Rolling suitcase

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Executive Summary

For this stage of the analysis, we have disassembled and analyzed a rolling "rollaboard" carryon bag. Our analyses included a usability study to Design for Manufacture (DFM) to Design for Assembly (DFA) to Design for the Environment (DFE) to Failure modes and effects Analysis (FMEA), each of which yielded new insights into the current state of the strengths and weaknesses of the rollaboard bag. Through the disassembly process of the bag, it quickly became apparent that the bag contained an extremely (>100) high number of parts, though most of them were simply fabric pieces cut into varying shapes and sizes and sewn together. That said, DFM and DFA did expose a high level of modularity and subassemblies, both with mechanical components and with pockets. The DFE analysis demonstrated that the highest environmental cost of the suitcase was its manufacture, so extending the lifetime of a bag is the best way to decrease its impact. Finally, FMEA demonstrated that the most concerning failure mode of the product was zipper failure, though some consideration should also be given to the other failure modes, such as wheels breaking, and the bag tipping over. Throughout this report, we will discuss these results in much greater depth, along with the other findings of our product analyses.

Product Stakeholders

The stakeholders, as well as their needs and wants are listed in the table below. We have determined that needs are something that must absolutely be included in the product for the stakeholder to use it, whereas wants are features that will benefit the stakeholder, but are not absolutely essential in the use of the product.

Stakeholder Needs and Wants
Stakeholder Needs Wants
ConsumerSecurely hold belongings, Reasonable product lifetime, Stability, Sized for airline storageEase of storage, Ease of motion, Protection against impact, Will not smack into heels, Well organized, Easily identifiable
Security Personnel Fits onto conveyor belt, Non-explosive Not metal, Fast inspection
Baggage Handler Strong handles, Ease of movement Balance on handle, Light, Stackable
Flight Attendant Good handles Idiot-proof storage
Retailers Works well empty Looks good, Feels good to use
Transporters Small, Light Smaller, Lighter

From this, we have determined that the consumer has the most detailed needs and wants, and thus we will focus primarily on their use for our re-designs. However, the other five stakeholders all have interesting points of view which we intend on considering throughout the re-design process.

Product Use Study

Using a rolling suitcase is something that most people have experienced at least once before, but in our usability study we tried to look at the product from the eyes of a novice. Even non-engineers had no difficulties in utilizing the basic functions of the suitcase. We find that using rolling luggage is not really about the luggage itself, but more about the process of traveling with the luggage. We considered usability from the primary user's standpoint, instead of from the viewpoint of one of the other stakeholders. We modeled our use flow chart on a traveler who is carrying the luggage onto an airplane, which requires many more steps to use than checking a bag on an airline or car travel. As is evident, there are many steps, and for the most part they get reversed from the time the user takes the flight.

Rolling Suitcase Use Flow Chart
Packed Luggage

One of the most important parts of using the luggage is packing it. For this particular model of suitcase, which is sized to store in an airplane overhead compartment, we were able to put a number of different pairs of pants and shirts into the suitcase, even without utilizing using any of the built in storage features. This suitcase features both interior and exterior pockets in which to place clothes, but from personal experience, we felt that they are rarely used in practice. Once full, the luggage can be zipped up and position can be changed. However, we noticed that after changing the position of the suitcase, the clothing inside the suitcase settled into a pile in the bottom of the suitcase, ruining any potential organization of the folded clothing and causing wrinkling.

Upright Luggage with Handle Extended

The next important step in luggage use is the process of rolling the luggage. For this action to occur, the suitcase has to be set onto the wheels, the handle has to be extended, and the suitcase has to be tipped towards the user. We found several difficult challenges in this process. First, raising and lowering the handle can be difficult depending on the position of the user in relation to the suitcase. At the wrong angle, for example, off to the side, it could be quite difficult to extend the handle. Also, the most natural hand positions for pushing the handle release button and for actually pulling the luggage were different, which means that the user must change hand positions to roll the suitcase. Additionally, having to tilt the luggage to roll it can be quite cumbersome when only moving a short distance, such as moving forward in the line for security. Of course, the luggage cannot be rolled up the stairs, which means that mobility with rolling is limited.

