User:MAE277 06 09
- Jeffrey Becker - Communication Liaison
- Stephen Harris - Group Leader/Wiki Manager
- Eric Jongsma - Solid Model Creator
- Garth Lester - Technical/Mechanical Expert
- Eddie Valentin - Technical/Mechanical Expert
Shortcomings and Capabilities
- Eric had worked in a bike shop and had a lot of relevant experience
- Garth and Eddie both had mechanical experience working with engines
- No one initially had any experience making a wiki page
- Group 6 had a lot of procrastinators
- A few of us had limited CAD experience but were not comfortable enough to do the solid modeling
The objective of this project is to better understand the product through dismantling, modeling and reassembly. The product is a min-bike not yet out on the market. It is designed only for recreational uses. Its top speed is approximately 10 mph. It stands up well without any external support and with its wide tires and low center of gravity is very stable even at very low speeds. The throttle is in the very convenient position of the right handlebar grip. The throttle signals the fuel air mixture flow mass flow rate to increase converting chemical energy to reciprocating mechanical energy and waste thermal energy in the combustion chamber then the reciprocating mechanical energy is turned into rotational mechanical energy by the clutch and transferred through the chain to the rear axle where the rear wheel in combination with the surface it rests on turns that rotary motion into linear motion.
Based on a surface inspection of the mini-bike it seems that it is held together entirely by hex bolts. We will be needing a socket set and ratchet as well as a set of end-wrenches for when more torque is required. Having not seen inside the engine we can’t accurately determine exactly what tools will be necessary, but I would guess we’d need a razor blade or some other kind of scraper to remove any gaskets, a flat-head screwdriver in case anything needs to be pried open and a pan and funnel for the engine oil. I’ve also found a magnet and needle-nosed pliers are always handy just in case a nut falls somewhere inaccessible.
In taking it apart, we’d first remove the frame from the engine. This would mean loosening the chain tensioner and removing the chain, disconnecting the engine mounts and throttle control and we’d probably have to remove the seat or disassemble part of the frame to get the engine out.
Before opening up the engine, we’d have to properly drain all of the fluids, so as not to spill them all over the lab creating a safety hazard. Since there is no gas in the tank, no coolant system, no transmission and the brake system does not use any fluid, we should only have to drain the engine oil.
When taking apart an engine it is a good practice to replace any gaskets or seals you remove, rather than reusing the old ones, but due to the nature of our project we don’t have that option. Since the mini-bike is fairly new there shouldn’t be much existing wear and tear on the gaskets and seals but we will still have to be careful not to cause any damage in their removal.
I would assume this engine will have a timing chain, or similar mechanism, so we will have to observe it carefully as we take it apart. That way we don’t risk destroying any of the valves when we start the engine back up.
Besides the aforementioned gaskets and seal removal the disassemle should be a fairly straightforward process of removing one piece at a time, although it is hard to tell until we actually open it up. An experienced mechanic could probably disassemble it in as little as half an hour to an hour, but I would estimate we need at least an hour for us. We need to be taking detailed notes and measurements as we disassemble the mini-bike so that we can reconstruct it in a solid modeling program later. Given that, I’d say disassemble will take three to five hours just to be on the safe side.
As far as the experience level of our group members we aren’t too bad off. Eric mentioned that he has worked on bicycles before. Eddie has a motorcycle and seems mechanically inclined; I don’t know if he’s ever taken it apart, but I’m sure he at least has a working knowledge of how the engine runs. I have decent mechanical experience, having worked extensively on my car the past two summers, although the frequency with which it breaks down is alarming. Stephen has been on a robotics team for the past six years so he is experienced with most of the tools that will be used. The other members of the team do not apparently have any mechanical experience beyond the average person. All in all, the engine on our mini-bike is pretty simple as engines go, and I’m confident that our group has the necessary skills to disassemble and reassemble it successfully.
Group six consists of five individuals with a variety of strengths and weaknesses that complement each other. The work for the project shall be evenly divided between its five members which each person responsible for a different main function and additional ancillary functions distributed in whatever manner results in the best project. Stephen Harris shall be the Project Manager and Wiki Manager. He will ensure all tasks proceed as planned and lend a helping hand when needed. He is responsible for the overall direction of the project and should help the group members when they are confused as to what task to proceed to. For example, Stephen should tell the group if they are dissecting the mini bike in an incorrect fashion, and give instruction on how to do it correctly. Finally Stephen will collect all individual assignments done by the group, proofread them and add them to the Wiki. Stephen’s leadership will be essential in the timely completion of all five gates.
