The FantastiCart

Collapsible Grocery Cart

APD 2006 Team 10 Kyle Klanow Marisa Liepa

Erling Norheim Jeffrey Waegelin

Many college students are faced with the problem of transporting groceries from the store to their home. They have to travel long distances, carry many bags at once, go up and down stairs, and consume valuable time that could otherwise be spent on schoolwork.

We have decided that this problem warrants a solution and have devised one. We have designed and built a collapsible hand cart that can easily carry multiple bags of groceries up and down stairwells that is lightweight and cost effective. We have also developed a business plan for this product which will allow for it to be sold in order to create a profit.

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Table of Contents

INTRODUCTION ..................................................................................................4

Project Inspiration........................................................................................................................................ 4

Problem Definition ....................................................................................................................................... 4

Solution Characteristics ............................................................................................................................... 4

User Profile ................................................................................................................................................... 4

Survey Data................................................................................................................................................... 5

Product Market ............................................................................................................................................ 5

Laws and Regulations .................................................................................................................................. 5

DESIGN OBJECTIVES ........................................................................................5

Survey Results............................................................................................................................................... 5

Product Differentiation ................................................................................................................................ 6

Quantification of Objectives ........................................................................................................................ 6

Cost ................................................................................................................................................................ 6

ALTERNATE DESIGNS .......................................................................................7

Jumbo Chrome Elite Metal Shopping Cart ............................................................................................... 9

Travelon Luggage Cart................................................................................................................................ 9

Clax Cart ....................................................................................................................................................... 9

VersaCart Folding Canvas Bag Cart........................................................................................................ 10

The Stair Climber....................................................................................................................................... 10

The FantastiCart ........................................................................................................................................ 10

PRODUCT DESCRIPTION.................................................................................10

Concept Generation.................................................................................................................................... 10

Concept Selection ....................................................................................................................................... 12

Alpha Prototype.......................................................................................................................................... 13

ENGINEERING ANALYSIS................................................................................18

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FEA Analysis............................................................................................................................................... 19

Dynamic Mechanism Stress Simulation ................................................................................................... 21

ECONOMIC ANALYSIS .....................................................................................23

Market Size and Demand .......................................................................................................................... 23

Market Analysis.......................................................................................................................................... 24

Capital, Annual, and Variable Costs ........................................................................................................ 26

Breakeven Analysis .................................................................................................................................... 26

Pro-Forma Income and Cost Projections ................................................................................................. 27

OTHER DESIGN CONSIDERATIONS ...............................................................28

Emotional and Aesthetic Design................................................................................................................ 28

Product Development Process ................................................................................................................... 28

Reflection of Personal Values in the Final Design ................................................................................... 28

CONCLUSIONS AND FUTURE WORK.............................................................29

REFERENCES ...................................................................................................30

APPENDIX A. BILL OF MATERIALS ................................................................31

APPENDIX B. FREE BODY DIAGRAMS...........................................................32

APPENDIX C. DESIGN PROCESS....................................................................33

APPENDIX D. TIME SCHEDULE.......................................................................33

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INTRODUCTION

Project Inspiration

Consider a college student, living in an apartment in an urban environment. He takes his car to the grocery store, and returns to his apartment in the midst of a driving rainstorm. He drives around for a few minutes, searching for a parking space close to his door, but he can’t find one, and has to park in a structure 2 blocks away. Not wanting to make multiple trips back and forth in the rainstorm, he grabs his books and multiple sacks of groceries, and trudges through the rain towards his apartment building. He gets to the door, and has to set down his many bags, open the door, transfer the bags inside, and then shut the door. Now that he’s inside, he drags the bags up the steps, sets them down again, opens the door, and repeats the shuffling process to get his groceries inside. Exhausted, with tired arms and a pile of soggy groceries, he thinks “there must be a better way…”

This problem is faced by many college students each time they return from the store. The purpose of this progress report is to clearly define the problem, recommend a product design that will solve this dilemma, and give the current status of our design. Problem Definition

There are many things that make it inconvenient to transport groceries from the store to a typical urban residence. The final product should address all of these issues and allow the user to be more efficient. To fully address these issues, the product must be able to transport a large amount of groceries a large distance, up or down stairs, and in inclement weather. The product should also be robust, collapsible for easy storage, and cost effective. It should also be visually attractive to appeal to the college student market. All of the above criteria are important, but the critical requirement is that the product must aid the user in transporting groceries or other similar items. Solution Characteristics

In addition to the main problems, the proposed design must also meet certain criteria to insure its success for both the user and the producer. Users should be able to store the product in both their homes and their vehicles. The product will be designed to carry paper and plastic grocery bags, but it should also be designed to accommodate other items, such as laundry, a backpack, small to medium sized boxes, or other small loose items. It will be designed to be used while transporting items to and from the car, but it should be able to be used in other situations as well. Based on the survey data, this product will probably be used 2-4 times per month, so it should be durable enough to withstand years of use. Because this product is designed to make the process of unloading groceries easier, it should require minimal physical and cognitive effort to operate. The product should also be able to withstand unexpected uses, as some users will likely use it for purposes we have not considered.

