Group 11 - Dual Stage Snow Thrower (Gasoline Powered) - Gate 2

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Preliminary Project Review

\'\'\'Changes to Disassembly Plan:\'\'\'

1) Disassembly of the Snow Blower took around 4 hours instead of the estimated 8.
2) The Impeller, Recoil Starter, Engine Block, and Fuel Tank proved unfeasible to remove from the frame with simple hand tools. Power tools of the needed configuration were unavailable.
3) The Fuel Tank and Fuel Lines were already drained prior to the start of disassembly. Hence, Step One was unnecessary.
4) We found it necessary to break down the Chassis prior to removing the pulley system.
5) Power tools were unavailable, and along with the Lubricating Oil were not used in disassembly.
6) Meeting on the weekends for disassembly was not possible because of the hours the Dissection Lab was open. Instead, the group convened on Mondays, 10/15/2012 and 10/22/2012.

\'\'\'Methods to address future obstacles:\'\'\'

We will have to be careful when reassembling, especially with rustier parts. There are also many nearly-identical screws and washers, which will require us to be meticulous to ensure that the reassembled snow thrower will work properly.
Also, our collective experience with 3-D modeling, and manufacturing, is somewhat limited.

Process of Disassembly

Step Zero.jpg

\'\'\'Difficulty levels\'\'\'

1-star: Removal presents little difficulty to the Technical Experts. The arrangement of parts is consumer-friendly and facilitates ease of service.
-Gas Cap
-Trigger Line
-Hand Crank

2-star: Small obstacles hinder the disassembly process. Placement of fastenings is awkward or the fastenings have rusted together, and some maneuvering is required to remove the parts from the machine. Alternatively, a significant number of fastenings needed to be removed.
-Rear Chassis Cover
-Side Plates
-Heat Shield

3-star: Various obstacles combine to make disassembly and removal difficult. The large number of fastenings, the rust fusion of the parts, and the awkward placement make the process a trying task. The fittings are not arranged in a consumer-friendly manner.
-Impeller Housing
-Pulley System

4-star: Parts, components, or systems are either highly unfeasible or physically impossible to remove with the tools on hand. The items and systems in question are obviously not meant to be taken apart by the consumer under most circumstances.
-Engine Block
-Hand Crank Reduction Set



