Group 17 - Beginner Dirt Bike

Gate 1: Request for Proposal

Request For Proposal Page

Gate 2: Preliminary Project Review

Dissection Report

The mini bike was a very complex product with different components that varied in complexity themselves. The bike consisted components such as a chassis, a frame, an internal combustion engine, and a carburetor. The components of the mini bike varied in ease of disassembly as well. A scale of 1-5 was used to represent the ease of disassembly of each piece. A 1 indicates that the component was very easily taken apart, requiring no tools, and low amounts of force to disassemble the component. A 5 would indicate that the component was very hard to take apart, requiring numerous tools, and a lot of force to disassemble that component. Chassis: 2 Image of Chassis In order to remove the plastic chassis from the mini bike’s frame, a P1 Phillips screwdriver, a P2 Phillips screwdriver, a socket wrench with a 10mm socket and a 15/16” socket, and a pair of needle nose pliers were needed. The chassis had a complexity of 2 to remove. First, to take off each of the side panels, one 10mm hex screw with a washer was removed with the socket wrench, two ½” screws were removed with a P1 Phillips screwdriver, and one ¾” screw with a 10mm hex nut sandwiching a rubber washer and a metal washer was removed using a P2 Phillips screwdriver. Next three ¾” screws were removed from the front mud guard with the P2 Phillips screwdriver. All three screws had ½” diameter metal washers. To remove the seat from the frame of the mini bike, two ¾” screws with washers were removed from the underside of the seat with a P2 Phillips screwdriver. This was a more complex step because the screwdriver had to be maneuvered into the space under the seat, which was very cramped. Next, one ½” screw was removed with the P2 Phillips screwdriver to remove the front cover of the mini bike. Two 1” hex screws with ¾” diameter washers were removed from the plastic gas tank with a P2 Phillips screwdriver. Finally, two ½” screws with metal washer were removed with a P2 Phillips screwdriver to remove the plastic guard over the chain. Frame: 3 To clear the frame of all parts that were to be farther disassembled, a socket wrench with 8mm and 12mm sockets were needed, a 1/8” flathead screwdriver was needed, and needle nose pliers were needed. The entire frame was a complexity of 3 to disassemble. One 4” screw with a metal washer and nut was removed from the top of the engine with the 13mm socket wrench. Next, all of the electrical cords were removed or unclipped where possible. In order to remove the chain from the engine to the back wheel, the master link in the chain had to be located. When this was located, the cover was removed by hand, and the link was opened using the flathead screwdriver. Two bolts with washers were removed from the spiral spring on the rear suspension by hand. This was a particularly complicated task because it was necessary to apply pressure to the suspension in order to make the bolts able to be removed. In addition, it was necessary that the chain was removed before taking off the rear suspension. Kickstand: 1 Image of Kickstand Removing the kickstand had a complexity of 1, requiring only a P2 Phillips screwdriver to disassemble. The kickstand was connected to the engine with four 1 ¾” P2 Phillips screws. Also, it was necessary to remove the spring connected to the kickstand and the engine before removing the kickstand itself. Failing to do so resulted in the spring shooting out from the bike. Engine Block: 5 Image of Side View of Engine Image Top View of Engine The engine block was the most complex component of the mini bike with a complexity of 5. This is because many of the parts were very tightly sealed, there was oil covering most of the engine block. In order to disassemble the engine block, a socket wrench with 8mm, 10mm, 13mm, 14mm, and 17mm sockets was needed. Two 2 ½” screws are removed from where the carburetor and spacer are connected to the elbow joint with a 10mm socket wrench. Replace the screws into the carburetor with the spacer. Next, remove the elbow joint from the engine block by removing two 1 1/8” screws with a 10mm socket wrench. The front cover of the engine block (where the carburetor meets the engine) is removed by unscrewing four screw caps with washers with a 10mm socket wrench. Next, a 4 ½” bolt connecting a silver cap and a hex nut is removed using a 10mm socket wrench. To remove this bolt, it is necessary to hold the silver hap in place, otherwise the nut will not unscrew. Then, use the 8mm socket wrench to remove the two 1” hex screws with welded washers located next to the bolt that was just removed. Remove the 1” hex screw connecting the grey section of the engine block to the black part of the engine block with the 8mm socket wrench. Now we moved to the black part of the engine block. The covering of the spark plug was removed by hand. Once again, we moved down the engine block, now to the final grey part. On the kick start side of the engine, an 8mm socket wrench was used to remove one 3 ¼” bolt, two 2 ¾” bolts, and five 1 ¾” bolts. Next, a 13mm socket wrench was used to remove the hex nut and washer from the gear cover. In order to remove the kick start itself, one 1/8” hex screw was removed with a 10mm socket wrench. The kick start was then pulled off by hand. The same method was used to remove the shifter connected to the transmission. On the side of the engine opposite of the kick start side of the engine, an 8mm socket was used to remove one 3 ¼” bolt, two 2 ¾” bolts, and 5 1 ¾” bolts. Finally, the engine was turned over and two bolts were removed from the bottom. The bolts were a 1” bolt with a washer removed with a 17mm socket wrench, and a 7/8” bolt with a spring removed with a 14mm socket wrench. This was the furthest the engine could be disassembled without risking great damage to the engine. Had we had heavy machinery to disassemble the engine, pistons and more gears would have become visible. Carburetor: 2 The carburetor was not a very complicated component, so it was rated with a complexity of 2. In order to disassemble the component, needle nose pliers, a 1/8” flathead screwdriver, and a P2 Phillips screwdriver were needed. Before anything was done to the carburetor itself, all 3 pieces of tubing connected to it were removed with needle nose pliers. Next, a P2 Phillips screwdriver was used to loosen one 1 ½” screw from the clamp holder on the air filter. After the air filter is removed, use a P2 Phillips screwdriver to remove 2 ¾” screws with washers from the carburetor cover. Removing the carburetor cover exposed a black piece of plastic connected to a spring, which vibrates to mix air and fuel in the carburetor. This is removed by hand by removing the thin rod above the spring, and removing the spring itself, taking care not to lose the spring connected to it. Next, the internal screws of the carburetor are removed with the 1/8” flathead screwdriver. The hex screw was in the middle, and the smooth screw was offset from the middle. Outside of the carburetor, opposite of the choke, there are two ¾” screws with springs. The diagonal gold screw was removed with a 1/8” flathead screwdriver, and the silver screw parallel to the air intake was removed with a 1/8” flathead screwdriver as well. To remove the choke switch from the carburetor, a ¾” gold screw with a washer fitting into a ¼” sleeve was removed with a P2 Phillips screwdriver. The remaining part of the choke is removed by hand.