User Profile

The intended user of our product is a college student aged 18-25 living in an urban environment. Other users such as the elderly may be able to make use of our product, but

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their needs will not be analyzed during this project. A typical college student fills their day with class and studying, with a variety of extracurricular activities such as professional societies, social organizations, various interest activities, and down time filled with video games and television. Because their day is completely filled with social and academic activities, they do not want to waste time on other activities such as going to the grocery store. A college student needs a solution to the problem described previously in order to make their life simpler so that they can focus on schoolwork or extracurricular activities. This product will improve their ability to quickly perform the task of bringing groceries home and insure they will have valuable time to attend to other responsibilities.

Survey Data

We collected survey data using students at the University of Michigan as our sample market because of our familiarity with and proximity to this specific set of users. The survey data was obtained from a number of potential users from the University of Michigan. The results of the survey helped us gain a better understanding about the target user group and their habits. The targeted user group purchases groceries at a supermarket not located on campus, and the large majority of students drive or ride in a car to get to the grocery store. Some students use their own cars and some carpool with roommates or friends if they do not have a car. Due to their busy schedule, the users go to the store infrequently and purchase large amounts of food. Our survey results show that the typical college student leaves the grocery store with 2-4 bags. This number of bags is very difficult to transport in one trip. The survey data collected demonstrates that a collapsible grocery cart would be useful to the average college student. Product Market

This product will be marketed towards busy college students. There are a number of methods of marketing and distributing this product. The product can be purchased from a vehicle manufacturer if it is integrated within a vehicle, or it can be manufactured separately from the vehicle and can be purchased from an independent retailer. The product user would purchase the cart in most cases, but if the product was integrated into a vehicle, the purchaser of the cart would be the purchaser of the vehicle. This product might affect many people besides the user, including vehicle manufacturers, cart manufacturers, cart sellers, and grocery stores. Laws and Regulations

An added benefit of our design is that there are no specific laws or regulations affecting at the device we aim to produce. Therefore, we are not restricted in our design and do not have to make costly design changes to accommodate current laws or regulations.

DESIGN OBJECTIVES

Survey Results

When coming up with ideas for our design, there were several requirements and objectives that had to be considered. We used a QFD chart, as seen in Figure 2 on the next page, to help select these objectives and find their relative importance. Many of

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these objectives were centered on the cart’s physical attributes. We wanted to create a product that could carry the most items, fit in the smallest space when collapsed, and be durable but lightweight. Using our survey, we determined that users want a cart that can hold up to 12 one-gallon jugs of milk, folds to the size of a briefcase, and weighs as much as a half gallon of milk. To meet these objectives, we designed a product that has a small collapsed size, large capacity, uses a small amount of material, and is still very robust. Product Differentiation

In addition to physical attributes, we also had to consider the operation of the cart. We wanted a design that was easy to operate, can be secured in a motor vehicle, and can easily be taken up a few flights of stairs. These three things are what we feel differentiates our proposed product from those already on the market. There are many alternatives available, as discussed previously, but no other product combines all of these elements. By combining these characteristics, our product best satisfies the needs of our user group, as it is designed specifically for those needs. The collapsing mechanism and stair-climbing ability are unique features, and ease of use will be a contributing factor for users to choose our product. Quantification of Objectives

From these design attributes, we were able to come up with a set of measurable design objectives. The expanded cart should be able to hold at least 3 paper grocery bags (>2.04 ft3), the collapsed cart should fit in the space of a standard briefcase (<0.31 ft3), and the cart should weigh less than one gallon of milk (<8.33 lbs). In addition, the design should be robust enough to not fail under normal loading conditions for a period of 5 years. There should also be a physical mechanism for climbing stairs present in the design. Finally, potential users should find the design visually appealing and easy to use. These last elements may be determined through the use of a survey or user trial process. Cost

Finally, cost to manufacture this product and the final cost to the consumer are also major objectives. We would like to produce a product that can be sold at retail outlets and which will produce a profit. The amount of materials used, the complexity of the design, and the number of features included will affect the manufacturing cost, and in turn, the consumer cost. Thus, these aspects must be weighed against all the physical and operational objectives when determining the final design. The overall goal of the project is to create a product that can be produced and sold for a price which consumers are willing to pay which will maximize profit.

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Figure 1: Quality Function Deployment Chart

Relationships++

+

-

- -

Quality Function Deployment (QFD)

Weight Capacity (

+)

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psed S

ize (

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Can b

e s

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apacity (

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Impact

Resis

tance (

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Dura

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rials

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Weig

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Sharp

edge/p

inch p

oin

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Lockin

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echanis

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Sta

ir C

limbin

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roduce (

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bili

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Wheel S

ize (

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Fin

ish

Exposed N

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/Bolts (

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Recycla

bili

ty (

+)

Ease of Operation 10 1 3 3 9 1 9 3 3 9 1Capacity 9 9 1 1 3 1 3 1 3Collapsable Size 8 1 9 9 1 1 3 3Securability 7 9 9 1 1

Durability 7 1 1 9 3 3 3 9 3 3 1 1Lightweight 7 3 3 3 3 9 9 3 1 3 1 1Safety 6 3 3 3 1 9 9 9 1 9 3Stair Climbling ability 5 1 1 9 3 3 3 9 3 3 1Cost to Customer 5 1 1 1 3 3 3 1 9 1 1 3 3 3Environmental Protection 5 1 3 1 9 3 1Can traverse rough terrain 4 1 3 1 1 9 9Visually Appealing 4 1 3 1 1 3 3 1 9 9Environmentally Friendly 3 9 3 9 3 1 9

