Group 5 - Motorized Scooter (Goped)/Gate 3

Gate 3

Project Management: Coordination Review

Cause for Corrective Action

While there are no problems that currently need to be resolved, the group has had to deal with a string of problems when removing the flywheel from the engine. During the dissection process it was decided to break the engine up into its subcomponents. After removing most of the sub-components from the engine, it was found that the flywheel could not be removed using the tools provided. As a group we brainstormed ideas based on availability, and cost on how to remove the flywheel. First, leveraging the flywheel out with a wedge was attempted but yielded minimal results due to the uneven force distribution. It was then decided to wait for the machine shop in Jarvis Hall to open the next day so it would be possible to use a flywheel puller. After procuring the flywheel puller it was attached to the flywheel, but the flywheel was too small to grip onto resulting in another failed attempt at removing the flywheel. The final idea was to use two bolts that fit in the threaded holes on the flywheel to apply an even force distribution to remove the flywheel. This was the last choice because it required an added cost and was slightly more time consuming. After researching the right bolt size and purchasing the right bolts the final method of removal was applied and the flywheel was finally removed, thus solving the group’s series of problems all stemming from the flywheel.

Product Archaeology: Product Evaluation

Component Summary

Product Analysis

Complexity Scale

Rating	Description	Example
1	Component has a simple geometry or a few curves, and is made from less than 2 sub-components and/or can be made from 1-2 manufacturing processes.	Deck
2	Component form consists of shapes based off of simple geometries, and/or needs more than 2 manufacturing processes to make between all sub-components.	Spindle
3	Component form is a combination of many geometries that may not be regular shapes, and/or require multiple manufacturing processes or sub-components.	Engine Block

Flywheel

Component Function

There are several purposes for a flywheel in an engine. In the case of the Goped however, its primary functions are to maintain the timing of the engine spark and create a rotational inertia to counteract the rotation of the crankshaft. This reduces vibration and motion of the engine, thus increasing its integrity. The flywheel serves in both the flow of the ignition system and as a part of the engines system. For the ignition system is serves as a signal to the magneto which then sends another signal to the spark plug. The flywheel serves as a force in the engine’s system as it creates a counter-moment to the keep the engine stable. The flywheel is housed inside the engine cowl and in between the engine and pull-start.

Component Form

• Shape: Circular with protruding fins
• Notable properties: Fins to provide extra cooling to the engine, Magnets located on the side of the part, Axial symmetric.
• Three dimensional
• 3 3/8” Diameter 1” wide
• Shape is influenced toward providing cooling of the engine
• Roughly weights around 1 lb.
• Made out of aluminum
• Manufacturing impacted this design by utilizing investment casting to make this part.
• A specific material property is not necessary for it to function
• Economic factors influence the design by using the cheapest method to producing a high volume of flywheels.
• The flywheel has fins on one side.
• The component does not have an aesthetic purpose; it located behind a shroud.
• The component is silver from the manufacturing process.
• Smooth surface finish from production, not aesthetic or functional

Manufacturing Methods

The engine’s flywheel is cast from Aluminum, and then the through hole for the crankshaft is machined afterwards in order to improve the surface finish. This is most reasonable method to assume due to the flywheel’s relatively simplistic geometric shape and relatively rough surface finish.

The need to make the flywheel out of metal would eliminate the possibility of using injection molding or additive methods. Because of the squared off keyway cut into the center hole, it is more likely that the entire shape of the flywheel is cast, as opposed to boring the through hole and machining the keyway after the casting is done. Additionally, because the flywheel has fins encircling the border for 360 degrees, it is impossible that it could have been extruded. Although it is possible to both forge and investment cast the flywheel, it seems unreasonable because the advantages these processes would implement are negligible and unnecessary in comparison to the additional cost.

Component Complexity

The flywheel is a 3 on the complexity scale due its complex geometric combinations that are more intricate than simple variations of regular geometric shapes, that would warrant a score of 2.

Muffler

Component Function

A muffler is used for two main reasons. The first is that it creates better airflow in the engine’s system which results in better combustion and thus performance. The muffler also functions to suppress the sounds of the combustion and valves. It does this by bouncing the energy waves that result around in a chamber until the sound is more dissipated. The muffler is only a part of the exhaust system at the final portion where the exhaust is expelled. It is covered by the engine cowl and is attached directly to the frame.

Component Form

• Shape: Square with rounded edges
• Notable properties: asymmetric, rounded edges
• Three dimensional
• 3.5” long 2.5” wide 1.75” thick
• Shape is influenced in providing a quieter exhaust
• Roughly weights two ounces
• Made out of two pieces of rolled aluminum
• Manufacturing impacted this design by using two pieces of stamped aluminum to create this part
• No specific material property is needed for it to function.
• Societal factor- Lower noise pollution
• Economic factor – cheap method of production, using stamped aluminum.
• No aesthetic purpose; covered by the engine shroud.
• The component is silver from the bare aluminum.
• Smooth finish from the stamping, not functional or aesthetic.