Another important part of using the luggage is lifting the luggage. This suitcase featured two stationary handles, one on the top and one on the side, which can be used to maneuver the luggage without the wheels. This is how the luggage is carried up the stairs or loaded into the overhead compartment. In the competitor product that we studied, the handles were quite sturdy and well-suited for lifting with. We found that the handles were in a good position to load the bag into specified positions, like the trunk of a car, the cargo bay of an airplane, or an overhead storage bin.

The final part of using the luggage is storing it between trips. This can prove to be quite difficult, because the luggage has a specific, unchanging size and shape. Many families of luggage, with pieces of different sizes, can be stored nested within one another. Other than this, there is no way to compact the bag for storage. The rectangular shape of the bag does allow for it to be stored with other boxes, or stacked with other things. Most pieces of luggage can fit under beds or in closets, but if storage area is limited, it can be quite difficult to find room to store the luggage.

Product Mechanical Function and Parts

Mechanical Functions

Manufactured Mechanisms

Handle Assembly: The handle allows the user to hold the bag while it rolls on the ground without bending over. It is also used to hold the bag still while waiting in lines or on escalators. The handle operates by sliding vertically out of the body of the suitcase. While in either the raised use position or the retracted storage position, the handle is held in place by a release mechanism.

Mechanical Systems Schematic

The release is activated by pressing a button (part 015) on top of the handle. This button pushes two plastic sliders (part 020) to pull on two cables (part 028). These cables run around the corner from the handle into the telescoping supports (parts 026 and 027). When the cables are pulled, the release slider (part 032) slides and retracts the locking pin (part 031). There are three return springs in the mechanism. The first two (part 030) are in the bottom of the telescoping support; they pull on the bottom of the release slider and provide tension in the cable. The third return spring (part 017) pushes up directly on the underside of the button. This helps the mechanism return and deals with the problem back-driving the system. There is one more feature in this mechanism: the plastic sliders each have a rack extending out past the center of the button. In between these racks there is a pinion gear (part 019) which forces the two plastic sliders to move opposite each other and release both sides simultaneously.

Wheel Assembly: The wheels on the rolling suitcase allow the user to roll the bag instead of carrying it. They are mounted on fixed axles so that the bag cannot roll sideways, but can turn by moving one wheel farther than the other. Each wheel is supported on the axle (part 043) by two bearings (part 042), giving it support at either edge. The axles are supported by the hard plastic corner pieces (parts 035 and 036) at the bottom of the suitcase.

Purchased Mechanisms

Buckle assembly (part 060): These buckles fasten the straps (part 061) which secure items in the interior of the main compartment. They are most useful for keeping the contents from shifting during travel when the suitcase is not full. They snap closed and release by squeezing both sides of the buckle simultaneously.

Zipper assemblies (parts 062 and 063): The zipper assemblies hold the pockets closed when the suitcase is traveling, and unzip to allow the contents to be accessed. They open and close by pulling the zipper pull along the length of the zipper in either the ‘open’ direction or the ‘close’ direction.

Wheel bearing assembly (part 042): This assembly is a component of the Wheel Assembly.


The following photos are the sub-assemblies that comprise the rolling luggage. See the Bill of Materials for part information corresponding to the part numbers labeled in the pictures.

The following picture shows the assembly of the main body of the bag itself.


This picture shows the assembly of the mechanical parts of the luggage, including the wheels and the telescoping handle mechanism.


This picture shows the assembly of one of the stationary handles on the bag. There are two of these on the luggage, one on the top of the bag and one on the side.


This images shows an assembly of one of the pockets on the bag. There are a total of five pockets in the bag, but this is a representative sampling of those five.