Jeffrey Becker will be the Organization Expert and Communication Liaison. As Organization Expert he will ensure the dissection of the product is done in a precise and orderly manner. This will be important in finishing gates two and four, in which the product will be taken apart and re-assembled. Jeffrey will be expected to make sure all parts of the engine are organized and easy to find. He will also take notes when necessary and make sure everyone in the group is on the same page. To facilitate this task Jeffrey will be head of communications. As head of communications he will compile and rout all information and make sure it gets to the entire group.
Our lead Solid Modeler will be Eric Jongsma. Jongsma having a great deal of experience with CAD software will make gate three easy to finish on time. He also has experience in a bike shop, and is expected to provide technical knowledge as to how the bike works. This will be helpful in gates two and four when we take apart and re-assemble the bike engine.
Technical/Mechanical Experts Eddie Valentin and Garth Lester will both be mechanics for this project. While Jeff, Eric, and Steve will help plan disassembly, Eddie and Garth will be actually dissecting the engine. Garth has experience with tools and will primarily take things apart. Eddie has knowledge as to how engines work and will handle the individual parts of the engine. Both are expected to take the engine apart without breaking it by using the correct tools and safety precautions. They will also re-assemble it, again using care and safety. This will help make gates two and four go smoothly.
Together, all five students will blend their knowledge and successfully meet all the project deadlines. As the project progresses work shall be assigned. The group will meet in 621 Furnas after every Wednesday class at Five PM, to discuss and work on the project. Additional work time will be scheduled by Steve. To contact Group Six, please email Jeffrey at firstname.lastname@example.org <mailto:email@example.com>.
Initial Product Assessment
The product for the assignment given to group 3 was the mini-bike. It is a small, one person unit capable of providing transportation over short distances at relatively low speeds (no more that 10 mph). Given its low power output the product should only be viewed as a recreational vehicle and not used for any professional purposes. Other than for the transport of a single person from one point to another, the mini bike serves no other purpose in its design and should be recognized as just that. The mini bike uses a simple gasoline engine from which all the power necessary for it to function is generated. Simply put, the chemical energy from the combustibles (gasoline and oxygen) is transformed inside the engine is into mechanical energy that causes the mini bike to move. While the mini bike does still work, it was discovered that if any time was wasted between turning the bike on and giving it throttle, the bike would choke up and shut itself off. Any speculation as to why this happens is currently unfounded; a reason for the malfunction is still an open question. The product in itself is of a very simple design, it consists of a simple aluminum frame with a gas tank, an engine, and a chain, all of that, with the obvious addition of a seat, handle bars and wheels consist of the product completely. It is more complex than a non-powered bicycle but significantly less complex than a motorcycle. From a simple initial overview of the product, it is obvious that aluminum, rubber, and plastic are the main components of the mini bike. If one were to think more, it would be logical to assume that copper wiring would be used in the system to pass on electrical systems from the throttle to the engine, from the ignition switch to the engine, etc. The product’s appeal resides in its simplicity, the fact that it is easy to use with minimal training required beforehand. It is relatively comfortable although upon riding it, it is easily noticed that the bike was designed for someone younger/lighter than the members of the group. As for maintenance, the only real issues with that would be making sure that the moving parts are well lubricated as needed, that there is gas in the tank, and that the necessary switches such as the choke and ignition are well maintained and not loose. In terms of other alternatives, a motor scooter or perhaps a dirt bike would be possible, all depending on whether u want more power, distance and mobility from your product. A scooter would be the closest thing to our current product in every cat4egory ranging from power given to distance to price, the advantage of a scooter would probably be the maneuverability provided, considering that it’s not as cumbersome as the mini bike, while the disadvantages would be comfort, since while some motor scooters provide seats, they would not be as comfortable as the mini bike’s.
