Revision as of 22:46, 15 November 2012

Using what we have learned in class, in this gate, we will be analyzing our bicycle's components as well as develop a functional model and analyse it at a subsystem level. Seeing as this product is already dissected, we will be able to analyze it in great detail.

We will first be talking about how our group works together and functions as a whole. We will then move on to talk about our product in a subsystem and component level. This will entail our bill of materials, product analysis, some 3D modeling, engineering analysis, as well as some design revisions of the product.

Project Management: Coordination Review

A big part of this project is to teach how to deal with working with other group members. It is important to realize what role one takes in a group to create the most efficiency. While being in a group brings in many different personality types, to be a successful engineer, we need to learn what to do when we have an issue with another person and how to deal with it.

Cause for Corrective Action

Even with the corrections made in the last gate, we are still having problems with the group.

Challenges

In the last gate we had the following major challenges:

• Communication
• Wiki Organization
• Attendence

Challenges That Have Been Addressed

Communication

The main communication problems were as follows:

• Primary mode of communication was text messaging.
• Miscommunication of assignment due dates.

These were addressed by adding more modes of communication.

• Emails are sent out weekly containing agendas of the meetings, due dates, new meeting times, etc.
• We have set up a photobucket.com account so all pictures will be available for anyone in the group to access.
• We have set up google docs account so all material being worked on will be available to each group member.
• We have meetings about once a week and the minutes can be found in the table below.
  • After the due date of this gate, the updated meeting minutes and table will be found on gate 4 with updated information.

Table 1: Weekly Schedule

Monday Meeting Minutes

Oct 22:

• Determined the time and date of dissection.
• Will meet Tuesday, October 23, 9am to 11pm in the lab.
• Lab is located in 621 Furnas.
• If we do not finish within the two hours, we will find another time to meet.
  • Added Tuesday: We will meet Wednesday, October 24, 10am to 12 pm, in the lab to finish dissection.

Oct 29:

• Determined group issues will be discussed at a meeting with the professors
  • Will meet Thursday , November 1, 11:30am in office hours.
  • Office hours are held in 203 Furnas Hall
• Hours each group member spent on Gate 2
  • Tiffany- 30
  • Nick- 5
  • John- 3
  • Liz- 1
  • Garrett- 1

Nov 5:

• Met in the dissection lab
  • Started work on Gate 3
  • Worked from 10:30am to 11:30am
  • Who was there: John, Liz, Tiffany, Nick
  • Who was supposed to be there: everyone
• Will meet Tuesday, November 6. Time and place TBD.

Nov 12:

• 2pm in the basement of Capen Library
• The meeting lasted about 15 minutes.
• Our agenda was to split up the parts for gate 3.
  • Cause for corrective action- Tiffany
  • Component summary- John
  • Product analysis- Nick and Tiffany
  • Solid Modeled Assembly- Started by Nick
  • Engineering Analysis- Liz
  • Design Revisions- Garrett

The parts will be finished and sent to Tiffany via email by 5pm on Wednesday

Nov 19: (Coming soon)

Nov 26: (Coming soon)

Dec 3: (Coming soon)

Dec 10: (Coming soon)

Wiki Organization

In our first gate, we were marked down highly because of our disorganization of the wiki page. We have changed roles and Tiffany has taken over the wiki programming. Comments from the grading rubric have been taken into consideration while this gate was being produced.

Unresolved Challenges

Attendance

A recurring problem we have been having as a group is the poor attendance not only to the weekly meetings, but to class as well. To solve this problem, we attempted to have a meeting with the professors that not everyone in the group attended. We address this as an unresolved challenge even through we have attempted to solve this problem a few times before.

We address this problem by sending emails to the professors, making them aware of the issues we are having. The emails contain all information covered in our meetings as well as who attended, who did not, the agenda of the meeting, time, place, etc. If needed the group member will be spoken to by the professors if they fail to meet the needs of the group.

Future Challenges

Some challenges we foresee are:

• Group members still not attending class and/or meetings.
• Group members refusing to participate.
• Group members continuing to hand in late work.
• Group members resigning the class.

If any of these situations occur we have the following solutions:

• Group members who fail to perform will be penalized in the group evaluations.
• For the upcoming gates there will be a due date for all gate parts, which will be split up among the group members. This due date will give the group members who participate enough time to pick up the slack if a part is not finished. The group members who do not participate and fail to hand in their part before the due date will not be asked to participate in the next gate. The professors will be alerted of the group members who were unwilling to meet deadlines and/or participate.

