Gate 2 - Product Dissection.
Cause for Corrective Action
Upon review of Gate 1, our group feels satisfied with our management and work plans. So far, they have worked as we hoped they would have. Our meeting times have worked out well, and this is mainly because we left a certain amount of flexibility for when we would actually meet. In our original Management Proposal, we had stated "we will decide at our Monday meeting which available chunk of lab time will be best for that particular week." This has worked great, because it allows us to choose a time when all members will be able to meet, as opposed to scheduling a meeting way in advance and having certain members missing due to unforeseen obligations. Sitting together in class each day has also helped us stay connected so each member of the group is aware of what the other members are doing.
Our work proposal was also very accurate. When we met to disassemble our leaf blower, we were able to follow the steps that were outlined in our work proposal very closely. Because of this, we stayed on schedule, and we were able to finish our dissection in roughly two and a half hours which is exactly what we had anticipated.
Conflicts to this point have been at a minimum. We seem to be getting along well as a group with no major problems. Constructive criticism has been very helpful in our group because it allows one member to make suggestions for improvement on what somebody else has done without angering that person. For future gates, we would like to utilize constructive criticism more by giving every member a chance to edit somebody else's work before it is posted to the wiki. Previously, one person would work on something and send it straight to the group leader to be turned in.
Although we are happy with how the group is interacting, we were disappointed with our grade for gate 1. As a group, we have decided that we would like to strive for higher quality work in the future. We do not feel that the our grade on the first gate was due to a problem with either the Work Proposal or Management Proposal, but rather an individual lack of understating for exactly what was expected for each part. Most of our points were lost to lack of detail and explanation, so we will focus more on small details in the future. To help with gathering details, each member of the group will have a chance to alter what somebody else has done (add more detail), in order to make it better. Also, detailed notes will be taken while we are actually working on the leaf blower rather than using bullets and then trying to fill in the details at a later time.
In conclusion, it is fair to say that we definitely have room for improvement when it comes to the final product that we turn in, but we are happy with our interactions and we have no unresolved challenges at the current time. For future gates, we plan to make improvements on an individual level more than on a group level.
Tools Required for Disassembly:
- Flathead Screw Driver
- Phillips Screw Driver
- 20 Piece Metric Standard Hex Key Set (Allen Wrenches)
- Standard 6 Point Screw Driver
- ½ inch Combination Wrench
Instructions for Disassembly:
Difficulty Rating: The difficulty rating for each step ranges from 1 - 3. In this scale, a "1" is the most simple and usually consists of just screwing a component in place. Similarly, a "3" is the most difficult and could require a significant amount of time and problem solving. The difficulty scale has been formed specifically for this leaf blower meaning no step would be harder than a "3", or easier than a "1".
Note: It should be noted that when we considered whether or not a component was meant to be removed, we analyzed from the stand point of an average user. Just because two components are held together with removable fasteners doesn't mean that the designers intended for an average user to take them apart. However, a trained mechanic who regularly takes things apart would be able to perform the disassembly with relative ease, completing the process in about an hour with the proper tools.
NOTE: One should plan to spend one to two hours when disassembling this leaf blower. Depending on problems faced, up to two and a half hours may be required.
Some of the Challenges Faced During the Dissection Include :
1. When disassembling the spring housing from the engine block, the spring fell out of its casing. A picture can be seen by clicking on "Uncoiled Spring". Because the spring was wound so tightly in the housing, it was very difficult to fit back into the casing. The spring is wound in a circular housing, and because the spring’s metal is so hard, it requires a lot of force to wind it back into its original shape. To overcome this challenge, we wound the spring a few inches at a time, taping it at every stopping point. This allowed the spring to remain in its circular shape until it was completely wound.
2. Another challenge faced was in our prediction of the order of disassembly. We had predicted that the handle was to be the second thing removed, after the air tube. After unscrewing the screws that held the handle in place, we found that the handle was still unable to be removed. We then noticed that it was also held in place by the plastic engine casing and that the casing must be removed before the handle is removed. To overcome this challenge, we removed the plastic engine casing and the handle was easily removed after.
3. There were also some instances where we were not exactly sure of the next step in the disassembly, and it took us several minutes to figure out. Although it never took us very long to figure any steps out, this poses as a problem for people who are not very familiar with engines. One example of such an instance was figuring out how to remove the piston from the crank shaft. Although they are just pinned together, it required some inspection to complete this step.
4. Time in the Lab was also a small problem. Because it did not take as long to disassemble each piece as it did to document each step, it was difficult to stay together. If the person taking the blower apart was moving too fast, the write up would be missing essential details. We dealt with this problem by communication with each other making sure each step was properly documented before moving to the next one. Although this made the process take longer, it allowed us to be more thorough and complete.
Connection of Subsystems:
The leaf blower consists of several subsystems that are connected together in a variety of ways. Through these connections, the different components work in unison to form a controlled stream of air that can be used to fulfill the overall function of the device: to blow leaves and debris.
The Individual Subsystems Acting:
- The Handle
- The Tube
- The Throttle and Primer Unit
- The Combustion Chamber
- The Piston
- The Crankshaft
- The Fan
1.) The handle is connected to the tube.
2.) The throttle/primer unit is connected to the combustion chamber
3.) The combustion chamber is connected to the piston
4.) The piston is connected to the crankshaft.