Causes for Corrective Action
Our group’s system of management and our work proposal require several upgrades to fit the current work situation. One of the major issues not dealt with in the original planning and execution of the first gate was the matter of specific timelines for completion of the gates of the project. In order to correct this oversight, a Gantt chart has been added to the wiki page explaining our projected completion dates. This chart demonstrates amended work schedules that represent a more realistic yet timely set of goals that must be met in order to successfully complete the gates. Another concern that needed to be addressed was the weekly team meetings. It was previously agreed that group 6 was to meet Wednesday evenings. Having had more opportunity to scrutinize our schedules, we have discovered that Thursday during lab hours (3:30-6:30) is the optimum time for our group to meet. A problem not originally addressed in the management and work proposal but discovered during the actual work process is the structure of said weekly meetings. Future weekly team meetings shall begin with each member reporting how much progress they have made on their long term projects and if any roadblocks have been encountered. If so we will proceed to work towards solutions of those blocks, then continue by proof reading of all written assignments as a group. Finally, we will end each meeting by assigning new tasks based on past performance and total workload of group members. Something we did not expect was the fact that disappearing parts have become an issue in the past couple of weeks, with both the gas cap and the muffler of our mini-bike going missing. We have also found that larger parts, such as the front wheel assembly, have been moved around the lab in our absence. Due to Group 6’s specific project, we do not have the option of storing it in another location. Currently, to minimize the risk, we will move the large parts of our product farther away from the trash can area and take all the smaller parts out of the lab. This should curtail the threat somewhat, although we have no way of completely preventing the theft and/or vandalism that is occurring. Finally, while personal conflict has yet to occur within group 6, the work ethic as well as attendance of group meetings has been poor lately. The new structure of our group meetings should hold members more accountable to their fair share of the work. On the off chance that any personal issues arise however, a plan for dealing with them has been devised to manage said issues depending on the severity and the type of the conflict. In the case of a verbal altercation over work load or quality, the group members not involved in the argument shall determine who was in the right and take whatever corrective action they deem necessary. This egalitarian process allows for a fairer and easier going working environment and will hopefully minimize any resentment. However, if the group cannot come to a consensus, the final decision will go to the group leader. In the case of a non work related verbal altercation, the members involved shall be told to refrain from such unprofessional behavior and be kept away from each other if necessary. If said problem persists to the point where it is affecting our project, it will then be dealt with as a work related problem. Finally, any physical altercation shall be reported to campus police and dealt with by the proper authorities.
Product Dissection Plan
|Product Dissection By Steps|
|Step||Description||Tool Required||Difficulty (1-5)||Photograph of Parts Involved|
|1||Removed the (4) screws from the bottom of the seat to disconnect it from the frame.||8 mm socket wrench||2|
|2||Removed the handle grips, brake lever and throttle from the handlebars.||Phillips screwdriver and 10 mm socket wrench||3|
|3||Removed the front steering assembly||13 mm and 15 mm socket wrench||1|
|4||Disengaged the chain from the wheel then removed the chain guard and chain tensioner.||6 mm Allen key||2|
|5||Removed the rear fender by unscrewing the (2) bolts.||10 mm socket wrench||2|
|6||Removed the rear wheel and axle from the frame, by unscrewing the axle bolt.||16 mm socket wrench||2|
|7||Removed the engine and engine plate from the frame by unscrewing the (4) bolts on the bottom.||Hands||3|
|8||Removed the engine mounted gas tank.||10 mm socket wrench||3|
|9||Removed the muffler and muffler cage.||(2) 10 mm socket wrenches||3|
|10||Removed the pull starter from the side of the engine by unscrewing the single shaft bolt connected to the main shaft of the engine.||12 mm socket wrench||1|
|11||Removed the carburetor assembly from the engine.||6 mm socket wrenches||3|
|12||Removed the magnetic ring on the engine shaft.||Pin spanner||4|
|13||Removed the top of the engine's combustion chamber by unscrewing the 6 bolts holding it to the engine block.||8 mm socket wrenches||2|
|14||Removed the spark plug and timing mechanism||16 mm socket wrenches||1|
Total dissection time: 3 hours.
*Note: the break down for the difficulty levels are as follows:
1 = easy, requiring no real thought or awkward positioning.
2 = medium, some awkward positioning to get to the part
3 = hard, requiring some very awkward positioning and thought.
4 = hard, requiring some thought multiple people wielding tools and a great deal of time.
5 = impossible with current tools and expertise.
Below are a few sample questions that address the purpose and methodology behind the drills design:
- Is the product intended to be taken apart easily?
The mini-bike is quite easy to take apart up until the engine. Standard tools such as metric wrenches and Phillips screwdrivers can disassemble the bike up until the transmission is reached. The transmission is press fit together which would require some kind of prying tool to get off and then some kind of press to reattach. Therefore the products engine is obviously not meant to be taken apart while as individual parts can be replaced on the frame of the bike.
-_Hurdles and Disappointments_
There were a few tough spots in this dissection. The first came when we lacked the proper tool to remove some springs. In order to combat this problem, Garth actually purchased a pin spanner tool in order to allow further dissection. The second major hurdle prevented taking the transmission apart. This was a major disappointment to the group as they all wanted to see the internals, including the clutch assembly. There were two parts that prevented the dissection. The first was a lock nut. The nut had teeth on the inner edge that prevented the nut from being turned counterclockwise. The group could not even nudge it even with all five members using their combined forces. The second part preventing assembly was a factory pressed part. It would be impossible to get off without using a factory press. There were thoughts of removing it with blunt force via a hammer. These thoughts were quickly quelled when it was realized that there would be no way to put the part back on without a press. The group spent two hours in addition to the three previous dissection hours trying to move forward. It was finally decided that there was nothing they could due given the circumstances, and we moved on to work on this report. This step is considered level five difficulty since it was impossible to complete with the current tools and expertise.