Total 150 224 192 171 29 194 257 68 210 208 179 134 255 86 76 83 47Normalized 0.58 0.87 0.75 0.67 0.11 0.75 1.00 0.26 0.82 0.81 0.70 0.52 0.99 0.33 0.30 0.32 0.18

Importance Rating 10 3 7 9 17 6 1 15 4 5 8 11 2 12 14 13 16Measurement Unit m^3 m^3 y/n lb # # lb # 1-5 ft/min $ 1-5 * mm * # %

Strong Positive Medium

Positive

Medium Negative Strong

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(+) => more is better

(-) => less is better

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ALTERNATE DESIGNS

The products pictured in Figure 1, below, are closely related to the product we aim to produce, the FantastiCart. They would all likely be direct market competition as they perform tasks similar to those in our design.

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Figure 2: Diagram of competing designs and the FantastiCart

A. Jumbo Chrome Elite B. Travelon Luggage Cart

C. Clax Cart D. Versa Cart

E. The Stair Climber F. The FantastiCart

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Table 1: Comparison Between Alternate Designs and The FantastiCart

Lightweight Collapsible Stair

Climbing Attractive

Weather-proof

Accessible Contents

Price

AJumbo Chrome Elite X X $51.95

BTravelon Luggage Cart X X X $35.99

CClax Cart X X X $299.00

DVersaCart X X X $49.95

EThe Stair Climber X X X X $34.95

FThe FantastiCart X X X X X X $57.00

Jumbo Chrome Elite Metal Shopping Cart

The collapsible metal shopping cart shown in Figure 2A allows for stable four wheel use as well as a very flat folded design. These carts are designed to have a large capacity and the ability to handle heavier cargo. Although it is quite durable, it also has a lot of features which we would prefer to eliminate from our design. It does not allow for multiple layer storage, and this design is fairly complicated in construction as the steel mesh requires a great number of welds. Also the almost complete use of steel in this design leads to a heavy finished product. It also appears that the conversion from folded form to final configuration may be awkward. It does not provide any sort of stair climbing ability. Travelon Luggage Cart

The second design, the luggage cart, folds quickly to a very small size. This design is shown in Figure 2B. However, because this design and most of the designs available on the market are constructed primarily of steel, they tend to weigh more. This design is inexpensive to manufacture because most of the components are economical bent steel rods or tubes. This design uses welds to connect the metal pieces, but when performed economically, the welding is sparse making for a weak design. However, with better welds this design could haul heavier loads. This design provides no provisions for stairway ascent/descent and also does not have a good storage system which is a major disadvantage. We performed reverse engineering on a similar design in a smaller scale to determine how effective this design was. We concluded that while it was a very economical solution to the problem, it does not have all of the aspects which we believe are necessary to solve our problem. Clax Cart

The Clax Cart is the most similar in design to an actual grocery shopping cart with a basket on the top layer and a shelf on the bottom. The Clax Cart is shown in Figure 2C. It utilizes a 4 wheel design with the front wheel providing the steering. It is touted as being able to close at the push of a button. When collapsed, the wheels fold into the body to minimize size. The stated weight of the product is 7kg (15 pounds). It is also rated to transport up to 130lbs. The design appears to be robust in the operation of its mechanism and folds down to a size comparable to the FantastiCart. However, the Clax cart has no provisions to assist in going up or down stairways. Also, the cost of the product, $299, is very expensive compared to the rest of the designs.

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VersaCart Folding Canvas Bag Cart

The folding canvas bag cart shown in Figure 2D is interesting because it folds much like a camping chair into a long cylindrical object. It appears to hold about as much cargo as the collapsible metal shopping cart with a much lower weight because of its utilization of fabric instead of steel. The construction of the design looks fairly simple with steel tubes, a few plastic pieces, swivel wheels, plastic handles, and canvas. The four swiveling wheels allow for maximum mobility on flat ground, but handling off of paved or smooth surfaces may be difficult. If the folding mechanism does not lock once opened and shut, operation may be difficult as it will have the tendency to alter its size depending on its orientation and how forces are being applied to it. This design does not assist in stair climbing or have provisions for multiple layers of cargo storage. The Stair Climber

The stair climbing folding cart shown in Figure 2E is lightweight and has a unique wheel design that allows it to more easily ascend/descend stairways. It also appears that the operation of the cart is very simple and intuitive. The construction of the cart is simple with few parts and plastic ends joining metal instead of welding. There are downsides of this design which we would like to avoid in our design. Because the vertical bar does not fold down, it does not collapse into a small area. The wheels remain in position and also result in a large folded size. In addition, the bag does not allow for multiple layers of storage and hinders the organizational process. The FantastiCart

While the designs above offer several features we intend to offer, no single design meets the goals we have established. Our design goal is to make a cart that is superior to all other designs. It will be lightweight through the use of plastics so it does not greatly increase the amount of weight carried when unloading groceries. It will be collapsible to allow for easy storage and transport when unloaded. The ease of use of the product is an important design feature, with intuitive use an imperative design feature. Easy stair ascent and descent will be possible with minimum effort and it will have the cargo capacity needed to satisfy the vast majority of users. Users will also have the ability to store cargo on different levels in order to preserve delicate items, or to otherwise separate and organize cargo. On top of all of these design features the design will be tailored for ease of manufacture with an emphasis on keeping the cost of the design as low as possible.