This shows the internal corner lining of the bag. It is meant to reinforce the corners under the mechanical components.


This shows the final major sub-assembly, which is a cross-sectional view of the piping that trimmed the bag.

Bill of Materials

Bill of Materials

The majority of the suitcase components are comprised of only a few types of fabric, cut to size and sown together. These fabrics are listed first in the table below, with an estimation of the total quantity used. The remainder of the table shows the different mechanical components that make up the handles, telescoping arm, and wheel base. Most of the 200+ scraps of cloth have been omitted from the table for simplicity. However, the subassembly section shows how the fabrics are stacked and sown together at seams, often with re-inforcement. These basic seams are repeated many times in the construction of the bag.

Cloth Types
Type Name QTY Weight (g) Function Material Manufacturing Process Image
1Exterior Fabric9 sq ft 40/sq ftHeavy duty fabric resistant to tearsNylonWoven
2Interior Fabric4 sq ft 20/sq ftLight fabric to line interior of suitcaseNylonWoven
3Foam Core4 sq ft21/sq ftPadding for mechanical componentsPolyurethaneChemical Process
4Synthetic Leather0.15 sq ft37/sq ftStiffens smaller fabric areasPlasticCoated onto Fabric
5Vinyl Cloth0.25 sq ft34/sq ftWater-proofs edgesVinylWoven
6Rubber Piping8 ft35/ftAdds support to edges where metal is not usedRubberMolded
7Textured Piping 2 ft 33/ftAdds rigidity to cornersRubberMolded
8Thread~100 ft1 g/ftHolds fabric components togetherNylonSpun
Part Number Name QTY Weight (g) Function Material Manufacturing Process Image
001Screw Type 1many4Fastens parts. Used primarily in the main compartment.SteelDrawn, cold headed, and thread rolled
002Screw Type 2many4Fastens parts. Same as type 1, but painted black to blend in with cloth and plastic.SteelDrawn, cold headed, and thread rolled
003Screw Type 3many3Fastens parts. Same as type 2, but a shorter length.SteelDrawn, cold headed, and thread rolled
004Screw Type 4many3Fastens parts. Used in untapped holes in injection-molded parts.SteelDrawn, cold headed, and thread rolled
005Screw Type 5many2Fastens partsSteelDrawn, cold headed, and thread rolled
006Screw Type 622Fastens parts. Used to hold axle cover onto outer wheel well parts.SteelDrawn, cold headed, and thread rolled
007Screw Type 7many3Fastens parts. Used in untapped holes in injection-molded parts.SteelDrawn, cold headed, and thread rolled
008Screw Type 823Fastens parts. Used to secure upper arms of telescoping handle to injection molded handle base.SteelDrawn, cold headed, and thread rolled
009Rivetmany2Fasten parts permanentlySteelStamped/pressed
010Washer Type 1many2Spacer between screws and nutsRubberReaction Molded
011Washer Type 2many2Spacer between screws and nutsRubberReaction Molded
012Washer Type 3many2Spacer between screws and nutsSteelStamped
013Nut Type 1many2Holds ScrewsStainless SteelMolded
014Nut Type 2many2Holds Screws. Same as type 1, but painted black to blend in with cloth and plastic.SteelMolded
Telescoping Handle
Part Number Name QTY Weight (g) Function Material Manufacturing Process Image
015Button152Engages handle gear mechanismPlasticInjection Molded
016Handle Top Case152Encases handle gear mechanismPlasticInjection Molded
017Spring152Restores button after it has been pressedSteelDrawn and Rolled
018Spring Pad152Restores button after it has been pressedPlasticInjection Molded
019Pinion Gear152Moves rack slidersPlasticInjection Molded
020Rack Sliders252Engages handle releasePlasticInjection Molded
021Bottom Case152Encases handle gear mechanismPlasticInjection Molded
022Handle Support Bracket Exterior152Stabilizes telescoping handlePlasticInjection Molded
023Handle Support Bracket Interior152Stabilizes telescoping handlePlasticInjection Molded
024Handle Alignment Adapter252Allows telescoping handle to pass smoothly through the top of the bagPlasticInjection Molded