Product Archaeology: Product Evaluation

This part of the project is helping develop the design and analysis skills of each group member.

Component Summary

A bill of materials, or BOM, consists of all the components of a product, as well as sub-assemblies, and the quantity of each needed to manufacture the end product. It is used as communication between engineer and manufacturer. It is referred to during manufacturing process, the design stage and again during sales and marketing.

The organization of the Bill of Materials is as follows:

(Item Number). Name

• Material
• Manufacturing Process
• Quantity
• Components

1. Component name, size, quantity, material, manufacturing process

Bill of Materials

1. Pedals: place where the force is transferred to the crank; grips to the riders shoes

• materials used: metal and plastic
• manufacturing processes: injection molding
• quantity: 2

2. Crank arms: increases the mechanical advantage and direction of motion of the force

• materials used: steel
• manufacturing processes: die casting
• quantity: 2

3. Crank assembly: transfers all energy from the rider to the front sprocket

• Components:

1. one axle shaft: die casting
2. two roller bearings
3. one retaining nut (steel) with one retaining ring (aluminum)
4. two 14mm nuts to hold the two crank arms on
5. two pedals

4. Front sprocket assembly: transfers the rotational force of the crank to the chain and increases the mechanical advantage depending on the sprocket in use

• materials used: aluminum
• manufacturing processes: metal stamping
• quantity: 1

5. Tires: allow the bicycle to ride smooth and hold traction

• materials used: rubber
• manufacturing processes: rubber mold
• quantity: 2

6. Rims: hold the tire and create a surface for the brake pads to grab a hold of

• materials used: aluminum
• manufacturing processes: starts with a lump of aluminum, which is then pressed through a template to create a profiled extrusion. The profile is then cut to length, rolled into a hoop, and joined
• quantity: 2

7. Rear hub/sprocket assembly: transfers the kinetic energy from the chain to the wheel. Also changes mechanical advantage using sprockets.

• materials used: aluminum and steel

1. uses two 15mm nuts with washers (steel)

• manufacturing processes: metal stamping and die casting
• quantity: 1

8. Seat: provides a comfortable place for the rider to sit.

• materials used: Rubber, foam, and steel.
• manufacturing processes: include a rigid seat of a molded, nylon-based plastic. The seat is then covered with some sort of padding and wrapped in a easy to clean cover.
• quantity: 1

9. Frame: provides a structure for all the components of the system to be mounted to.

• materials used: steel
• manufacturing processes: tig welded bent tubing
• quantity: 1

10. Handlebars: allow the rider to hold on to the bike and steer the bike.

• materials used: aluminum
• manufacturing processes: bent tubing
• quantity: 1

11. Handgrips: give the rider a comfortable place to securely hold on to the handlebars

• materials used: rubber
• manufacturing processes: injection molding
• quantity: 2

12. Derailleur: moves the chain onto different sprockets

• materials used: aluminum, steel, and plastic
• manufacturing processes: metal stamping and injection molding
• quantity: 2

13. Chain: transfers the mechanical energy from the front sprocket to the back sprocket

• materials used: steel
• manufacturing processes: metal stamped pieces are press fitted together
• quantity: 2

14. Kickstand: props the bicycle up when not in use

• materials used: steel
• manufacturing processes: cut and bent steel rod
• quantity: 1

15. Brake levers: pull the cable to apply the brakes and increase the mechanical advantage to pull harder on the cable given a force from the riders hand

• materials used: aluminum
• manufacturing processes: molded
• quantity: 2

16. Brake cables: transfer the energy from the brake levers to the braking mechanisms

• materials used: braided steel cable in protective plastic sleeve
• manufacturing processes: multiple drawn fine steel cables are combined for strength and protected by a plastic sleeve
• quantity: 2

17. Handlebar clamp: holds the handlebars onto the steering stem

• materials used: aluminum

1. uses two 6mm x 1.5" allen bolts

• manufacturing processes: die casting
• quantity: 1

18. Steering stem: transfers the rotational force from the handlebars down to the front fork of the bike

• materials used: aluminum and steel

1. uses one 6mm x 6.5" allen bolt with an expansion nut

• manufacturing processes: die casted piece is welded to steel tubing
• quantity: 1

19. Gear selectors

• materials used: plastic and aluminum
• manufacturing processes: injection molded plastic levers riveted to a bent steel band
• quantity: 2

