Group 6 - Mini-Bike
- Jeffrey Becker - Communication Liaison
- Stephen Harris - Group Leader/Wiki Manager
- Eric Jongsma - Solid Model Creator
- Garth Lester - Technical/Mechanical Expert
- Eddie Morales - Technical/Mechanical Expert
Gate 1: Request For Proposal 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 email@example.com <mailto:firstname.lastname@example.org>.
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 spreader||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 spreader was used to remove the locking collar holding on the magnetic ring.
Function: To filter exhaust gasses and mute the sound of the engine.
Materials: Iron or Steel.
Manufacturing Processes: made from two pieces of rolled iron or steel pressed into shape and then folded together around a catalytic converter and then spot welded to give a good seal between the two halves.
Dimensions: Our muffler is approximately 17cm by 8cm by 5.5cm.
Other info: 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
• 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). Steel was probably chosen because it has better heat resistance than aluminum, and because it is stronger. Two sheets of rolled aluminum would be pretty flimsy, while the steel gives the necessary structural support, and is still thin enough to quickly conduct heat out of the muffler to the outside air.
The muffler was made in two parts so that the catalytic converter could be easily placed inside. Each half could simply be pressed from a flat sheet of steel, so no molding would be required, simplifying the manufacturing process considerably. All in all it is a simple, functional and efficient design.
Function: The metal shield acts as a physical barrier to the engine.
Manufacturing Processes: The shield is made from rolled aluminum that is then pressed into shape
Dimensions: 12cm by 7cm by 5.5cm
Other info: The metal shield is built to withstand forces due to vibration from the bike but otherwise is not very strong. It’s not a load bearing component, so it doesn’t need to be very strong and it’s not so brittle that vibration would pose a threat.
Hand Brake Lever:
Function: Transmits energy from user’s hand to brake cable
Materials: Aluminum and plastic
Manufacturing Processes: The aluminum is cast and the plastic is molded and the two parts are joined by a connecting rod around which the metal handle pivots.
Dimensions: 16.5cm by 8.5 cm by 3.5cm
Other info: No force applied to the hand brake lever under normal operating circumstances is enough to break it. The only times they have been known to break is during collisions, if they strike the ground or the wall.
Function: Protects the muffler from damage and protects hands against accidentally brushing against a hot muffler.
Manufacturing Processes: The steel is extruded to form wires which are then bent into the shape for the cage and painted black. Dimensions: 18cm by 9cm by 4cm
Other info: The muffler cage is built to withstand impacts as well as to protect people from the heat of the muffler. It’s cheap and simple to manufacture, but it’s effective and does exactly what it’s designed to do.
Function: Covers handlebar and gives the user a place to grip.
Materials: Synthetic Rubber
Manufacturing Processes: Molded
Dimensions: 12.5 cm long and 4.5cm in diameter
Other info: The reason for using synthetic rubber for the handle is that it provides a high-friction but non-abrasive surface, ideal for gripping with the human hand. In terms of forces applied, sometimes a twisting force will pull the handle off, but in most cases a force being applied the handle simply deforms it slightly and it springs back.
Function: Connects the rear wheel to the frame and provides an axis for it to spin around.
Manufacturing Processes: Cut from stock by machine
Dimensions: 25.5 cm long, size 15mm head.
Other info: The axles carry quite a good deal of load, which is why the bolt is designed so thick. Rather than making an axle from scratch, using a long, heavy-duty bolt saves on production and design costs and as such is a good manufacturing decision.
Function: This records the spinning of the flywheel and sends a charge that activates the spark plug. It is used to keep the engine cycle in sync.
Materials: Plastic, aluminum, synthetic rubber
Manufacturing Processes: The plastic components were probably injection molded. The wires were extruded and the metal in the mechanism itself is machined from stock.
Dimensions: 7cm by 5.5cm by 3.5cm
Other info: The timing mechanism is well protected, but it can still be subjected to engine vibration, and, because it is so close to the engine, could also be damaged by heat.
Often the timing mechanisms are mechanical, such as having a timing belt or timing chain. Having an electronic timer reduces wear and tear, but increases manufacturing costs.
Gas tank/engine interface:
Function: This is a thin metal sheet that separates the gas tank from the engine. It’s there to add another layer of protection to the gasoline in the tank and better guard it from the hot engine.