PRODUCT DESCRIPTION

Concept Generation

A number of concepts were generated during the brainstorming period. Our final product was a result of a combination of many different features which were investigated. Selected concepts are illustrated and described in this section.

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Figure 3: Two dimensional collapsible design with stair climbing wheels

The design shown in Figure 3, above, employs a slip fit structure that allows the unit to collapse to a much smaller size compared to its fully expanded dimensions. It collapses using telescoping rods in two dimensions, with a locking mechanism which ensures that the cart will not collapse during operation or open when collapsed. The frame would be made of metal or plastic, with a waterproof fabric covering to prevent the loss of items from the cart and for weather protection. It also features a patented three wheel design for moving the cart up or down stairs. This cart was designed using a cube shape which can easily fit through doorways but does not have a large capacity. Because it does not have a shelf, only one layer of storage is possible. It would be possible to add a shelf, provided it can also collapse to a smaller dimension. This design has many feasible aspects; the ability to collapse in two dimensions has the possibility of resulting in large cargo size when fully open and very small collapsible size. However, this would require that the mechanism be designed extremely well and will add much complexity to the design. The wheel mechanism, while a useful design, is patented and would require us to purchase patent rights to the design. Our aim is to use another suitable alternative that does not require the purchase of patent rights.

Figure 4: Folding box design with tracked stair climbing mechanism

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The design concept shown in Figure 4 is made of solid pieces of plastic which fold into a flat rectangular shape when not in use. The pieces are locked into place at the folded edges to prevent cart collapse during use. It features two standard wheels for use along smooth surfaces, and a track wheel mechanism along the back which allows for motion up or down stairs. The expanded and collapsed size and functionality of this design concept are acceptable for the user group, but there are difficulties with the design. The folding mechanism, while simple in theory, would likely be difficult and awkward to use. The track mechanism appears to be a good way to move the cart up or down stairs, but the manufacturing cost may prove too expensive to consider for production.

Figure 5: One dimensional collapsible design with stair skids

The design concept shown in Figure 5 features a rectangular shape which collapses in one dimension using a series of folding bars. The bars lock into place with the application of a small force, and the standard wheels allow for the cart to roll easily. Motion up and down stairs is aided by the skids located on the back of the cart which can rest on the stairs to allow for a smooth ascent or descent on the stairs. This design also uses a plastic or metal frame covered in waterproof fabric to decrease weight and increase protection from external sources such as rain and dust. Concept Selection

The design shown in Figure 5 is lightweight, allows for a large expanded and small collapsed size, motion up and down stairs, weather protection, and intuitive use. Because

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of these features and using the Pugh chart shown in Figure 6 below, this design was selected as the design concept which will be investigated in the future.

Figure 6: Pugh Chart Comparing Concept Designs Design #1 Design #2 Design #3

Sk

etc

he

s Two dimensional

cube cart with three wheel mechanism

Folding box with track mechanism

One dimensional box with skid mechanism

Design Criteria Weig

ht

Ease of operation > 75% of survey respondents find

it easy to use

10 6 4 7

Capacity Volume > 3 paper bags = 3528 in

3

= 2.041 666 667 ft3

9 6 7 7

Collapsible size Volume < Std. Briefcase size (528

in3)= 0.305 555 556 ft

3

8 8 7 7

Durability Life > 5 years

7 7 6 7

Weight < 1 gallon of milk (1gal water=8.33lbs)

7 7 5 8

Safety No easily exposed pinch points, stays open and upright under normal operating conditions

6 5 5 6

Stair climbing ability Physical mechanism present

5 9 8 7

Cost to consumer < $40

5 7 4 8

Visually appealing to college student

4 6 6 6

Total Points 6.721311 5.737705 7.032787

Alpha Prototype

In building the first prototype for the FantastiCart we determined that our initial design concept was worth improving. The alpha prototype was built with a variety of materials purchased at a scrap store, so it was not to scale and the strength of the materials used was not appropriate. However, we got a very good picture of the overall design of the product and how the folding mechanism should work. Although we have confidence in our selected design concept, if problems arise it can be altered using a combination of other design aspects discussed previously.

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Design Process

The process used to design the optimal personal grocery cart was as follows: Initially, we realized that a personal grocery cart could be designed to improve college students’ efficiency. We then surveyed potential users to determine who would be interested in purchasing the product and what they would like in that product. Next, we developed a plan to solve the problem and set design goals as demonstrated in the problem definition. From these goals, we developed several ideas of how to solve the problem, and concepts that would fit those ideas. An analysis of how each concept fits the design criteria was performed using a Pugh chart to determine the best concept. We also tested a similar product to determine weaknesses present in other products so that they can be avoided in our design. Once we had a solid, refined concept, we produced an alpha prototype to further investigate our concept. From this initial prototyping, we were able to find some flaws in our design, as well as added features to improve the design. We used this knowledge to refine our design and produce a beta prototype. We then continued to improve the beta prototype, and performed detailed engineering and economic calculations to arrive at a final design concept. The final design was then tested for functionality. Because the final prototype could not be made with appropriate materials, a scale model will need to be manufactured and tested before final manufacturing can be started, but problems in this process are not anticipated because an engineering analysis of the product has been performed. Current Design Concept

The alpha prototype and further investigation of the needs of the consumer led to a refined cart design, the beta prototype. The improvements made include an added mechanism for stair-climbing skids and the alteration of top and bottom shelf mechanisms. The original design included stair-climbing skids which were attached directly onto the cart frame. The updated design includes a mechanism which extends the skids at a 30° angle to allow for easier stair climbing. This mechanism also extends the handle to 40” so that the cart is an appropriate height for the majority of our customer base. This target number was determined from ANSUR anthropometric data. The bottom shelf mechanism was altered in order to decrease the number of mechanisms needed. In the previous design, the top shelf was smaller than the bottom shelf so that it did not stick out above the cart. By making the shelf into two pieces, it can now cover the entire length of the cart.

