Winter 2014
Progress Report
Modular Accessory Attachment System
Group Members
Rhett Metcalf | Chet Thomas | Thom Vigeon | Alexander Puddu
Portland State University – Faculty Advisor
Dr. Huafen Hu
Showers Pass – Industry Advisor
Kyle Ranson
Executive Summary
A modular accessory attachment system enables cyclists to quickly and easily add or
remove accessories. Many cyclists use bicycles for multiple purposes, commuting and race
training rides for instance, and require different accessory configurations for each use.
Currently, accessories are mounted in a semi-permanent fashion and the length of time required
to add or remove such accessories restricts reconfiguration. This lengthy reconfigure time forces
the avid cyclist to acquire multiple bikes, each configured for a different purpose.
The objective of the Showers Pass Capstone Team is to design and build an accessory
attachment system that employs a quick releasing mechanism to facilitate reconfiguration with a
significant reduction of install time required for a typical rear-of-bike pannier rack. This proof-ofconcept could then be expanded to other accessories.
To date, the team has identified product design specifications (PDS), completed two
phases of external searches for existing products, and conducted general idea gathering
sessions with the intent of developing and evaluating various concepts. The team is currently in
a third phase external search for small parts that can be directly applied to design, and entering
the detailed design phase of product development.
The PDS has determined key points to be size, weight, cost, and speed at which the device
can be deployed. An external search identified potential established solutions to design
requirements. Important search parameters include materials, manufacturing, attachment types,
and aesthetics.
The team has developed three concepts to be evaluated based on the PDS criteria. The
concept that will be selected for final evaluation will meet the customer requirements while
minimizing specialized fabrication and materials, reducing manufacturing costs and increasing
market viability.
Table of Contents
Introduction ............................................................................................................................................ 1
Mission Statement ................................................................................................................................. 2
Project Planning..................................................................................................................................... 2
Finalized PDS Summary ........................................................................................................................ 3
Table 1. Product Design Specification – Highest Priority PDS Requirements............................... 3
External Search ...................................................................................................................................... 3
Internal Search ....................................................................................................................................... 5
Table 2. Design Matrix ....................................................................................................................... 5
Design Evaluation and Concept Selection ........................................................................................... 7
Term Conclusions and Next Steps ....................................................................................................... 8
References ............................................................................................................................................. 9
Appendix A – Detailed Project Schedule............................................................................................ A1
Appendix B – Product Design Specification ...................................................................................... B1
Introduction
Showers Pass is a Portland based company that designs and sells gear for urban bicyclists.
Showers Pass specializes in waterproof jackets and other apparel. Recently, they have
progressed into the bicycle accessory market through their innovative hydration system, the
VelEau, which is shown in Fig. 1. This seat-mounted accessory provides riders with a
convenient, backpack-free way to access their water supply while on the go.
Figure 1. VelEau – This hydration system was designed by Showers Pass, and is their first
bicycle mounted accessory. [Ref. 1]
The company is now looking for a solution to a major shortfall within the bicycle accessory
market. In the current market, accessories such as pannier racks, fenders, and seat bags are
very labor intensive to install or uninstall. Avid bicyclists often perform multiple activities on their
bikes, such as commute, race, tour, and pleasure ride. The current best method for the avid
cyclist to participate in these activities is to collect multiple bikes to support multiple
configurations.
The goal of this project is to design a quick-release mechanism which will enable a cyclist to
quickly reconfigure the attachments on a single bicycle for multiple activities. Showers Pass has
expressed desire in market viability; therefore this design will be light weight, strong, carbon bike
frame friendly, and aesthetically pleasing.
The Showers Pass Capstone Team has made significant progress towards this goal. The
Team has defined the product specifications, researched existing designs, brainstormed
multiple implementations, and narrowed the design to three detailed concepts.
