4 bladed rotors, you will need to use the 4-pin inner and outer hubs.

Attach the blades in the same way that you attached the blades to the 6-pin hubs.

** To make the 1 bladed rotor, you will need to attach the blade balancer. Attach the blade

balancer in the same way you would a normal blade. Make sure that it is lined up directly

opposite of the single blade you are also attaching.

Remember, don’t be afraid to be creative!!

Mix and match blades to see what happens to the performance. What does this do to the weight

distribution of the rotor? Would a real wind turbine behave the same as our smaller model? What other

changes could you make?

36

ADDITIONAL ITEMS NEEDED

Before you give your students the chance to experiment with AirTwist, you will need to get a hold of the

following items:

Box Fan

Multimeter with necessary wires

10 ohm Resistor

After you have these items, you are ready to use AirTwist.

BUILDING THE AIRTWIST KIT

First, read through the background section and student instruction set yourself so that you have an idea

of what they will be building. Next, give your students the AirTwist kit and Instructions labeled for

students. As they follow the instructions, they will be asked to retrieve the box fan, multimeter and 10

ohm resistor from you. When they reach the step with the multimeter, set the device up in the following

manner. Plug the red and black cables into the correct female jacks on the multimeter. Turn the knob so

that it is reads in DC millivolts. Next, attach the 10 ohm resistor across the connectors from the

multimeter. Using a second set of cables, connect each end of the resistor into the female ports located

on the wind turbine.

As your students near the end of the instructions and prepare to test the wind turbine, make sure that

they stay clear of the moving blades. The blades do spin fast and can cause injury if not properly

handled.

Throughout the building phases, encourage your students to take note of what aspects of the wind turbine

they are building, such as the rotor and tailfin. After they have tested the initial three bladed rotor,

experiment with other blade shapes and arrangements. Use the various support shafts to demonstrate

the effect of wind speed on generated power. A helpful tool to provide your students with would be an

Instructions Instructions

multimeter 10 ohm resistor AirTwist

37

anemometer which measures the wind speed. Have the students hold the anemometer at the different

heights which the rotor can be at to observe how this affects the output.

When testing these different variables, make sure to hold certain variables constant so that you can

observe a trend. For example, you make want to stick with one blade shape and rotor height, and simply

change the number of blades on the rotor. As your students modify various components of AirTwist,

make sure that they record both their observations and measured results.

AFTER THE TESTING

Once all of the testing has been completed, it is time to have your students analyze their results. A

helpful tool to visually show what they have learned is through graphs. A few examples of what they can

graph are listed below:

Power vs. blade shape

Power vs. # of blades

Power vs. height of rotor

Some relationships are harder to show through a graph and are better suited for discussion after the

activity. A few suggested topics you could talk about include:

What does gearing do to a wind turbine? How does it affect the speed of the blades and motor?

What is the importance of a tailfin?

Does mixing different blade shapes together increase or decrease the power? Why do you think

this is so?

How come adding more blades does not always increase the power?

How does changing the height affect the power? How would this apply to full scale wind turbines?

Because AirTwist has so many different design configurations, it may be helpful to have different groups

of students test different configurations. Once they finish testing, have all of your students group back

together and share with the class what they found. Using all of the group’s results, have your class

determine the various correlations between different design parameters and output power.

But the most important thing to keep in mind as you use AirTwist in your classroom, is to encourage

creativity. Let the students mix and match blades and create their own designs. Kids will be more likely

to remember what they learn when they are the ones deciding what to test. Some students may need

more guidance however during the testing. Asking them a few of the questions above and then hinting at

ways they could test that would be a good start at encouraging them to design their own windmill. As

your students play and experiment more with the windmill, you will soon find that they will get very excited

about what they are creating.

38

Appendix E – Tables, Charts, Patents, and Calculations

E.1 - Gantt Chart

E.2 - Original Project Black Box Model

Input

Output

Wind Energy →

Windmill Kit Velocity → → Visual Output

Angle of Wind Speed →

39

E.3 - Quality Function Deployment (QFD) Chart for AirTwist

Engineering Requirements Benchmarks

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x x x x x

fun x x x x x

safe x x x x

durable x x x

easy to understand

x x x

units W $ times RPM in parts

>.1 30 5 2500 >.01 20

Engineering Targets

E.4 - Wind Turbine Types and Efficiencies12

40

E.5 - Detailed Calculations

Governing equations for efficiency of motor Tin=Kt*Ia+Tloss;