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BETA PROTOTYPE

Figure 7: Beta Prototype in Travel Configuration

Figure 8: Beta Prototype Bottom Cargo Compartment Mechanism

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Figure 9: Beta Prototype Fully Collapsed/Transport Configuration

Figure 10: Beta Prototype Fully Expanded/Stair-climbing Configuration

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Figure 11: Beta Prototype in its final form

The beta prototype, as pictured in Figures 7-10 on the previous page, is the current design of our project. It allows for a maximum cargo capacity of 3.75 ft3 which meets and exceeds our desired goal of 2.04 ft3 by about 180%. The prototype weighs 15 lbs total. Aluminum is used extensively for its combination of lightweight and strength. (The rest of the materials used are detailed in Appendix A) The collapsed width is 5 inches, as that is the diameter of the wheel utilized in the design. Also, with the innovative 3 stage handle design, the cart design is easy to use for both walking and going up and down stairways. The collapsibility of the cart is achieved by two separate systems. In the first system, the cargo compartment, a bar in slot mechanism is used to achieve the bottom half of the system (Figure 8). Using a solid bar on either side allows us to rigidity attach a shelf for maximum support. For the top half of the cargo compartment a hinge mechanism is utilized. The other system involves the handle/stair climbing mechanism. There are three stages of this mechanism. In the first stage (Figure 9), the handle is completely down for transport of the cart. In the next stage, the handle extends and locks into place for travel. In the last stage (Figure 10), the handle extends further and the stair climbing mechanism, which is controlled by handle movement, moves into place. To allow for multiple levels of cargo storage, we have designed an intermediate shelving system. This system consists of two panels that fold down, as desired by the user, or stow vertical for unrestricted use of the full compartment. The panels will hinge along the same axis as the top bars of the folding mechanism as well as rest on ledges attached on the bars for support. The panels and the supports can be seen in both configurations in Figure 12. For display purposes in the beta prototype, a clear plastic acrylic will be used for the shelving surfaces. In later versions, stronger and cheaper plastics will be utilized.

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Figure 12: Beta Prototype Top Shelves Shown

ENGINEERING ANALYSIS

In completing the engineering analysis, free body diagrams of the cart were created and are shown in Appendix B. The moments at each contact point are not shown on the diagrams so that the diagrams are easier to read. An engineering analysis was performed on the FantastiCart design in order to determine the dimensions of the product which should be used in order to minimize the total weight of the product without applying stresses greater than the yield stress. The thickness of the shelves, bar diameter, and overall dimensions were determined so that the maximum stresses placed on them would not exceed the yield stress of 30 MPa of ABS plastic. A safety factor of 5 was also included because a number of assumptions were made to simplify the calculations and to maximize the life and durability of the product. The Solver tool in Microsoft Excel was used to calculate the optimal dimensions while minimizing the total weight of the cart. The final dimensions solved by the Solver Tool, and rounded to dimensions which can be easily manufactured are shown in Table 2. The optimization equations are shown below, with weight being minimized with respect to the geometry of the design as related to the maximum volume and stresses less than the yield stress. The bar diameter was found to be the variable which affected the weight the most. The shelf thicknesses found by the solver tool were increased for ease of manufacturing and strength.

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YMaxBottom

YMaxShelf

YMaxBar

GeometryofFunctionV

VWeight

σσ

σσ

σσ

ρ

<

<

<

=

=

,

,

,

Table 2: Important Design Criteria

Product Design Attribute Dimension

Height 26”

Length 15”

Width 22”

Top Shelf Thickness 0.25”

Bottom Shelf Thickness 0.25”

Design Variables

Bar Diameter 0.5”

Optimized Design Parameter

Weight 10.5 lbs

FEA Analysis

To ensure that our design would work if constructed out of ABS plastic we performed a FEA analysis on the structure. This was done using the structure application in Unigraphics NX 3.0. A 3D tetrahedral mesh was utilized for the analysis mesh. The model was constrained along the bottom face on the side of the structure where the wheels are present. This is to represent the load while it is being moved as this would be the orientation that would subject the structure to the largest stresses. A 100 pound force was applied uniformly to the bottom shelf of the design while a 25 pound force was applied uniformly to the top shelves. These forces were chosen as what the structure would be subjected to under extreme loading conditions. It is meant to represent 15 gallons of water. This is beyond what the cart would be expected to hold since its primary cargo is intended to be groceries. With the exaggerated loads, the stress on the structure does not exceed the ultimate or yield strength of ABS, the lower of which is 30 MPa with a substandard grade of ABS plastic. The average ABS plastic has yield and ultimate strengths of about 40 MPa. As seen in figure 13, the highest stress on the structure is 3.36 MPa. With the low estimate for yield strength the factor of safety is 30 MPa /3.36 MPa = 8.93. Since our analysis of the structure is simplified and doesn’t account for part tolerances and assumes the structure is static, the actual factor of safety will be lower. However, since the factor of safety is large under the exaggerated load, the factor of safety in reality will likely still be high (much greater then 1).

