From DDL Wiki

Executive Summary

To optimize the design of a chain tensioning device (be in powered by human power or an external source), the first step was to dissect the use of an existing application. A single, fixed-gear bicycle was acquired and dissected; areas of improvement were addressed via DFMA, FMEA and DFE.

Results from the product usage and evaluation study had proven that the system was not only incredibly non-intuitive, but required far too many specific tools to work on in an emergency situation. Though the subject was technically inclined, results from an attempt tot tighten the chain were incredibly poor and could easily result in injury. Even when this task was completed successfully, the tire was crooked, another opportunity for injury.

Results from the DFMA analysis... [BRIAN]

From the FMEA analysis... [ADAM]

From the DFE analysis... [ANNE]

Thus, the existing product was found to have quite a few issues. It is the goal of this team to improve the existing design as well as possible within the budgetary restrictions. Subsequent analysis will investigate these points further and determine possible design solutions.

Primary Stakeholders and Product Needs

The primary stakeholders in this supply chain are the Manufacturers, the bike shops who will retail this and the bike riding consumer.

Consumers:
Consumers are the target audience who purchases the product, these people would most likely own one or more single speed road bikes and may or may not be hipsters (but probably)

• Ease of use for both alignment and tensioning of the rear wheel
• Robust construction for reliable road use
• Low weight because this is a human powered vehicle
• Lowest possible cost for a quality product
• Ease of maintenance
• Compatible with many bike frame designs, IE not a custom part for each frame
• Easily installed on bikes not currently using it
• Weather resistance

Retailers:
These are the people and companies that would sell the product to the consumers Most likely this would be from specialized bike shops (IE iron city bikes)

• Small size for easy storage
• Universal compatibility use so they do not have to stock more than a couple sized/configurations
• Ease of maintenance
• Low price

Manufacturers:
Manufacturers create the product for sale and effects on time and pricing impact the entire supply chain.

• Time to manufacture is important and all custom machined parts slow down the process
• Cost to manufacture and of materials; exotic materials would not be good here.

Product Function and Evaluation

The MSR MiniWorks Pump operates via an oscillating piston with two one-way valves. A duck valve is inline with the pump head and housing to prevent excessive pressure buildup in the housing. The entire product can be completely dismantled in-field, and can be maintained with little prior knowledge. The design seems very simple yet efficient in its purpose.

Usage
Find the cleanest possible source of water. The intake hose is unwound, and then the intake hose is inserted into the water source. Attach the pump to the water container. Pump water at a steady rate, until container is full. Pull the intake hose out of the water, and pump to clear pump of any additional water.

Usage Flow Chart

Mechanical Function
The product contains a lever that is attached to an oscillating piston with two check valves. On the intake stroke, the intake check valve allows water to travel through the water source into the piston. On the compression stroke, the intake check valve is closed and the bottom check valve allows water to be forced through the filter chamber. The filtered water is then sent out of the pump. A duck valve lies between the pump head and housing to prevent a buildup of pressure. If the input flow is greater than the outlet flow, then the spring on the duck valve will compress and pressure will be released.

User on bicycle

Full Drivetrain

Rear Chain Tensioner

Preliminary User Study
Our group conducted a preliminary user study and determined that the product was self explanatory for either experienced hikers or anyone with moderate technical know-how (i.e. CMU engineering majors). Our group was able to completely dismantle the product without the use of any tools and easily discern the purpose of each part. This product would only need to be purchased by someone with a lot of experience in hiking and the outdoors, as someone without this experience should not be taking trips during which they won't have access to drinkable water. Therefore, nobody should be using it without any prior knowledge.

There are many well-thought-out features which exhibit themselves through simple use. First off, the outlet of the pump is threaded the same size as a Nalgene bottle, so that the pump can sit directly on the bottle and there is no risk of contamination. The included cap for the outlet of the pump also serves to reduce contamination when not in use. The rubber hosing wraps around the pump housing and is secured by a small c clamp in the handle. This serves to not only hold the handle down when when not in use (and prevent incidental breaking), but the c-clamp is properly sized so that it squeezes the hosing closed to prevent excess contamination. Finally the handle is contoured to fit well with the averaged sized in a comfortable pumping position.

Not many issues arise when using the MSR water pump. The most notable problem lies in the fact that the pumping action is cramped and requires several minutes to fill a hiking-sized water bottle. If there were a way to reduce the pumping effort required while keeping the small footprint of the product, it would probably be very beneficial. The only other foreseeable issues are broken parts or a clogged filter, which we didn't encounter and couldn't simulate during this study.

Exploded View

Intake Hose

Piston Assembly

Piston Assembly

Piston Assembly

Piston Assembly

List of Parts

The following details the list of parts of a fixed gear bicycle tensioner and drivetrain.

