Group 15 - Craftsman Weed Whacker
(→Initial Product Assessment)
(→Initial Product Assessment)
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== Initial Product Assessment ==
== Initial Product Assessment ==
Revision as of 22:41, 9 October 2011
Gate One: Project Planning and Proposal
Before starting on a major project it is important to understand what you are getting yourself into; this particularly important in a group setting. It is very important to know the strengths and weaknesses of each individual so that it is possible to maximize the group’s effectiveness. In this gate of the project we will go over the approach we will take in disassembling and reassembling our product, we will go over what tools we will need to do this, and address our strengths and weaknesses as individuals and a group as a whole.
Table 1.1 - A short profile of the team members.
|Brent Haseley|| -Experience with tools and machines
-Worked 4 years in warehouse maintenance
| -Not CAD expert
-Very busy with overwhelming schedule and workload for other classes
|Charles Kalbfell|| -Quick learner
-Proficient writer and editor
| -Not familiar with 3-D modeling
-Poor presentation skills
|Frances Kalbfell|| -Good writer
-Willing to work hard
| -Tendency to wait until the last minute
-Limited experience with AutoCAD
|James Quirk|| -Proficient in CAD and 3-D modeling
-I have trouble focusing on one task
|James Ziccarelli|| -Performs confident work with hands when dealing with a product
- Has great interpersonal and communication with others
| - Not totally efficient with AutoCAD or Pro-Engineer
- Busy between school and a part-time job
Table 1.2 - A brief description of the roles assigned to each group member.
|Brent Haseley||Documenter: I will be responsible for documenting and|
photographing every step of the product dissection.
Wiki Designer: I will be the person doing most of the
|Charles Kalbfell||Project Manager: I will be tasked with setting meeting|
dates, internal group deadlines, resolving conflicts,
and keeping the project on track. I will also read over everybody’s
|Frances Kalbfell||Chief Editor: I will be in charge of thoroughly going over|
everyone’s parts to make sure that they are technically
and grammatically correct. I will also have to put all of the parts
|James Quirk||Communication Liaison: I am in charge of communication between|
my group members and the instructors. When the group
needs a question answered, I am the person who expresses this via email
|James Ziccarelli||Main Technical Expert: I am in charge of the actual product dissection.|
Will also be responsible for developing a thorough knowledge of the
physical product and understanding how it will be reassembled.
- For all gates our group has made plans to meet at least one time each week out of class and lab to ensure that we get the gates done ahead of time.
- Each group member plans on going to the lab at least one time each week.
- The group also meets briefly at the end of every lecture to discuss progress of the project.
Initial Product Assessment
The weed wacker was invented in the 1970s by George Ballas , and it has been a staple of the lawn care industry ever since. The design of weed wackers has continued to evolve and improve, resulting in the machines we know today. The product we are working on is a 26cc Craftsman weed wacker that was manufactured in 1991. The Craftsman weed wacker was intended to be sold in areas of the world were people have lawns and where they would have sufficient discretionary income to allow the purchase of luxury items such as a tool that performs such specific (and non-essential) jobs as a weed wacker. The typical areas where these criteria are met are in middle and upper class regions of the United States and Europe, though they have steadily migrated to areas in South America, Asia, Australia, and Africa as well. There are now people on all populated continents that tend to ornamental lawns.
One of the more pressing economical and global concerns at the time of the widespread adoption of the weed wacker was the price of gasoline. In early 1990 the average U.S. price for a gallon of regular gasoline was about $1.07 and over the course of the next year it went to as high as $1.42 (which represents about a 33% increase). Therefore fuel economy would have been a major consideration for the designers of any product in 1991 - especially an item such as a weed wacker that is not a necessity. So it is safe to assume that this particular weed wacker was designed to be as fuel efficient as possible while not sacrificing too much power. This ties in very nicely with one of the big global concerns of the day, keeping the environment clean . During the early 1990’s people began to become increasingly worried about what pollutants were doing to the environment. This might have caused the designers of our weed wacker to make sure our product was as fuel efficient as possible and wasn’t exhausting excessive dangerous chemicals into the environment. The overall goal of designers of any tool is to make it efficient (and there are many different criteria for “efficient”).
Currently Craftsman ships products to over 90 countries around the world . However, our weed wacker was almost certainly not sold in all of these countries. Craftsman has diversified its products and suppliers since the 1990’s so it is very likely our weed wacker was only available in American and well-off areas of Europe. Craftsman would have only been interested in selling their product where there was sufficient demand to ensure profitability, so they most likely did not try to establish markets in less affluent areas, or in areas where the climate meant there was little lawn maintenance (whether because of deserts or harsh winter conditions). Their marketing strategy would have been geared towards people in regions where their product could have made them an adequate profit even after establishing a support infrastructure. It is also worth noting that the weed wacker has a relatively small impact on society since its only function is to make a lawn look neater.