\'\'\'Step\'\'\' \'\'\'Difficulty\'\'\' \'\'\'Details\'\'\'
\'\'\'Step 1:\'\'\'
Figure:1 Remove Discharge Chute
1-star Using an 11 mm Socket Wrench, the nuts preventing the removal of the bolts are evicted. The bolts are pulled out, and the Discharge Chute comes free. Time of removal was 20 seconds.
\'\'\'Step 2:\'\'\'
Figure:2 Remove Key, Gas Cap, Starter Handle, Hand Crank, Hood, and Panel Cover
1-star The Gas Cap and Key are removed by hand. The Starter Handle had a crusted knot that needed some loosening before it could be untied by hand. We use the 11 mm Socket Wrench to remove the screws keeping the Hand Crank on the steel handle protrusion. Using a Phillips Screwdriver, we loosen the top panel and ease it off the assembly. We use a Socket Wrench with a 3/8 inch attachment to remove the Panel covering the Control Panel. Time of Removal was 5 minutes.
\'\'\'Step 3:\'\'\'
Figure:3 Remove the Discharge Chute Gear Assembly
2-star The eight screws keeping the rotation mechanism attached to the Chassis are removed using the 11 mm Socket Wrench and a set of pliers to hold the nuts steady. Time of Removal was 5 minutes.
\'\'\'Figure:4 Gear Reduction Assembly\'\'\'
4-star Our group could not find a way to remove the pushnuts at either end keeping the gear assembly intact without inflicting damage to the unit. The Reduction Assembly was set aside as is.
\'\'\'Step 4:\'\'\'
Figure:5 Remove the Impeller Housing and Rear Cover
3-star The five screws holding the back of the housing were only accessible through a narrow space. The nuts on the other side required that the machine be tipped forward almost 50 degrees to allow simultaneous access to both ends. Rust Fusing added to the difficulty, requiring a great deal of leverage before the screws would begin to move. They were removed using the 11 mm Socket Wrench and a set of pliers, along with two additional screws attaching the housing to the side panels. The Rear Cover was removed with the same tools by loosening the two nuts inside that held the Control Panel to the handle protrusion with the cover sandwiched in between. The Choke lever was threaded out of the hole in the Rear Cover, and the cover was carefully slid out. Time of Removal was 15 minutes.
\'\'\'Figure:6 Electrical Panel\'\'\'
4-star Removal was deemed unfeasible on the grounds that electrical components are far more delicate than the mechanical components. As the Starter and Key are critical in the operation of the unit, we decided not to attempt removal to avoid rendering the entire machine inoperable upon reassembly.
\'\'\'Step 5:\'\'\'
Figure:7 Remove the Side Panels
3-star From the back, the left side panel had four screws keeping it pinned to the Chassis. The right side panel had seven screws holding it up. All were removed using the 11 mm Socket Wrench. The panels were then pulled off. Time of Removal was 10 minutes.
\'\'\'Step 6:\'\'\'
Figure:8 Remove the Pulley Assembly
4-star Removed all the Bolts using 11mm Socket Wrench and a combination Wrench which connected the arm brake, pivot plate assembly, spring, Idler arm assembly and the belt to the pulley assembly. But we could not dissect the engine pulley, and the rotor pulley which connected the engine and the rotor with the pulley assembly respectively. This is due to lack of experience and being unable to remove the Hex Head Screw that connects the engine to pulley assembly, though three of our members worked on it for around 20 minutes.
\'\'\'Step 7:\'\'\'
Figure:9 Rotor and Impeller
4-star The right end of the Rotor was removed during the dissection of Right side panel. The Flange-Bearing attached to side panel, which had three 11mm Bolts removed using the socket wrench. The left end attached to the pulley assembly was unable to remove as Rotor pulley prevented access to the Nuts that connected rotor to the pulley assembly. So it was left along with the Pulley assembly. The time we spent attempting to complete removal was 15 minutes.
\'\'\'Figure:10 Engine Block.\'\'\'
4-star We were unable to remove the engine from the chassis. The drive shaft was permanently embedded within the support plate of the frame, and none of our tools would budge the bolts holding it in place.
\'\'\'Step 8:\'\'\'
Figure:11 Remove the Handle Assembly
2-star The final step in our dissection process. It was kept until the end to assist us to hold and tip the machine as required during the dissection. The handle assembly was only left with the Rotor Drive. A Hex screw driver and a Flat head screw driver used to remove the 6 screws connecting the handle to the main frame. Time of Removal was 10 minutes.

Subsystem Analysis

\'\'\'Chassis\'\'\' Components: Hood, Steel Handle Protrusion, Rear Cover, Side Panels, Wheel Assembly
Functions: The chassis serves to provide structural integrity for the rest of the machine, effectively transforming all of the subsystems into one unit. This has the physical effect of making it easier to transport, and ensuring continued interaction between the active systems.

\'\'\'Rotational Assembly\'\'\' Components: Hand Crank, Gear Reduction Assembly, Gear Collar
Functions: The crank is the interface for the machine operator, serving as a manual aiming system for the snow. The gears allow it to turn on demand while still holding the chute at the desired position absent operator input.

\'\'\'Engine Block\'\'\' Components: Cylinder Block, Spark Plug, Piston Shaft
Functions: The engine accepts fuel and air into the cylinder, ignites them with the spark plug, and converts chemical energy into the rotational shaft energy that powers the impeller. With two pistons and cylinders, it ensures that the rotation is only one way.

\'\'\'Fuel Storage\'\'\' Components: Fuel Tank, Fuel Line
Functions: It stores and supplies fuel needed for the engine to burn. The tank allows for a means of supplying the fuel without activating the engine, as adding fuel to an active machine is far more dangerous and complex.

\'\'\'Recoil Starter\'\'\' Components: Starter Cable, Flywheel, Spring, Permanent Magnet, Magneto Coil
Functions: The operator yanks the drawstring, engaging an inner gear, and spinning a flywheel. The flywheel coils interact with the magnets inside, generating the current to begin firing the spark plugs in the engine. In other words, it converts human mechanical energy into electrical energy, and then into heat energy.