Labeled Components

Labeled Components

Labeled Components

Labeled Components

Parts list table

Part Number	Name	Quantity	Mass (g)	Subassembly	Function	Material	Manufacturing Process/ Purchased Component	Image
1	Dustcaps	2	<1	Crank Assembly	Keep dirt out of bottom bracket	Plastic	Injection Molding
2	Lock nuts	2	6	Crank Assembly	Retainment/Assembly	Steel	Catalog Purchase
3	Nut w/ integrated lock washer	2	16	Crank Assembly	Retainment/Assembly	Steel	Catalog Purchase
4	Toe strap holders	2	6	Pedals	Ability to secure toe	Plastic	Injection Molding
5	Flange nut	4	<1	Pedals	Attach toe strap holder to foot grip	Steel	Catalog Purchase
6	Screw w/ integrated washer	4	<1	Pedals	Attach toe strap holder to foot grip	Steel	Catalog Purchase
7	Screw	8	<1	Pedals	Attach foot grip to pedal	Steel	Catalog Purchase
8	Pedal cap	2	<1	Pedals	Keep dirt out of pedals	Plastic	Injection Molding
9	Foot grip	2	27	Pedals	Prevent foot from slipping off pedal	Aluminum	Die Casting
10	Outer jam nut	2	9	Sprocket Assembly	Retainment/Assembly	Steel	Catalog Purchase
11	Washer	2	<1	Sprocket Assembly	Retainment/Assembly	Steel	Catalog Purchase
12	Inner jam nut	2	7	Sprocket Assembly	Retainment/Assembly	Steel	Catalog Purchase
13	Pedal	2	54	Pedals	Central Component in Pedals	Aluminum	Die Casting
14	Ball bearings	24	<1	Pedals	Friction Prevention	Steel	Catalog Purchase
15	Nut	2	3	Pedals	Retainment/Assembly	Steel	Catalog Purchase
16	Double D Washer	2	<1	Pedals	Catalog Purchase	Steel	Catalog Purchase
17	Nut w/ seat for ball bearings	2	5	Pedals	Retainment/Assembly	Steel	Catalog Purchase
18	O-ring	2	<1	Pedals	Keeping lubricants inside pedal	Rubber	Catalog Purchase
19	Chain	1	304	Drivetrain	Drive rear sprocket using rotation of front sprocket	Steel	Stamping and Pressing
20	Crank	1	260	Spindle/Crank Assembly	?	Steel, aluminum	Die Casting
21	Crank w/ sprocket	1	626	Spindle/Crank Assembly	?	Steel	Assembly - Stamping and Die Casting
22	Rear sprocket	1	82	Rear Hub Assembly	?	Steel	Stamping with Post Machining
23	Bearing	2	19	Rear Hub Assembly	?	?	Catalog Purchase
24	Rear wheel	1	?	Rear Hub Assembly	?	Steel, Rubber, Aluminum	Assembly - Catalog Components Mated with a CNC lathed hub
25	Rear axle	1	101	Rear Hub Assembly	?	Steel	CNC Lathing
26	Sprocket retaining ring	1	15	Rear Hub Assembly	?	Steel	Catalog Purchase
27	Ball bearings	2	14	Spindle/Crank Assembly	Countering Friction in Pedals	Steel	Catalog Purchase
28	Left threaded cap	1	54	Spindle/Crank Assembly	Retainment/Assembly	Steel	Catalog Purchase
29	Spindle	1	209	Spindle/Crank Assembly	Allow wheel to move	Steel	CNC Lathing
30	Right threaded cap	1	47	Spindle/Crank Assembly	Retainment/Assembly	Steel	Catalog Purchase
31	Crank Spacer	1	47	Spindle/Crank Assembly	Retainment/Assembly	Steel	Stamping

Design For Manufacturing and Assembly

Design For Manufacturing [DFM]

Notice the extra lip on the inside diameter of the sprocket required for the retaining ring to seat against. This feature may be designed away.

