Group 8 - Lawnmower (Gasoline Powered)
Gate 1 - Project Planning
In this project, we will analyze a Toro gasoline-powered, self-propelled lawnmower with a Briggs and Stratton four-stroke engine. Throughout the course of this project, we will disassemble the lawnmower and identify the factors that were considered by the company when this product was being designed. We will move in a linear fashion, starting with an overall introduction and topical assessment of the product, then actually reverse-engineering the lawnmower and evaluating its individual components, and finally drawing conclusions from these evaluations and documenting them for presentation.
The plan to reverse engineer the lawnmower is to meet as a whole group at Evan’s house off campus. He has all of the necessary tools and equipment to disassemble the mower. We plan on going step-by-step taking apart each component of the lawnmower, taking photographs of the different components as we encounter them. We will work from the outside-in, starting with the handle, wheels, etc., and eventually moving into the engine block. From initial inspection, the tools that are required to disassemble each part of the lawn mower include, but will not be limited to:
- 3/8 and ½ drive socket set with multiple length extensions, many different metric sizes
- Multiple length, and size, Philips head and regular (flat head) screwdrivers
- Torx screwdrivers
- Needle nose pliers
- Rubber mallet
- Penetrating oil/lubricant (PB Blaster)
The estimated time that it will take to fully disassemble the lawnmower is 3-5 hours, depending on what complications we run in to. Some challenges we may encounter as we go are frozen and/or stripped bolts, and sheared bolts. We do not plan on removing any parts that are riveted together because we won’t be able to reassemble those parts correctly, so removing rivets will not be a challenge.
- Our group, as a whole, has at least a basic competency necessary to work with the mower, and specifically the engine; this includes skills with technical aspects such as disassembling the machine and identifying the functions of parts, as well as a grasp of the concept associated, i.e. how a gasoline engine works.
Project work is to be split up as evenly as possible between the five members of our group. Tasks that require specific skills or tools, such as solid modeling or component removal, will be assigned based on each member's strengths. Based on these strengths, we created titles for each member within the group:
- Project Manager , Kevin Bartosiewicz (firstname.lastname@example.org): Responsible for the successful planning, execution, oversight, and completion of a project. This includes coordinating information across the group, setting up team meetings, ensuring Gates are completed in a timely manner, and regularly assessing the collective productivity of the group. Strengths include consistent punctuality, effective written and oral communication, and strong organizational skills; hands-on skills and knowledge of combustion engines are limited.
- Technical Expert , Evan Farino (email@example.com): Responsible for overseeing of disassembly of lawnmower, as well as analysis of the different components and access to necessary tools. Strengths include several years' experience working with mechanical systems and good group collaboration; skill with computers (solid modeling, Wiki, etc.) are basic.
- Communication Liason , Anibal Martinez (firstname.lastname@example.org): Responsible for coordination of communication between our group and the professors, will take note of any question that the group has and address it to the professors and/or TA’s, and make sure that everyone in the group is aware of their tasks. Strengths are hands-on experience with combustion engines and good organizational skills; public speaking and time management are not strong points.
- Solid Modeler/Factotum , Jordan Pytlak (email@example.com): Responsible for computer-generated models of machine components, as well as helping any group member if they are having trouble and performing general work necessary for the project, but not covered specifically by any other person. Strengths include familiarity with Solidworks, good teamwork, and strong problem-solving; writing skills and combustion engine knowledge are limited.
- Group Collaborator/Reporter , Andrew Serwon (firstname.lastname@example.org): Responsible for editing and combining different pieces of each Gate from each member and posting them to the group Wiki page, as well as any additional work necessary. Strengths include strong writing skills and ability to learn quickly; time-management and hands-on skills are somewhat lacking.
Group meetings will be held weekly or bi-weekly (depending on availability) at 3:30 p.m. on Thursdays in the Silverman Library (Capen Hall). These meetings will include:
- discussion of upcoming projects (assigning tasks to members, creating group due dates, etc.)
- a check on the status of the current project
- working through any problems in the project that a member may be unable to overcome
- the addressing of member concerns (i.e. regarding other group members, upcoming due dates, or work loads)
Any meetings that require work with the lawnmower (disassembly, photography, part documentation...) will be held at Evan's house, and dates and times will be decided at the preceding Thursday meeting based on the availability of the group as a whole.