- What fasteners are used and why?
The fasteners used are:metric bolts sizes 8mm, 10mm, 12mm, 13mm, 15mm and 16mm. These standard metric bolts are used for ease of replacement and removal
Phillips screws. These common screws are used for ease of replacement and removal
Locking collar. This is used to hold on the magnetic collar and is not so easy to replace or remove so that the magnetic ring stays in place even with all the vibration from the engine shaft it rest on.
- Are special tools required?A Pin spanner was used to remove the locking collar holding on the magnetic ring.
Component SummaryThe questions for the component summary were given as follows.
- What forces are applied to the components,
- If forces are applied estimate their magnitude
- Does the material choice affect the manufacturing process?
- Does the shape affect the manufacturing process?
- Why was each manufacturing process chosen for that component
- Do any components have a particular shape? Why?
- Is the component functional, cosmetic, or a combination of the two?
- Why do you think the manufacturing process was chosen for a given component?
- How complex is the component?
The folowing is a breakdown of where each of the questions in the gate 3 requirements for the components is answered. Some of the questions, specificly those about the manufacturing process, had a lot of overlap and did not necessarily apply to every component, so for the purposes of the summary they have been combined.
Name of Component
Why was this process chosen
- Why was each manufacturing process chosen for that component
- Why do you think the manufacturing process was chosen for a given component?
- Do any components have a particular shape? Why?
- Does the shape affect the manufacturing process?
- Does the material choice affect the manufacturing process?
- What forces are applied to the components
- If forces are applied estimate their magnitude
Functional or Cosmetic
- How complex is the component?
- 1 - Single piece of one type of material with simple shape e.g. washer
- 2 - One piece, one material, more complex shape e.g. dipstick
- 3 - Multiple materials, no moving parts e.g. brake lever
- 4 - Moving parts e.g. throttle assembly
- 5 - Electronics e.g. timing mechanism
- Is the component functional, cosmetic, or a combination of the two?
|Name of Component||Materials Used||Manufacturing Process||Why this process was chosen||Forces Applied||Complexity||Functional or Cosmetic|
|Muffler||The outer shell is made of steel and the catalytic converter inside is made of a ceramic substrate and a catalyst such as platinum.||The outer shell is made from two pieces of rolled steel pressed into shape and then folded together around a catalytic converter and spot welded to give a good seal between the two halves.||The materials in the catalytic converter were chosen for their heat resistance and the way they react with exhaust gasses produced by the engine. Steel was chosen for the shell because it is strong and resistant to heat damage. Picking steel meant that a fairly thin sheet of metal could be used for the shell, and that meant rolling it rather than casting a thicker piece of aluminum which saves significantly on manufacturing cost.||The muffler is not subject to forces of any significant magnitude. The only forces present would be from the vibration of the bike while the engine’s running, inertial forces from slowing down, speeding up or turning, and the air flow through the catalytic converter. None of these pose any threat to the structural integrity of the muffler. In case of a collision or another force that the muffler was not designed to deal with, it is covered with a protective cage (which we’ve treated as a separate component).||3||functional|
|Metal Shield||The metal shield is a thin, curved plate made of aluminum||The shield would have been made from aluminum rolled into a thin sheet, then cut to a specific template and bent into its curved shape.||Aluminum was chosen for the metal shield because it is lightweight and cheap, but still strong enough to provide a layer of protection between the engine and the user. All in all it was chosen because it was cost efficient.||Under regular operating conditions, the metal shield is only subject to the forces from the vibration of the engine.||1.5||Both|
|Hand Break Lever||The metal hand break lever is made mainly of aluminum and plastic.||The aluminum parts of the handle would be cast and machined into shape, while the plastic parts were probably injection molded.||Aluminum and plastic were chosen for their lightweight strength at a relatively cheap price. Choosing a combination of plastic and aluminum means using two different manufacturing processes to make the part. Using all plastic might make it too weak, while using all aluminum would be more expensive, but would also save money by simplifying the manufacturing process.||It is subject to the force of a hand gripping it. In the engineering analysis section we looked at failure of the break system and determined that the average grip strength of a human is 67N, which is the force that would most commonly be applied to it.||3||Mostly functional|
|Muffler Cage||The muffler cage is made of wire, probably steel or aluminum, coated with latex.||The metal would be extruded to form it into wires, which would be cut, bent and welded into place. Then it would be coated with latex paint.||The metal would be chosen for support, since the cage is designed to protect the muffler. The latex would be to absorb vibration, and to insulate against the heat of the muffler so that if anyone were to touch the cage, they probably wouldn’t burn themselves.||It, like the muffler, is subject mainly to the force of vibration from the engine, although it is designed to absorb impacts to the muffler.||3||functional|