025Lower Arm End Cap252Aligns upper and lower armsPlasticInjection Molded
026Upper Arm252Slides in and out of the lower armSteelExtruded
027Lower Arm252Allows upper arm to slide in and out to extend or contract the telescoping handleSteelExtrusion
028Cable252Connects push button mechanism to slide release mechanismSteelExtruded and Woven
029Cable End Crimp452Keeps woven cable togetherSteelExtruded
030Tension Spring252Engages locking pinSteelDrawn and Rolled
031Locking Pin252Holds telescoping handle in collapsed or extended positionPlasticInjection Molded
032Release slider252Releases locking pinPlasticInjection Molding
033Release Housing252Contains releasing mechanismPlasticInjection Molding
Part Number Name QTY Weight (g) Function Material Manufacturing Process Image
034Wheel Frame Width Plate152Mounts wheel wells. Provides structure to bottom of suitcase and maintains spacing between wheelsPlasticInjection Molded
035Wheel Well Interior Right252Mounts exterior wheel wellPlasticInjection Molded
036Wheel Well Interior Left252Mounts exterior wheel wellPlasticInjection Molded
037Wheel Well Exterior Right252Mounts wheel axle and protects wheelPlasticInjection Molded
038Wheel Well Exterior Left252Mounts wheel axle and protects wheelPlasticInjection Molded
039Threaded Insert252Mounts axle coverBrassCast
040Skid Plate152Prevents excess wear on bottom of the bagPlasticInjection Molded
041Wheel252Allows bag to rollPlasticInjection Molded
042Bearing Assembly452Allows wheels to spin smoothly about the axleSteelPurchased Part
043Axle252Holds wheel to bag and allows it to spin freelySteelExtruded
044Axle Cover252Protects axle from water and other damagePlasticInjection Molded
Cloth Handles
Part Number Name QTY Weight (g) Function Material Manufacturing Process Image
045Handle stabilizing piece452AestheticSynthetic leatherStamped
046Bent Metal Connector45Attached buckle to bag.SteelStamped
047Buckle413Attaches handle to suitcase bodyNickleCast
048Synthetic Leather Cuff213Softens handle for easier pick upPlasticMolded
049Thick flat rope220Provides strength to handleNylonWoven
050Plastic Strip27Provided rigidity to the handlePlasticStamped
051Synthetic Leather Anchor44Houses bent metal connectorPlasticMolded
Main Body
Part Number Name QTY Weight (g) Function Material Manufacturing Process Image
052Interior Bottom Lining169Presentable appearance for main compartment. Hides structural components. ClothWoven
053Interior Bottom Padding121Cushioning for main compartmentFoamSheet Extruded and stamped
054Interior Top Lining179Same as (052)ClothWoven
055Metal Support Frame1457Rigid Structural FrameSteelStamped and bent
056Support Frame Cover146Protects other components from sharp edges of metal support frame.VinylSheet extruded
057Plastic Support Frame1447Rigid Structure for suitcasePlasticSheet extruded and bent
058Edge support wire - side226Rigid support for seamSteelDrawn
059Edge support wire - bottom112Rigid support for seamSteelDrawn
060Buckle Assembly16Hold down extraneous itemsPlasticInjection Molded
061Buckle Straps26Hold down extraneous itemsClothWoven
062Small Zipper Assembly16Holds suitcase compartments closedPlasticPurchased Part
063Large Zipper Assembly16Holds suitcase compartments closedPlasticPurchased Part
064Luggage Tag Sleeve110Holds luggage tagSynthetic LeatherWoven
065Accessory Support Post18Post for accessories to clip on toPlasticInjection Molded
066Foot29Support Luggage when sitting uprightPlasticInjection Molded


Design for Manufacturing and Assembly

In our analysis of the competitor product, we identified several interesting choices made by the competitor in regards to the design for manufacturing and assembly. While some of the choices on the part of the competitor were useful for cheap and efficient manufacturing and assembly, there were a few choices that we feel can be improved upon for more economical product manufacturing and assembly.