- Note: Any conflicts will be handled through group communication. Small conflicts will remain within the group, with any group members not involved in the conflict acting as mediators to resolve the issue. If this does not solve the problem, or the problem is too substantial for the group to handle, it will be discussed with a Teaching Assistant or professor of our MAE 277 class.
Based on pre-dissection observation, there are many bolts, all metric sizes, that are the majority of the “fasteners” holding each part together. As long as those come out, there should be no problem disassembling the lawnmower. There is nothing more difficult than just unscrewing pieces from other pieces.Development Profile : The Toro Company History). A majority of Toro corporate offices are located the United States. In the 1990s, the U.S economy was very strong under President Clinton’s time in office. In addition, the North American Free Trade Agreement was implemented in 1994. This resulted in the immediate reduction of export tariffs between the U.S and Mexico. In general, this was a prosperous time for manufacturers in America. As shown in the chart, Toro lawnmowers are sold in the United States, Europe, Australia, Asia, Canada, and Latin America. This lawn mower is intended to be accessible to consumers in both operation and price, many of whom own the product for residential use. Of course, the simple goal of a lawn mower is to effectively cut grass. Usage Profile :
Energy Profile : There is chemical, thermal, kinetic and electrical energy being used by the lawn mower. The engine has a container where gasoline is stored until it is ready to be used. The engine that our lawn mower has uses the four stroke cycle. This means that chemical energy from gasoline is the main source of energy for the engine. But in order for the engine to start up in the first place it needs input from the user.
- To start the mower, the user has to pull on a cord. This pulling allows the user to transfer kinetic energy through the cord to the flywheel, causing it to rotate. Through its connection to the crankshaft, the flywheel causes the crankshaft to move. This rotation causes the piston to move linearly within the cylinder; the crankshaft also causes the camshaft to rotate.
- The intake valve is opened in the cylinder by one of the cams on the camshaft. This allows a combustible gasoline-air mixture to enter into the cylinder. The piston is moving towards the bottom of the cylinder at this point due to the start cord being pulled (Intake Stroke).
- The rotation of the crankshaft causes the piston to move to the top of the cylinder, compressing the fuel and air mix (Compression Stroke).
- When the piston reaches the top of the cylinder, the spark plug fires providing energy in the form of electricity, which it draws from a source such as a battery or magnet. This spark will cause the fuel mixture to explode, converting its chemical potential energy into thermal energy. A controlled explosion will happen at this point which will push down on the piston head, transforming the thermal energy to kinetic energy so that the piston begins to move downward. This linear motion is the converted to rotation by the crankshaft (Power Stroke).
- The energy that the crankshaft received from the piston in the previous step is then transferred to the blades, which in turn spin to cut the grass, achieving the goal of the lawn mower.
- Finally, the remaining kinetic energy from the crankshaft's rotation causes the piston to move back towards the top of the cylinder, where the exhaust valve will open. The piston will force the combusted gases from the explosion out of the engine (Exhaust).
- The cycle is restarted from step 2, and continues until either the user lets go of the throttle on the mower's handle (causing the flywheel, and thus the piston, crankshaft, camshaft, intake and exhaust valves, and blades, to stop moving) or all of the gasoline stored in the tank is used.
Complexity Profile : The lawnmower is a combination of many different parts that work together. There are many small components such as bolts and screws that keep the lawnmower together as well as springs. The major components consist of:
- Self-propelled system: A plastic handle is pushed down by the user while the safety lever is against the handle, which allows a transmission to engage on the axle connecting the rear wheels. The transmission runs off of a belt that is connected to the main shaft of the engine under the deck. It uses gears to turn the horizontal circular motion of the shaft to vertical motion to move the wheels forward along the ground. As the user pushes the handle farther, the faster the mower moves.
- Engine: The engine is the most complex part of the lawnmower. It is started by a pull start. This means that the user pulls a string that is connected to the flywheel on top of the engine. As it spins from the outward pull, the internals of the motor are in synchronized motion. As long as the pull start is pulled hard enough, the spark plug will spark and ignite the fuel and air mixture, then the engine runs on its own without the user constantly pulling on the string. The internals are extremely complicated, and have to run in sync with each other perfectly or the engine will encounter major failure.