14

where Ia=Ke*ω/(RL+Ra);14

RL+Ra= 17 ohms Ke= Kt=Tstall/Istall;

14=0.017 Pin=ω*Tin Tout=Kt*Ia;

14 Pout=ω*Tout

Power drill into generator data

Speed (rpm)

Voltage (V)

Resistance (ohms)

Power (W)

196 0.19 10 0.00361

397.5 0.37 10 0.01369

600 0.55 10 0.03025

804.2 0.746 10 0.0556516

997 0.993 10 0.0986049

1196 1.08 10 0.11664

1401 1.25 10 0.15625

1590 1.39 10 0.19321

1800 1.57 10 0.24649

2000 1.74 10 0.30276

2590 2.17 10 0.47089

Speed was measured with a tachometer, and power was calculated by P=V2/R. The equation found relating power to speed was found to be Power=2*10-7*ω1.9.

Drop test data

Mass (g)

Time (s)

Distance (in)

Weight (lbs)

Torque (in-lbs)

Speed (rev/s)

RPM Power In

Power Out

Efficiency

10 2.1 28 0.0002 0.00014 3.3953 203.718 0.0281 0.00488 0.173727

20 1.7 28 0.0004 0.00028 4.19419 251.651 0.0694 0.00729 0.105058

30 1.12 28 0.0007 0.00041 6.36618 381.971 0.1579 0.0161 0.101964

40 0.53 28 0.0009 0.00055 13.4531 807.184 0.445 0.06672 0.149954

50 0.43 28 0.0011 0.00069 16.5817 994.901 0.6855 0.09927 0.144802

60 0.39 28 0.0013 0.00083 18.2824 1096.94 0.907 0.1195 0.131751

70 0.26 28 0.0015 0.00096 27.4236 1645.41 1.5873 0.2582 0.162664

Mass, time, and distance were measured. The weight was a conversion to pounds. Torque=.625*weight, where .625 in is the radius of our wheel attached to motor shaft. Speed=distance/(2*π*.625*time). To find RPM, this value was multiplied by 60. The power in is

41

RPM*torque. The power out was found using our equation Power=2*10-7*ω1.9. The efficiency is just the power in/power out. Tip speed ratio = 6 6= r*ω/Vair

ω=6* Vair/r

Vair= 7 mph = 3.129 m/s r= 7 in = .1778 m ω=1008.3 RPM Tip speed ratio = 9 9= r*ω/Vair

ω=9* Vair/r Vair= 7 mph = 3.129 m/s r= 7 in = .1778 m ω=1512.5 RPM From Chart Appendix 8.4 Maximum efficiency of rotor = 48% From Figure 17 of report Expected efficiency of motor = 22% Max power of wind14 P=(1/2)*ρ*π*r^2*v^3 ρ=1.168 kg/m^3

r= 7 in = .1778 m v= 7 mph =3.129 m/s P= 1.777 Watts Torque of the rotor Trotor = P/Assuming 700 RPM rotor speed and calculated power (neglect drag) = 73.3 rad/s P = 1.777 Watts Trotor = 0.0242 N-m For a rotor spinning at 700 RPM, a torque of 0.0242 N-m must be applied to the turbine blades by the wind in order to provide 1.777 Watts to the wind turbine. Generator Output Assuming 25% mechanical losses through a transmission. = Ptran. out/Ptran. in

Ptran. out = .75 * 1.777 Watts Ptran. out = 1.333 Watts Ttran. out = Ptran. out/tran. out Gear ratio = 2:1 ωtran. out = 73.3*2= 146.6 rad/s Ttran. out = 0.00909 N-m

42

Ptran. out = Pgen. in

Assuming generator efficiency is 43% = Pgen. out/Pgen. in

Pgen. out = .22 * 1.333 Watts Pgen. out = .293 Watts

E.6 - Jameco Motor Specifications

E.7 - Concept Possibilities Matrix

Axis Orientation

Number of Blades

Blade Type Blade Attachment

Base Type Drive Type Motor Location

Output Accessories

Concept A

Horizontal 3 Twisted Sheet

Snap-in 4-Leg Stand

Straight Housing Measurable Adjustable Height

Concept B

Vertical 3 Twisted Sheet

Fixed Desk Light Style

Straight Base Visual and Measurable

Concept C

Horizontal Variable (2-6)