Manufacturing Processes: The aluminum is rolled and then pressed into shape
Dimensions: 14cm by 10.5cm by 2cm
Function: This handle is the same as the left except that it also integrates the controls for the throttle
Materials: synthetic rubber, plastic, copper
Manufacturing Processes: The wires are extruded, and the throttle mechanism put together by machine, after which the injection molded handle is placed over the assembly.
Dimensions: 12.5cm long and 4.5cm in diameter
Other info: The right handle reuses the same mold for the left handle, and then puts that around the components that control the throttle, in an effort to make the manufacturing process more efficient. The only significant force applied is the twisting applied to open up the throttle, which is exactly what it is designed for.
Function: Connects the right handle to the throttle on the engine.
Manufacturing Processes: It is extruded in thinner wires and then twisted to form the cable.
Dimensions: 110cm by .2cm in diameter
Function: The switch is a device used to turn off the engine
Materials: Plastic, synthetic rubber, copper, steel
Manufacturing Processes: Any wires are extruded and coated in synthetic rubber, and then the switch itself is made from injection molded plastic
Dimensions: 4.5cm by 4.5cm by 2cm
Function: Transfers energy from the brake lever to the actual brake on the rear wheel
Manufacturing Processes: The steel is extruded into thin wires and then twisted to from a cable
Dimensions: 150cm long and .2cm in diameter
Function: Washers are generally placed on bolts to use as spacers or to diminish friction between two parts rotating on a common access
Materials: Steel or Aluminum
Manufacturing Processes: Washers are usually machined from stock
Dimensions: There are 13 washers on the mini bike (that aren’t included in other components) that range in size from 2.1cm in diameter to .9cm
Chain Tensioner (pulley):
Function: This is a moveable pulley which is used to keep the chain taught.
Materials: The outside is made of Plastic while the inside has metal washers and bearings to allow it to spin
Manufacturing Processes: The washers and bearings would be machined, and the plastic is injection molded
Dimensions: 3.3cm long by 4.5cm in diameter
Other info: Based on observation, the pulley doesn’t turn even though it is built to. Instead the chain just glides over the pulley. This seems like bad design and energy is lost to friction.
Function: The gaskets separate metal components and act as seals to prevent leaks. There were three gaskets that we were able to get to and two more in the engine that we could not because we didn’t have the right equipment to open it up.
Materials: thin layer of aluminum or steel coated in adhesive and some kind of paper product
Manufacturing Processes: the gasket is cut out of rolled metal then coated.
Dimensions: The range from 11cm by 8.5cm to 5cm by 3.3cm
Function: Serves the same function as regular gaskets, except that the material is different
Materials: Synthetic Rubber
Manufacturing Processes: Injection molded
Dimensions: 7cm by 75cm
Other info: The rubber makes the gasket more compressible, meaning that it works better than a metal gasket when it separates two components that may move relative to each other slightly.
Function: Used to measure oil level
Manufacturing Processes: It was injection molded
Dimensions: 6.5cm long by 2.5 cm in diameter
Other info: The dipstick is not subject to much stress and as such is made from cheap plastic to save cost on materials.
Axle Bolt Cover:
Function: Protects the outside tips of the axle from damage
Manufacturing Processes: Injection Molded
Dimensions: 2.7cm long by 2.9cm in diameter
Engine Spacer Plate:
Function: Separates engine from frame, providing stability and countering vibration
r> Materials: Steel
Manufacturing Processes: Cast from a dye (could have also been rolled and cut but the edges are too smooth)
Dimensions: 12.5cm by 8.4cm by.5cm
Other info: The spacer plate allows for a slightly increased tolerance between the engine and the frame, thus reducing the vibration transmitted to the frame.
Function: Is bolted over the chain to keep loose articles of clothing from getting caught in the chain
Manufacturing Processes: Injection Molded
Dimensions: 25cm by 12.5cm by 7cm
Other info: While the bike would function perfectly well without it, the chain cover shows that the engineers were thinking about possible hazards to the future users of this bike when they built it.
Function: Contains the chemical reaction that drives the mini bike
Materials: Aluminum, Plastic, and many more
Manufacturing Processes: The casing for the engine was die cast (as evident from the tapered ridges) then machined where necessary until the desired result was achieved. Plastics were used to make the o-rings which were probably injection molded.