1
Mission Statement
The Showers Pass Capstone Team will design and prototype the Modular Accessory
Attachment System (MAAS). This system will enable a cyclist to quickly and efficiently attach
and detach a rear pannier rack. In addition to a rack, MAAS will be capable of supporting other
accessories such as fenders, seat bags, and lights. The team will design appropriate retail
packaging to support sales of MAAS. The team will document each step of the project, and
provide periodic progress reports. A final summary will be issued to Showers Pass in June of
2014, including specifications, analysis, drawings, testing data, bill of materials, production
schedule, and cost analysis.
Project Planning
At the project’s conception, a schedule was created to track progress of MAAS. A truncated
version of the schedule with important milestones can be seen in Fig. 2. MAAS has not
encountered scheduling setbacks and is on track to being completed on time. The team has
selected three different general concepts, and is progressing towards a final detailed design,
which will be completed in Spring term. A detailed project schedule can be seen in Appendix A.
Figure 2. Gantt Chart – Top-level schedule of the Showers Pass project
2
Finalized PDS Summary
A Product Design Specification (PDS) was created, and then finalized via a meeting with the
project sponsor on January 22, 2014. This specification set a baseline for the performance of
the accessory attachment system by defining the requirements in a measurable metric. Table 1
shows the highest priority requirements. The complete PDS can be found in Appendix B.
Table 1. Product Design Specification – Highest Priority PDS Requirements
Priority
[1-5]
Requirement
Customer
Metric
Target
Target Basis
Verification
5
Support two loaded panniers
Showers Pass
Weight [lbs.]
40 lbs.
Weight of two loaded panniers
Testing
5
Attach to carbon bikes
Showers Pass
Yes / No
Yes
Showers Pass Requirement
Prototyping
5
Attach to bikes without eyelets
Showers Pass
Yes / No
Yes
Showers Pass Requirement
Prototyping
Withstand all weather conditions
Showers Pass
Yes / No
Yes
Weather in Portland
Testing
Production cost
Showers Pass
Money [$]
1/4 Retail Cost
Room for profit
Prototyping
Minimal size
Showers Pass
Volume [in^3]
3
1 in^3 per mounting point
Design
Structural integrity
Showers Pass
FOS
1.5
Max loading of competitor’s
racks
Testing
Performance
Environment
5
Costs
5
Size/Shape/Weight
5
Safety
5
External Search
The purpose of the external search was to explore, identify and examine existing products
that relate to MAAS. There is a significant market specific to bicycle accessory options,
however, there are no products that satisfy the PDS requirements of a quick, universal
attachment mechanism. The absence of products like MAAS demonstrates that this design is an
innovative step towards increasing bicycle functionality.
Related Technologies
Some accessory manufacturers have begun to incorporate easy attachment into their
designs. The following figures are a sample of currently available bicycle accessories that
employ “easy attachment” designs.
3
Figure 3. Skewer Mounted Rack – This design utilizes the rear skewer as a loading
point and is for use on bicycles that do not have eyelets. It is relatively easy to use,
but requires time, and removal of the rear wheel to dissemble. [Ref. 2]
Figure 4. Fender – Current market option for quick disconnect fenders on bicycles
without eyelets or where weight of fender accessory is a concern. This mechanism
will not withstand repetitive use, or excessive loading. [Ref. 3]
Figure 5. Seatpost Rack – An alternative to the traditional eyelet mounted rack. The
design is not universal for other accessories. It carries significantly less load than a
traditional rack, and is not compatible with panniers [Ref. 4]
4
Internal Search
Summary
The objective of this analysis was to determine if any pre-existing quick attachment mechanisms
could be utilized within the design. Table 2 shows the ranking of six market options with respect to five
design considerations. Vibrational sensitivity was chosen for analysis because the rider cannot be
subjected to excessive noise. Each design was also rated based on cost, ease of use, strength, and
resistance to dirt and grime.