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Figure 13: Stress on Structure

Figure 14: Displacement of Structure

As seen in figure 14, the maximum displacement of the structure under the 125lb load is roughly 6.5mm which is present on the upper shelf. This defection would not result in any material failure and since the actual stress is still low, this is acceptable.

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The overall shape of the structure will remain the same between this stage of design and final. However, individual pieces will be optimized to reduce mass and volume. The top and bottom shelves would likely adopt a structure similar to that which is seen used for milk crates (Figure 15). The frame would be redesigned to minimize material use, optimize for production, and also for aesthetics.

Figure 15: Generic Milk Crate

Dynamic Mechanism Stress Simulation

The bars that connect the upper and lower mechanism are precisely placed to insure proper movement of the mechanism and because it is necessary that they maintain their original dimensions, they were analyzed to check for yield. This analysis was based on the specifications of the Beta prototype. Because the force applied to the bars which connect the upper and lower mechanisms is variable, Adams 2005 was used to verify that the calculated dimensions would withstand a large force applied to the closing mechanism. The bars are relatively small and are attached to the upper and lower links with bolts. Near the bolt holes, the cross sectional area of the bar decreases significantly (by roughly 50%).

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Figure 16: ADAMs Model of Cart Mechanism in Open and Closed Positions

A 15 pound force was exerted on each upper bar, as shown in Figure 16, to give a total closing force of 30 pounds. This was chosen as an upper force limit because at this input the cart would close in roughly 2/10 of a second as determined from simulation. It would be unlikely that a force larger than this would be applied to close the cart. With this input, the maximum force on each connecting bar is 140 lbf (Figure 17).

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Figure 17: Maximum Stress on Individual Bar

The area of the smallest section of the bar is 0.1875” x 0.25” = 0.04688 in2. Therefore the stress if given by:

psiArea

ForceStress 3009

04688.0

141===

The lowest rated yield stress of 6061 aluminum is 28000 psi. This is much greater than the calculated stress meaning the bar will not yield for our prototype design. Should the same geometry be adopted in the production model using ABS plastic it will likely not yield as the lowest rated yield stress of ABS plastic is 4300 psi. However, with ABS there is a much lower factor of safety, 1.42 for ABS vs. 9.30 for aluminum. This analysis ensured us that our decision to increase the cross section area of the bar for the ABS part was a good design choice.

ECONOMIC ANALYSIS

Product price can play a large role in the success or failure of a product. The microeconomic demand linear model suggests that the demand for the product will decrease as the price increases. If the FantastiCart price is too high, the demand will be low. A high price has to be justified through high quality of materials, mechanisms and functionality. Although a low price will lead to a larger demand, it can also give the customer a sense of poor quality that the product won’t last very long. Market Size and Demand

We determined that the total market size was 450,000. This number was found from the assumptions that out of 18,000,000 total college students, 50% have cars and 5% of these students would be interested in purchasing a cart to help them move their groceries. This population will also be constantly changing due to the 4-5 year time frame that students spend in college. The average price of grocery carts currently on the market is about $88,

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with prices ranging from $35 to $300. Because of the features of our design and its competitive price of $57, we are confident that the FantastiCart will be easily marketable. Market Analysis

College students who own a car are the target consumers of the FantastiCart. This user group generally lives in off-campus housing, frequently with stairs and limited parking. They also go to the grocery store infrequently and purchase large quantities of food. The FantastiCart was designed specifically for them, and fits their needs perfectly. Because the FantastiCart is marketed to a technologically educated population, much of the advertising will be done online and at a low cost. The marketing will make students aware of their need for a collapsible cart as well as persuade them to purchase our collapsible cart. Survey Results We conducted a survey of typical college students in order to gain more information on the preferences of potential users. From this data, we determined that around 50% of college students have cars and most get 2-4 bags of groceries when they shop. A conjoint analysis was used in this survey to find the relative importance of capacity, folded size, weight, and price, as shown in Figure 18, below. This data shows that low price and high capacity are the most important design attributes, while weight and folded size were less important.

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Figure 18: Part Worths

Design for Engineering versus Design for Engineering and Marketing

Designing from only an engineering viewpoint, the product is designed to fulfill the engineering requirements, and profit is then determined from this criteria. Designing taking into account engineering criteria and marketing data, the profit is maximized while still taking into account engineering constraints. Design variables are changed to increase profits using the results from the part worth survey data. With our design, this resulted in a design that is more profitable than a design based on engineering objectives alone. Competitive Analysis

There are currently several collapsible carts on the market. These products have a variety of features attractive to students, which are also included in the design of the FantastiCart. Each of these products does not meet at least one of the criteria important to the college population. The FantastiCart combines all of these features into one

Capacity

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7

No. of Paper Grocery Bags

Pa

rt W

ort

hs

Price

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-0.4

-0.2

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0 10 20 30 40 50 60 70

U.S. Dollars

Pa

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Weight

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0

0.2

0.4

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0 0.5 1 1.5 2 2.5

Gallons of Milk (8.33 lbs)