Causes for Corrective Action

Work Proposal:

In our initial disassembly process we said that we would basically take off the outer pieces of the dirt bike and work our way towards the engine. This was the general direction we took in dissecting the product. But we did figure out that it would be easier to leave the tires and suspension on until we got the engine off. We decided this because the tires would allow us to sit the bike up while we took off the engine. Our initial disassembly plan also said that we would remove the clutch, air filter, and transmission prior to removing the engine. We then decided that it would be easier to get the engine off with all of these parts attached and to then disassemble them from the engine separately. For a large product like this it is a good idea to take off small portions and then separately disassemble them.

Management Proposal:

In our initial Management Proposal, we said that our meeting times would be Mondays at 4:50 pm right after class and Wednesdays from 5-6. Although we usually met on Wednesdays, our dissection typically lasted longer than an hour. However, now that dissection is over, our meetings will primarily be on Mondays from 4:50-5:30 pm, allowing us to have more time to work on delegated tasks according to our Gantt Chart. One very successful part of our Management Proposal has been the delegation of roles. The Design Specialist did a fantastic job in the lab leading the team through dissection, our Lead Wiki Developer has edited our wiki to make it as user friendly as possible, and the Communications Manager has sent the notes from lab to the group to ensure everyone had the material. The Communications Manager will also now be responsible for double-checking the gate requirements and relaying to the group which aspects still need to be fulfilled.

Unresolved Challenges:

A continual problem with such a large scale project is balancing the time required for this class with other school material. There were some instances were group members didn't attend scheduled meeting times. In order to overcome this challenge, we will all commit to attending the meetings every Monday. The Communications Manager will also take brief notes at each meeting in order to keep everyone on task and send out an email Sunday reminding everyone to attend the following day’s meeting. In addition, if there is a conflict to a meeting time, we will contact the other members of the group prior to the meeting.