Airfoil Sandwich in Hub

Desk Light Style

Geared Housing Visual and Measurable

Switch Output,

Clear Housing, Rotating Housing

Concept D

Horizontal 2 Twisted Sheet

Twist Lock Desk Light Style

Drive Train Base Visual, Measurable, and Audible

Adjustable Pitch

Jameco P/N 238473

Mfg JAMECO RELIAPRO

Mfg # RF370CA-15370

RoHS? No , Find compliant

In Stock Yes

Nominal Voltage (VDC) 12

Voltage Range (VDC) 3-12

Current @ Max. Efficiency (A) 0.07

Speed @ Max. Efficiency (RPM) 1970

Torque @ Max. Efficiency (g-cm) 16

Efficiency 61.4

Terminal Type Solder

Shaft Diameter (inch) 0.078

Shaft Length (inch) 0.346

Size (Dia 0.960 x 1.213

43

E.8 - Concept Selection Matrix

Concept A

Concept B

Concept C

Concept D

Selection Criteria Weight Rating Weight Rating Weight Rating Weight Rating Weight

Low Cost 0.05 4 0.2 3 0.15 3 0.15 2 0.1

Industrial Design 0.05 2 0.1 2 0.1 4 0.2 3 0.15

Performance 0.15 2 0.3 2 0.3 4 0.6 3 0.45

Durability 0.1 3 0.3 3 0.3 3 0.3 3 0.3

Educational Value 0.15 2 0.3 2 0.3 4 0.6 3 0.45

Ease of A/D 0.15 3 0.45 4 0.6 3 0.45 3 0.45

Safety 0.15 3 0.45 3 0.45 3 0.45 3 0.45

Compactness 0.1 2 0.2 4 0.4 3 0.3 3 0.3

Simplicity 0.1 4 0.4 4 0.4 3 0.3 2 0.2

Total 2.7 3 3.35 2.85

Rank 4 2 1 3

Continue? No No Yes No

E.9 - AHP (Analytical Hierarchy Process) Matrix for AirTwist

Low

Co

st

Ind

ust

rial

De

sign

Pe

rfo

rm

Du

rab

ility

Edu

cati

on

al

Val

ue

Ease

of

Ass

emb

ly/

Dis

asse

mb

ly

Safe

ty

Co

mp

act

Sim

plic

ity

Tota

l

Wt.