Table 2. Design Matrix – Based on the total, the ranking in order of best design is the ball lock, pipe clamp and
slide lock. [Ref. 3 & 5]
Visual
[1 - 5]
Vibrational
Sensitivity
[1 - 10]
Ease of
Use
[1 - 10]
Load
Bearing
[1 - 3]
Environmental
Durability
[1 - 2]
Total
[30]
Push Pin
4
2
6
3
2
17
Cotter Pin
5
2
3
3
1
14
Slide Lock
2
6
8
2
2
20
Rubber Latch
1
10
1
1
1
14
Ball Lock
3
8
8
3
1
23
Pipe Clamp
3
8
6
3
2
22
Connector
Type
Cost
5
Push Pin
A push pin is a rod with a retracting ball protruding normal to the surface of the pin. It is designed to
slide through a collar and expand to prevent the pin from further lateral movement. The push pin is
relatively low cost and easy to use. A typical design employs steel and would provide adequate shearing
strength. The clearance tolerances are usually loose or free running fit and vibrational sensitivities are
high which would result in excessive noise for the rider. The pin design is not air or water tight and is
prone to failure in environments with excessive dirt and grime.
Cotter Pin
A cotter pin is similar to a push pin, but uses the interaction of two separate pieces to lock in place.
This system uses a solid shaft and is therefore less expensive and stronger, but due to the additional
components it is more difficult to use in all weather conditions and may not be easy for all types of
cyclists. It would also be prone to vibrational noise during use.
Slide Lock
A slide lock is a spring lock slide gate that clips onto a pin used to mount two flat plates. This system
is more expensive and weaker in than the solid pin in shear. It would be easier to use, less noisy, and
less prone to clogging.
Rubber Latch
A rubber latch mechanism is currently deployed as a quick release for bicycle fenders as seen in Fig.
4. The design utilizes a rubber strap that wraps around the frame and clips the mounting point in place
via frictional forces. As this type of connection is mass produced, the cost is very low. This type of mount
creates almost no audible vibrations. However, it has poor load bearing capabilities and fails under cyclic
loading, especially with extreme variations in temperature and/or humidity.
Ball Lock
The ball lock mechanism is most commonly used in compressed air systems. The mechanism is
more expensive than the pins or slide lock but can be loaded in compression instead of shear. Therefore,
they would provide adequate loading capabilities. This mechanism maintains ease of operation and
connection abilities in environments contaminated with dirt and grime and forms a tight seal that does not
vibrate during use.
Pipe Clamp
The pipe clamp system is derived from the flanged pipe connection design utilized in current
industrial applications. This system is very tight, would not vibrate, and is able to withstand excess dirt
6
and grime. It will not fail after repetitive engagement. However, scaling this system down may result in
higher costs.
Design Evaluation and Concept Selection
After researching existing latching mechanisms, three concepts were chosen to meet the PDS
requirements. The design metrics used for evaluating the designs can be found in the PDS criteria.
The slide lock, ball lock, and pipe clamp were identified as viable design choices.
The first critical implementation issue was to define the location of the mounting points on the
bike frame. Some bicycles have eyelets to facilitate mounting accessories, but MAAS must work
without them. It is desired to use a triangulation loading method which will lead to increased stability.
Two of the three points are to be located at the ends of the rear wheel’s quick-release skewer.
Figure 6 shows the collar mounting bracket with one half of the quick-release mechanism attached
to the skewer. This mounting point is to remain on the frame when the attachment system is not in
use.
SKEWER
Figure 6. Skewer Mounts – Skewer add-on to employ the MAAS system. The component is a
bracket that collars the original skewer shaft with a quick attach point ready for mating to the
desired bicycle accessory.
7
The third mounting point is to be attached to either the seat post or share the rear brake bolt.
Current market rack implementations have used these two locations with success. A preliminary
design, which utilizes the seat post as a mount, is shown in Fig. 7.
SEATPOST
Figure 7. Seat Post Mounts – Upper mount for MAAS. The quick mount system will achieve
stability through a third point by utilizing the strength of the seat post through a tube bracket.
Term Conclusions and Next Steps
The Showers Pass team has finalized the PDS, completed the internal and external phases of the
brainstorming, and selected three concepts – of which two will be further defined in a detailed design. An
additional meeting with our sponsor has been scheduled, and his input will ultimately direct which final
design is prototyped.