Gate 3: Coordination Review

Component Summary

Component	Function	Material	Forces	Shape	Manufacturing Process	Complexity*	Picture
Handlebars (1)	Functional: provides a means for the driver to steer the bike	Steel, Rubber, and Plastic. Steel for structural integrity. Rubber for the grips for extra traction of riders hold on handlebars. Plastic used to secure brake line to hand brake.	Minimal forces applied on handlebars, normal force and tension balance gravity.	Allows for comfort for riders grip	Sand cast because shape is symmetric and relatively low precision necessary. Material has no effect.	3
Chassis (1)	Functional/Cosmetic: shelters other components from environment while providing color and design to the model	Plastic for ease in fabrication/lightweight.	Minimal forces act on the chassis. Forces of tension and friction between the chassis and frame in equilibrium, keeping the chassis in place.	Necessary shape because covers frame/other components	Chassis molded for cost effectiveness and because plastic is easy to mold	2
Frame (1)	Functional and Cosmetic: provides stability and shape to bike	Steel for structural integrity.	Weight of chassis-7 lb, tension and torque at joints and connections all in equilibrium	Best shape possible for rider comfort and functionality	Die casted individually, bended and welded together	4
Compression (1)	Functional: absorbs shock and impact	Steel and Rubber. The spring is coated in rubber but everything in the compression system is made of steel. Also a rubber washer in place in order to prevent wear.	Forces applied from weight of frame and chassis, approximately 75 lb.	Necessary shape in order for spring to compress	Spring made by coiling, die casting used for the rest of system. Steel is malleable/ductile.	5
Rear Wheel Suspension (1)	Functional: keeps wheels in place and helps with some shock absorption	Steel and Rubber. Steel for structural integrity. Rubber piece serves as a cushion for the chain, resulting in less friction and ultimately less wear.	Some weight from frame and chassis, approximately 15 lbs and additional weight when rider is added. Forces of tension, torque and joints and connections in equilibrium	Designed to keep back tire secure and provide stability	Die casting used for individual pieces, then welded together. Ductility of steel is beneficial.	4
Front Wheel Suspension (1)	Functional: keeps wheel in place and helps with some shock absorption	Steel is used because of the structural integrity. Rubber washers in place to aid with shock absorption and prevent wear.	Forces on front suspension include some weight of frame.	Designed to work with steering column and keep front tire in place	Left piece die casted for precision. Circular shape allows for pressure fitting to fit perfectly with cut steel rod.	3
Front Wheel Steering Column (1)	Functional: causes the tires to turn	Steel for strength and stability	Forces acting on the steering column include the weight of the handlebars, approximately 7 lb. Torque is also applied when turning.	Designed to compliment front suspension and handlebars design	Turning used to create threads, sand casting used to make plate unsmooth finish and low precision necessary, shape and material have little effect.	4
Exhaust System (1)	Functional: removes exhaust from the engine	Steel for structural integrity	Minimal forces applied, air pressure from exhaust applied when in use	Shaped to help funnel exhaust away from bike	Steel tubing is heated then bent, welded to a sand casted materials	3
Kick Start (1)	Functional: Start engine	Steel and Rubber. Steel for strength, rubber for traction	Minimal forces on kick start when not in use. Applied force from the rider must create enough torque to force the crank shaft to start moving the pistons, approximately 50 lb is applied on average though less is necessary.	Shape based for user ease/maximum torque generation	Long thing piece steel that was heated and bent, and welded to a sand casted pieces on either end.	3
Fuel Tank (1)	Functional: provides a place for fuel storage	Plastic because lightweight, easy to form as one compound piece	Forces on the fuel tank include the weight of the fuel in the tank, approximately 6 lb. Also, there are forces between the gas tank and the frame which are in equilibrium.	Designed for helping fuel leave tank	Molded plastic, for ease	2
Carburetor (1)	Functional: blends air and fuel for engine	Steel for structural integrity, filter is steel/wool mesh	Minimal forces act on the carburetor	Designed to maximize efficiency	Variety of parts casted/molded then assembled.	5
Engine Block (1)	Functional: provides energy for the bike to move	Aluminum for strength	Forces acting on the engine are minimal, while forces in the engine are much more complicated. Pistons, spark plug, etc all provide internal forces.	Shaped to fit maximum number of components in small space.	Variety of pieces casted, welded and assembled.	5+ (many internal parts)
Gear (1)	Functional: causes rear wheel to rotate	Steel is used for its strength and ductility, high resistance to frictional wear	A contact force is applied between the gear and the chain and friction between the gear and drive shaft	Teeth to have easy transfer of chain links, gear size chosen for maximizing turn of wheel	Die casted for general shape. Teeth created by turning, and holes created by drilling. Steel is a good choice because malleability.	4
Gear Chain Link (1)	Functional: connects transmission to rear wheel	Steel, for ductility and high resistance to frictional wear	There is a contact force that acts between the chain and the gear. There is also an equal tension between each of the chain links.	Chain links made to work with size of teeth on gear	Links casted and then attached together.	3
Tires (2)	Functional and Cosmetic: Tires provide a means for the bike to move, but design of spokes can change	Steel and Rubber. Steel for spokes, rim, center for strength and rigidity. Rubber for tire for traction and give with uneven surfaces.	Between the two tires there is approximately 50 lb of force (assuming the kickstand is down)	Circular to help ease of motion, treads for traction control, spoke design for support	Rim die casted and adhered to spokes which were sand casted. Spokes adhered to sand casted center.	3
Drum Brake (1)	Functional: Brakes are necessary for the bike to stop: Part # 6-5.5	Aluminum and Steel. Aluminum for brake hub for its strength and light weight, while the attachment from the brake to the suspension is made of steel for its strength.	Forces acting on brake are minimal, except when brake is in use. Here, a force of friction will be applied,	Shape and size based of wheel design	Both pieces sand casted then connected with screw	2
Kickstand/Pedals (1)	Functional: allows the bike to stand on its own/provides a place for riders feet to rest	Steel for strength and rigidity	The kickstand supports majority of the weight of the bike, approximately 80 lb. The pedals are securely fastened to the frame, and the forces there are in equilibrium.	Kickstand designed to support weight of bike, pedals shaped to support feet/ provide traction	Individual pieces of pedals sand casted, then welded together. Spring is made by coiling. Kickstand casted then attached with bolt	3
Cables (3)	Functional: needed for brake system	Plastic covering in order to protect interior cables from environment	When the rider squeezes the brake, the cables become taught and apply a force on the brake, causing it to clamp shut. The force applied on the brake would directly result from how much force is applied by the rider.	Shaped for flexibility	Multiple wires weaved for strength, covered with insulting plastic	2
Screws (67), Washers (26), Nuts (14)	Functional: keeps other components in place	Steel for structural integrity	Forces acting on these components are normal forces.	Screws shaped for stability and tight fit, washers shaped to keep connection between screw and surface tight, nuts are hexagons for ease of tightening.	Screws made by turning, washers made by die casting, nuts made by casting then bored and turned.	2