Dissection of the fixed gear drive train revealed several areas for improvement. The majority of the drive train consists of cast or stamped steel and aluminum components which allows for a high volume of relatively cheap parts to be made. High tolerance components such as the rear axle, hub and spindle are likely CNC lathed in order to achieve required tolerances for bearing surfaces. Unfortunately this drastically increases the time and money spent to produce such parts. However, considering the cost of machining the rear hub it is multifunctional: it locates the bearings, provides torque transfer and mounting for the sprocket and secures the wheel. It should be noted some components of the pedal assembly (dust cap, toe strap holders) are injection molded plastic, allowing for very cheap manufacture after initial mold investment. Interestingly, it seems the use of injection molded plastic for other applications such as the pedal and pedal grip could be a viable option at the expense of some durability. Furthermore, standardizing bearings between the pedal set, crank assembly and hub could reduce costs and increase the feasibility of injection molding the pedal set. Other notable components include the rear hub, sprocket and retaining ring and their method of interface. The hub uses a stepped threaded area in order to accommodate the larger diameter sprocket and smaller diameter retaining ring. This setup increases manufacture time and cost by requiring two separate sized threads to be machined onto the hub as well as a lip machined into the sprocket for the retaining ring to seat against. Instead a single diameter thread may be used along with a locking nut. A similar oversight occurs in the pedals where ball bearings are retained by a special nut and jam nut instead of a single bearing set and lock nut assembly.

Overall the materials and production methods provide a durable, well finished system but certainly leave room for improvement. By minimizing part count, standardizing components and design features and simplifying parts it should be possible to reduce the production cost by a fair margin.

DFM Summary

• The drive train is made of durable, aesthetic pieces at the expense of production cost.
• Casting and stamped processes are used where applicable to reduce high-volume cost.
• The drive train uses many non-standardized parts across the system.
• Some components are excessively complicated or superfluous for their function

Design for Assembly [DFA]

The pedal bearing set consists of many separate parts which must be installed in a specific order and orientation. Also note the obstructed access to pedal removal when pedal grip is in place.

Dissection of the fixed gear drive train show inconveniences that negatively affect assembly time, assembly worker training and labor cost. It is likely several of these inconveniences are a result of the fact that assembly is completed by the customer as well as standard bike specific tooling. An experienced user is required to install the drive train assembly correctly as there are many components with no clear assembly order, especially in the bearings for the pedals. Additionally parts must be installed from several directions and access is often obstructed if the system is assembled in the incorrect order. For example, there is no feature in the pedal grip to allow for pedal removal. Instead, it is necessary to remove the pedal grip to gain access to the nut for pedal removal. This may be easily remedied through a clearance hole in the pedal grip. Additionally, the use of unnecessarily thin retaining rings and sprocket requires 2 special bike wrenches which are significantly thinner than standard wrenches. While this is relatively standard in the biking industry for enthusiasts or shops, it certainly inconveniences an average user looking to conduct maintenance or repair. Also, special care is required when installing the pedal bearing set as it is made up of many individual parts and requires specific assembly order. Tens of ball bearings must be installed, followed by a custom nut requiring specific orientation, a washer and lastly a jam nut. This is a mistake prone assembly and also requires quite some time to install due to the many separate components. There are, however, some well thought out components which ease assembly. For example, the pedal grip uses slots for mounting which maximizes installation compliance, even in the event of a warped or damaged grip assembly. Also, integrated washer/nuts are used to hold the wheel to the frame, minimizing the number of fasteners on a part which is likely removed often.

While there are some positive points for the drive train assembly there are still numerous ways to improve upon installation simplicity and time. We believe there may have been a lesser focus on design for assembly due to the fact that these components are often assembled by the customer. As such the manufacturing company realizes no lost revenue (other than customer backlash) due to the relatively inefficient design.

DFA Summary

• The designers likely did not prioritize installation simplicity or speed.
• Special tools are required for proper assembly.
• The installation process is mistake prone and requires a fair amount of experience.

Failure Mode and Effect Analysis [FMEA] [ADAM]

Design for Environment [ANNE]

Team Members

Michael Ornstein - Team Leader

Rob Wojno - Product Function, Evaluation and Usage Study

Anne Dirkes - DFE

Brian Langone - DFMA

Adam Brecher - FMEA

Each member of the team expressed interest in their assigned field; work is done on a regular basis with Mr. Ornstein overlooking the direction and making sure it's in line with expectations.

References

Cascade Designs, Inc. MSR MiniWorks EX Water Filter. 24 Jan. 2012. Instruction Manual. Seattle, WA.

Carnegie Mellon University Green Design Institute. (2008) Economic Input-Output Life Cycle Assessment (EIO-LCA), US 1997 Industry Benchmark model [Internet], Available from:<http://www.eiolca.net> Accessed 23 September, 2012.

Dieter, George E., and Linda C. Schmidt. Engineering Design. 4th Edition. New York, NY: McGraw-Hill, 2009. 707-715. Print.

"MSR® MiniWorks™ EX Microfilter Schematic." MSR. Cascade Designs, Inc. Web. 12 Feb. 2012. <http://cascadedesigns.com/msr/water-treatment-and-hydration/expedition-water-treatment-and-hydration/miniworks-ex-microfilter/product>.