Group 21 2012 Gate 3
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.
In the last gate we had the following major challenges:
- Wiki Organization
\'\'\'Challenges That Have Been Addressed\'\'\'
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.
Our progress in our Project Timeline as well as our meeting minutes can be seen in our Project Management page.
\'\'\'\'\'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.
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.
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. This includes analysis of the product containing equations, dimensions, materials, interactions as well as design revisions of the product. We will see how each of these are important to decision making during the engineering process.
In order to properly analyze all the necessary parts and mechanisms to our system we fully dissected our bicycle and examined all the necessary components. Pertinent information included purpose, quantity, used materials, manufacturing processes used, part numbers, and other useful information. Information was gathered upon physical observations and close research. Information regarding the manufacturing processes used was taken from the in class supplement given. Examples include riser marks, parting lines, and undercuts. Other information was also gathered from other research such as the manufacturing process for sprockets, where metal is stamped using a die to cut, shape, and form the proper pieces. All hardware was recorded and the purpose of each was listed. As displayed, no system can properly work without a properly organized and placed set of components and subsystems.
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. All information can be found in Table 2.
\'\'Table 2: Bill of Materials\'\'
|Item/System Number||Name||Function||Material||Manufacturing Process||Quantity||Components||Picture|
|1||Pedals||place where the force is transferred to the crank; grips to the riders shoes||metal and plastic||injection molding||2||N/A|
|2||Crank Arms||increases the mechanical advantage and direction of motion of the force||steel||die casting||2||N/A|
|3||Crank Assembly||transfers all energy from the rider to the front sprocket||Steel and aluminum||die casting||1||
|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||aluminum||metal stamping||1||N/A|
|5||Tires||allow the bicycle to ride smooth and hold traction||rubber||rubber mold||2||N/A|
|6||Rims||hold the tire and create a surface for the brake pads to grab hold of||aluminum||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||2||N/A||see above|
|7||Rear hub/sprocket assembly||transfers the kinetic energy from the chain to the wheel. Also changes mechanical advantage using sprockets||aluminum and steel||metal stamping and die casting||1||uses two 15mm nuts with washers (steel)|
|8||Seat||provides a comfortable place for the rider to sit.||Rubber, foam, and steel.||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.||1||N/A|
|9||Frame||provides a structure for all the components of the system to be mounted to.||steel||tig welded bent tubing||1||N/A|
|10||Handlebars||allow the rider to hold on to the bike and steer the bike.||aluminum||bent tubing||1||N/A|
|11||Handgrips||give the rider a comfortable place to securely hold on to the handlebars||rubber||injection molding||2||N/A|
|12||Derailleur||moves the chain onto different sprockets||aluminum, steel, and plastic||metal stamping and injection molding||2||N/A|
|13||Chain||transfers the mechanical energy from the front sprocket to the back sprocket||steel||metal stamped pieces are press fitted together||2||N/A|
|14||Kickstand||props the bicycle up when not in use||steel||cut and bent steel rod||1||N/A|
|15||Bike 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||aluminum||molded||2||N/A|
|16||Brake cables||transfer the energy from the brake levers to the braking mechanisms||braided steel cable in protective plastic sleeve||multiple drawn fine steel cables are combined for strength and protected by a plastic sleeve||2||N/A|
|17||Handlebar clamp||holds the handlebars onto the steering stem||aluminum||die casting||1||uses two 6mm x 1.5" allen bolts|
|18||Steering stem||transfers the rotational force from the handlebars down to the front fork of the bike||aluminum and steel||die casted piece is welded to steel tubing||1||uses one 6mm x 6.5" allen bolt with an expansion nu|
|19||Gear selectors||plastic and aluminum||injection molded plastic levers riveted to a bent steel band||2||N/a|
|20||Gear selector cables||transfer the energy from the gear selectors to the derailleur mechanisms||braided steel cable in protective plastic sleeve||multiple drawn fine steel cables are combined for strength and protected by a plastic sleeve||2||N/A|
|21||Reflector||reflects light to provide a safer riding environment for the rider at night||aluminum and plastic||injection molded plastic riveted to a bent steel bracket||1||N/A|
|22||Front/ Rear braking assembly||stops the bike using the friction between the rim and the brake pads||2||
- 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:
Here we want to analyze some decisions we would make as an engineer if we were to design the product. We will answer the questions provided on Table 1 in the Gate 3 outline, justify the components we chose and tell how they are important to the user\'s experience.
