Group 11 - Dual Stage Snow Thrower (Gasoline Powered) - Gate 4

Revision as of 17:49, 30 November 2012

Intro

In this stage, we reassemble the machine, detail our reassembly process and speculate about the original assembly process, examine a crucial mechanism, and propose some possible design revisions to the machine.

Final Critical Review

Group Cohesion
Only two of us were familiar with each other before the project, so our roles and strengths weren't apparent. All that was required to address this was time to chat, and introduce each other.

Procrastination
We had and still have a habit of laying things to the side until the last day. We addressed that by constantly reminding each other to put their part up before hand, to minimize the last minute additions.

Collective Inexperience
Only one person had direct experience in Manufacturing. Only one person had current experience with CAD modeling. Only one person had a clear idea of the workings of the machine. We split up along our individual strengths, and fully investigated the subsystems of the machine to learn about it.

Communications Problems
A number of times, we were out of touch with each other, and couldn't call each other. We utilized Facebook as a means of talking, by leaving messages the other group members would later read and answer to. Additionally, because three of our group members are from foreign countries, the other two needed to proofread the work before posting it.

Incomplete Disassembly
We were not able to fully disassemble the machine with the tools on hand. We chose not to attempt it due to not knowing the proper procedure or to avoid damaging the components. Whatever was readily accessible, we removed it so we could examine the immobile parts.

Product Reassembly

Mechanism: Gear Reduction Assembly

1. Spur gear: It is the simplest type of gear. It consists of a cylinder with the teeth projecting radially, and although they are not straight-sided in form, the edge of each tooth is straight and aligned parallel to the axis of rotation. The single spur gear is used to make the whole gear system more stable.
Specs:
Number of teeth=13
Module =2.33
Face width= 18 mm
Diameter of outside circle= 35 mm

2. Bevel Gear: It is specifically a crown gear. A crown gear is a particular form of bevel gear whose teeth project at right angles to the plane of the wheel; in their orientation the teeth resemble the points on a crown. This crown gear is meshing with spur gears. Then the crown gear interacts with the two spur gears.

Number of teeth = 26

3. Worm Gear: A worm gear is sharing the same axle with the spur gear; the spur gear rotates with the bevel gear and rotates the worm gear. They have the same angular velocity. The worm gear motivates the discharge chute to direct the snow's outlet.

Equation -- Gear Ratio:
Where Teeth_B is the number of teeth in the bevel gear, Teeth_SW is the number of teeth in the spur gear, v_B is the velocity of the bevel gear, and v_SW is the velocity of the spur and worm gears. Teeth_B/Teeth_SW = v_B/v_SW
Therefore,
26/13 = v_B/v_SW
v_B/v_SW = 2

Possible Design Revisions
(Note: As previously stated, the title is misleading. The Toro CCR-2000 is a single-stage blower.)

1: Wider intake scoop. This would require a longer auger, a wider upper shroud, and a smaller reduction ratio on the pulley.
Global factors: The blower would be able to handle more snow at a time.
Societal factors: Its improved capacity means it takes even less time and effort to clear the same area. That is less time for the operator to spend outside in the freezing cold.
Economic factors: By having to go back and forth less times while running the engine, this revision saves time, money, fuel, and maintenance needs, making the machine pay for itself sooner.
Environmental factors: Less time spent in operation means less overall pollution from the combustion engine.

2: Add an icebreaker auger, making it a dual-stage. The second auger will be larger, but will rotate much more slowly. It will also be made of steel, with blades to loosen up the snow and break apart ice. It will require a more powerful engine, an additional axle and pulley system, and a metal intake shroud to efficiently support the weight.
Global factors: The blower will become a heavy duty machine instead of a light duty one.
Societal factors: This revision would make the blower ideal for areas with heavy snowfall or icing problems.
Economic factors: It will be more expensive in materials and fuel, since there would be a good amount of metal to be machined and added to the blower. Metal is much more expensive than ABS plastic, and the extra weight would tax the engine more.
Environmental factors: Because of the need for a more powerful engine, it will burn more fuel at a time. However, it will burn less overall compared to using a light duty machine for heavy duty work.

