Group 10 - Line Trimmer/Request for Proposal

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Request for Proposal

Delivery Date: 10/09/2009

Work Proposal


We plan to completely disassemble the line trimmer as far as possible with the tools we have readily available. From there we will select some of the major components that make the line trimmer run and function the way that it does. We will make solid models of these components on a computer, perform an engineering analysis of them and try to develop possible revisions that could be made to make these components even better. Lastly, we will reassemble the line trimmer into the same condition we started with.

Required Tools for Dissection

Socket Wrench Set - Used to remove several nuts that are on the product

  • Bottom of the trimmer
    • There is a nut holding in place the plastic disk which holds the trimming pieces
    • There is a nut between the plastic disk and the metal shaft
  • Spark plug
    • We will need a wrench to remove the spark plug

Flat head screwdrivers - These will be used to remove flat headed screws and pry open certain areas of the line trimmer

  • Bottom of the trimmer
    • There are two screws holding the plastic foot guard on
  • Top of the trimmer
    • External coverings that would be best removed by prying with a flat headed screwdriver
    • There are some visible flat head screws that are used for making tuning adjustments to the engine which will need to be removed

Phillips head screwdrivers - These will be used to remove Phillips head screws

  • Top of the trimmer
    • Four Phillips head screws keeping the trigger hand grip on
    • Two Phillips head screws holding the cover of the choke box on
    • Under the external coverings we expect to find additional Phillips head screws holding down more coverings and pieces to the main frame

Allen Wrench Set – These will be used to remove screws with an Allen head on them

  • Top of the trimmer
    • There are six Allen wrench screws on the bottom of the engine and tank cover
    • There are four Allen wrench screws on the top of the engine and gas tank cover

Small Hammer - It will be used for loosing parts that need to be pried off
Needle-nose pliers - These will be used for removing springs and the throttle cable

Potential Challenges and Outcomes

Refer to Gantt Chart (Figure 1) and Timeline in the Management Proposal

Durability of Parts - If we break a piece during our disassembly or reassembly, it will take time to replace the piece properly. This will also present a challenge as it will be necessary to find an almost exact replica of the part to ensure proper reassembly.

Scheduling Conflicts Among Group Members - It is possible that tests, homework, sports and various other activities could interfere in the ability of the group to coordinate meeting times. This could slow down any phase of the project because full group cooperation is what is needed to create and provide a complete and well coordinated analysis.

Possible Emergency - Emergencies happen and the ability of the group to maintain on the predicted timeline may be a challenge as major emergencies are not accounted for in the timeline.

Ability to Assemble/Reassemble Product - Based on experience in the group, the amount of time to assemble the trimmer will vary. While minor variations are accounted for in the timeline, a major problem in our ability to disassemble/reassemble will cause our group to fall behind schedule.

Member’s Capabilities and Shortcomings

Andrew Engelbach-Schafer

  • Capabilities
    • Some Autodesk Inventor experience
    • Some experience in disassembling products
    • Group project experience from PLTW courses in High School and Architecture internship
  • Shortcomings
    • No experience with a Wiki
    • Never disassembled a small engine

Ryan Adams

  • Capabilities
    • Experience with group projects
  • Shortcomings
    • No experience with solid modeling

Damitha Abeykoon

  • Capabilities
    • Experience with automotive engines
  • Shortcomings
    • Not familiar with small engines
    • No experience with engineering analysis

Patrick Smith

  • Capabilities
    • Wiki administration experience
    • Autodesk Inventor experience
    • Exposure to reverse engineering techniques from PLTW courses
    • Experienced in group settings
  • Shortcomings
    • No experience in disassembly of gas engines
    • Poor coordination when dealing with small components

Justin Storms

  • Capabilities
    • Experience with group projects through clubs, engineering internship and previous courses
    • Knowledge of tools from previous jobs and projects
    • Quick learner to Wiki software
  • Shortcomings
    • Little experience with small gas engines
    • No experience with 3D modeling

Management Proposal

Group Meetings

The group plans to manage the work through a sustained effort during the semester. The roles listed below assign responsibilities to each member and hold them accountable for the completion of certain tasks. The tasks that need to be done are listed in the timeline. The timeline and Gantt chart will serve as a guide for the group to gauge and evaluate the overall progress towards the final completion of the project throughout the semester.

The group will have regular meetings each Thursday at 3:30pm in 101 Bell to discuss the previous week’s work and the next week’s work. Each member has a copy each others’ schedule and contact information so it will be easy to have many informal meetings and communications for work done in smaller groups. The point of contact or communication liaison for the group will be the Project Manager Justin Storms.

Group Roles

Project Manager - Justin Storms

The Project Manager of the group will oversee that the project is moving along at the scheduled pace. He keeps up communication and organization of the group in order to keep everyone on the same page. Communications and questions with the course instructor and teaching assistants can be handled through the project manager.

