Difference between revisions of "Group 27 - Weed Wacker"

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===Operation===
 
===Operation===
  
Because the trimmer requires gas, we were unable to operate and test the product. However, from prior knowledge, a typical gas-line trimmer has a small engine that spins a shaft. Ours appears to spin a flexible one, which connects to the head. The head contains three slots for cutting "fingers" that flare out when subjected to rotation. These fingers are responsible for trimming.
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Because the trimmer requires gas, we were unable to operate and test the product. However, from prior knowledge, a typical gas-line trimmer has a small engine that spins a shaft. Ours appears to spin a flexible one, which connects to the head. The head contains three slots for cutting "fingers" that flare out when subjected to rotation. These fingers are responsible for trimming lawns, weeds, etc.
  
 
===Components/Material===
 
===Components/Material===

Revision as of 19:50, 3 December 2008

Contents

Executive Summary

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Our reverse engineering team project product was a Weed Eater gas-powered line trimmer. We were asked to document our disassembly, analysis, and reassembly of the product.




Introduction

Disassembly Product

Our product was a 1989 Weed Eater gas-powered line trimmer, model LT7000. It is powered by a single cylinder two stroke engine, and is used to trim off unwanted weeds and plants. We were unable to test it prior to disassembly because of regulations and safety concerns with fuel.

Group Members

Our team consists of five people:

  • Joe Herman (Group Leader): Disassembly / Presentation / Reassembly / Wiki Editing
  • Clyric Ng: Disassembly / Presentation / Reassembly / Wiki Editing
  • Blaine Reeher: Disassembly / Reassembly / Wiki Editing
  • Konrad Sontag: Disassembly / Reassembly / Wiki Editing
  • Neil Taras: Disassembly / CAD / Presentation / Reassembly

Before Disassembly

Purpose

The purpose of a gas-line trimmer is to cut, trim, and shear different types of grass, weeds, and small plants using a flexible line. This line is rotated about a reel/head powered by an internal motor. Connected to a shaft, the motor creates enough torque to make the line functional. The line then rotates and the purpose of the gas-line trimmer is performed. Both potential and kinetic energies are used here. More specifically, elastic potential energy and rotational kinetic energy drive the trimmer. A coil spring contains elastic potential energy, which is then transformed into rotational kinetic energy in the reel.

Operation

Because the trimmer requires gas, we were unable to operate and test the product. However, from prior knowledge, a typical gas-line trimmer has a small engine that spins a shaft. Ours appears to spin a flexible one, which connects to the head. The head contains three slots for cutting "fingers" that flare out when subjected to rotation. These fingers are responsible for trimming lawns, weeds, etc.

Components/Material

Without disassembling the product, the gas-line trimmer appears to be made up of 30-35 components. Because it is gas-powered, it will contain more parts than an electric trimmer. These components are all made up of a variety of different materials. The most visible and most common material is molded plastic. This material can be found in components such as the housing, head guard, trigger, handle, gas tank and smaller plastic components located inside the housing. The trimmer also contains a shaft made of aluminum. The line used is made of nylon but contains three individual lines, each thick in diameter to provide more strength and durability. All screws, nuts, and fasteners, along with a coil spring, are made of metal, most likely steel. Assuming the trimmer contains a piston-cylinder device to drive the motor along with the motor itself, we can assume the two to be made of steel as well. The startup rope is most likely made from nylon or polyester. Knowing several of the components and the materials they are made from, we can now begin the disassembly portion and compare what we saw with what we predicted.

Gas Trimmer Pictures From Different Angle

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UB08G27 Motor assembly final.jpg
UB08G27 Motor assembly ISO.jpg
UB08G27 Motor assembly side.jpg
UB08G27 Motor assembly top.jpg

Disassembly Procedure

Step # Procedure/Difficulty Time Spent Tools Used Pictures
Start The whole gas trimmer 0 0
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1 Disconnect reel guard from shaft via two screws

Easy

20 seconds Phillips Head Screwdriver
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2 Disconnect reel head from shaft via

Easy

10 seconds
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3 Remove trigger handle from shaft via four screws

Easy

40 seconds Phillips Head Screwdriver
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4 Remove throttle cable from trigger handle

Easy

5 seconds No tools
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5 View of throttle cable attached to choke

N/A

N/A N/A
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6 Remove choke housing from main housing

Easy

20 seconds Phillips Head Screwdriver
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7 Remove air filter to expose choke cover

Easy

2 seconds No tools
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8 Remove interior choke cover and selector

Easy

20 Seconds Allen Key Set
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9 View of interior choke cover and selector

N/A

N/A N/A
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10 Remove choke from engine

Easy

20 seconds Allen Key Set
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11 Disconnect throttle cable from choke

Easy

2 seconds No Tools
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12 View of choke cover connected via screws

N/A

N/A N/A
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13 Remove top choke cover

Easy

40 seconds Phillips Head Screwdriver
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14
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15 Remove idle adjustment screw and spring

Easy

10 Seconds Phillips Head Screwdriver
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16 Remove lower choke cap

Easy

5 seconds Phillips Head Screwdriver
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17 Removing the throttle disc

Easy

20 Seconds Phillips Head Screwdriver and Needle-Nose Pliers
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18 Removing a governing screw from the choke

Easy

5 seconds No tools
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19 Assembled Side View of choke

N/A

N/A N/A
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20 Assembled view of trigger and throttle cable