The biggest success of the competitor’s design for manufacturing was the relative standardization of design features. One of the most prominent examples of this standardization is evident in the corners of the bag. All corners on the bag, including that of the main storage compartment as well as the exterior pockets, were the same radius. This means that the same manufacturing process can be used for the construction of every corner. Another example of standardization of design features is that some parts looked as if they could be interchanged between various models of suitcases. For example, the wheelbase of the suitcase could be assembled for three different widths of suitcase. This allows for larger manufacturing quantities of injection molded parts, thus leading to a lower cost per part. Another notable thing about the manufacturing decisions of the competitor is the choice of material. All of the materials chosen for the product were fairly easy to work with. These include plastic for injection molding and metal for extrusion, which are both inexpensive materials to manufacture with in large quantities. We found a number of competitor manufacturing choices that can be improved upon in order to simplify the manufacturing process. The first major complaint we had about the competitor product is that they used a huge number of different parts. There were a hundred different shapes and kinds of fabric used in the construction of the bag. We feel that many of these layers served little purpose and could be eliminated or replaced with one layer of higher quality material. Additionally, the competitor used a very large variety of different fasteners throughout the product. Depending on how the competitor laid out the assembly process, all of these different fasteners could cause confusion. We hope to eliminate the majority of these fasteners and replace them with parts that snap or slide together.


One of the best choices that the competitor made for the assembly of the product was the use of subassemblies. Many of the external pockets on the bag, as well as some of the internal mechanical components of the luggage, were probably assembled separately and then inserted and attached to the final bag. This allows for workers that can be specialized for one assembly function, thus streamlining the assembly process. Another decision made by the competitor that specifically benefits assembly is the use of fastener slots on injection molded parts. These slots are used in the place of holes for attaching two parts together with fasteners. They aid in assembly because they allow some tolerance in the spacing of parts. This saves time used for alignment in the assembly process. Another thing that the competitor designed into their product to help with alignment in assembly was self-centering mechanisms for many of the internal mechanical parts of the bag. For example, the wheelbase for the bag was a subassembly that was assembled to the correct width of the bag, so that it could be inserted into the bag without the need for additional measurement. The bag also features a chamfered opening in this wheel base, which the telescoping handle fits into. Both the wheelbase and these chamfered openings speed up the assembly process. Although there was clearly thought put into design for assembly of the competitor product, there were also clearly areas for improvement. One of the largest problems we identified was the huge quantity of different parts. Having so many parts to assemble quickly becomes costly and cumbersome. Additionally, because of the complexity involved in so many parts, the assembly of the non-mechanical parts is by no means fool-proof. There is a large potential for error in the assembly of the internal clothes holding features, such as the layers of padding, the pockets, and the straps. This complexity could lead to waste, which only increases the costs of manufacturing and assembly. We feel that many of these internal features could be simplified or eliminated without a noticeable difference in usability.

Failure Mode and Effect Analysis

In our analysis of the competitor product, we identified several different potential failure modes in using the competitor product. These are enumerated in the table below. This uses the FMEA method described in Section 14.5 of Dieter and Schmidt’s Engineering Design. Note that we felt that none of the cases were very severe. There is likely a very low chance of injury from using this product.