\'\'Introduction and Justification\'\'
We will be identifying each component by their component number from the previous components list. Here we will identify the component and justify why we chose them to analyze.
- \'\'\'Component #1- Pedals\'\'\'
- The pedals are the component where the user turns it\'s signal into force which essentially drive the entire movement component of the bike. If there were no pedals on the bike, it would be much harder to apply the force to turn the chains which turn the back wheel, thus allowing the bike to move.
- \'\'\'Component #5- Tires\'\'\'
- The tires are the components that create the frictional force between it and the ground. Without this force, the rims would spin and spin and no movement would be created.
- \'\'\'Component #6- Rims\'\'\'
- The rims are used to hold in the tire as well as used for frictional forces for the brakes. Without this component, the brakes would not work as intended. Also, there would be no mechanism used to hold the tire which creates the frictional force required to drive movement.
- \'\'\'Component #8- Seat\'\'\'
- The seat allows the user to rest comfortably while riding. This part is essentially needed for social factors. Many users have bicycles as their primary mode of transportation. They are traveling long distances and want to be comfortable while using the product for long periods of time.
- \'\'\'Component #9- Frame\'\'\'
- The frame is the most important component of the bicycle. It holds all of the subsystems together so they can work as one.
- \'\'\'Component #10- Handlebars\'\'\'
- Handlebars help the user stabilize the bike. Not every user has the balance to ride the bike without using the handlebars. They make the product more socially acceptable and gives stability.
- \'\'\'Component #13- Chain\'\'\'
- The chain is the connector between pedals and back wheel. Without the chain, the bike will not move when the user exerts force on to the surface of the pedals, which defeats the purpose of the product in this day. In the past, a bike was used in this manner. With the new technology that has been developed throughout the years, we have found a more efficient way, thus the chain component.
- \'\'\'Component #16- Brake Cables\'\'\'
- The brake cable is needed for the brake pad to create friction with the rim. Without the cable, the braking mechanism on this bike would not function. Another braking mechanism would need to be added, or the user would have to put down their feet to stop the bike. The braking cables allows the user to slow down and stop safely.
Here we will be talking about what components functions they perform, what flows they are associated with and what environment it functions in. We have discussed this concept for each component in Table 3.
Here we will be talking about the geometry, material and appearance of the component. For geometry, the general shape, properties, how it influences the function of the component, weight, etc. For material, we will be talking about what the component is made of as well as manufacturing methods, which will include aesthetics. We have discussed this concept for each component in Table 3.
We will be specifying out manufacturing choices with evidence and conclusions coming from shape, material and GSEE factors. We have discussed this concept for each component in Table 3.
We will define a meaningful scale to how complex our component is. We will also discuss the complex the connections. We have discussed this concept for each component in Table 3.
\'\'Table 3: Product Analysis\'\'
|Component Number||Component Name||Component Function||Component Form||Manufacturing Methods||Component Complexity|
Many factors play a role in the design of the handlebars.
Solid Modeled Assembly
As one of the most important parts of a bicycle, the mechanical system chosen here is the crank assembly. Without the crank assembly, there would be no way to transfer energy from the rider to the bicycle. It is the component of a bicycle drive train that converts the reciprocating motion of the rider\'s legs into rotational motion used to drive the chain, which in turn drives the rear wheel. It consists of one or more sprockets attached to the cranks, arms, or crank arms to which the pedals attach. It is connected to the rider by the pedals, and to the bicycle frame by the bottom bracket. Cranks are constructed of either an aluminum alloy, titanium, carbon fiber, chromoly steel, or some less expensive steel. This may be the single most important mechanical system on a bicycle and is important to understand thoroughly.
The crank axle is a rotating shaft encased in a tubular mount. The shaft rotates within roller bearings inside the mount. The tubular mount is welded onto the frame of the bicycle. In the above diagram, the crank axle is the symmetric white shaft located inside the outer tubular mount. The roller bearings are depicted by the four white circles which ride on the outer grooves of the crank axle. This piece connects the left and right crank arms.