• *Complexity is measured with 1 being easy to create (simple casting) and 5 difficult to create (multiple processes necessary).

Design Revisions

Exhaust:

On the mini bike, the exhaust pipe was made of steel with a steel cover over it. When the bike is running, the metal on the pipe gets hot. The cover does protect the rider from some of the heat, but if the heat came into direct contact with skin, it could burn the rider. The rider would likely be using the bike for recreational purposes, meaning that the rider would not always wear appropriate clothing. Assuming the rider was wearing shorts, as many recreational riders would, the exhaust could burn him. To prevent this, the cover should have a layer of rubber over the steel to further dissipate heat. This addition to the bike would not cost much to add to the bike because it is not very intricate in design.

Kill switch:

Another safety feature that is missing from the bike is that there is no kill switch. If the rider were to fall off of the bike while it was moving, the bike would continue to move until it fell over or crashed. If there were a kill switch connecting the bike and rider, then the engine would stop the moment the rider fell off. The kill switch would be a moderately expensive addition to the mini bike; however it would make the bike safer for the rider. Safety should be the first priority while manufacturing a product that could be potentially dangerous.

Gas gauge:

A flaw in design on the mini bike is that there is no accurate way to tell how much fuel is left in the gas tank. The bike should have a gas gauge. This would be a relatively inexpensive addition to the bike, and it would assure that the rider knew how much fuel they had at all times. This would make riding the mini bike safer as well. It would be safer because the rider would not run the risk of running out of fuel while making long rides far from any fueling stations.

Solid Model

The air filter is an integral part of the analysis of the piston cylinder engine system. To the right is a model of the air filter as assigned this group.