Lead Wiki Developer - Patrick Smith

The Lead Wiki Developer of the group will assure that the Wiki site is being maintained and properly formatted. He will assist other group members in learning how to post to the Wiki correctly in order to make optimal use of it.

Dissection/Assembly Leaders - Andrew Engelbach-Schafer and Ryan Adams

The Dissection/Assembly Leads of the group will work together to manage the disassembly and recording of each step. They will also oversee the reassembly of the product and are primarily responsible for the successful reassembly of the product back to working order. The leaders will verify that documentation is done for both the dissection and reassembly processes. Any major obstacles encountered in the dissection or assembly of the product will be directed to the Dissection/Assembly Leaders to solve.

CAD Model Leader - Damitha Abeykoon

The CAD Model Lead will do a large portion of the three dimensional solid models of the components of the dissected product. He will teach and show other group members working on the modeling what must be done. The CAD Model Lead monitors the progress of the models and assures that they will be accurate and complete by the deadline.

Along with the above mentioned roles, each member of the group will take some part in each of the major areas of disassembly, assembly, component and engineering analysis, creating design revisions, CAD modeling, documenting the steps, and posting to the Wiki. The Dissection/Assembly Leads will keep each other up to date and work together to ensure that what is taken apart can be put back together the proper way. Each member is responsible for reading and reviewing written parts that will be handed in and posted to the Wiki. One of the main management goals of the group is for each member to take on a larger responsibility in one area while still receiving help and helping others successfully fulfill their roles.

Conflict Resolution

With a project of this size, between the five group members there bound to be some conflicts and issues that will arise during the semester. This could include inabilities to complete certain stages of the project, failure for members to attend meetings, etc. In order to more effectively handle these conflicts, the following procedure will be followed.

  1. The conflict will be presented to the group during a regularly scheduled group meeting. Those members not in attendance will be filled in via email.
  2. The project manager will assist in guiding the group towards a resolution to the conflict.
  3. The project manager will outline the conflicts and resolutions in the causes for corrective action section of each gate.
  4. Any further assistance that is needed will be sought through the course instructor or teaching assistants.


1. Request for Proposal - Due 10/9

1.1 Work Proposal (9/27-10/7)
The work proposal was discussed during a group meeting. Andrew took on the responsibility of expanding on what we discussed and typing up a formal proposal to be submitted. It will be read and reviewed by the rest of the group before submission.
1.2 Management Proposal (9/27-10/7)
The management proposal was discussed during a group meeting. Justin took on the responsibility of going into detail and giving formal descriptions of the things discussed. He will send the report around for review by the rest of the group before submission.
1.3 Initial Product Assessment (9/27-10/7)
The initial product assessment was handled by Damitha and Ryan. They put the responses into a technical writing and will send around the final report for review by the other group members.
1.4 Wiki Posting (10/7-10/9)
Patrick will post the entirety of the request for proposal in proper format on the Wiki site as the Lead Wiki Developer.

2. Preliminary Product Review - Due 10/30

2.1 Dissection Process (10/10-10/23)
The dissection process will be managed by the Dissection/Assembly Leads. They will work to solve many of the problems the group members encounter with taking apart each part of the line trimmer. This will include finding out what the proper tools are for each part in the dissection process.
2.2 Write Dissection Report (10/17-10/28)
The group will develop a scale for ease and complexity. It will then explain and discuss each step of the disassembly and relate it to the established scale. Pictures and videos will be included on the Wiki site.
2.3 Causes for Corrective Action (10/24-10/28)
By the last week of the preliminary product review the group will meet and assess its standing compared to the previously drafted timeline. Decisions will be made on whether to adjust or change responsibilities, roles and work. A formal write-up will be done if there are major changes by the Project Manager.
2.4 Wiki Posting (10/26-10/30)
The Wiki posting of the dissection report will be posted in the last week of the preliminary product review. All of the group members will try to help Lead Wiki Developer to get everything posted on the Wiki in presentable format including text, pictures and videos.