|Left Grip||The left grip is made from synthetic rubber.||The rubber would have been injection molded.||The rubber was chosen because it is compressible, and durable, and also makes for a comfortable handhold. This is not to mention that it is cheaper than some alternatives.||The grip would be subject to two major forces. It would be subject to the grip force of a human hand, which was shown earlier to be 67N. It would also have the weight of a person’s arm resting on the hand on the grip. We’ve estimated a human arm to weight about 3 or 4 kg. Multiplying the weight times gravity, we find that would be a force of approximately 30 to 39 N.||2||Mostly functional|
|Rear Axle||The rear axle is a long steel bolt.||Like any bolt, it would start off as stock which would be machined to specifications.||Steel was chosen because it is a very strong material. Since the bolt was threaded, the machining process was necessary to get the proper specifications correct. The bolt was probably chosen because it was easier/cheaper to order pre-made bolts than to design and manufacture an axle for that specific vehicle.||We estimated our minibike’s mass to be about 30kg. The force on the rear axle would be roughly half of the force generated by that mass, which would be 147 N.||2||Functional|
|Timing Mechanism||Our timing mechanism is made from plastic, aluminum and synthetic rubber.||There are a pretty wide variety of processes used because this is a complicated part. Much of the metal in it was machined for a precise finish and the rubber and other synthetics were injection molded.||These materials were mainly chosen for their electrical and magnetic properties. None of them were incredibly strong, but they did their job electronically. Because of the varied materials and complexity of the part, the manufacturing process would have to be fairly complicated and therefore pretty expensive.||It has to deal with vibrations from the engine and not much else, so the forces it is subjected to are small but steady.||5||Functional|
|Gas tank/Engine Interface||The interface is a thin plate made of aluminum.||The interface would have been made from aluminum rolled into a thin sheet, then cut to a specific template.||Aluminum was chosen for the interface because it is lightweight and cheap, but still strong and heat resistant enough to provide a layer of protection between the engine and the gas tank.||Under regular operating conditions, the interface is only subject to the forces from the vibration of the engine.||1.5||Functional|
|Right Handle||The right handle is made from synthetic rubber, plastic, steel.||The rubber and plastic are injection molded, while the steel is cut to shape.||The right handle has the same grip as the left, but is also the throttle control, so turning it forward causes acceleration. The plastic was chosen for being cheap and having a good strength to weight ratio. The steel was used as a spring to return the throttle control to the usual position, and the rubber was chosen for its comfort and durability.||It is susceptible to similar forces to the right handle as well as the twisting force used to activate the throttle. This is estimated to be less than 60N.||4||Functional|
|Throttle Cable||The throttle cable is made of steel surrounded by a plastic sheath.||The steel is extruded in thinner wires and then twisted to form the cable.||Twisting steel strand together yields a strong but flexible cable, which is ideal for transferring force over a distance||Forces on the throttle cable are significantly less than those on the break cable because it is only used to transfer a signal, rather than power from the hand to the brake pads, even though it is constructed from the same material, so it is more than able to take the strain of ordinary use.||2||Functional|
|Cutoff Switch||The cutoff switch is made of plastic, synthetic rubber, copper, and steel.||Any wires are extruded and coated in synthetic rubber, and then the switch itself is made from injection molded plastic||The components were chosen for their electrical properties, copper is a good conductor while plastic is a good insulator, and because they are lightweight and cheap, lessening the manufacturing cost||The only significant force applied to the switch would be from a finger pressing the button, which is not enough to cause any kind of failure.||4||Functional|
|Brake Cable||The break cable is made of steel surrounded by a plastic sheath.||The steel is extruded into thin wires and then twisted to from a cable.||Twisting steel strand together yields a strong but flexible cable, which is ideal for transferring force over a distance||In the Engineerig Analysis section, it was determined that the brake cable rarely experiences more than 140N of tension while it could withstand over ten times that amount||2||Functional or Cosmetic|
|Washers||The washers were made of steel or aluminum||Washers are usually machined from stock.||Washers are machined from stock because it is the simplest way to make them. It also means that they can be made to very exact tolerances||Though there are a lot of washers on the bike, subject to different forces, generally washers are subject to compressive forces, and because of their shape they can withstand a great deal of force without failing||1||Functional|