The current designed drawings, upon successful prototyping, will meet or exceed each of the
requirements of the PDS. Prototypes will be made and tested for loading capabilities and ease of use.
Based on the testing results, the finalized design will undergo iterative revisions to optimize performance.
Retail packaging that aligns with the existing Showers Pass product line will be designed and
implemented. Lastly, a final report will be written that fully documents the design process.
8
References
[1]
VelEau Hydration System
http://www.showerspass.com/catalog/accessories/veleau-42
[2]
Skewer Mounted Pannier Rack
http://www.cyclebasket.com/m5b0s144p2367/BLACKBURN_EX1_Disc_Compatible_Pannier_Rack_
[3]
Quick Disconnect Fenders
http://www.excelcycle.com/planet-bike-speedez-700c-narrrow-quick-on-fenders.html
[4]
Arkel Seatpost Mounted Rack
http://www.adventurecycling.org/cyclosource-store/equipment/sp/arkel-randonneur-rack/
[5]
Quick Disconnect Attachment Systems
http://www.mcmaster.com/
9
Appendix A – Detailed Project Schedule
A1
Appendix B – Product Design Specification
Priority
Requirement
Performance
5
Support two loaded panniers
5
Attach to carbon frame bikes
5
Attach to bikes without eyelets
Customer
Metric
Target
Target Basis
Verification
Weight [lbs.]
40 lbs.
Weight of two loaded panniers
Testing
Yes / No
Yes
Showers Pass Requirement
Prototyping
Yes / No
Yes
Showers Pass Requirement
Prototyping
Yes / No
Yes
Weather in Portland
Testing
Time [years]
5 years
Industry standard
Testing
Yes / No
Yes
Avoid repurchasing entire system
Prototyping
Money [dollars ($)]
≈ $50.00
Approximate cost of popular
racks
Prototyping
Money [dollars ($)]
1/4 Retail Cost
Room for profit
Prototyping
Attachment size
[in3]
3 in3
1 in3 per mounting point
Design
Weight [grams]
<100 grams
Ability to leave on bike
Design
Packaging size
Padded
envelope
Minimize cost to end-user
Prototyping
Time [min.]
<30 min.
Length of time for initial
installation
Prototyping
-
Common Tools
Avoid specialty tools purchases
Prototyping
Time [min.]
<5 min.
Length of time to attach two
panniers
Prototyping
Time for Arrival
3-5 days
Length of ground shipping times
Design
Yes / No
Yes
Minimal prototyping costs
Design
-
1 prototype
Proof of concept
Prototyping
Showers
Pass
Yes / No
Yes
Maximize product market
Design
Showers
Pass
FOS
1.5
Max loading of competitor’s racks
Testing
Showers
Pass
Showers
Pass
Showers
Pass
Environment
5
Withstand all weather
conditions
3
Life in service
Showers
Pass
Showers
Pass
Maintenance
3
Replacement Parts
Showers
Pass
Costs
3
Retail cost
5
Production cost
Showers
Pass
Showers
Pass
Size/Shape/Weight
3
Minimal size
3
Low weight
2
Minimal shipping costs
Showers
Pass
Showers
Pass
Showers
Pass
Ergonomics/Ease of Use
3
Set-up time
2
Tools needed
4
Quick Connect/Disconnect
Manufacturing & Materials
Readily available
2
parts/materials
3
Manufacturing at PSU
3
Quantity needed
Compatibility / Standards
Compatible with multiple
3
racks
Safety
5
Structural integrity
Documentation
5
PDS
Showers
Pass
Showers
Pass
Showers
Pass
Showers
Pass
Showers
Pass
Showers
Pass
Dr. Sung Yi
Deadline
2/4/2014
Due Date
Grade
5
Progress Report
Dr. Sung Yi
Deadline
3/13/2014
Due Date
Grade
5
Final Report
Dr. Sung Yi
Deadline
≈ 6/14/14
Due Date
Grade
B1