3. Coordination Review - Due 11/23

3.1 Component Summary (10/31-11/20)
All of the group members will work on the components summary to answer the questions listed on the coordination review assignment sheet. The Project Manager will type up these results into a presentable manner for the Wiki.
3.2 Design Revisions (10/31-11/20)
All of the group members will discuss ideas for possible design revisions. After deciding on three design changes, one of the Dissection/Assembly Leads will write a technical report explaining the design changes. This will be then posted to the Wiki.
3.3 Solid Model Assembly (10/31-11/20)
The CAD Model Lead will create solid models of four components that he and the group choose from the line trimmer. Other group members will try and assist in drawing some of the components as much as they can. The final assembly of the components in sequence will be passed on to the Lead Wiki Developer to post to the Wiki.
3.4 Engineering Analysis (10/31-11/20)
All of the group members will discuss and give engineering analysis on the line trimmer. One of the Dissection/Assembly Leads will write a technical report explaining the engineering analysis that was done on the product. This will be then posted to the Wiki.
3.5 Causes for Corrective Action (11/18-11/22)
By the last week of the coordination review the group will meet and assess its standing compared to the previously drafted timeline. Decisions will be made on whether to adjust or change responsibilities, roles and work. A formal write-up will be done if there are major changes by the Project Manager.
3.6 Wiki Posting (11/5-11/23)
Many of the group members should be posting to the Wiki as they finish up their parts of the report. The Lead Wiki Developer will make sure that everything is posted by the due date in a neat and professional looking manner.

4. Critical Project Review - Due 12/7

4.1 Reassembly Process (11/24-12/2)
The reassembly process will be managed by the Dissection/Assembly Leads. They will work to solve many of the problems the group members encounter with putting each part of the line trimmer back together in the proper way. This will include finding out what the proper tools are for assembling each part and making sure the product works.
4.2 Write Reassembly Report (11/28-12/5)
The group will explain and discuss each step of the assembly with specific detail on unique challenges. Pictures and videos will be included on the Wiki site of the assembly process.
4.3 Wiki Posting (12/2-12/7)
Many of the group members should be posting to the Wiki as they finish up their parts of the report. The Lead Wiki Developer will make sure that everything is posted by the due date in a neat and professional looking manner.

5. Delivery - Due 12/11

5.1 Compliance Matrix (12/6-12/10)
The group will meet and go over the compliance matrix. The Project Manager will type any notes that need to be made with respect to the compliance matrix.
5.2 Oral Presentation Preparation (12/4-12/9)
All of the group members will meet to devise the points that need to be covered in the oral presentation. Each member will receive a topic to discuss and present.
5.3 Finalize Wiki (12/3-12/11)
This includes the addition of an executive summary, introduction and list of references. Everything else in the Wiki must be in good order and format and ready for final submission.