\'\'\'Pulley System\'\'\' Components: Pulley Wheels, Belt, Input Shaft, Impeller Shaft
Functions: Due to the placement of the engine and the need for a compact arrangement, the engine is not on the same line as the impeller. To rectify this, the pulley system is required to transfer the shaft rotational energy to the impeller, which is parallel to the engine. Also, it reduces the rapid rotation of the engine shaft to something more usable for the impeller through a reduction ratio.

\'\'\'Impeller and Discharge System\'\'\' Components: Impeller Flap, Discharge Chute
Functions: As the impeller rotates due to the energy supplied by the engine, its shape allows it to scoop up the snow and literally throw it up and out the discharge chute in the direction the chute is currently facing.

\'\'\'Safety Systems\'\'\' Components: Drive Control Handle, Key Starter, Solenoid Switch, Spring
Functions: The key port must be turned to the on position in order to allow the machine to function. Failure to do so results in an opened circuit that will not allow the current to flow to the spark plug and begin firing the engine. When it is turned, the solenoid switch closes, allowing the engine to fire. Turning it to the off position also kills the engine, allowing a rapid power down by the operator as needed. The drive control handle is what allows the impeller to turn. If it is not pulled, the engine shaft does not engage with the pulley system, and the impeller does not spin. This ensures that if the operator somehow loses hold of the machine, it will not harm anyone, as the sole external moving part will stop spinning.

\'\'\'Connective Analysis\'\'\' The starter acts as the single point access of the entire machine. When disabled, the machine is about as useful as a paperweight. Only when enabled can it fulfill its intended function. After that, operation is dependent upon three things: continued fuel supply, the closed electrical circuit, and the engagement of the drive control handle.

The fuel is the source of the chemical energy, so the fuel tank\'s importance is evident in the fact that when it runs empty, the machine can no longer sustain operation. Similarly, the electrical current, initially generated by the starter, and then continuously supplied by the engine\'s own rotational energy, is vital to provide the heat for the chemical reaction. These two components are hard dependencies, without which the machine cannot function at all. The drive handle\'s engagement, by contrast, is a soft dependency. The machine can continue to run without it. The impeller simply won\'t move. This may be desirable at times, such as when moving over clear area without snow for the machine to work with. Keeping the drive shaft engaged in that case wastes fuel unnecessarily.

Once fuel and electricity are supplied, the engine can convert them into the mechanical energy needed for the machine. The constant and sequential ignitions of the cylinders induce rotation in the central shaft at very high speeds. It also generates heat to counter the cold conditions the machine is utilized in, and ensures that the blower does not freeze during operation. The rotational energy presents two problems to the machine, however:

1) The impeller cannot be spun that fast.
2) The impeller cannot be directly connected to the machine because of the need for compactness.

To address this structural problem, the pulley system allows the energy to be transferred to the impeller in parallel. The pulley system also uses different size wheels at a certain ratio to allow the impeller to spin more slowly than the piston shaft of the engine. Were the impeller to spin faster, it might be severely damaged by chunks of ice that may form within the snow that needs to be moved.

The final aspect regarding the machine\'s operation is the direction of the output. The chute has one entrance and one exit. That exit is directly in front of the operator. Without the chute, the snow would billow straight up, where the wind could scatter it haphazardly. Potentially, it could blow back at the operator, or at the area which was just cleared. Neither are desirable, so the chute is there to direct it forward, and to the side as aimed by the operator. The gear system provides a reliable means of rotation while also locking the chute in position when not receiving input from the operator.


Global factors:
-The components and connectors must be able to withstand the cold, snowy -- and therefore wet -- environment in which the snow thrower will be used.
-The housing protects interior components from the environment as much as possible.

Societal factors:
-The fuel tank, recoil starter, and ignition are all conveniently located so that the casual user can easily operate the snow thrower.
-There are enough connectors to hold all components securely, which impacts safety, reliability, and customer satisfaction.
-There is a diagram of the pulley assembly on the side plate adjacent to the pulley in case a component needs to be replaced.

Economic factors:
-Components are as close to each other as functionally feasible so as to minimize material needed.
-Connectors are made of the most economically advantageous type of metal so that they are reliable but not unnecessarily expensive

Environmental factors:
-The exhaust and snow are directed away from the operator so as to protect the operator\'s health and safety.
-Fuel lines, tank, and engine are constructed in such a way as to prevent leaks.