Cranks arms are attached to either side of the crank axle typically by either using threaded holes or a keyed or shaped hole tightened into place using nuts that thread onto the outer ends of the crank axle. This is the case on our bicycle. The arms are mounted 180 degrees apart from each other. The opposite ends of the arms are then "attached" to the rider by the pedals. Crank arms can technically increase the mechanical advantage of the crank assembly. A longer crank arm produces more torque but, too long of an arm does not allow the rider to pedal quickly enough due to the rider having to pedal in a larger circular motion.
The difference between the left and right crank arms is that the right arm has five mounting brackets to which the front sprocket is attached using bolts.
The front sprocket is how the rotational motion is transferred from the crank assembly to bicycle chain. The bicycle chain the turns the back wheel.
The frame is a key component of the bicycle. It is the backbone, which supports and connects all of the other parts. It also contributes to a large percentage of the bicycle’s weight, which is a huge factor in a bicycle’s performance. Lastly, the frame plays a big part in determining the final cost of the product since different frame materials are more expensive than others. To a consumer, those are the two biggest concerns: performance and cost. For these reasons, it is a component that would require a lot of engineering analysis during the design and testing stages of the design process.
Engineers first need to determine the problem to be solved. In this case, the problem is deciding the best material to be used in the bicycle frame. To begin, certain questions need to be asked. Who is the target audience? Are they a casual or competitive rider? Are they male or female? What is their weight and height range? They also need to know what the factors are that decide performance and make one material better than other. What are the equations that are used to determine that?
First we must understand the loads that the bicycle frame is subjected to and must be able to withstand. The following system diagram is helpful to visualize it:
There are two main factors, stiffness and strength, that determine how well the frame is able to support these forces. These two factors, along 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 impacts and rough surfaces, and it has a low weight so that it can accelerate and go uphill faster (“aluMATTER”).
Depending on the audience, different assumptions can be made. For example, if the audience is a child, it can be assumed that cost will be a big factor, since children grow out of bicycles quickly and need to replace them more often than an adult. It can also be assumed that the child won’t take care of it very well, and get in a lot of damaging collisions and impacts, therefore it will also need to be strong enough to withstand those impacts. This is why knowing the audience is a big part in analysis, and is one of the first questions asked.
Different materials perform better than others in tests for these factors. We must also take into account the fact that some materials weigh more than others, so stiffness and strength need to be based on a strength-to-weight ratio and a stiffness-to-weight ratio. For example, aluminum weighs less than steel, but a tube of aluminum is less stiff than the same exact same size tube made of steel. Aluminum can be stiffer than steel though if the diameter of the aluminum tubing is increased. Of course this would increase the weight, but compared to the steel, it already weighs a lot less, so the extra weight is allowable (“Ultracycling”). For this reason weight is taken into account in stiffness and strength by dividing by the material density. The following equations are used to determine the specific stiffness and specific strength for different materials (“aluMATTER”):
The formula for stiffness is based off of the elastic beam theory and the following equation for the deflection of a beam:
Using these equations, we can then calculate the values for different materials to see which ones will perform better. The specific stiffness and specific strength (fatigue resistance) for different materials common materials are plotted below. The materials highlighted in blue are materials that have been used in bicycle frames already (“aluMATTER”).
\'\'\'\'\'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. This makes sense because CFRP is known to be very light and very strong, which is why it’s a great alternative to the common steel frames. Notice also that the metals all have roughly the same stiffness, but vary in strength, with titanium and magnesium being stronger than steel and aluminum, which makes sense if you think about common objects made from each of those materials.
While CFRP is the better material, it is also very expensive. Steel on the other hand, is known for its strength but relatively low cost, which is why it’s still used widely in bicycles today. It would probably be the best material to be used in a bicycle aimed for children. Engineers will need to build different bicycles with different materials to satisfy a range of audiences. Engineering analysis is used to determine the best design for a specific audience, and what tradeoffs will need to be made to accommodate that audience. For example, a casual rider that uses a road bike will not care as much for performance and care more for cost, so in the analysis, the engineer will have to sacrifice performance for cost. 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. The analysis process will need to be used to determine exactly what the audience is, and what kind of tradeoffs need to be made to satisfy them.
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.
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.
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.
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.
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.