Other info: The engine was designed to have a high surface area to weight ratio, in order for it to cool efficiently. An interesting thing we found was that the inside of the combustion chamber had the piston and the valves were on the same side of the chamber. This meant that there was no risk of the piston ever hitting the valves, which is a real problem with automobiles, should the timing chain get worn or break. (shown below is a piece of the casting of the engine to demonstrate the high surface area to volume ratio)
Function: Controls the oxygen and fuel reaching the engine
Materials: A large variety
Manufacturing Processes: most parts were made from rolled and cut aluminum, but there are many processes involved in making an assembly this complex
Function: Holds the fuel for the mini bike
Manufacturing Processes: 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.
Dimensions: 25cm by 13cm by 8cm
Other info: The gas tank sits directly above the engine, so gravity feeds the gas. This is a much more efficient system than cars, which require a fuel pump to get the gas from the tank to the engine. Obviously, putting a car’s gas tank over its engine would be difficult and frankly irresponsible, but with the mini bike it is actually a good solution.
Function: Gives structure to the mini bike, and serves as an anchor for the rest of the components.
Manufacturing Processes: 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.
Other info: There does not appear to be machining anywhere on the frame. Even the holes for bolts have a low enough tolerance that simply casting them is sufficient. This cuts down on manufacturing cost considerably
Function: The wheels are the only points of contact with the ground (except the kick-stand) and are the means by which the spinning of the motor is transferred to horizontal movement.
Materials: The wheels are alloy or aluminum with rubber tires.
Manufacturing Processes: The tires and wheels would be manufactured separately and then assembled together. The tires would be injection molded plastic around fiber. The wheels could be cast and then machined as necessary.
Function: Covers the starter motor and redirects air to cool engine
Manufacturing Processes: It was rolled and pressed into its current state.
Dimensions: 20.5cm by 12.5 cm by 6 cm
Other info: The starter cover is an efficient deign because it is also the base for the pull cord.
Nuts, Bolds, Screws:
Function: Hold the components of the mini bike together
Manufacturing Processes: Machined from stock
Other info: Many of the nuts and bolts used in the bike were the same size, presumably to save money when purchasing them.
Function: Provide a place for the user to sit comfortably while making use of the mini bike.
Materials: Plastic, foam, steel
Manufacturing Processes: 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.
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 chosen assembly was the rear wheel assembly. It was chosen because of its central nature to the propulsion of the min-bike. Propulsion is the key feature of the mini-bike product.
· 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
Ø 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
3. 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.
Table 4: Problem 3 Assumed Values
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
∑▒〖M_fulcrum =0=T_cable*D_(perp cable)-F_centroid*D_(perp brake lever) 〗 such that ∑▒M_fulcrum is the sum of the moments about the hinge, T_cable is the tension force in the cable, D_(perp cable) is the perpendicular distance between the tension force in the cable and the hinge, F_centroid is the imaginary force applied at the centroid of the distributed load to represent the distributed force at a point, D_(perp brake lever) is the perpendicular distance between the hinge and the force acting at the centoid of the distributed load.
F_centroid=F_hand, the force F_centroid equals the force applied by the hand F_hand
Centroid=the middle of the distributed load since it is an equally distributed load.
D_(perp brake lever)=centroid+minimum perpendicular distance to the fulcrum
ultimate tensile force=ultimate tensile strength*Area
Safety factor=(maximum load)/(applied load)
D_(perp brake lever)=centroid+minimum perpendicular distance to the fulcrum=(.1016 m-.0254 m)/2+.0254 m=.0635 m
D_(perp cable)=.03048 m
T_cable=(F_centroid*D_(perp brake lever))/D_(perp cable) =(67 N*.0635 m)/(.03048 m)=140 N
ultimate tensile force=ultimate tensile strength*Area=760 MPa*(〖10〗^(6 ) Pa)/MPa*〖((.001588 m)/2)〗^2*π=1505.2 N
Safety factor=(maximum load)/(applied load)=(1505.2 N)/(140 N)=10.75
Solution Check: 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 noteAll the same tools were used to reassemble the product as were used in its dissassembly
End Result of Reassembly notesAfter 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.Product Recommendations Our main recommendation concerning the product given our trouble with the reassembly is to make the throttling assembly more robust.