3: Change to a 2-cylinder engine. This may require an enlarged chassis and a larger capacity fuel tank.
Global factors: The blower would be capable of operating faster and more consistently. It would also be capable of dealing with heavier loads, though not as heavy as a Dual-Stage blower.
Societal factors: A more powerful engine keeps the operator warmer and completes the job faster. Some users also like to show off or brag about a more powerful engine.
Economic factors: The machine will cost more, and use more fuel at a time.
Environmental factors: A 2-cylinder engine burns more fuel at a time than a single-cylinder engine. This revision will increase pollution from exhaust gases.

Procedure

Difficulty scale
1: Simple and quick. One person could do it in 5 minutes at most.
2: Complicated or tedious. The step is a little tricky or takes a long time.
3: Complicated and tedious. Two people are required for the task and the process takes time to complete.

Step	Difficulty	Tools Used	Actions	Same as Disassembly?	Originally Assembled
Step 1	2	13mm socket and socket wrench	Reattach upper handle to lower handle. The difficulty in this step is mainly caused by the unwieldy nature of the mostly-disassembled snow thrower.	Yes.	Using power tools. In all cases below, "power tools" is used to mean an electric nutdriver, power socket wrench, or similar.
Step 2	1	11mm socket and socket wrench	Bolt center of left side panel to frame.	Yes.	Using power tools.
Step 3	1	By hand	Return pulley belt to proper position as shown on diagram on inside of right panel cover.	Yes.	By hand.
Step 4	1	11mm socket and socket wrench	Reattach right side panel to frame.	Yes.	Using power tools.
Step 5	1	10mm socket and socket wrench	Reattach engine cover to engine assembly.	Yes.	Using power tools.
Step 6	2	½” socket, socket wrench, and ½” combination wrench	Reattach more of the left side panel to the frame.	Yes.	Using power tools.
Step 7	3	11mm socket, 14mm socket, socket wrench, and pliers	Reassemble pulley assembly per drawing on interior of right side panel cover.	Yes.	Using power tools and working per print, pliers not required.
Step 8	2	By hand	Replace bottom flap between frame and lower discharge assembly. It is somewhat difficult to line up the holes in the flap with the holes in the frame and the lower discharge assembly, particularly since the flap has three extraneous holes. Upon inspection, it is obvious where the flap belongs; however, holding it in place while sliding bolts through the holes is a two-person operation.	Yes, except that disassembly did not require careful positioning.	By hand per a print.
Step 9	3	11mm socket, socket wrench, and pliers	Reattach lower discharge assembly to frame, right side panel, and left side panel.	Yes.	Using power tools, no pliers.
Step 10	3	12mm socket, socket wrench, hammer, and pliers	Reattach recoil support to engine assembly. It does not fit easily back into its slot. The necessity of the hammer and the use of pliers in concert with the socket wrench cause this to be a difficult task.	Yes.	Using power tools, no hammer or pliers. Originally, the recoil support was probably a clearance fit; that is, it did not require a hammer.
Step 11	1	10mm socket and socket wrench	Reattach left side panel to frame.	Yes.	Using power tools.
Step 12	1	by hand	Replace fuel tank and muffler in proper positions. Mechanically, this is a simple step so long as care is taken not to twist the fuel line. However, the orientation of each item is not completely intuitive and requires looking at disassembly pictures and careful observation of the components.	No, disassembly did not require careful positioning.	By hand per a print.
Step 13	2	11mm socket, 14mm socket, socket wrench, 11mm nutdriver, and pliers	Secure fuel tank to recoil support. This requires some awkward angles. Rusty nuts and bolts necessitate the use of tools on both the bolt side and the nut side.	Yes.	Using power tools, no pliers.
Step 14	1	By hand	Reattach the spark plug cover to the spark plug.	Yes.	By hand.