5.) The crankshaft is connected to the fan
6.) The fan is connected to the tube.
The General Arrangement / Location of Subsystems:
The general arrangement of the subsystems in the leaf blower rely heavily on what its function is. In general, each subsystem is placed next to a subsystem that it interacts with, as shown in Figure 1. A detailed description of each subsystem's location can be found below.
Individual Assessment of Subsystem Location:
1.) The handle is physically connected to the tube by the plastic housing surrounding the engine. Both of these subsystems are connected to housing, so they will move as a single unit. When the user inputs a signal (direction) into the handle, the tube points in that direction causing the air to blow the way the user wants it to. This particular connection is implemented by screwing a series of molded plastic parts together with metric sized allen head screws. This connection could have been influenced by a series of concerns including global, economic, and societal factors. A global aspect that was considered was where the product would be sold and used. We know this because the manufacturer used metric screws which are used all over the world as opposed to English sized screws which would generally only be used in America. One economic concern that would have been important is cost of production. Using plastic to connect these two subsystems would be much cheaper than something like metal would be. It should also be mentioned that plastic would be well suited for this connection, because it will not be exposed to high levels of stress or strain. The connection of the tube to the handle addresses societal concerns by making use of the product easy for the consumer in several ways. First, using plastic to manufacture the handle, tube and engine housing reduces the weight of the unit. Also, because these two components are connected directly to the housing, the whole unit moves as one, making use very self explanatory for the operator.
2.) The throttle and primer are physically connected to the combustion chamber by two small rubber hoses that allow for a mixture of gasoline and air to enter the engine. Signals are also transmitted through this connection in the form of the amount of gas entering the combustion chamber. This is determined by human signal at the throttle. Mass and chemical energy are also transferred through the tubes in the gasoline. These two subsystems have to be connected because the engine relies on information from the throttle to run at a level desired by the operator. As previously stated, this particular connection is implemented by two small rubber hoses. Because high performance is not needed, rubber will work fine as opposed to a more expensive material such as stainless steel. This connection was mainly based on economic factors. The rubber tubing is cheap to produce, and easy to assemble which is why designers would have favored this type of connection.
3.) The combustion chamber is connected to the piston mainly through the transmission of energy. The piston is located in the combustion chamber, but they are not physically connected together. This connection is necessary because it harnesses the energy from the burning gasoline so it can be converted into rotational energy. This connection is implemented in the form of a metal piston housed in the engine casing. Environmental and societal concerns were likely considered when designing this connection along with a strong influence from the performance required. These two parts are made of metal because they need to withstand high amounts of heat, vibration, and stress. For this reason, a material like plastic would not be appropriate. Using a material that does not emit harmful chemicals when exposed to high heat would have been an environmental concern that was considered. Societal concerns that influenced this connection are related to the user. Because these parts are durable and rigid, they are safe for the user and there is almost no chance that they will unintentionally become separated.
4.) The piston is physically connected to the crankshaft. As the piston moves up and down, it rotates about the crankshaft creating a rapid rotation. These two components are connected for the sole reason of transferring the energy from the burning gas into rotational energy acting along the crankshaft. The piston rod is connected to the crank shaft using a small metal pin. This pin is very durable as, again, this component is subject to high amounts of motion and heat. Economic and societal factors likely influenced the design of this connection. The use of a small pin that can be easily manufactured provides for cheap assembly. This makes the overall cost of the leaf blower cheaper for the consumer and the manufacturer. The durability of this piece is in the best interest of the user because it is safe, and it should not require any maintenance. Providing a product that is reliable will significantly improve the user’s attitude towards the product, its reputation, and therefore, future purchases of the product.
5.) The connection between the crankshaft and the fan is very simple. The end of the crank shaft is a half cylinder, and the fan is molded to snap directly onto it. This again makes assembly very cheap and easy. Signal is transferred through this connection in the form of a maintained speed from the crank shaft. The rotational energy from the crank shaft is also transmitted to the fan. The main factor addressed here is the economic concern of cost. Because the plastic fan is not subject to a high level of stress, this simple connection will work fine.
6.) The connection between the fan and the tube is in the form of signal and energy. The fan is placed at the opening of the tube, but the two components are not physically connected. Pneumatic energy is transferred from the fan into the tube. Signal is also transferred from the fan to the tube in the form of speed. The speed that the fan rotates is directly related to the speed of the air forced into the tube. This connection addresses both environmental and economic concerns. Because no excess material was used to mount the fan to the end of tube, less plastic is used in production. The apparatus may have been physically stronger if it were braced to the end of the tube, but designers felt that the products durability would be high enough without it considering high performance is not a necessity here. Because less material is used, the unit is cheaper, and it has a smaller impact on the environment when the unit is discarded. Although it seems like a small amount of plastic, many leaf blowers are produced, and these materials accumulate quickly.
There are a few subsystems on the leaf blower that cannot be placed next to each other. The combustion chamber cannot be adjacent to the tube because the tube is plastic and the heat produced from the burning gas would melt the tube. In addition to this, the fan should be placed nowhere near the throttle or choke. This is because it is extremely dangerous to put parts that require user interaction next to fast moving parts. These same safety concerns can be applied to the spinning of the crankshaft. The further these parts are from the user, the better.