Group 7 - Lawn Mower Engine - Request For Proposal
Request for Proposal
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Initial Product Assessment
1. This motor is intended to power a lawn mower, which is meant to cut grass as a part of basic lawn maintenance. The engine is specifically designed to spin the mower's blade with sufficient speed and power to cut grass at a desired height.
- This product can be used either at home or professionally, because lawns need to be maintained wherever a clean appearance is desired.
- This size engine is typically used in a smaller push-mower, which is intended for trimming around obstacles such as buildings and trees where larger mowers cannot reach, as well as in small areas such as lawns in residential neighborhoods.
- It is likely that this particular mower is designed for domestic use. With an engine of this caliber and the subsequently estimaed 17-21" cutting width, it is likely that it is suited best for and designed for smaller scale yards. A professional contractor would more than likely use an engine with a larger cutting width or at least use a more powerful engine.
2. A lawnmower engine works similarly to any basic motor of similar size. The throttle and choke control the ratio of gas to air in the mixture that is applied to the engine and lit by the spark plug to generate energy from combustion. It uses pull start rather than an electric start, and therefore requires mechanical energy input by the user. Essentially, the combustion in the engine turns the blades that allow the lawn mower to work.
- The electricity in the system is developed in a way that difers from mamy traditonal 4-stroke engines. While many systems use a battery to generate the current through the system, this particular engine uses an electromagnet. As the flywheel is rotated by the starter, a magnetic plate mounted on the inside of the flywheel passes an electro-magnet and generates a current. As the current becomes high enough from many passes by the plate, the current passes through a coil of copper wires of to sizes which increases the overall voltage. The output voltage, of about 45-90 volts is powerful enough to arc across the spark plug and ignite the compressed air fuel mixture. The voltages mention are estimates based on the anaylsis problem discussed during the symester.
- Chemical potential energy is converted to thermal (heat) energy by combustion. This energy is harnessed as mechanical energy for output, converting potential energy to kinetic energy to do work on the grass. Electrical energy is also involved in the generation of an electric arc via a spark plug.
- A mixture of gas and air is ignited with electric arc from the spark plug to provide extremely exothermic reaction (releasing chemical potential energy as thermal energy), which is harnessed by the mechanism of the motor into mechanical energy that initiates the motion of the blades.
3. This product is not currently functioning because it does not have all of its parts. Gas and oil would also be necessary in order to test to see if it would run. Due to the high number of visibly incorrect parts and evident other issues not visible prior to dissection, we can conclude that there is no feasable way to test functionality until all problems are corrected which involves dissection to locate problems. We conclude there are internal problems in at least two places based on evidence of a collision inside the engine block restricting rotation of the flywheel and also a problem with the starter engaging correctly.
- Upon initial inspection, it appears that the fly wheel may be missing a piece that allows the gears for the pull start to catch. The gear shaft is difficult to spin, even when torque is applied directly instead of with the string. It may be that there is something like corrosion or worn parts preventing the shaft from rotating and that this is why the engine is not able to run.
- This engine is fairly well used; many of its parts show a good deal of wear. The pull-start does not turn the motor over properly, and without fuel and lubrication it is difficult to analyze the engine for other issues because it cannot be started. A question that arose was whether it was put together correctly by a previous group, because some of these parts do not function as it seems they should. Loose parts, like a spring and strips of metal, were also found lodged inside the engine.
4. One approach to the complexity of an engine is to consider how many parts it has. This small two-stroke engine is not as complex as larger engines, such as those designed for cars, because it contains fewer parts. For instance, the lawn mower engine has one piston to convert the chemical energy to mechanical work, while a typical car engine has anywhere from four to eight separate cylinders. This means that a car engine would have many more components to make the pistons move together smoothly, including timing the spark plugs to allow for the proper sequence of firing.
- This size engine has approximately 10 main components, which are brought together by many minor components that are designed to work together in unison. Though they are not named specifically, these minor components are just as important to the overall function of the engine. Primary components of the lawn mower engine include:
- Carburetor (assembly)
- Pull start (assembly)
- Fan blade
- Gas tank
- Fan cover
- Spark plug
- Based on previous projects similar to teh dissection of this engine and other experience with such motors suggest a total number of parts and components to be in excess of 60 with an additional 40+ nuts, bolts, screws, and other fasteners.