Step 15	1	By hand	Replace upper shroud assembly.	Yes.	By hand.
Step 16	1	By hand	Replace starter panel, pulling the rope through the hole for the starter pull.	Yes, though during disassembly the rope fell by itself.	By hand.
Step 17	1	By hand	Replace starter pull, pull the rope through the hole through its center, and tie a knot in the rope to secure the pull.	Yes, though during disassembly the rope fell by itself after the knot was untied.	By hand.
Step 18	1	11mm socket, socket wrench	Bolt upper shroud assembly to frame.	Yes.	Using power tools.
Step 19	1	By hand	Place discharge chute ring on lower discharge assembly, taking care to orient it such that the flats are aligned.	No, orientation was not important during disassembly.	By hand.
Step 20	1	10mm socket, socket wrench	Bolt discharge chute support ring to lower discharge chute assembly.	Yes	Using power tools.
Step 21	1	By hand	Correctly orient chute ring retainers on chute support ring.	No, orientation not required for disassembly.	By hand.
Step 22	2	11mm socket, socket wrench, 11mm nutdriver, and pliers	Bolt discharge chute ring retainers to chute support ring. Again, rusty nuts and bolts are a factor.	Yes.	Using power tools, no pliers required.
Step 23	1	By hand	Replace lower shroud assembly.	Yes.	By hand.
Step 24	2	11mm socket and socket wrench	Reattach top of discharge chute to the main discharge chute.	Yes.	Using power tools.
Step 25	1	By hand	Replace discharge chute assembly.	Yes.	By hand.
Step 26	1	11mm socket, socket wrench	Bolt discharge chute to chute support ring.	Yes.	Using power tools.
Step 27	2	11mm socket, socket wrench, and pliers	Reattach lower shroud assembly to frame	Yes.	Using power tools.
Step 28	1	By hand.	Replace gas cap.	Yes.	By hand.
Step 29	1	By hand.	Replace heat shield. This is somewhat awkward due to the angles, but its orientation is fairly straightforward.	Yes, though the angles were not as awkward during disassembly.	By hand.
Step 30	2	10mm socket, socket wrench, and pliers	Reattach heat shield to housing. The housing itself makes it a struggle to reach every bolt and ensure all are tightly secured. This step absolutely requires two people.	Yes.	Using power tools and a procedure to ensure best practice for securing all bolts.
Step 31	3	flathead screwdriver, strong piece of string	Reattach right side of starter cover to starter panel. The cover must surround parts of the upper and lower shroud assemblies, but the panel has a tendency to fall into the machine and is very difficult to replace, making this a frustrating multi-step process. The string is placed through two holes and pulled tightly in order to hold the panel in place while another person screws down the left side and a third person holds the housings in place.	No, disassembly required only basic unscrewing.	Using power tools and a specialized tool or process to hold the starter panel in place rather than string.
Step 32	3	flathead screwdriver, strong piece of string	Reattach center and left side of starter cover to starter panel. One screw is not enough to keep the panel from tilting inwards too far to be reached by the short center screw. The string must be placed through two holes on the left side of the panel.	No, disassembly required only basic unscrewing.	Using power tools and a specialized tool or process to hold the starter panel in place rather than string.
Step 33	1	By hand	Replace starter key in ignition.	Yes.	By hand.
Step 34	1	By hand	Replace control bar, taking care to orient it properly and use the correct holes and spacers.	No, disassembly did not require orientation, the control bar and spacers simply fell off.	By hand per a print.
Step 35	2	13mm socket and socket wrench	Reattach control bar to handle assembly.	Yes.	Using power tools.
Step 36	1	by hand	Replace spring and clutch cable assembly.	Yes.	By hand.
Step 37	1	by hand	Replace chute crank assembly.	Yes.	By hand.
Step 38	2	13mm socket and socket wrench	Secure chute crank assembly to handle assembly.	Yes.	Using power tools.
Step 39	2	10mm socket, socket wrench	Secure right cover panel.	Yes.	Using power tools.