N/A

N/A N/A
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21 View of internal end of the throttle cable

N/A

N/A N/A
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22 Remove the plastic engine housing via 4 Allen screws

Easy

2 Minutes Allen Key Set
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23 Remove Engine from housing via several Allen screws and bolts

Easy

2 Minutes Allen Key Set
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24 View of the top of the engine with upper housing removed

N/A

N/A N/A
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25 View of engine showing wire to be disconnected

N/A

N/A N/A
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26 Second view of engine showing wire to be disconnected

N/A

N/A N/A
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27 Remove cable covering spark plug and disconnect spark generator from engine via connecting bar/2 Allen screws

Easy

25 seconds Allen Key Set
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28 View of disconnected spark generator

N/A

N/A N/A
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29 View of connecting rod and 2 Allen screws

N/A

N/A N/A
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30 Remove gas tank housing from other exterior housing via several Allen screws

Easy

40 seconds Allen Key Set
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31 Remove engine from housing via 4 Allen screws

Easy

40 seconds Allen Key Set
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32 Underside view of detached engine, showing muffler, cylinder, and gasket

N/A

N/A N/A
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33 Remove spark plug and detach cylinder/muffler from flywheel via 2 Allen screws

Easy

25 seconds Allen Key Set
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34 View of two Allen screws connecting cylinder to flywheel

N/A

N/A N/A
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35
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36
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37
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38
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39
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40
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41
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42
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43
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44
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45
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46
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47
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48
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After Disassembly

Part Table, including:

Part # Part Quantity Material Manufacturing Process Picture CAD file
1 Gas Tank/Housing 1 Plastic Injection Molding
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2 Choke assembly 1
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3 Engine Housing 1 Plastic Injection Molding
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4
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5 Coil Spring/Housing 1 Steel/Plastic Coil Spring: Rolling/Bending

Housing: Injection Molding

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6 Handle 1 Plastic Injection Molding
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7 Inner choke housing 1 Plastic Injection molding
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8 Reel Guard 1 Plastic Injection Molding
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9 Choke Housing 1 Plastic Injection Molding
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10 Trigger Handle 1 Plastic Injection Molding
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11
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12
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13
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14
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15
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16 Cutting Head 1 Plastic Injection Molding
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17 Choke Selector Lever 1 Aluminum Stamped
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18 Coil Spring housing 1 Sheet-Steel Stamped
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19
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20 Throttle Trigger 1 Plastic Injection Molding
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21
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22
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23
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24
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25
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26
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27
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28
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29
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30
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31
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32
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33
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34
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35
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36
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37
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38
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39
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40
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Assembly

Assembly was fairly straightforward, though some of the steps had varying levels of difficulty. The assembly steps were as follows:

  1. Re-house the coil spring into the front plastic housing
    • Very difficult to correctly position spring. The housing process took more than a dozen trials.
    • Tools used:
      • Needle-nose pliers
      • Pliers
      • Flathead screwdriver
      • Small butterfly binder clips
    • Time spent: approximately 12+ man hours.
  2. Fit the reel with nylon string into place.
    • Difficult to correctly align with internal coil spring.
    • Tools used:
      • Phillips-head screwdriver
      • Needle-nose pliers
    • Time spent: roughly 15 minutes on successful trial.
  3. Piece engine together, attach to reel
    • Fairly easy to fit together from spark plug to piston, some lubrication lacking.
    • Grease applied where needed, engine needs two-stroke fuel priming.
    • Tools required:
      • Hex key
      • Adjustable wrench
    • Time spent: 20 minutes after some trial and error with confusing bolts.
  4. Piece together choke
    • Moderately difficult due to small parts and spring-loaded assembly, but quick to fix small errors.
    • Tools required:
      • Hex key
      • Needle-nose pliers
      • Phillips-head screwdriver
    • Time spent: 30 minutes
  5. Assemble housing
    • Very easy once we identified bolt/screw positions.
    • Tools required:
      • Hex key
      • Phillips-head screwdriver
    • Time spent: 15 minutes
  6. Attach guard, reel and handle to pole
    • Easy to piece together and adjust.
    • Tools required:
      • Wrench
      • Pliers
      • Phillips-head screwdriver
    • Time spent: 10 minutes
  7. Attach pole to housing, and throttle cable to choke.
    • Easy to piece together.
    • Tool required:
      • Hex key
    • Time spent: 5 minutes

After Assembly

  • Does it still work?
  • Conclusion remarks

Engineering Analysis

  • “Explain how analyses could be used to design and test your product (or some of its components). What type of basic engineering models could be used? Could you use estimates or would you need very precise models?”
  • For this issue, you need to discuss what kind of engineering models you could use to design your product. We went through a number of different models types in class (semantic, graphical, analytical, physical). While you could comment on the use of semantic, graphical, and physical models in the design of your product, I am more interested in the use of analytical (mathematical) models. You should address what kind of mathematical engineering models could be used to design your product. You need to consider what kind of engineering science principles are critical to the operation of your product. Some examples could include fatigue models, circuit models, power transmission models, thermodynamics/heat transfer models, fluid flow models, static loading models, material stress/strain models, etc. You don’t need to develop those models, but should discuss what kind of models are necessary and explain why you think those models are necessary and how they could be applied to your product.

References

APA Style You must use this format (It's easier than MLA, so don't worry).