- Of the above listed components, the carburetor assembly is the most complex in terms of the number of parts involved. The carburetor is where the gas and air are mixed for combustion, and incorporates such pieces as the spark plug, a combustion chamber, intake and exhaust valves, and the piston. Some of these main components are only made up of one piece, such as the piston, crankshaft or camshaft. However, the piston must be carefully machined to the exact size to fit without any breaks in the seal. The shafts are simple but important, as they transfer the mechanical energy from one place to another. The fan blade is also simple, but its fins need to be designed with the proper angle to provide an optimal amount of engine cooling. The purpose of the gas tank is straight forward; the challenge is how to shape the tank so that it fits around the rest of the engine properly. Assemblies such as the pull start and the flywheel contain many interdependent parts, making them more complex than single-part components, but not as involved as the carburetor. We will gain a greater understanding of how these assemblies work and how complex they really are once we begin the disassembly process.
5. Materials used in this product include steel, cast iron, a variety of plastics, rubber, and string.
- Visible materials include the string for the pull-start, plastic for the casing and gas tank, rubber for the tubing and primer bulb, a spark plug (ceramic and steel), and steel for the screws, bolts, and primary engine housing. The engine block itself appears to be made of cast iron, though may be made of cast alluminum.
- Most of the possible materials are visible, but there are likely copper wires that you cannot see. Some of the bolts have metal washers that are not visible. Also, the oil cap has a dip stick that cannot be seen until the cap is removed.
6. Assuming this engine part of a lawnmower and not just the engine by itself, this would be a satisfactory mower for moderately small sized lawns. It is clearly not intended for big lawns due to its small size and relatively lower power output. It would work well for getting into small areas where larger mowers cannot go.
- The lawnmower is comfortable for the user because they stand and walk behind the engine, although physical labor is required to push the mower during use.
- The lawnmower is simple to run. Once it is running, there is little that must be done to use it properly. However, the engine alone would be difficult to start without the necessary missing parts.
- Performing regular maintenance, like changing the oil or filling the gas tank, would be easy for a consumer that is familiar with small gas engines. Otherwise this engine could be sent in for regular maintenance, ideally about every six months. The mechanic could change the oil as well as clean the deck and sharpen the blades. Without training, it may be difficult to service and should be left to a professional.
7. There are various alternatives to this product for different intended uses. Competing push-mowers are available that are designed for tasks such as trimming around obstacles or mowing hard-to-reach areas. For a small step up in price, there are self-propelled mowers, which use a part of the engine's power to drive the mower forward. Another option is the riding lawnmower. These machines are much more expensive and are designed to cover much more ground than push mowers can, with longer blades and larger engines.
- Lawn mowers have a wide range of costs, and this mower would cost approximately $100 new. Approximate prices are shown below :
- Push mowers of comparable size: $150 - $300 (21” mower deck)
- Self-propelled mowers: $330 - $530 (21” mower deck)
- Riding mowers: $1,000 - $5,000 (42” to 60” mower decks), though certain brands and styles can be in excess of $10,000. Many of such styles have multiple functions aside from mowing.
- Advantages to this size mower are that it is able to mow hard to reach places, and that the 10 cubic inch motor is lighter than larger mowers, making it more maneuverable.
- Each syle of mower has pros and cons to its use. The smallest mowers, similar to the one in this particular dissection, as mentioned, are easy to maneuver, light-weight, a benifit to older and disabled users, and also are great for precision mowing. The larger push mowers and self propelled engines are again easy to maneuver and are designed again for precision but are heavier and consume more gasoline than the smaller engines. Smaller riding mowers are designed for larger lawns and are made to get the job done quickly. however, due to the larger size of these mowers, precision is sacrificed. Thoughsome riding mowers are "zero-turn," or made for precision, they still do not fit in tight areas. These mowers are also quite loud and quite inefficient in fuel consumption. The largest of riding mowers are also designed for the largest lawns and the fastest mowing times but again at a sacrifice to precision and easy of maneuverability. Again these mowers are loud and inifficient consumers of fuel. Other riding mowers, also known as garden tractors, are able to be used with other attatchments and used for other functions, but again do not have the precision of small, push mowers.
- Disadvantages to such a small mower include that it takes a long time to mow larger areas. Larger mowers also have more power, which allows thicker or longer grass to be mowed more effectively.
 Based on prices found at www.lowes.com
Group 7 of the Fall 2009 M.A.E. 277 class consists of the following five members who have been assigned these titles and will each be the leader of their component of the project. Members will take part in all aspects of the project if requested to by the member in charge of each area. However, each member will only have decision making authority over his or her own section. The group plans to meet regularly on Tuesdays and Thursdays from 3:30 until 5:00 P.M. to conduct work on the project until it is complete. The Project Adviser will decide where the group will meet based on what needs to be accomplished during that meeting. Should the need arise to meet more often, the group has set aside time to meet on Sundays, Mondays, and Wednesdays.
