Group 17: Gate 2: Product Dissection
Using the groundwork laid out in Gate One, we have now dissected the line trimmer. In this gate, we have documented the entire process, as well as the obstacles we encountered within it. Additionally, we evaluated how successfully we followed our original plans, along with any adjustments we have had to make to them.
Project Management: Preliminary Project Review
Cause for Corrective Action
- The first challenge in dissecting the weed whacker was gaining access to space in the dissection lab. There was a limited amount of time that the group was available to work together. When the group finally assembled in the lab, it was full with zero table space available. So, we found space outside of the lab in the hallway and went to work on the floor.
- Snap rings were not expected to be used in the production of the weed whacker, so the need for snap ring pliers was also unexpected, and thus they were inaccessible. In order to remove the snap rings a flat head screw driver was used to pry the snap ring out of its housing. The snap rings were bent and destroyed, but their removal was necessary for complete dissection of the weed whacker.
- In Gate 1, there was a miscommunication as to who would be doing the final draft. This caused the group to be rushing through that part of the project. We fixed this for Gate 2 by giving each person a specific part to be working on along with dates to have them completed by. The group was able to get much more accomplished through this method.
Product Archaeology: Product Dissection
Parts Not Intended for Removal
- Fuel Lines
- The fuel lines are not intended to be separated from the carburetor, or fuel tank, without being cut or ripped. The reasoning being that if they need to be replaced they can be cut or ripped off. As a result, in order to remove the gas tank and carburetor completely from the rest of the engine, the fuel lines needed to be cut using a pair of wire cutters.
- The Piston and Crank Shaft
- The piston arm is attached to the bottom of the piston head on one end, and was attached to the drive shaft on the other. The piston arm was attached to the drive shaft using a pressed fitting, preventing the removal of both the piston from the chamber, and crank shaft from it housing. Being that a press was not readily available in the dissection lab, the piston arm needed to be bent off of the crank shaft with a hammer allowing for the crank shaft to be removed, and subsequently allowing for the piston to be removed.
- The Fly Wheel
- The fly wheel is fit tightly to the crank shaft in order to prevent it from falling off during use. A press was required for proper removal. However a hammer was used instead to force the fly wheel free from the crank shaft.
Ease of Dis-assembly The overall dissection of the weed whacker was relatively simple. There were a few times when multiple tools were required to take it apart. In some instances the screws were extremely tight and took patience to remove. The difficulty of removing each part of the weed whacker is measurable in accordance with the scale detailed below:
- Red will be used for the most difficult tasks. These tasks required three or more people involved, using a combination of tools and in some cases strength.
- Blue will be used for above average tasks. These required one to two people involved and using one or a combination of tools.
- Green will be used for easy tasks. These required only one person and only one tool.
- Note: Some steps might not fit exactly within the criteria of the scale but just were simply much more difficult for no obvious reason.
The fact that the weed whacker was primarily assembled using Torx screws and Philip head screws indicates it was meant to be able to be taken apart. However, many parts were not intended to be able to be taken apart. Based on the difficulty of removing the fuel lines, piston, crank shaft, and the fly wheel were not intended to be removed. here
- T15 Torx screwdriver
- Phillips #2 screwdriver
- ¼” Socket wrench
- Snap ring pliers
- Note: if a press is not available and the weedwacker does not need to be reassembled, the parts can be removed by leverage and brute force.
- Step 1 – Remove shaft assembly from motor casing by removing 2 Torx screws and pulling them apart.
- Step 2 – Disassemble the shaft assembly into two separate parts, the straight shaft and the curved shaft. This is held together with a single Torx screw. The foam grip can then slide off of the shaft.
- Step 3 – Remove the handle on the top part of the shaft by unscrewing a single wing nut.
- Step 4- Remove the deflector shield from the shaft using a ¼” socket wrench.
- Step 5 – The spool head of the weedwacker on the bottom of the shaft has a cap that unscrews. Unscrewing this will allow 4 parts to separate, the shaft, spool casing, spool, and cap.
- Step 6- The motor casing has two parts, one red and one black. Separate them by removing the torque screws around their edge.
- Step 7 – Once the cases are off, the throttle cable can be removed my hand.
- Step 8 – The gas tank is held in by one Torx screw. Once unscrewed the gas lines must be detached so that the tank can separate from the motor.
- Step 9 – The crankcase cover has 6 Torx screws holding it in place. Once these are removed, lift it away to reveal the crankshaft, counterweight and piston connecting rod.
- Note: The screws were on extremely tight making this much more difficult then usual.
- Step 10 – The muffler assembly can be taken off with two #2 Phillips screws. This removes the muffler, muffler gasket, and heat shield from the motor.
- Step 11 – The air box and air box cover is held in by one Torx screw. Unscrewing this will allow for the removal of the part.
- Step 12 – A gasket is located on the opposite side of the primer bulb on the carburetor that can be pried off.
- Step 13 – The carburetor assembly can be removed by unscrewing two Torx screws and lifted off the rest of the motor.
- Step 14- Remove the ignition module by removing the single Torx screw holding it in place and pulling it away. Also, be sure to disconnect the spark boot from the spark plug.
- Step 15- Remove the spark plug using a ¼” socket wrench
- Step 16- Remove the centrifugal clutch assembly by twisting it off using vice grips, while bracing the motor block.
- Step 17- Remove starter assembly by removing snap rings on crankshaft and lifting off.