Gantt Chart

Figure 1 - Gantt chart of projected reverse engineering project execution

Group 10 Gantt Chart

Initial Product Assessment

  1. The line trimmer can be used for finer purposes such as cutting, trimming, and edging grass. The user can also cut through thicker brush in smaller areas that lawn mowers cannot reach or fit.
    • This particular line trimmer appears to be mainly for home use based on the size of it. The line trimmer seems to be medium size compared to other ones. Larger and heavier duty line trimmers are normally used by professionals that do landscaping.
    • The line trimmer can be used for landscaping around the yard. It works great for tidying up the edges the lawn mower cannot get close to and the areas that are too small for it to fit at all. The thin plastic line that normally comes with the product can be changed with other attachments to give it other uses. For example, the line might be replaced with a plastic blade for heavy work like cutting thick brush.
  2. A gas line trimmer uses a small two stroke internal combustion engine. This engine is fueled by an unleaded gasoline and two stroke oil mixture. The fuel is mixed with air in the carburetor and flows into the combustion chamber where the spark plug ignites it. This drives the piston which turns a shaft that translates this energy down the shaft of the line trimmer to spin the cutting device on the bottom1. The user can control the speed of the device using the throttle trigger located on the handle below the engine.
    • There are many different types of energy used in a line trimmer. These include some of the major forms of energy such as chemical energy, internal energy, kinetic energy, electrical energy, thermal energy and mechanical energy.
    • These energies are all used and transformed to carry out the function of the line trimmer. There is chemical and internal energy contained in the two-stroke gasoline and oil mixture. This fuel containing the chemical energy is fed into the carburetor where it mixes with outside air. This mixture then moves into the internal combustion engine. A spark plug supplies a spark of electrical energy which ignites the fuel and air mixture. This converts the chemical, internal and electrical energy into kinetic energy and work through combustion. The energy of combustion process drives the piston down which rotates a shaft. The process also involves kinetic and mechanical energy. This energy is then translated down the shaft of the line trimmer to the bottom cutting piece which rotates and does shaft work, which is a form of energy. During these conversions some energy is lost to frictional forces. Another byproduct of the combustion process is thermal energy, which is dissipated into the surroundings in the form of heat.
    • Essentially all of the controls on the line trimmer are mechanical devices. The trigger on the line trimmer uses a thin steel cable to attach to the throttle which is help back by springs. By pulling the trigger for the throttle this uses mechanical energy. When pull starting the device there is mechanical energy being used to get the engine going.
  3. The line trimmer looks as though it is in good shape, however it does not run.
    • After fueling up the line trimmer with the appropriate fuel and trying to start it for 20 minutes there was no success. The group tried adjusting the choke to different positions, but did not see any hope.
    • The pull start string on the device does not retract all the way back into the product. This seems like it could be part of the problem. The line trimmer does not sound like it is igniting inside. The spark plug seems to be good on the device and fuel was being pumped into the combustion chamber. The group’s best guess is that the problem lies somewhere in the pull start, but we will not know until we disassemble the device.
  4. In terms of landscaping tools, the most complex thing would be a large tractor and this would rate as a 10 on a scale from 1 to 10. The simplest type of landscaping tool would be something like a pair of gardening shears, which would rate at a 1. The line trimmer falls at around a 3 on this complexity scale. It is not a purely human power device and it has a small gasoline internal combustion engine.
    • There are probably around 15 to 20 major components on the line trimmer. These include the gas tank, the carburetor, the combustion chamber, the choke, clutch guards, drive cables, throttle cables, throttle trigger, gear boxes, spark plug, pull start, handles, foot guard, cutting disk and covers to name many of them. If we consider screws and other small components like nuts and washers there are probably around a hundred things.
    • Most of the parts on the line trimmer are not very complex at all. They have been around for many, many years. Perhaps the most complex components are the parts of the engine if the user is not familiar with small gasoline engines. However, to an individual with mechanical knowledge this would be rather simple and basic.
  5. The materials used in the product are plastic, steel, iron, copper, rubber, and nylon.
    • The visible materials are the plastic, metals, rubber and nylon. The plastic makes up the casing around the engine, the handle, the gas tank, and the guard around the trimming part. Steel cable is used in the throttle and drive cables. The shaft and chassis of the line trimmer are made up steel most likely. Copper is used for the wires that connect the spark plug and rubber insulates those wires. Nylon is what the string for the pull start is made of.
    • Some of the internal materials that are assumed are cast iron for the engine and combustion chamber. The oil and gasoline mixture that is inside serves as both a fuel and lubrication for the moving parts.
  6. This is a product that most users would be pleased with if we could get it to run. In its current state the user would probably be disappointed because it will not start up. It seems like it is a rather minor problem that could be fixed.
    • This line trimmer would be comfortable for use on a small lawn. The device is heavier than many of the other comparable and newer models, so it would not be ideal for trimmer a large lawn for a long period of time because it would get heavy. The device seems to be on the medium to small side, so for taller users it might not be as comfortable. For individuals less than six feet tall it seems like it would be the perfect size. The addition of a sling to help support the weight of the engine on the user’s shoulder might be a good addition.
    • The product was not able to start, so in this regard it is not easy to use. However, similar models are relatively easy to use. The user simply needs to adjust the choke to the proper position, pull in the throttle trigger and pull the starter. These engines typically take a few pulls before they begin running. Once they are running though and heat up for a few second the user simply needs to adjust the choke and then it can be used to start trimming. The line trimmer extends at a good angle to allow for easy cutting. To turn off the device there is a stop button located right by the pull start that the user simply needs to switch to shut it off.
    • The line trimmer does require some maintenance. The trimming tools attached on the bottom that do the cutting need to be replaced every so often. It needs to be refueled with a gasoline and oil mixture after every couple hours of use. After a few years, the spark plug may need to be changed depending on how heavily the device is used. After a decade or so, the line trimmer might need an engine tune up or need to be cleaned up inside to keep it running smoothly. This type of service would be more difficult and something that most users would not be able to do on their own. However, most of the maintenance such as refueling and replacing the trimming attachments can easily be done by the user.
  7. There are other brands and models of line trimmers that exist that can do the same task. Some are better, while some are not quite as good. There are more expensive gasoline line trimmers that are light weight, heavy duty and more comfortable to use. There are also electric line trimmers that are smaller, cheaper and quieter.
    • Our particular line trimmer probably costs around $80. Comparable models can be bought for the same price by the same company and other companies. Some of the more expensive line trimmers that run up to $200 offer features such as being more light weight or comfortable to hold. The electric line trimmers are cheaper than our gas line trimmer; however, the user must drag an electrical cord around them or use a battery that can drain quickly. The gasoline line trimmer offers more freedom and extended use.
    • The gasoline line trimmer compared to electric ones gives the user more freedom as mentioned before. The user is not attached or restricted to a certain area of use by an extension cord. The device does not have to recharge, it can just be refueled instantly when it runs low. The device is powerful and can cut through thick brush with the correct attachments.
    • Some disadvantages of the gasoline line trimmer are the size and weight of it. Carrying the device around can get tiring for the user. The product is a little noisy when it runs and it vibrates a lot. Electric line trimmers quieter and often times lighter. The engine can get hot and leak fuel or oil on the user.

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