The group chose the filter for the purpose of its complexity in analysis as well as simplicity in application. The air filter is functional in directing oxygen richer air than ambient air (by filtering out unnecessary particles) to the engine intake valves. During the combustion process, the efficiency of the engine is directly tied to the heat of combustion as well as the pressure ratios. These are as well tied to the air intake which is the working fluid for the compression process.

Engineering Analysis

Problem Statement:

Engine flooding is a big problem that engines with carburetor’s have. A major cause of this is a rich fuel-air mixture. When your fuel-air mixture is to rich it won’t be ignited by the spark plugs. So far the fuel-air mixture to ignite properly it must be below the upper explosive limit and above the lower explosive limit. The question being asked is: What is the maximum and minimum volume of gasoline needed to properly ignite a fuel-air mixture with 5500 mm3 of air?

Diagram of System

Assumptions:

- Gasoline is the fuel used

- Upper explosive limit = 7.6%

- Lower explosive limit = 1.4%

- Standard Atmospheric Pressure

- Temperature = 20°C

Governing Equations:

- Explosive Limits = (VFUEL/VAIR)X100%

Calculations:

- Upper Explosive Limit = (VFUEL/5500 mm3)X100%

- VFUEL = (7.6%/100%)X5500 mm3 = 418 mm3

- Lower Explosive Limit = (VFUEL/5500 mm3)X100%

- VFUEL = (1.4%/100%)X5500 mm3 = 77 mm3

Solution Check:

If there is 5500 mm3 of air in the carburetor then 418 mm3 and 77 mm3 of gasoline are plausible values for the volume of the fuel.

Discussion:

- Since we know the dirt bike runs on gasoline we should declare that the fuel used is gasoline which allows us to get specific values for the upper and lower explosive limits. We could have done the calculations using a different fuel and got different values for the upper and lower explosive limits. These values were attained from the website www.engineeringtoolbox.com.

- Using standard atmospheric pressure and 20°C gives us an ideal conditions to calculate find the values for upper and lower explosive limits.

Gate 4: Product Reassembly Plan

We worked on the reassembly of our dirt bike with group 11. Our group was in charge of reassembling the engine and group 11 was in charge of reassembling the frame and everything else.

Recommended Tools:

- Wrench/Ratchet Set

- P12 Screwdriver

- Hands

Steps to Reassembling

• *See Group 11 for reassembly of frame

Step*	Instructions	Tools Required	Time Required	Difficulty	Picture
1	Set left side casing over engine block and screw on 2 Hex Nuts to hold casing on engine block	18 mm and 14 mm Socket Wrenches	2:00	1
2	Put chain gear back using (2) ½” screws	P12 Screwdriver	1:30	2
3	Now insert 2 Hex Nuts to completely secure casing onto engine block	8 mm Socket Wrench	1:00	1
4	Replace front of transmission block with 4 Nuts and 4 Washers	10 mm Socket Wrench	3:00	2
5	Replace Air Intake elbow joint using 2 8" Screws	P12 Screwdriver	2:00	1
6	Set Right Side casing onto engine block	Hands	20:00	5 (piece was offset and wouldn't fit back into place)
7	Slide Kick Start and Clutch back into place and tighten bolts	10 mm Socket Wrench	5:00	3
9	Use 12 bolts to secure casing to engine block	9 mm Socket Wrench	15:00	4 (lots of bolts with different lengths)
9	Reattach Carburetor to elbow joint	9 mm Socket Wrench	2:00	2

• *Difficulty is measured with 1 being easy to reassemble (little effort) and 5 difficult to reassemble (multiple parts and lots of effort).

Post-Reassembly Analysis

How the Product Runs

- Our product ran before we dissected and reassembled it. After reassembly the product did not run anymore. This is due to a missing piece to the Carburetor. To solve this all we should need is replace this piece and our bike should be running again.

Differences between Reassembly and Disassembly

- A major part of reassembly that is different from the disassembly is how the pieces fit together. We had several problems with pieces not fitting back in place. This required a trial and error type reassembly.

- For the most part the same tools were used. The only difference is we didn't have to use needle nose pliers to pull off tight pieces.

- We were almost able to completely reassemble the engine. The only thing that we didn't completely reassemble was the Carburetor because the piece was missing.

Final Recommendations

- To build the bike using the same size bolts and screws. If there was a standard size of bolts and screws it would've been so much faster and easier to reassemble and to disassemble.