- Other, less complex systems: Included are the adjustable height, the blade and the chute. The adjustable height works by adjusting the angles of the four wheels. The user pulls a tab out and lifts or lowers the deck and then pushes the tab into the desired height level “notch”. The blade is bolted to the bottom of the engine’s shaft and turns with the revolutions of the motor. There are two chutes on this lawnmower. One on the side opens when the user pulls it up. There is a spring holding it down against the side of the deck until the user lifts it. There is a hole in the deck behind that plastic piece. When it is lifted, grass can exit the hole. The second shoot is on the back of the deck. This one works the same way as the one on the side, and the user can attach a bag behind it to catch the grass, unlike the side chute.
The adjustable height and chutes are not very important in the overall working condition of the mower. On the other hand, the self-propelled system with the safety lever, and the engine, have to work together in order for the lawnmower to cut the grass and move forward at the same time. Also, the blades have to be attached to cut grass. Once the motor is started, the blades are spinning under the deck. Then, the user holds down the safety lever as they push down on the plastic handle, which gives the mower forward motion while cutting the grass. This is a necessity for the lawnmower to function as it was designed to.Material Profile : Materials that are clearly visible include steel, cast iron, plastic and rubber. The handle is made of steel tubing; the individual components of the motor and transmission are made of steel plate. The throttle and safety cable is made of steel cable. The motor and deck are made from cast iron due to the complex contours and shapes. There are various hardness’ of plastic throughout the lawnmower. The wheels are made of a very hard, thick plastic for strength. The chute covers, gas tank, and propelling handle are made of a similar plastic, and the engine cover is made of a thinner, flexible plastic. The gas line and belt is made of rubber. What cannot be seen from the outside observance of the mower are gaskets in the engine and transmission, which should be made of rubber. Other internal parts should be made of steel as well.
User Interaction Profile : The user starts the mower by priming the engine, and then pulls the pull-rope while keeping the lever pressed down against the handle. Once started, just stand behind and push it wherever the grass needs to be trimmed. The user must at least know rudimentary engine parts like the throttle and choke, these can also be looked up in the owners manual if not familiar with gasoline engines at all. The mower is very easy to use, however it does take a little bit of brute strength to start. It is self-propelled so you don’t have to push it the whole time and tire yourself out, just walk behind it and point where you want to go. Some maintenance is required, that comes with all gasoline engines. Regular oil fills, keep the filter clean, make sure spark plugs are working, and keep it topped off with gas. Not too difficult for the everyday person. On the mower, the blades must be kept sharp in order for the machine to perform its job efficiently; this can be done at home, but it is recommended that it be done by a professional in order to ensure the sharpening is done correctly and to minimize the risk of the user getting injured.
Product Alternative Profile : There are very few alternatives to this product:
|Gasoline/Electric Manual-Push Lawnmowers||Lawnmowers, either powered by combustion or electricity, that have no form of self-propulsion and must be pushed by the user.||These models are generally less expensive than self-propelled mowers.||User-propelled models create require the user to propel the machine forward as well as to turn it, causing more effort to be needed.|
|Completely Manual Lawnmower ("Reel Mower")||These models have no engines, and are propelled and powered solely by manual work by the user.||Much less expensive than any gasoline- or electric-power models; gives off no emissions.||User must put in large amounts of work to propel the machine, and mowing time is generally longer than with a powered model.|
|Ride-On Lawnmowers/Tractors||Riding mowers are ideal for large plots of land, such as parks, fields, and farms. They are generally gas-powered.||Allow grass to be cut much quicker and easier, as the user needn't put more effort in than pushing a pedal and steering; models with seats and only a spot to stand can be found; some models include cup holders.||Generally much more expensive than push models, and the size of residential grassy areas generally don't rationalize the extra money necessary to purchase a riding model rather than a push model.|
|Neglect||Leaving the grass to grow without cutting it.||User doesn't have to put in any work; no gasoline/electricity necessary.||Extremely long grass is unsightly; may warrant rodents and other pests to live among the grass; owner could face fines from local government.|
|Livestock||Animals such as goats, cows, rabbits, and others that eat grass could be set on their own to maintain the lawn.||Animals require no gas or electricity; potentially sustainable due to reproduction; feces can be used as fertilizer.||Require a constant source of food, may not be viable if grass growth is erratic; owner may face fines from local government.|
Overall, the model we have chosen is the best choice for residential use; it is within the middle range of pricing, requires less fuel and maintenance than some alternatives, and can perform its task with a small amount of work from the user, all while performing its intended job consistently. Self-propelled mowers similar to the one we chose generally average around $400; user-propelled combustion/electric mowers generally average about $250; completely manual models average around $150; riding mowers generally cost between $1,000 and $2,000; uncut grass fines are usually about $150.