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Folded Size

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-0.2

0

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0 0.5 1 1.5 2 2.5 3 3.5

No. of Standard Briefcases

Pa

rt W

ort

hs

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product, adding significant value for the customer, and increasing our marketability. A sample of other carts on the market can be seen in Figure 2 on page 9. Capital, Annual, and Variable Costs

The costs related to the FantastiCart can be divided into a one- time investment, annual costs, and variable costs. The one- time investment costs include the puchase of five injection molding machines so that the product can be made of ABS plastic. The annual costs include labor and rent costs. These costs can be seen in Table X below, and were assumed based on typical values in Ann Arbor, MI. Ann Arbor was chosen as the manufacturing facility based on its proximity to a college campus which contains a large sample of our product market. The variable costs include the costs associated with the production of each individual part. These include the materials needed and shipping and handling, as seen in Table 3, below.

Table 3: Production Cost Breakdown

Capital Costs No. of Units Unit Price Total

Injection Molding/Machine Tools 5 $38,000.00 $190,000.00

Total Capital Costs $190,000.00

Annual Costs No. of Units Unit Price Total

Rent for Warehouse (sq ft.) 5000 $3.50 $17,500.00

Marketing/Sales 2 $50,000.00 $100,000.00

Laborers 7 $30,000.00 $210,000.00

Supervisor 1 $40,000.00 $40,000.00

Logistics/Supply Mgt. 1 $50,000.00 $50,000.00

Engineers 2 $60,000.00 $120,000.00

Manager 1 $80,000.00 $80,000.00

Maintenance 1 $15,000.00 $15,000.00

Total Annual Costs $632,500.00

Variable Costs (per unit) Unit Price Total

Plastic for molding $9.00 $9.00

Wheels $2.00 $2.00

Fabric Cover $1.00 $1.00

Shipping and Handling $1.00 $1.00

Total Variable Costs $13.00

Breakeven Analysis

Using the market size assumptions described previously, taking into account the costs listed in the table above, and running a profit-maximization routine, the optimal price for the FantastiCart is $57. At that price, the market is approximately 213,000 users. Assuming that 5% of the potential market purchases the product in the first year, and 5% is added each year after that, PPD will break even after 1.4 years. The table and Figure 19 summarize this information.

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Figure 19: Market Size Assumptions

Total Number of College Students 18,000,000

Number who own cars (50%) 9,000,000

Number interested in product (5%) 450,000

Optimal Unit Price $57

Market Size at Optimal Price 213,000

Initial Market Penetration 5%

Additional Each Year 5%

Breakeven Point 1.4 years

Breakeven Analysis

-1000000

-500000

0

500000

1000000

1500000

2000000

2500000

0 1 2 3 4 5 6

Time (yrs)

Pro

fit

(US

D)

Pro-Forma Income and Cost Projections Based on the cost and market information determined above, the costs and revenue associated with this product can be analyzed. Table 4, below, shows the data for the first three years.

Table 4: Three- year Profit Analysis Year Market Share Quantity Cost Revenue Profit

0 (investment) $822,500.00 0 -$822,500.00

1 0.05 10627.35 $896,891.45 $605,758.95 -$291,132.50

2 0.1 21254.7 $781,282.90 $1,211,517.90 $430,235.00

3 0.15 31882.05 $855,674.35 $1,817,276.85 $961,602.50

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From these projections, it was determined that an initial investment of approximately $2.5 million was needed. The Internal Rate of Return (IRR) was found to be about 17% for the three-year period.

OTHER DESIGN CONSIDERATIONS

Emotional and Aesthetic Design The FantastiCart was designed with aesthetic design in mind. The cart mechanism was designed by engineers interested in optimizing the functionality of the cart, while a designer created an attractive exterior frame which does not affect the function of the cart. The design implements rounded edges and corners, an attractive weatherproof exterior, and a modified frame shape which uses repeated parallel lines to attract the customer. Product Development Process

The development process changed during the project in two main areas. The business plan involved more detailed analysis than originally anticipated. It originally included only a cost analysis, but was changed to include information about marketing, survey results, profit analysis, and the internal rate of return. Also, because of delays in the prototype production, customer interaction with the final design could not be completed as thoroughly as originally desired. Reflection of Personal Values in the Final Design

Our team values art, ethics, and people’s familiarity with similar products as the most important aspects of design. The FantastiCart was designed with these values in mind. Our product design is helpful to society, but not in a very direct manner. It is designed to be used by busy college students who could be spending their time solving pressing societal issues instead of hauling their groceries. By saving their time and energy during their grocery shopping, students can devote more effort to their schoolwork, thereby improving society. Although our product is not dangerous when used correctly, it can cause injury to the user or the cart contents if it is used improperly. Some features have been added to the cart to minimize the damage that can occur from improper usage, such as rounded edges, plastic components, and a safety factor of more than 3. In order to reduce the amount of incorrect usage, the cart should be sold with labels reminding consumers of the dangers of incorrectly using a large product. This will eliminate any ethical problems we have with selling a product which can be dangerous if used incorrectly, and will also eliminate any possible legal issues that might arise from the same problem. The FantastiCart was designed with the personal values of each team member in mind. Extra features which do not affect the basic functionality of the design were added which make the cart more artistic and safe. Also, the cart was designed with other similar products in mind so that the design would not be so foreign to the consumer that they would not buy it.