|Chain Tensioner||The outside is made of Plastic while the inside has metal washers and bearings to allow it to spin.||The washers and bearings would be machined, and the plastic is injection molded.||The washers and bearings have to be able to slide past each other and fit to within exact tolerances, which means that machining is the best way to manufacture them.||The forces applied to the tensioner would be proportional to the tension in the chain itself. When we received the bike the tensioner was pretty loose, so the force on it was small.||3||Functional|
|Gaskets||Gaskets are made from a thin layer of aluminum or steel coated in adhesive and some kind of paper product||The gasket is cut out of rolled metal then coated.||Gaskets have to be very thin and flat, and the best way to achieve this is with rolled metal.||Gaskets, like washers, are designed to take incredible compressive force. In doing so, they deform slightly and form a seal.||3||Functional|
|Rubber Gasket||It was made from synthetic rubber||It is injection molded.||Rubber tends to be difficult to machine, and cannot be treated like most other materials used in manufacturing because it is so soft. Therefore it is almost always injection molded.||The rubber gasket is similar to the metal gaskets, although it isn’t able to take as much force. However, because it is softer, not as much force is needed for it to form a seal.||2||Functional or Cosmetic|
|Dipstick||Our dipstick was made from hard plastic.||It was injection molded and then the threads were machined||Molding is a cheap, fast way to shape plastic, but then the threads have to be machined in order to make user they fit with the right tolerance.||The only significant forces applied to the dipstick are when it is unscrewed by hand in order to check the oil level. This is why it could be made from lightweight, brittle plastic||2||Functional|
|Axle Bolt Cover||The axle bolt cover was made from hard plastic||It is injection molded.||Injection molding is a very cheap, fast way to manufacture plastic, and since the cover does not have to be exact, it was the most cost-efficient way to manufacture it.||Under everyday use, no significant force is applied to the cover. If the bike falls over, the cover cushions the harder axle, and will probably take some damage, but it is not an essential part||1||Both|
|Engine Spacer Plate||This was made from a thick piece of steel.||Cast from a dye (could have also been rolled and cut but the edges are too smooth)||The piece of steel could have been rolled, but it was very thick, which means that it would have been a lot harder to cut into shape, while casting it from a dye means that there is no need to cut through it.||The spacer plate is subject to compressive forces from the bolts holding the engine to the frame. It also takes the brunt of the engine vibration.||1||Functional|
|Chain Cover||The chain cover was made from plastic.||It was injection molded.||It is a plastic component that does not have to fit to exact tolerances, so injection molding was the fastest and cheapest way to manufacture it.||The chain cover is not subject to any significant force. It covers the moving chain to prevent clothes getting caught, but it does not support any weight||2||Both|
|Engine||Our engine used a lot of aluminum, as well as steel and synthetic rubbers and many more materials.||The casing for the engine was die cast (as evident from the tapered ridges) then machined where necessary until the desired result was achieved. Synthetic rubber was used to make the o-rings which were probably injection molded.||The engine has a very large surface area, and machining the entire thing would not be cost-effective. Instead, casting the engine, then machining any surfaces that have to fit to exact tolerances saves a lot of time and money in the manufacturing process.||The engine, pr rather the gas in the engine is what is applying most of the forces in the bike. The explosive forces of the gas, are turned by the pistons into rotational forces which are transmitted to the wheels by the chain||5||Functional|
|Throttle/Choke Assembly||The throttle assembly used a variety of metals.||Most parts were made from rolled and cut aluminum, or machined from stock, but there are many processes involved in making an assembly this complex||The goal in manufacturing is to make a part that does what it needs to do, as cheaply as possible. Therefore, rolling and cutting, or die casting is preferable to machining even though machining is more accurate. So when a more expensive method can be avoided, it is.||Much of the assembly is rather delicate. Thankfully the only forces applied to it come from the throttle cable, and are probably just a few Newtons||4||Functional|
|Gas Tank||The gas tank is aluminum.||It’s made in much the same way as the muffler in that it started out as rolled aluminum and was cut and then pressed into two parts which were joined to make the tank.||It is simpler than casting a tank and bolting it together, and insures that no more material is used than necessary.||The gas tank is subject only to the weight of the gas in the tank which given the materials involved is essentially negligible.||2||Functional|
|Frame||The frame is aluminum.||Much of the frame is made from tubes which are extruded, cut, bent into the proper shape and welded together. The base plate for the engine and a few other flat pieces are rolled and cut aluminum which is also welded on. Once the whole frame is together it is then painted red.||Extruded tubes of metal provide lightweight strength while the flat pieces served as better anchors for other components. The welding held the frame together and the paint made it look more professional and prevented against rust.||The frame is very strong because it is subject to most of the forces in the bike. It holds the load of the bike, and serves as an anchor for the engine which means that it is being acted on by a great deal of force.||2||Functional|