Gate 2 - Product Dissection
The purpose of this Gate in the project is to being the dissection of our lawnmower. Here, we will document the process of dissecting the product, and then analyzing the arrangement of the subsystems throughout the mower.
Preliminary Project Review
The goals that were initially set forth in the Work Proposal have been met with general success. While the plan that had been outlined was not entirely descript, it left room for our group to assess our needs and goals as we went along. Ideally, it would have been best to create an all-encompassing, detailed dissection plan/proposal from the very start, but this is the first group project of such a magnitude that most members have dealt with. As such, group members may have felt hesitant to take the lead since a strong team dynamic and level of comfort had yet to be established in the early stages of the project. At the time of writing, we have collectively developed a better sense of what is expected from by the professors, as well as what we can expect from each other. In the following two sections, we will look at each facet of our original work and project proposals to discuss what pertinent information may have been absent and how, or if, this affected our group’s performance.
Work Proposal Review:
- As outlined, the lawnmower was dissected at our Technical Expert’s residence. The proposal did not set forth an exact date or time, but these details were easily agreed upon through consideration of each member’s availability. Luckily, all members were available at the same time, on fairly short notice (2-3 days ahead of time). To avoid the possibility of a schedule conflict in the future, our timetables will be discussed at the early stage of each project gate.
- A dissection plan was not explicitly provided in Gate 1. This is likely the result of two circumstances. Firstly, the majority of the group has not done a complete mower (and engine) teardown in the past. Secondly, our Technical Expert was trusted to have intimate knowledge of this process. At the expense our Gate 1 score, we did not take the initiative to research the specifics or elaborate on our knowledge. This could have turned out to be very problematic, but our Technical Expert did, in fact, competently lead and help the other group members through the dissection process. In the remaining gates, it will be necessary to have a more structured approach in order to avoid a possible roadblock if our group collectively lacks a particular skill or skillset.
- While we did not allude to the specific tasks of each member for the dissection process, our roles were established as we went along, rather naturally. For example, the Project Manager and Group Collaborator had the least experience in breaking down an engine, so they were charged with documenting a photographing the steps taken during dissection. In addition, it was a good chance to broaden their knowledge of 4 stroke engines as the other members explained the inner-workings of our project as we progressed. This builds confidence in technical knowledge for future gates. The Technical Expert was in charge of leading the teardown. Since the remaining two members also were comfortable in a hands-on setting, they jumped in when it was possible to work on two or more components at a time.
Management Proposal Review:
- From the start of the project, it was understood that the workload for each assignment was to be split as evenly as possible by each group member. In general, this has been accomplished. When delegating tasks needed to complete each gate, a group discussion is held to determine which member has the skills to handle the job, and the time required to complete said job is considered. When possible, or necessary, tasks are completed collectively. For example, the dissection process was completed as a group, as described above. After this collaborative effort, the written portion of Gate 2 was discussed and divided between members based on their title.
- Project work is split up as evenly as possible between the five members of our group. Specific tasks are assigned based on each member's area of expertise. Upon dissection on the lawnmower, it was determined that each member had the knowledge required to complete any area of the written assignment. As such, these tasks were delegated based on the time required and personal interest. The only exception was found in the “How To” portion of this gate. We found our Technical Expert to have the most intimate knowledge of the mower breakdown. In addition, completion of the final draft and wiki upload was to be performed by our Group Collaborator. Out of fairness, and in order to leave time for error checking, each written task must be submitted roughly three days prior to the due date.
- The group meetings have been held often and successfully. In our initial proposal, we did not outline a meeting schedule, but we had agreed to make ourselves available every Tuesday and Thursday at 3:30pm, as needed. Via email and our interactions preceding every MAE277 lecture, we assess what has been accomplished, and decide whether or not a deeper discussion needs to take place. Generally, we end up meeting at least once a week, sometimes twice a week. The Project Manager mediates these sessions, and we have gravitated to a regular itinerary. We normally begin by reviewing what we are expected to determine, both individually and as a group, and then move on to finding solutions to any roadblocks. For example, if a member is unsure of the best way to present a collection of data and information, a friendly argument regarding which type of graph would most easily aid the reader ensues. Or, if a task requires the research of additional information, this data is obtained as soon as possible during the meeting.