The intended impact for the consumer is relatively straightforward for this product. Weed wackers are intended to simplify lawn maintenance, allowing for a more esthetic presentation with reduced effort (more satisfaction while enjoying more free time). These machines are very effective in attaining these goals, as evidence by their broad market penetration. Though this is a relatively mature product, there is still continuing development. Current environmental concern are pushing manufacturers to look to alternatives to 2 cycle engines; the most promising are 4 cycle wackers (primarily Honda), or rechargeable electric weed wackers (Worx and multiple others).
There are some weed wackers that can do many different jobs because of available attachments, but the 1991 26cc Craftsman weed wacker we are dissecting this semester fills a very specific role. This machine is intended to be used to trim vegetation in areas around the world where people maintain decorative lawns. You would never try to cut an entire lawn with a weed wacker because it would be very tedious, and it probably would not look good anyway because it would result in a very uneven cut. Trying to cut anything bigger than small to medium weeds would similarly be out of the question. If you tried to cut anything too thick it would merely result in overheating the engine and broken string, and if you tried to cut something like a vine it would most assuredly get tangled in the head of the weed wacker and either the engine or transmission (or both) would seize. The ideal use of a weed wacker like this is to cut the grass and other small plants on the perimeter of a small lawn, or to trim around trees or other objects.
Almost every landscaping company in America uses weed wackers to finish off their trim work, but they almost certainly do not use a 26cc Craftsman weed wacker from the early 1990’s. There may be other considerations (for instance, some companies prefer to use slightly older weed wackers with adjustable carburetors because they allow you to change the power to fuel economy ratio with the turn of a screw whereas this feature is illegal on newer models), but product evolution means the more modern a weed wacker is the better you would expect it to perform. Regardless, this particular weed wacker is not durable enough to handle the rigors of commercial use – it was clearly designed to a lower price point, yet it is still tough enough to be acceptable to a residential homeowner. In that light, this is a very efficient design. It is a low maintenance device that is very good at doing what it was designed to do, and it is durable enough to provide a very long service life for a once-a-week user intent on tidying his/her lawn.
There are a multitude of different types of energy utilized in our 26cc Craftsman weed wacker, the most prominent of which are inside the machine itself. The energy of the system all comes from the chemical energy that is provided by combusting the gasoline that is put into the machine. The actual ignition of the gas is accomplished by the sparkplug. There is a flywheel in the powerhead that serves many functions – it is what the recoil starter engages to start the engine, its mass smooths out the power pulses generated by the engine, it incorporates an integral fan that provides engine cooling, and it has magnets on it that generate electricity as they spin by an ignition coil. From here this electricity is converted by an electronic ignition module, and then it is fed out to the sparkplug. The plug then forces the electricity to jump across a gap to get to the electrode, providing the spark that initiates the combustion process. The energy in the gasoline is then released resulting in a controlled explosion. This explosion then causes the piston to move down, which causes the crank shaft to move, and then its rotational inertia forces it back up, which results in another combustion cycle. The crank shaft then imparts rotational kinetic energy to the head of the weed wacker, which does the actual cutting.
There is also user input energy that goes into making our weed wacker a functional tool. Our weed wacker does not feature automatic/electric start, so to initiate operation the user must apply some amount of force to the rip-cord. This provides the energy necessary to begin the self-propagating operation as outlined above. Our weed wacker does not have any type of propulsion, so the user must carry the machine while using it. Even though it may seem negligible there is still also energy involved with the user squeezing the trigger on the handle of the weed wacker, which eventually results in the release of gasoline into the combustion chamber.
All of the information above can also be found in the chart provided below.
