Difference between revisions of "Group 27 - Weed Wacker"

From GICL Wiki
Jump to: navigation, search
Line 433: Line 433:
 
|-
 
|-
 
| align="center" |44
 
| align="center" |44
| align="center" |
+
| align="center" |View of detached reel/rope from housing
| align="center" |
+
 
| align="center" |
+
N/A
 +
| align="center" |N/A
 +
| align="center" |N/A
 
| align="center" |[[Image:SPA55157.JPG|center|thumb|100px]]
 
| align="center" |[[Image:SPA55157.JPG|center|thumb|100px]]
 
|-
 
|-
 
| align="center" |45
 
| align="center" |45
| align="center" |
+
| align="center" |After reel is detached, remove coil spring HOUSING OR COVER, NOT SURE WHAT TO CALL IT to reveal coil spring
| align="center" |
+
 
| align="center" |
+
Easy
 +
| align="center" |5 seconds
 +
| align="center" |No Tools
 
| align="center" |[[Image:SPA55158.JPG|center|thumb|100px]]
 
| align="center" |[[Image:SPA55158.JPG|center|thumb|100px]]
 
|-
 
|-
 
| align="center" |46
 
| align="center" |46
| align="center" |
+
| align="center" |View of housing where coil spring/reel rested
| align="center" |
+
 
| align="center" |
+
N/A
| align="center" |[[Image:SPA55159.JPG|center|thumb|100px]]
+
| align="center" |N/A
 +
| align="center" |N/A
 +
| align="center" |[[Image:SPA55160.JPG|center|thumb|100px]]
 
|-
 
|-
 
| align="center" |47
 
| align="center" |47
| align="center" |
+
| align="center" |Finally, remove shaft/cable line from housing via CANT REMEMBER HOW IT WAS CONNECTED
| align="center" |
+
 
| align="center" |
+
Easy
| align="center" |[[Image:SPA55160.JPG|center|thumb|100px]]
+
| align="center" |15 seconds
 +
| align="center" |NOT SURE
 +
| align="center" |[[Image:SPA55159.JPG|center|thumb|100px]]
 
|-
 
|-
 
|}
 
|}

Revision as of 23:46, 4 December 2008

Contents

Executive Summary

SPA55014.JPG

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/ Wiki Editing

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

SPA55014.JPG
SPA55015.JPG
SPA55016.JPG
SPA55017.JPG
SPA55018.JPG
SPA55019.JPG
SPA55020.JPG
SPA55021.JPG
SPA55022.JPG
SPA55023.JPG
SPA55024.JPG
SPA55025.JPG
SPA55026.JPG
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
SPA55014.JPG
1 Disconnect reel guard from shaft via two screws

Easy

20 seconds Phillips Head Screwdriver
SPA55027.JPG
2 Disconnect reel head from shaft via SCREW?

Easy

10 seconds PHILLIPS HEAD?
SPA55028.JPG
3 Remove trigger handle from shaft via four screws

Easy

40 seconds Phillips Head Screwdriver
SPA55029.JPG
4 Remove throttle cable from trigger handle

Easy

5 seconds No tools
SPA55030.JPG
5 View of throttle cable attached to choke

N/A

N/A N/A
SPA55031.JPG
6 Remove choke housing from main housing

Easy

20 seconds Phillips Head Screwdriver
SPA55032.JPG
7 Remove air filter to expose choke cover

Easy

2 seconds No tools
SPA55033.JPG
8 Remove interior choke cover and selector

Easy

20 Seconds Allen Key Set
SPA55034.JPG
9 View of interior choke cover and selector

N/A

N/A N/A
SPA55035.JPG
10 Remove choke from engine via Allen screws

Easy

20 seconds Allen Key Set
SPA55036.JPG
11 Disconnect throttle cable from choke

Easy

2 seconds No Tools
SPA55037.JPG
12 View of choke cover connected via screws

N/A

N/A N/A
SPA55038.JPG
13 Remove top choke cover

Easy

40 seconds Phillips Head Screwdriver
SPA55039.JPG
14 Remove idle adjustment screw and spring