- Step 18- Remove flywheel
- Note: a press would be required to properly remove flywheel, however we were able to remove by means of leverage and brute force
- Step 19- Disassemble starter assembly into five parts. They can be taken apart by hand.
- Step 20- Remove piston and crankshaft
- Note: piston and crankshaft were only possible to remove using brute force and would not be removed during a normal dis-assembly
- The Driveshaft is sealed inside shaft assembly, and removing it would require cutting through the entire assembly. We assumed it is a cable drive due to the uniform diameter of the shaft assembly, leaving no space for a universal joint. Also, because the shaft operates at a constant angle, there would be no reason to justify the cost of a CV joint.
- All Torx screw heads are T15
- Motor Assembly
- Motor Block
- Spark plug
- Crankcase cover
- Air box
- Air box cover
- Fuel cap
- Throttle cable
- Starter Assembly
- Gas Tank
- Carburetor Assembly
- Centrifugal Clutch
- Ignition Module
- Crankshaft and counterweight
- Shaft assembly
- Straight Shaft
- Curved Shaft
- Foam Grip
- Spool head assembly
- Spool casing
- Deflector Shield
- Handle w/ trigger
- Motor Casings
Subsystems of the Weedwacker
Connections between the subsystems
- The safety system is connected to the fuel system
- The safety system is physically connected to the fuel system by way of a safety trigger that must be pressed in order to open the throttle. The safety trigger and throttle are both located in a housing on the shaft of the weed whacker. There is a hook that is attached to the safety trigger that does not allow the throttle trigger to be pulled. In order to move this hook out of the way the safety trigger must be pressed in order to engage the throttle. The housing holds the triggers in place. The housing is held together by standard bolts with TORX heads on them.
- The fuel system is connected to the motor
- The fuel system is connected to the motor by cables that are connected to the throttle trigger. There is a cable that runs from the housing to the carburetor, which is located on the motor. When the trigger is pulled the throttle is opened and fuel flows from the fuel tank into the carburetor (mass). The fuel then flows into the cylinder (mass) of the motor where it is ignited by the spark plug, where compression is created (energy). As a result of the compression, the piston moves inside the cylinder and causes the crankshaft to spin.
- The motor is connected to the power transfer system (the cable in the shaft that makes the head turn)
- The motor is connected to the power transfer system because the crank shaft and cable both meet in a housing located at the end of the shaft that is connected to the motor. The crankshaft then spins the cable which transfers power (energy) down the shaft of the weed whacker.
- The power transfer system is connected to the head of the weed whacker
- The power transfer system is connected to the head of the weed whacker by way of a male/female connection. The square male end of the cable fits into the square female end of the head which allows energy to be transferred to the head of the weed whacker, causing it to spin and cut weeds.
These subsystems are all connected so that energy can be created by the ignition of gasoline, then energy can be transferred from the motor to the head of the weed whacker, and then the head of the weed whacker can spin. Basically, the subsystems are connected so that the weed whacker can function correctly.
- This whole system is meant to use gasoline and other types of fuels to decrease the amount of labor that has to be done. This would make it as a focus of first world countries, where the use of gasoline to lower labor is used quite often.
- The safety system was influenced by society because it would appeal to the consumer more if they knew they were buying a safer product. It is most likely a marketing strategy that is playing on what society wants.
- The subsystems are all relatively simple and made with cheap materials so that the product can be sold at a cheaper price. Plastic and steel can all be used at a relatively cheap price. There is also no complicated assembly work involved with this weed whacker. A weed whacker of this type can be bought for 50 dollars on sale for this reason. In addition, the weed whacker subsystems are all efficient enough that a small amount of fuel is used. This allows for cheaper operation because fuel is the main cost of operation.
- The motor subsystem uses such a small amount of fuel that it is not really of environmental concern when people consider the output of greenhouse gases that cars and power plants cause. In addition, none of the subsystems contain any
Performance and Connection
- The connections need to be as efficient at transferring energy as possible so there is less fuel consumption
- The connections also need to be made in a way that failure will not be a common occurrence. This is the reason for simple, mechanical wires. If these were to fail commonly, performance could be hindered.
- The connection between the engine and the head is a steel chord going through the metal shaft. This chord has to be strong enough to have the amount of resistant torque the head would endure in usage.
Arrangement of Subsystems
- The safety system and throttle trigger are located near the center of gravity of the weed whacker for ease of use. The fuel tank and system are located in such a manner that gravity will allow gasoline to flow through the carburetor into the engine. The motor is located in such a fashion that the crankshaft is pointing in the same direction as the cable that transfers energy to the head of the weed whacker so that the cable and crank shaft can meet inside of the housing described previously. The cable is curved for ease of use so that the head can point downward and be used in an ergonomic way.
- The reason for the arrangement of the subsystems is such that the weed whacker is easy to use and balanced. The subsystems are also arranged in such a manner that allows each subsystem to sequentially do its job in order to transfer energy from gasoline, to the motor, down the cable/shaft, and into the head of the weed whacker.
- All of the subsystems could be adjacent, but if some of the subsystems were near each other than the weed whacker would be unbalanced and unpleasant to use. The way that the subsystems are arranged now is most likely the best arrangement. It would not be very smart if the throttle trigger and safety trigger were near the head because that would be placing the users hand in danger. Other than this the subsystems could theoretically be placed near each other