20. Gear selector cables: transfer the energy from the gear selectors to the derailleur mechanisms

• materials used: braided steel cable in protective plastic sleeve
• manufacturing processes: multiple drawn fine steel cables are combined for strength and protected by a plastic sleeve
• quantity: 2

21. Reflector: reflects light to provide a safer riding environment for the rider at night

• materials used: aluminum and plastic
• manufacturing processes: injection molded plastic riveted to a bent steel bracket
• quantity: 1

22. Front/ Rear braking assembly: stops the bike using the friction between the rim and the brake pads

• components:

1. two brake pads (rubber and aluminum)
2. two return springs (steel): returns brakes to the "off" position
3. two 10mm x 1" steel bolts with washers: hold the braking mechanism to the frame
4. two brake arms: applies the force from the cable to the brake pads
5. four spacers (aluminum): keep the proper distance between the brake pads and the brake arms
6. two cable clamps (steel): attach the brake cable to the cable between the brake arms

23. Hardware Listing

• one steel 13mm x 1.5" bolt with nut and washer (seat clamp)
• two steel 15mm nuts with washers (hold front hub onto the front fork)
• four 1/4-20 bolts with nuts (tighten clamps on both gear selectors and brake levers)
• three 1/4-20 bolts (attach both derailleurs and the reflector to the frame of the bike)

Part Numbers and Prices

All available OEM parts can be found at:

http://www.searspartsdirect.com/partsdirect/part-model/Sears-Parts/All-Products-Parts/Model-655475550/0934/1303200/00052548/00001?blt=06&prst=&shdMod=

Product Analysis

Component Function

Component Form

Manufacturing Methods

Component Complexity

Step #	Part Name	Component of which subsystem?	Tool Used	Comments	Time (minutes)	Physical Effort (1-5)	Overall Difficulty (1-5)	Picture
1	Front Wheel	Steering/Body	13 mm wrench	Few turns and the two nuts came off the axle. Tire came off easily.	1	1	1
2	Front Brakes	Brakes	10 mm wrench	Few turn to take off two bolts. Wiring was difficult to maneuver.	5	2	3
3	Shifters	Shifting/Power	Phillips head screwdriver	Took more time because of rust.	3	2	2
4	Hand Brakes	Brakes	Allen wrench	N/A	3	1	2	See above
5	Handlebars	Steering	Allen wrench	Very easy.	2	1	1
6	Handlebar Brace	Steering/Body	Allen wrench	N/A	1	1	1
7	Seat	Steering/Body	13 mm wrench	Took a long time because seat axle was very rusty.	10	4	4
8	Rear Brake Pads	Brakes	10 mm wrench	N/A	5	2	3
9	Reflecter	Body	10 mm wrench	Popped right off.	2	1	1
10	Rear Gear System	Shifting/Power	15 mm wrench Phillips head screwdriver|	N/A	5	2	2
11	Rear Wheel	Power	15 mm wrench Phillips headscrewdriver|	Couldn't remove until we removed the rear gear system. Tire was taken off easily after.	3	1	1
12	Pedals	Power	13 mm wrench Bearing Press|	Very difficult and very rusty. Tried many different methods before this one worked.	45	5	5
13	Chain Protector/Mover	Shifting/Power	10 mm wrench	Gravity took it off during our dissection, but in normal cases, use the tool specified.	1	1	1
14	Kickstand	N/A	10 mm wrench	Rusty and needed some man power to finally remove from frame after bolts were removed.	10	4	3

Solid Modeled Assembly

Engineering Analysis

Component

The frame is a key component of the bicycle. It is the backbone, which supports and connects all of the other parts in order for it to perform correctly. It also plays a big part in determining the final cost of the product since different frame materials are more expensive than others. Lastly, it contributes to the main appearance and overall attractiveness of the bicycle, determining whether it looks sleek or bulky, plain or colorful. To a consumer, those are the three biggest concerns: performance, cost, and appearance. In the design and testing stages of the design process, several factors are taken into account to try to improve these concerns, and various trade offs are then made depending on the target consumer.