|Wheels||The wheels are alloy or aluminum with rubber tires.||The tires and wheels would be manufactured separately and then assembled together. The tires would be injection molded synthetic rubber around fiber. The wheels could be cast and then machined as necessary.||The wheels had to be machined to make sure they were round and well balanced, and the rubber for the tires had to be molded because of the nature of the material||The wheels take the force of gravity on the bike, which comes out to roughly 150N each||3||Functional|
|Starter Cover||Aluminum||was rolled and pressed into its current state.||The starter cover did not have to be very thick or have exact fits, so a simple rolling and stamping procedure produces a workable but cheap part.||The cover serves as an anchor to the pull start, so any force on the cord is transferred to the cover||3||Both|
|Foam Seat||The seat is made of plastic, foam, and steel nuts||The seat is made from injection molded plastic covered with foam and stitched leather stapled to the plastic frame. There are nuts glued to the inside the plastic frame to provide lightweight threaded holes to secure the seat to the metal frame.||The foam and plastic are chosen for lightness and comfort. The nuts are used to provide sturdy threads for the holes in the plastic so that the company can save money by not having to use a harder plastic or metal base for the seat.||The seat supports the person riding the mini-bike. The recommended maximum weight is 150lbs, which is roughly 68kg. That would yield a downward force of 667N||3||Both|
|Nuts, Bolts and Screws||Steel||Machined from stock||That is standard procedure for nuts bolts and screws as they have to fit to exact tolerances.||The forces applied vary, but the design generally spreads any forces over several connectors rather than just a single bolt.||1.5||Functional|
1) The mini bike has a chain tensioner that is clearly designed to be a pulley and yet rather than rotate with the chain, it lets the chain run over it, causing wear and tear to both it and the chain. Giving the tensioner better fitting bearings could solve this problem and eliminate all the unnecessary wear and tear and wasted energy. It would mean a slight increase in the cost of the bike however, and though it might be more fuel efficient, consumers might not notice the small increase in efficiency when compared to an increase in price.
2) Our mini bike is somewhat underpowered. One way to deal with this would be decrease the diameter of the wheels. This would give the bike a little more torque, although its top speed would be lower. The target consumers for the mini-bike are not people that want a lot of speed, because the mini-bike was never fast to begin with. However, we would be giving them a better functioning product that was less likely to stall as you try to start it up. Also, smaller diameter wheels would contain less material and therefore be less costly to produce.
3) The electronic timing mechanism that detects the position of the flywheel and controls the firing of the piston could be replaced with a timing chain. The timing chain might not be as precise, but it will be much more cost effective, and there seems no point in having an expensive electronic timing mechanism on an otherwise practical and simple vehicle. The only difference customers would notice would be the drop in price.
- The rim is aluminum
- The tire is rubber and is tubeless, which means that the tire is pressed against the rim due to the air pressure in the tire
- The sprocket is made of aluminum
- There are 70 teeth on the sprocket
- It is mounted by 6 bolts to the rim of the wheel
Disc brake rotor:
- Made of aluminum
- Has holes on the contact surface to dissipate the heat of braking
- It is mounted to the rim by means of 6 bolts
- Is mounted to the motor
- Transfers the energy of the motor to the wheel and sprocket
Problem Statement: Find out the stress on the brake cable of the mini-bike for group 6 and evaluate it with respect to the ultimate tensile strength.
Assumptions: There are multiple assumptions to be made to check for failure of this system. The perpendicular distance between the forces and the hinge remain constant. The cable does not deform under stress in such a manner as to significantly reduce its cross-sectional area. The distributed load exerted by the hand is evenly distributed for the distance that it is applied. The force applied by the hand to the cable is applied over enough time so that it acts as a loading situation (gradual increase in force over time) as opposed to an impact (sudden application of force) situation.
|diameter of steel wire||0.001588 m|
|ultimate tensile strength of steel wire||760 MPa|
|force applied by hand||67 N|
|distributed force minimum perpendicular distance to fulcrum||0.0254 m|
|distributed force maximum perpendicular distance to fulcrum||0.1016 m|
|cable fulcrum perpendicular distance||0.03048 m|
Sources: http://en.wikipedia.org/wiki/Tensile_strength Steel, high strength alloy ASTM A514 for the ultimate tensile strength of the wire
Brake cables on bikes are not known to fail under ordinary operating conditions so the large difference between the applied force and the maximum force the cable can take is as expected.