Energy Profile Table
|Types of Energy Used in the System||How it is Used in the system||How Energy is imported|
|Internal Combustion||The most prominent form of energy in a weed wacker comes from the gasoline you put into the machine. The weed wacker’s engine produces power by internal combustion that turns the shaft. From there a transmission modifies it so it spins the head (and string) parallel to the ground.||Chemical potential energy is added in the form of gasoline. The gasoline is drawn into the combustion chamber where it is ignited.|
|User input energy||Human energy is also need so that the weed wacker can run. Someone has to pull the rip-cord so the weed wacker will start. A person has to pull the trigger so that the engine will get gas. Since it cannot move on its own someone needs to carry the weed wacker around.||The user does work on the system.|
|Rotational Kinetic Energy||Energy is converted into kinetic energy as the motor spins the shaft and head (this also creates momentum – you can see this because when you turn off the weed wacker the head continues to spin).||The combustion of the gasoline results in the piston going up and down, which moves the crankshaft that turns the drive shaft.|
|Heat||Substantial thermal energy is created by all the above mentioned processes (to the point where many weed wackers actually stop working due to overheating). All the explosions and friction create immense amounts of heat.||Heat energy is brought into the system through friction and chemical combustion.|
|Electrical Energy||Two magnets on a flywheel (called a magneto) spin around and pass a coil. As they spin past they generate an electrical current that then passes though the ignition system and into the sparkplug. The plug then creates a spark at the electrode gap.||Electrical energy is generated in the system when spinning magnets pass a coil.|
|Chemical Energy in Fuel||Chemical energy is stored in the bonds of the gasoline. When they are broken through combustion the controlled explosion’s energy becomes kinetic energy, which powers the system.||Chemical energy is imported to the system when gasoline is poured into the weed wacker.|
|Potential energy stored in a Spring||Potential energy is stored in the various springs of a weed wacker. There are springs in the shafts of many weed wackers, the trigger system, the head, and in the pull cord’s recoil mechanism.||The user introduces potential energy when he compresses (or stretches) a spring.|
|Kinetic Energy||Energy is converted into kinetic energy inside the engine itself. The piston of the weed wacker moves up and down due to the explosion caused by the gasoline, causing the crank shaft to move.||Kinetic energy enters the system made when the piston moves due to the controlled explosion of the gasoline. Kinetic energy is also stored in the rotating head, shaft, and string.|
|Part Description||Fastener||Tool Required||Time (minutes)|
|Muffler Cover||2 Self-Tapping Screws||Phillips Driver||3|
|Air Filter||2 Machine Screws||Allen Wrench||1|
|Carburetor (from motor)||2 Machine Screws||Phillips Driver||2.5|
|Carburetor (from throttle)||2 Bolts and Nuts||Crescent Wrench||2|
|Spark Plug Ground||Friction||Hand||.5|
|Engine Cover||8 Machine Screws||Allen Wrench||3|
|Pull Start Coil||4 Machine Screws||Allen Wrench||2|
|Shaft Joint Cover||2 Machine Screws||Allen Wrench||1|
|Hose Clamp||1 Machine Screw||Flat Head Driver||1|
|Trigger and Housing||1 Machine Screw||Allen Wrench||1|
|Forward Hand Grip||1 Screw with Knob||Hand||1|
|Head Guard||2 Self Tapping Screws||Flat Head Driver||2|
|Head||1 Machine Screw||Phillips Driver||.5|
|Strap Loop||1 Bolt and Nut||Crescent Wrench||1|
|Total Disassembly Time||21 minutes|
(All times listed are with the assumption that all the parts are going to come off easily, however we know that this is not the case and the dissection will indeed take longer than the time we have listed.)
- Several metal components are rusted and may strip easily, delaying our product dissection
- There have been a few home repairs on this product that may force us to deviate from the disassembly plan that would be used on a new product. Most notably, the rear hand grip and trigger line are held together with a hose clamp.
- The product was not in a running state before the project began (gas line was cut and the primer was ripped out), so it is highly unlikely that it will run after reassembly unless replacement parts are installed.
- Due to the restrictions imposed on us for Gate One, we have as yet been unable to inspect the actual engine to determine its condition. A rusted and/or deteriorated engine will hinder dissection
Table 1.4 - a general timeline of projected project deadlines.
|Task||Subtasks||Stating day||Optimal Completion|
|Gate 1||September 9, 2011||October 10, 2011|
|Project Management Decisions|| Work Proposal
|September 12, 2011||September 28, 2011|
|Project Archeology|| Preparation and Initial
|September 30, 2011||October 10, 2011|
|Gate 2||October 10, 2011||October 26, 2011|
|Cause for Corrective Action||October 10, 2011||October 20, 2011|
|Product Archaeology||Physical Dissection||October 10, 2011||October 17, 2011|
|Documentation of Dissection|| Notes in lab
Written up documentation
| October 10, 2011
October 10, 2011
| October 17, 2011|
October 19, 2011
|Gate 3||October 26, 2011||November 14, 2011|
|Cause for Corrective Action||October 26, 2011||October 30, 2011|
| Component Summary
Solid Model Assembly
| October 26, 2011
November 1, 2011
October 26, 2011
October 26, 2011
| November 3, 2011|
November 12, 2011
November 8, 2011
November 10, 2011
|Component Assessment Questions||November 1, 2011||November 12, 2011|
|Gate 4||November 14, 2011||December 2, 2011|
Critical Project Review
|Cause for Corrective Action||November 14, 2011||November 18, 2011|
|Product Reassembly||November 14, 2011||November 18, 2011|
|Design Revisions||November 14, 2011||November 28. 2011|
|November 14, 2011||November 29, 2011|
|Gate 5||December 2, 2011||December 16, 2011|
| Finalization of Deliverables
| December 2, 2011
December 2, 2011
| December 8, 2011|
December 10, 2011
| Technical Report
| December 6, 2011
December 2, 2011
| December 12, 2011|
December 14, 2011