- Christopher Germain- Lead C.A.D. Designer and Modeling Representative. Chris will be responsible for coordinating 3-D modeling processes throughout the project duration and will be in charge making final decisions and approvals of all modeling material to be posted.
- Colton Steiner- Communications Diplomat and Project Adviser. Colton will be in charge of communicating with group members to coordinate meetings and time management. Colton will also act as the connection between the group and the class instructors, Erich and Phil. Colton will monitor each group member's performance and advise them as to how he thinks time should be spent if they are not in time with the Gannt chart.
- Dharan Shah- Director of Documentation and Media. Dharan will lead the group in documentation of work. He will be the lead photgrapher and videographer of all engine components and dissection processes. Dharan will be in charge of uploading approved media elements to the page and will have authority to discard or make changes to any media elements. Dharan Shah resigned the course on consequently has left the group as of November 13, 2009.
- Gregory Muench- Technical Expert and Dissection Executive. Greg will be in charge of technical work and lead the dissection process. Having the most experience in the group with mechanical engine work, Greg will be the authority fr all disassembly and re-assembly work. Greg will also manage tools and component storage during the dissection.
- Julia Perot- Editor in Chief. Julia will be in charge of all editing processes. She will proof read all work before it is published and will be in charge of confirming the information posted to the Wiki site. Julia will make sure that all appropriate work is posted neatly and on time and will make changes in format as she sees fit. She may change spelling, grammar, and follow other standard editing procedures but will only remove content with approval from the other group members.
The following Gantt Chart is a representation of the estimates we have made determining how long each required task of the four gates of the project will take us.
The process to reverse engineer the engine will be very challenging and has already required extensive research into the engine specifications and diagrams. Upon receiving the engine, there were several areas of concern. Fins on the flywheel and piston cover were chipped. It seems as though the entire engine has not been assembled properly; the engine does not turn over and the starter assembly does not engage the engine correctly. There were several other damaged areas. There is a spacer split in the engine shaft. The flywheel head has a crack that looks as though it may have been put there by a hammer. Finally, the throttle linkage was found dismantled inside the flywheel cover.
The group feels very confident in its ability to dismantle the engine because each member experience with reverse engineering products as well as modeling and documenting components. Technical Expert and Dissection Exectutive, Gregory Muench, has also had extensive experience working on small gasoline engines, especially with various lawn mowers.
The group estimates that the dissection should take an overall time of 2 and 2-1/2 hours. This estimate comes from several factors including prior experience with similar engines, previous group's wiki pages, a technician's handbook provided by the manufacturer on their website, and the apparent complexity of components.
One possible shortcoming the group will face is that each member has a very tight schedule. A Doodle poll as set up by communications director Colton Steiner, and revealed availible times for each member to meet and quickly identified the best meeting times of the group. A copy of a portion of the poll is shown here, though the information is incorrect for Chris Germain. As shown, the best time to meet was determined to be Tuesday at 3:30 P.M.
Should the process take more time than anticipated, coordinating meetings will be difficult. Scheduling conflicts have already begun to arise during the approved regular meeting times. Although those other obligations are not consistently interrupting any member's attendance, it still puts a strain on others. Another possible shortcoming is the differences in residence of group members. Three members live in the Ellicott housing complex, but the remaining two reside off campus as far as 45 minutes away. Based on this assesment, the group concludes that the previously mentioned meeting times will be the best for the project. There are not special requirements or exceptions for the commuters as they are required to be on campus for classes over an extended period of time and there is ample time between classes for the two group members to complete work. Though Dharan would have the most difficulty in meeting the deadlines and completing his portion of the work, that is no longer an issue, as he ahs resigned the course. The third shortcoming remains that two members hold part time jobs and a third member holds a full time job at his family's business, which makes time management more difficult because they have unpredictable work schedules. The group is confident, however, that it will work through these challenges and manage time efficiently when given the opportunity to meet.
One of the potential challenges the group will face during dissection is determining the correct assembly of the engine components, as it was not assembled properly by a previous group. This will be important when trying reassemble it correctly in the future. A second challenge lies with the removal of the flywheel. Based upon experience with lawn mower engines, removal of the flywheel is likely to be the most difficult procedure, requiring precision and strength. The process is likely to become even more challenging because it will require special care not to damage the flywheel head any further.
The group has determined that the tools required for the dissection are as follows: Socket set with corresponding wrenches, a ball-peen hammer, an allen wrench set, a flywheel puller, which is optional, needle-nose pliers, a screwdriver set, and spark plug socket. The required tools of this dissection are determined based again off of the technicians handbook, previous group's dissections, and visible parts.
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