Mechanism Analysis

The frame is subjected to many forces in its lifetime. It must be able to support the bending, tension and compression due to the rider’s weight, the torsion due to the pedaling, and the vibrations due to impacts and rough ground. There are two main factors, stiffness and strength, that determine how well the frame is able to support these forces. These two factors, combined with the main design factor, weight, all affect the general performance of the bicycle and must be taken into consideration during the design process. The ideal frame has a high stiffness so that it can support the mentioned loads with minimal elastic deflection (bending). It has a high strength to avoid cracking and fatigue due to stress from impacts and rough surfaces, and it has a low weight so that it can accelerate and go uphill faster. Different materials perform better than others in tests for these factors. Since minimal weight is the main design factor, and different materials have different weights, stiffness and strength are based on a strength-to-weight ratio and a stiffness-to-weight ratio. The weight is taken into account by dividing by the material density. The following equations are used to determine the specific stiffness and specific strength for different materials:

Stiffness equation used for analysis

The formula for stiffness is based off of the elastic beam theory and the following equation for the deflection of a beam:

Deflection equation used for analysis

The specific stiffness and specific strength (fatigue resistance) for different materials are then plotted like in the chart below. The materials highlighted in blue are materials that have been used in bicycle frames already.

Figure 1: Specific stiffness and specific strength plot. Referenced from http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=89&pageid=2144417038

Figure 1: Specific Stiffness and Specific Strength Plot Analysis

This chart shows that carbon fiber reinforced plastic (CFRP) is the material that will provide the best performance as it has a high stiffness and strength (fatigue index) while also providing a minimal weight. Plastics are the worst because they will either weigh too much or not be stiff enough. Notice also that the metals all have roughly the same stiffness, but vary in strength, with titanium and magnesium alloys being stronger than steel and aluminum alloys.

Cost Analysis

While CFRP is the better material, it is also very expensive. When cost, instead of weight becomes the main design factor, as is the case for most road bikes, the stiffness and strength indices above, must be divided by the cost per kg (Cm) of the material. The chart above then changes to look like this:

Figure 2: Modified stiffness plot. Referenced from http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=89&pageid=2144417040

Figure 2: Modified Stiffness Plot Analysis

This then shows that steel frames will provide the most stiffness and strength for its price, while CFRP, though better in performance, is very expensive and only worth buying if cost is not a constraint by the consumer.

Engineers will need to build different bicycles with different materials to trade off performance for lower cost. A casual rider that uses a road bike will not care as much for performance and care more for cost, so CFRP may not be the best option in designing a bike aimed for that kind of audience. The opposite can be true. A more competitive rider who cares most about speed and performance will want the best material and care less about cost. Bicycles targeted for that audience, will have a more expensive, yet better performing frame.

Aesthetics

Lastly, in the design process, engineers have to appeal to the eye of the consumer. The color, the size, and the overall external appearance are all still important to the consumer, as well as performance and cost. A flashier and sleeker bike will look more attractive and most likely sell better.

Targeted Audience

What the engineer chooses for the final design all depends on the targeted audience. For example, with our product, the targeted audience seems to be casual riders that want a low cost bicycle and don’t seem to care too much about performance. This can be concluded by the fact that the frame is made of steel, which doesn’t perform as well as other materials, but is relatively cheap. It can also be reasonably concluded that it is targeted to female consumers since the color of the frame is baby blue. These are all factors that an engineer needs to take into account for analysis during the design process. Tradeoffs will always have to be made in order to satisfy different audiences.

Design Revisions

Pedal Axle

The first component that would undergo design changes is the Pedal axle, or the axle in which the pedals rotate about. The main problem with the existing pedal is its near impossibility to replace or repair. While the part will remain in the bicycle (which is a good thing), it the owner needs to repair or replace a broken axle he/she will find it impossible to do so (which is not a good thing). We propose adding a locking mechanism that would hold the axle in place during use, but could be disengaged to allow for quick and easy maintenance. This solution will drastically increase serviceability, and as a result, will mean less bikes will need to be bought when they can be more easily repaired, which addresses economic concerns.

Pedals

The next pedal that will need replacing is the pedals themselves. The existing pair are a tad to large and are heavy. We propose replacing them with a pair of much lighter weight plastic pedals. While the durability of plastic is less than that of the steel pair, they are not susceptible to rust and are not subject to the standard wear and tear on the rest of the bicycle, and as a result, the loss in durability is negligible. By reducing the weight, and the price, this addresses both social and economic concerns by allowing the bike to be more accessible to a larger market.

Bottle Holder

While not an essential part in the operation of the bicycle, it is still an important user accessory. The current component is extremely loose and does not effectively hold bottles. A simple swap with a different model would provide a much more effective and reliable way of holding bottles. This addresses the societal factors in that it increases the comfort of the rider by providing him/her and easy source of water.