Easy

10 Seconds Phillips Head Screwdriver
SPA55041.JPG
15 Remove lower choke cap

Easy

5 seconds Phillips Head Screwdriver
SPA55043.JPG
16 Removing the throttle disc

Easy

20 Seconds Phillips Head Screwdriver and Needle-Nose Pliers
SPA55044.JPG
17 Removing a governing screw from the choke

Easy

5 seconds No tools
SPA55046.JPG
18 Assembled Side View of choke

N/A

N/A N/A
SPA55040.JPG
19 Assembled view of trigger and throttle cable

N/A

N/A N/A
SPA55128.JPG
20 View of internal end of the throttle cable

N/A

N/A N/A
SPA55129.JPG
21 Remove the plastic engine housing via 4 Allen screws

Easy

2 Minutes Allen Key Set
SPA55130.JPG
22 Remove Engine from housing via several Allen screws and bolts

Easy

2 Minutes Allen Key Set
SPA55131.JPG
23 View of the top of the engine with upper housing removed

N/A

N/A N/A
SPA55132.JPG
24 View of engine showing wire to be disconnected

N/A

N/A N/A
SPA55134.JPG
25 Second view of engine showing wire to be disconnected

N/A

N/A N/A
SPA55137.JPG
26 Remove cable covering spark plug and disconnect spark generator from engine via connecting bar/2 Allen screws

Easy

25 seconds Allen Key Set
SPA55139.JPG
27 View of disconnected spark generator

N/A

N/A N/A
SPA55140.JPG
28 View of connecting rod and 2 Allen screws

N/A

N/A N/A
SPA55141.JPG
29 Remove gas tank housing from other exterior housing via several Allen screws

Easy

40 seconds Allen Key Set
SPA55142.JPG
30 Remove engine from housing via 4 Allen screws

Easy

40 seconds Allen Key Set
SPA55143.JPG
31 Underside view of detached engine, showing flywheel, muffler, cylinder, and gasket

N/A

N/A N/A
SPA55144.JPG
32 Remove spark plug and detach cylinder/muffler assembly from flywheel via 2 Allen screws

Easy

25 seconds Allen Key Set
SPA55146.JPG
33 Disassembled view of cylinder/muffler, showing spark plug, spark plug ring, and two Allan screws

N/A

N/A N/A
SPA55153.JPG
34 View of two Allen screws connecting cylinder to flywheel

N/A

N/A N/A
SPA55145.JPG
35 Remove INSULATOR? from cylinder via 2 Allen screws

Easy

20 seconds Allen Key Set
SPA55147.JPG
36 View of detached cylinder/muffler assembly

N/A

N/A N/A
SPA55148.JPG
37 View of piston connected to crankshaft

N/A

N/A N/A
SPA55149.JPG
38 Alternate view of piston/crankshaft along with gasket

N/A

N/A N/A
SPA55150.JPG
39 Underside view of CRANKSHAFT?

N/A

N/A N/A
SPA55151.JPG
40 Remove piston from crankshaft

Easy

5 seconds No Tools
SPA55152.JPG
41 View of housing/components after engine was removed

N/A

N/A N/A
SPA55154.JPG
42 Closer view of reel/rope to be removed

N/A

N/A N/A
SPA55155.JPG
43 Remove reel via 2 bolts and rope via small screw/nut

Easy

30 seconds Phillips Head Screwdriver
SPA55156.JPG
44 View of detached reel/rope from housing

N/A

N/A N/A
SPA55157.JPG
45 After reel is detached, remove coil spring HOUSING OR COVER, NOT SURE WHAT TO CALL IT to reveal coil spring

Easy

5 seconds No Tools
SPA55158.JPG
46 View of housing where coil spring/reel rested

N/A

N/A N/A
SPA55160.JPG
47 Finally, remove shaft/cable line from housing via CANT REMEMBER HOW IT WAS CONNECTED

Easy

15 seconds NOT SURE
SPA55159.JPG

After Disassembly

Part Table, including:

Part # Part Quantity Material Manufacturing Process Picture CAD file
1 Gas Tank/Housing 1 Plastic Injection Molding
SPA55169.JPG
2 Choke Assembly 1 Steel and Aluminum Stamping/Machining
SPA55170.JPG
3 Engine Housing 1 Plastic Injection Molding
SPA55171.JPG
4 Spark Plug Line and Assembly 1 Plastic Injection Molding
SPA55172.JPG
5 Coil Spring/Housing 1 Steel/Plastic Coil Spring: Rolling/Bending

Housing: Injection Molding

SPA55173.JPG
6 Handle 1 Plastic Injection Molding
SPA55174.JPG
7 Inner choke housing 1 Plastic Injection molding
SPA55175.JPG
8 Reel Guard 1 Plastic Injection Molding
SPA55177.JPG
9 Choke Housing 1 Plastic Injection Molding
SPA55178.JPG
10 Trigger Handle 1 Plastic Injection Molding
SPA55179.JPG
11 Motor Assembly 1 Steel Casting and Machining
SPA55180.JPG
UB08G27 Motor assembly final.jpg
12 Piston Assembly 1 Steel Casting and Machining
SPA55181.JPG
UB08G27 Piston assembly 08.jpg
13
SPA55182.JPG
14
SPA55183.JPG
15
SPA55184.JPG
16 Cutting Head 1 Plastic Injection Molding
SPA55185.JPG
17 Choke Selector Lever 1 Aluminum Stamped
SPA55186.JPG
18 Coil Spring housing 1 Sheet-Steel Stamped
SPA55187.JPG
19
SPA55188.JPG
20 Throttle Trigger 1 Plastic Injection Molding
SPA55189.JPG
21
SPA55197.JPG
22
SPA55191.JPG
23
SPA55192.JPG
24
SPA55193.JPG
25
SPA55194.JPG
26
SPA55195.JPG
27
SPA55198.JPG
28 Air Filter Support 1 Aluminum Stamped
SPA55199.JPG
29
SPA55200.JPG
30
SPA55201.JPG
31
SPA55202.JPG
32
SPA55203.JPG
33
SPA55204.JPG
34
SPA55205.JPG
35
SPA55206.JPG
36
SPA55207.JPG
37 Pull Start Reel 1 Plastic Injection Molded
SPA55208.JPG
38 Pull Start Line and Handle 1 Plastic Injection Molded
SPA55209.JPG
39 Reel Attachment Hardware 1 Steel Machined and Stamped
SPA55210.JPG
40 1 Plastic Injection Molded
SPA55211.JPG

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

Final Function

We were once again unable to secure a source of fuel for testing our Weed Eater.

Concluding Remarks

After more than 30 man hours of work, we were successful in reassembling our Weed Eater. In retrospect, this project was straightforward in theory, though difficult in practice. Disassembly was not very complicated, and we were able to finish within two hour-long sessions. There were a large number of parts, some of which we grouped together for ease of differentiation among their types. The most hazardous part of disassembly was removing the coil spring, which released tension on us very suddenly. Aside from that, it was a smooth process.

Reassembly, however, was a different story. It was easy to understand what we needed to do by simply reversing the process according to the extensive pictures we took. The initial steps proved to be a challenge for us. We spent far too much time trying to re-coil the coil spring: three meetings with four people per meeting, dozens of successful re-coils but unsuccessful placements, many minor fixed damages, a call to Weed Eater support, and much frustration later, we were able to re-seat the coil spring where it was supposed to go.

Beyond this major reassembly setback, the rest of our operation went smoothly. We decided to add a touch of grease to let the flywheel spin more freely. Cosmetically, the Weed Eater looks markedly similar to its initial state, with the same two missing fingers as it had when we began. Functionally, the Weed Eater seems to behave the same way as far as we know. Perhaps the only noticeable difference is the pull cord's incomplete retraction, our final penalty for our extended troubles with the coil spring. Assuming one can pull fast enough, the cord will still work, at least in theory. The single cylinder will need fuel/oil priming before its first reassembled run-- we were not able to add any sort of oil or gas to the product as stated previously. The pull string retracts and spins the flywheel, and upon a pull, one can feel and hear the piston compressing the cylinder's air.

In retrospect, this project was much more difficult and time consuming than we initially imagined. For future disassembly projects, we would not recommend this product without a simpler way to safely re-house and re-coil the coil spring.

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).