- Thus far, we have not had any member conflicts. As it was described earlier, the workload is divided as fairly and evenly as possible through member discussion. Tasks are determined collectively, not dictated by a sole member. In the future, if a member falls behind in their assignment, we will collectively step in and help finish the workload. However, this is a situation that we have yet to encounter.
Listed below is the step-by-step process we took in disassembling the lawnmower. The steps are numbered in the order in which each part was removed. Listed with each part is whether or not the part is intended to be disassembled, the tools used to disassemble it, and the difficulty of its removal (on a scale from 0 to 10, where 0 is no work necessary, and 10 is extremely difficult to remove. The scale is based on the amount of energy spent removing a part, and how accessible each bolt or screw holding the part on was; also, the factor of needing more than 2 hands is considered in the rating.)
|Component Number||Component Name||Tools Used||Difficulty||Image|
|1||Handle (Safety Lever and Self-Propulsion Engagement)|| Hand: Unscrew two "nuts."
Needle-nose pliers: Pull off cable mount from bracket next to carburetor and the other from bracket on rear axle; pull each side of the handle outward off of the bolts
The subsystems involved:
These subsystems are connected as follows:
How the connections are implemented: All of the subsystems are implemented automatically when the engine is started except the wheels and handle. After the pull cord is pulled and the engine starts, the blades start to spin due to the force applied by the piston onto the driveshaft. The piston is powered by the combustion of the air that that comes through the air filter and mixes with gasoline in the carburetor. After combustion the exhaust gasses are forced through the muffler. This all happens without any human interference. However, in order to get the mower to move, the user must push on the handle and transfer that energy to the wheels.
Gate 3 - Product Analysis
In Gate 2 of this project, there was one unresolved challenge facing the group:
While working on this gate, we also encountered a new temporary setback:
Evidence for certain manufacturing processes are riser marks (injection molding, die casting, investment casting), parting lines (injection molding, die casting), positive draft angles (injection molding, die casting, forging), axially symmetrical features (turning), elongated forms with elongated features (extrusion, drawing),axially asymmetric or non-molded holes (drilling), intricate detail (machining, investment casting), specific surface finishes (machining, grinding), and thin, sheet-like metal (rolling).
Note: Component complexities are "not very," "moderately," or "very" complex. These ratings take into account the difficulty of the manufacturing process used, the connections of each analyzed component to other components, and the type of movement of the component under normal operation of the mower.
Solid Modeled Assembly
One of the most important parts of a lawn mower, are the blades. Without them, you wouldn’t have a lawnmower. In the beginning, some person probably sat down and figured out how to attach a sharpened blade to the output shaft of an engine to create a motorized lawnmower. It needed to be sharp enough to slice the grass as it spins, and sturdy enough to hold up to the spinning and stress put on from cutting large amounts of grass or brush. Once the design was created, it was made and attached to the output shaft. Testing would be physical, since there was no such thing as simulations or really even a household computer at the time of its creation. Things to watch for while cutting the grass is if the blade spins evenly-that it is centered on the shaft, and if it can cut all of the grass that the lawnmower passes over with accuracy(no flexing in the blade or missed patches of grass). For an engineer to do a proper analysis of the blade on a single shaft lawnmower, all they would really need is to know the center of mass for the blades, the sharpness needed to cut the grass, and the speed at which the blades must spin in order to cut grass well.
Gate 4 - Product Explanation
Critical Project Review
At this point of the semester-long project, we have been able to complete the assignments with few noteworthy issues. Also, we have yet to encounter any group conflicts.
The lawnmower was most likely originally assembled by hand due to the many pieces and materials combined into one machine. The assembly is very similar to the disassembly, although you have to pay attention to the correct order of things, which makes the assembly harder than the disassembly.
Figure B shows a simple representation of a crank-slider mechanism. As the crank rotates clockwise from the 9 o’clock position to the 3 o’clock position, the connecting rod, and thereby the piston, move to the right. Then, as the crank continues to rotate from the 3 o’clock position back the 9 o’clock position, the connecting rod and piston traverse back to the left. The rightmost position of the piston is referred to as Top Dead Center, "TDC," (minimum volume in combustion chamber), and conversely, the leftmost position corresponds to Bottom Dead Center, "BDC," (achieving maximum volume in combustion chamber). In a 4-stroke engine, it will take 2 complete rotations of the crankshaft to complete a cycle (Table 1); consider the cycle when beginning at TDC (Note: Rotation/Movement of the Crank and Slider is in relation to Figure B):