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CONCLUSIONS AND FUTURE WORK

In conclusion, the FantastiCart is a useful product which can be successfully marketed and sold to the college student population. From our research, we have determined that the design will be profitable in less than two years. This product is different from others currently on the market since it combines many desirable attributes into a single cost effective design. Low weight, large volume capacity, collapsibility, stair climbing ability and attractive design are all feature that ensure the FantastiCart will be a financial success. The future work involved in moving forward would include: improving the design of the prototype to maximize strength and manufacturability while minimizing mass, testing the design under various real world conditions, receiving market feedback on the design, having users test the design, exploring other markets the product could be used in, and further expand the marketing survey and analysis to a market base beyond that of the University of Michigan students.

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REFERENCES

[1] "Overview - Acrylonitrile Butadiene Styrene (ABS), Molded." MatWeb. 8 Dec. 2006 <http://www.matweb.com/search/SpecificMaterial.asp?bassnum=O1100>.

[2] "Clax Utility Cart." Frontgate. 10 Dec. 2006 <http://www.frontgate.com/jump.jsp?itemID=4966&itemType=PRODUCT&path=1%2C2%2C137%2C141&iProductID=4966>. [3] "Folding Shopping Carts." Elder Store. 10 Dec. 2006 <http://www.elderstore.com/folding-shopping-carts_102.aspx>.

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APPENDIX A. BILL OF MATERIALS

Beta Prototype

Bill of materials and Cost

Part 1 2 3

Quantity

Mate

rial

Sourc

e

Siz

e

Mate

rial

Costs

($)

Labor

Costs

($

)

Part

Cost ($

)

Tota

l C

ost

($)

Cart x 1 216.6

Frame x 1 Aluminum 14.19

Long Frame Piece x 4 Aluminum Buy Length: 26" 2.37 5 7.37

Dimension: 1" sq tube 1/16" wall thk.

Short Frame Piece x 4 Aluminum Buy Length: 20" 1.82 5 6.82 Dimension: 1" sq tube 1/16" wall thk.

Cargo Mechanism x 160.34

Lower Mechanism Arm x 2 Aluminum Buy 14"x1"x1/4" 5.83 2.5 8.33

Upper Mechanism Arm x 4 Aluminum Buy 7.5"x1"x1/4" 6.25 5 11.25

Upper Shelf x 2 Acrylic Buy 7"x19.5"x1/8" 4 5 9

Lower Shelf x 1 Acrylic Buy 14"x19.5"x1/8" 4 4 8

Slotted Bar x 2 Aluminum Buy 16.5"x1"x1/2" 13.75 25 38.75

Link Connectors x 2 Aluminum Buy 14"x1/2"x1/4" 6 10 16

Upper Shelf Supports x 4 Aluminum Buy Length: 4" 4 10 14

Dimension: 3/4"x1/4" Lower Shelf Supports x 2 Aluminum Buy Length: 10" 6 10 16

Dimension: 3/4"x1/4"

Round Aluminum Bar x 5 Aluminum Buy Length: 23" 15 10 25

Dimension: 1/4 Dia

L-bracket x 4 Aluminum Buy 2"x1"x1mm 1 1 2

Spacer x 2 Aluminum Buy 1"x1"x1mm 0.25 0.25 0.5

Nut x 4 Steel Buy 1/4-20 0.25 0 0.25

Bolt x 8 Steel Buy 8-32x3/8 0.48 0 0.48

Bolt x 2 Steel Buy 1/4-20x1/2 0.12 0 0.12

Rivets x 26 Aluminum Buy 1/8" 3.58 4 7.58

Clips x 18 Steel Buy N/A 1.08 2 3.08

Handle Mechanism x 1 17.95

Handle Bar x 1 Aluminum Buy Length: 10" 1.5 1 2.5

Dimension: 1" sq tube 1/8" wall thk. Skids x 2 Aluminum Buy Length: 23" 3.5 2 5.5

Dimension: 1" sq tube 1/8" wall thk.

Link x 2 Aluminum Buy Length: 12" 1.8 1.25 3.05

Dimension: 1" sq tube 1/8" wall thk. Handle Slider x 2 Aluminum Buy Length: 23" 2.65 2 4.65

Dimension: 3/4" sq tube 1/8" wall thk.

Bottom Bar mount x 2 Aluminum Buy Length: 1" 0.25 2 2.25

Dimension: 1" sq tube 1/16" wall thk.

Wheels x 14.12

Wheel x 2 Plastic Buy 5" Deck Wheel 11.96 0 11.96

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Nut x 2 Steel Buy 1/2"-13 1.04 0 1.04

Bolt x 2 Steel Buy 1/2"-13x3" 1.12 0 1.12

Mesh x 1 Cloth Buy 36"x72" 5 0 5 5

Assembly x 1 N/A N/A N/A 0 5 5 5

APPENDIX B. FREE BODY DIAGRAMS

Front

Back

Right Side

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APPENDIX C. DESIGN PROCESS

APPENDIX D. TIME SCHEDULE

A schedule of necessary tasks which were completed is shown in the Gantt chart in Figure 15, below. The tasks were assigned deadlines which allowed for a timely completion of the project. Throughout the project, the some tasks took a slightly different amount of time than anticipated, but overall, the project was completed by the overall deadline.

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