Failure Modes and Effects Analysis - Rolling Luggage
Item & Function Failure Mode Effects of Failure S Causes of Failure O Design Controls D RPN Recommended Actions
Zipper - holds pocket closedPull Breaks Suitcase no longer contains clothes3Fatigue/Direct Force10Load testing on zipper pull130Choose less fatigue prone pull material
Teeth Break5Fatigue/Poor Construction8Use testing on zipper280Use a higher quality zipper
Fabric Caught in Teeth3User Error/Poor Placement in Design10Clearance testing around zipper180Give more tolerance for zipper installation
Wheel support - holds wheels to bagFracture/Plastic DeformationBag no longer rolls properly5Overloading, rough terrain4Analysis of dynamic loading on wheel base240Increase strength of plastic
Wheel rubber-provides smooth rollingAdhesive FailureWheel rubber falls off, more wear on skid plate3Adhesive strength too low3General wheel testing218Better control of adhesive application or use of a stronger adhesive
Entire suitcaseTips overSuitcase falls on floor or user's foot4Suitcase is set off-balance10General stability testing140Give the suitcase a wider base or add more mass toward the bottom of the suitcase
Extendable handleJammed openTelescoping handle won't stay up4Poor handle alignment3Test handle extension alignment224Add handle extension guides to maintain alignment
Push buttonSticks open or closedTelescoping handle can no longer be activated4Poor button alignment3Test button alignment224Use a stronger spring
FabricRipsLuggage no longer holds items2Fabric catches on corners or other sharp objects2Test fabric strength28Use tougher fabric

From this, it is evident that the highest priority risks involve the zipper. We anticipate using a higher quality zipper in order to address the potential failure of the zipper. Another area of concern seems to be the balance of the bag in general. We plan on exploring different ways to make the bag more stable, both while full and while empty. The final major area of risk that was identified in the competitor product was damage to the wheel support from overloading or wash-board terrain. We believe that strengthening the material of the wheel support will be sufficient to prevent damage, though we are also considering using a different configuration of wheels to prevent fracture.

Design for Environment

While examining the competitor product, we also considered the environmental effects of manufacturing and using this type of product. Using EIO-LCA model developed at Carnegie Mellon University, we estimated the environmental impact of the product manufacturing, as shown below. The analysis was performed using a 2002 purchaser price model for the Other Leather and Allied Product Production sector (Sector 316900). We used the manufacturing of one suitcase as the reference unit, because that is the amount of luggage most people purchase at a time. Only one unit is consumed per product life, and the cost per lifetime is the cost of one unit, estimated to be about $100. From this, we were able to learn the information below.

Production Phase mtCO2e Estimates
Sector Number 316900
Sector mtCO2e per $1M 543
Implied mtCO2e per product life 0.00543
CO2 tax @ $30/mtCO2e ~ $0.16

As is evident, the carbon dioxide tax on the manufacturing of this product would be negligible for a single bag, and would likely not affect production in any way.

We feel this analysis is fairly inaccurate for our product, because as shown below, the second largest contributor to these values is from the Cattle Ranching and Farming sector, which would be less applicable to the competitor product we studied, which was made almost entirely out of synthetic materials. For more accurate results, a more detailed analysis of the product’s environmental impact would be necessary.


We chose to disregard the use phase, because the primary environmental effect of the use of luggage is a result of the fuel economy of the method of transportation used in travel. We determined that the weight of the actual luggage was negligible in all cases compared to the weight of the user and the items contained within the bag, and thus any change in fuel consumption due to bag is also negligible.

Group Dynamic

Team Leader: Mallory Elbert

Safety Expert: Fritz Langford

Manufacturing Expert: Eric Lawson

Environmental Expert: David Stonestrom

As a team, we have all worked with one another (though not all at the same time) on various other projects, so we already have a good sense of how everyone else thinks and works. We have allotted two weekly meeting times to use as necessary, but because we know eachother outside of the scope of the course, it has been easy to schedule additional time as necessary.


Dieter, G. and L. Schmidt, Engineering Design, 4th edition, McGraw-Hill, 2009, pages 707-712.

Carnegie Mellon University Green Design Institute. (2008) Economic Input-Output Life Cycle Assessment (EIO-LCA), US 1997 Industry Benchmark model [Internet], Available from:<> Accessed 7 January, 2011.

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