Fin

al W

eigh

t Low Cost 2 1/3 1/2 1/2 1/3 1/3 1/2 1/2 5 0.057 0.05

Industrial Design 1/2 1/3 1/2 1/2 1/3 1/3 1/2 1/2 3 1/2 0.04 0.05

Performance 3 3 2 1 1 1/2 2 1/2 13 0.148 0.15

Durability 1/2 2 1/2 1 1 1 2 1 9 0.102 0.1

Educational Value 2 2 1 1 1 1 2 2 12 0.136 0.15

Ease of A/D 3 3 1 1 1 1 2 1 13 0.148 0.15

Safety 3 3 2 1 1 1 2 2 15 0.17 0.15

Compactness 2 2 1/2 1/2 1/2 1/2 1/2 1 7 1/2 0.085 0.1

Simplicity 2 2 2 1 1/2 1 1/2 1 10 0.114 0.1

Total 88

44

E.10 - Axis Oriented Selection Matrix

Vertical Axis Horizontal Axis

Selection Criteria Weight Rating Weight Rating Weight

Low Cost 0.05 3 0.15 3 0.15

Industrial Design 0.05 3 0.15 4 0.2

Performance 0.15 2 0.3 4 0.6

Durability 0.1 3 0.3 3 0.3

Educational Value 0.15 3 0.45 3 0.45

Ease of A/D 0.15 2 0.3 3 0.45

Safety 0.15 3 0.45 3 0.45

Compactness 0.1 3 0.3 2 0.2

Simplicity 0.1 3 0.3 2 0.2

Total 2.7 3

Rank 2 1

Continue? No Yes

E.11 - Output Selection Matrix

Measurable (connectors for

multimeter) Measurable and

Visual

Measurable, Visual, and

Audible

Selection Criteria Weight Rating Weight Rating Weight Rating Weight

Low Cost 0.05 4 0.2 3 0.15 2 0.1

Industrial Design 0.05 1 0.05 4 0.2 5 0.25

Performance 0.15 3 0.45 3 0.45 3 0.45

Durability 0.1 3 0.3 3 0.3 3 0.3

Educational Value 0.15 2 0.3 4 0.6 4 0.6

Ease of A/D 0.15 4 0.6 3 0.45 3 0.45

Safety 0.15 3 0.45 3 0.45 3 0.45

Compactness 0.1 3 0.3 2 0.2 2 0.2

Simplicity 0.1 4 0.4 3 0.3 2 0.2

Total 3.05 3.1 3

Rank 2 1 3

Continue? No Yes No

45

E.12 - Drive Type Selection Matrix

Straight Geared

Selection Criteria Weight Rating Weight Rating Weight

Low Cost 0.05 4 0.2 3 0.15

Industrial Design 0.05 2 0.1 3 0.15

Performance 0.15 1 0.15 3 0.45

Durability 0.1 3 0.3 3 0.3

Educational Value 0.15 3 0.45 3 0.45

Ease of A/D 0.15 3 0.45 3 0.45

Safety 0.15 3 0.45 3 0.45

Compactness 0.1 4 0.4 3 0.3

Simplicity 0.1 4 0.4 3 0.3

Total 2.9 3

Rank 2 1

Continue? Develop Develop

E.13 - Net Present Value (NPV) Chart for AirTwist

E.14 - Educational Toy Survey

Toy Survey Name:__________________________ Gender: M F Age:______________________

Favorite Toy while in Elementary School:_____________________________________________

As a kid, did you prefer toys with instruction manuals or toys which relied on your imagination? ______________________________________________________________________________

As a kid, did you enjoy educational science toys? If so, what was your favorite part about them? _____________________________________________________________________________

46

E.15 - Educational Toy Survey Results

1) Eric Carothers Male 21 Power Rangers Imagination No ____________

2) Jon Rahenkamp Male 21 Hockey Equipment Instruction Manuals No ____________

3) Andy Seward Male 20 Ninja Turtle Dome Imagination No ____________

4) Patrick Mohrbacher Male 20 Gameboy Instruction Manuals Yes, always found them interesting ____________

5) Kristen Marshall Female 13 Legos Imagination No ____________

6) Dan Mills Male 22 Legos Imagination Figuring out how to put things together ____________

7) Calvin Ruth Male 18 Legos Instructions No ____________

8) Leah Ruth Female 21 Microscope Instruction Manuals Yes, let’s you understand the world around you better ____________

9) Dustin Ottemiller Male 21 Electric Track Racers Instruction Manuals Yes, understanding how it worked ____________

10) Dustin Ottemiller Male 21 Electric Track Racers Instruction Manuals Yes, understanding how it worked ____________

11) Hailey Aranowicz Female 17 Building Blocks Imagination Yes, getting messy ____________

47

E.16 - Competing Wind Powered Educational Toys

Image 1 – Loopwing Wind Power Generator Set - $46.49 Image 2 – Solar Wind Turbine - $39.00

Image 3 – WindLab Jr. - $35.00 Image 4 – Wind Power Science Kit - $47.95

48

E.17 - US Patent A

49

E.18 - US Patent B

50

E.19 - US Patent C

51

E.20 – Taguchi Array

Taguchi Array Set-up

Run # Run Order a b c X

1 1 1 1 1 0.99 X1

2 3 1 2 2 0.84 X2

3 5 1 3 3 0.85 X3

4 6 2 1 2 0.97 X4

5 7 2 2 3 0.73 X5

6 8 2 3 1 1.29 X6

7 9 3 1 3 0.7 X7

8 2 3 2 1 1.1 X8

9 4 3 3 2 0.99 X9

Variables

a=angle

b=length

c=mid-blade width

X=voltage

Testing Parameters

a1 10 degrees

a2 0 degrees

a3 -10 degrees

b1 7 in

b2 6 in

b3 5 in

c1 3 in

c2 2 in

c3 1 in

Taguchi Array Results

Xa1 0.893333 Xa2 0.996667 Xa3 0.93

Xb1 0.886667 Xb2 0.89 Xb3 1.043333

Xc1 1.126667 Xc2 0.933333 Xc3 0.76

52

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

1.02

10 0 -10

Leve

l Ave

rage

a Values

Tip Base Angle

0.8

0.85

0.9

0.95

1

1.05

1.1

7 6 5

Leve

l Ave

rage

a Values

Blade Length

0

0.2

0.4

0.6

0.8

1

1.2

3 2 1

Leve

l Ave

rage

c Value

Mid-Blade Width

53

E.21 – Gear Specifications

Large Gear Small Gear

Number of Teeth 20 10

Pitch 26 26

Pressure Angle 20 degrees 20 degrees

Face Width .25 in .25 in

E.22 – Polymer Information Sheet18

54

E.23 – Polymer Pricing Sheet18,19