Discussion of Results:
The scenario for failure of the group 6 mini-bike was the failure of the brake cable. As shown in the calculations the ultimate tensile force that the steel cable can withstand is 1505.2 N while the ultimate tensile force the cable will experience is only 140 N. The safety factor calculated for this problem of 10.75 means that under the assumed conditions there will be no failure of the specified component in the specified way. The limitations to this solution are numerous. The assumed hand force applied is only a rough guess given some slight experimentation meaning the maximum force could be higher especially since humans have a wide range of strengths. The distance and position over which the hand force is applied in reality would vary widely for different sized hands and grips though the distance and position assumed in this problem is a pretty common one for a standard brake grip (determined though life experience on bikes with friends and family). The exact material of the cable is unknown however the steel ultimate tensile strength used is a relatively low and common one so a reasonable maximum tensile force should have been obtained. This evaluation of the ultimate tensile force applied vs the ultimate tensile force that the cable can withstand would be improved by better knowledge of the geometry of the cable at its ends.
1. Cylinder head and gasket: 6 bolts, 10mm socket wrench: when tightening the head back on, a torque wrench should be used to a specific torque specified by the manufacturer. But since we did not have one, we tightened them to the best of our abilities.
a. Spark plug: 19mm socket wrench
b. Spark plug cover + timing mechanism: 2 - 10mm bolts for the timing mechanism: It was difficult to adjust the timing mechanism to the proper position. The mechanism itself is magnetic and it hovers over the magnetic flywheel and is held on by 2 bolts. In order to secure it, you have to hold the mechanism over the magnetic flywheel, which can be difficult.
2. Carburetor and gaskets: 2 – 8mm bolts. The carburetor slides onto 2 rails , with a gasket on the inside and the outside. Since the gaskets were specific to there respective side, it took a minute to figure out which one went where.
3. Air filter: 2 – 8mm bolts. The air filter went on the outside of the carburetor on the same rails that the carburetor slid onto.
4. Throttle assembly: This was the most difficult part of the reassembly process. This was due to the fact that there were 2 springs that attached to the motor in different points, and we referred to pictures to see where they attached.
5. Muffler and gasket: 2-8mm socket wrench: This also includes the muffler cage. One of the springs of the throttle assembly was attached to the muffler cage to keep the assembly in proper tension.
6. Starter assembly: 3-9mm socket bolts: The starter assembly goes on the opposite side of the clutch and flywheel, which turns the motor over.
7. Gas tank and shield: 10 mm , 3 bolts : The shield goes under the gas tank which keeps the heat of the engine from heating up the gas in the tank. We also had to make sure we hooked up the gas line tube from the tank to the engine.
8. Kill switch: The kill switch has 2 wires that attach to the motor at 2 different points. One is a ground that bolts directly to the engine block and the other attaches to the timing mechanism. At this point, all the components that attach to the motor are secured.
9. Rear wheel assembly:
a. Sprocket: 6 bolts, 5mm hex wrench. The sprocket goes on the left side of the wheel and the bolts have to be tightened in a star pattern with a torque wrench.
b. Brake rotor: 6 bolts, 5mm hex wrench. Is secured on the same way as the sprocket in a star pattern.
c. There are 2 different size spacers. The larger of the 2 goes on the left side, or the drive side, while the smaller of the 2 goes on the right.
d. There is a 14mm bolt that is secured on with a lock nut.
10. Steering wheel & handlebar assembly:
a. A large 14mm bolt goes through the top of the assembly and is secured on by a 16 mm nut on the bottom of the headset.
b. The brake lever is reattached using a 5mm hex wrench and the cable is fed through at the top of the handle.
c. The throttle is attached to the right side of the handle bars and is secured using a 3mm hex wrench.
d. Rear fender: There are 2 bolts with rubber washers that attach the fender on. The rubber washers go in between the mounts and the bolts to prevent chattering noise when the fender is vibrating.
11. 2 Chain Guards: the chain guards cover the path of the chain for the safety of the rider. The rear chain guard goes on first, and then the front chain guard overlaps it.
12. Seat: There are 3 – 10mm bolts that secure the seat
Post Reassembly analysis
Reassembly Process note </blockquote> All the same tools were used to reassemble the product as were used in its dissassembly</blockquote> End Result of Reassembly notes </blockquote>After Reassembly the bike no longer works. The problem with the bike appears to be related to the throttling assembly which unfortunately no longer function properly due to the fact that at one of its pivot points it is missing a piece to hold it on. To correct the problem our group suggest looping a metal ring through the throttle assembly and the pin on that pivot to prevent the throttling device form popping off.</blockquote> Product Recommendations Our main recommendation concerning the product given our trouble with the reassembly is to make the throttling assembly more robust.