Manufacturing Methods

The method by which the muffler was manufactured can be determined by the fact that it is comprised of two pieces of shaped sheet metal. In order to create this geometry, a sheet of Aluminum would have to be rolled thin so that it could then be placed in a die to be stamped. The two pieces of stamped Aluminum make up the two halves of the muffler. To complete the manufacturing, they are lined up so that their edges can be rolled together. In addition to the Aluminum halves, the muffler has a metallic mesh screen inside of it that is made from one piece of material. This is made by punching it out of a piece of sheet Aluminum into the desired shape.

Because of the thin material and hollow nature of the muffler, it is unlikely that the outer halves would be cast due to geometrical and structural limitations. Additionally, their three dimensional nature would prevent them from being extruded or drawn. This narrows the possible methods of manufacturing to compressive shaping, which is the actual method that is used. Because the muffler must be made from metal due to the high temperatures it encounters, it cannot be made from conventional plastics. Therefore, the options of injection molding and rapid prototyping can be ruled out as well. Although there are not necessarily a wide variety of methods that can be utilized, the economic benefits of rolling and stamping over other processes confirms that this is the best process for muffler production.

Because of the similarly thin nature of the mesh sheet inside of the muffler to the halves of the muffler itself, many of the same geometric and material limitations are encountered in its production. Because this mesh is made from one solid piece of metal, the possibility of drawing many wires and winding them together can be eliminated as well. The stamping process is relatively quick and easy, thereby minimizing the cost associated with the production of the mesh sheet.

Component Complexity

The muffler is a 2 on the complexity scale due to its variation on simple geometries and use of subcomponents. It did not rate higher on the scale because it lacked the combination of different geometries required to rate a 3 on the complexity scale.

Deck

Component Function

The purpose of the deck is to provide a spot for the user to stand on while operating the Goped. The sole function of the deck is to provide an area for which the user can stand as it is connected to the frame and nothing else. The only flow that this component could be associated with is the frame as this, when stood on, would apply a force to the frame. It is completely exposed and primarily rests under the rider.

Component Form

• Shape: Square with a slight curve towards the nose.
• Notable Properties: Cut outs designed around the engine/frame.
• Primarily two dimensional
• 19” long 9 ¼” at widest point 3/8” thick
• Shape is influenced on provide a large foot platform around the size of the frame.
• Roughly weights around a ¼ lb.
• Made of wood
• Manufacturing decisions impacted this design by providing a cheap yet durable platform to stand on.
• There is no specific property needed for it to function.
• Economic factors influenced the design by making it cheap to produce.
• Goped is printed in grip tape on top of the deck, along with a logo in the upper right corner.
• The surface coloring is light brown from a staining.
• The staining provides an aesthetic design to the deck along with providing a protective layer around the wood.

Manufacturing Methods

The deck that the rider stands on while operating the Goped is machined from a large piece of stock plywood. It can either be machined by hand or with a CNC, depending on the manufacturer’s budgetary constraints, and is finished by rounding the edges with a router. The final deck then has a precut pattern of grip tape adhered to its surface.

Component Complexity

The deck is a 1 on the complexity scale because it made from a single piece of plywood that derives its overall form from a series of cuts, but did not rate higher on the complexity scale due to a lack of subcomponents and further variation in the basic geometry of the board.

Cylinder Head

Component Function

The function of a cylinder head is to provide the top half for the combustion chamber of the engine. Here, it also provides the areas for air and fuel to be brought into the chamber. The cylinder head also provides spaces for valves, the spark plug and ports. This component works in conjunction with the fuel system, intake system, exhaust system and the ignition to enable the engine to function. The cylinder head can be associated with all of the above systems, toward the end of each flow. While the cylinder head does not perform a physical, mechanical function, it serves as more of a door to the engine and therefore can be associated with numerous flows. The component functions as a part of the engine and within the engine case. It is partially exposed where the spark plug is located and is connected to other subsystems by various hoses.

Component Form

• Shape: Square with fins
• Notable properties: Fins provide cooling to the cylinder, machined cylinder and ports
• Three dimensional
• 2.5” by 2.5” square head, 2 1/8” tall
• Shape is influence by providing maximum cooling to the cylinder head.
• Roughly weights three ounces
• Made out of aluminum
• Manufacturing impacted this design by utilizing investment casting to make this part.
• Heat dispersion is a property necessary to the cylinder head.
• Economic - influenced this design by using a cheap method of producing a high volume of cylinder heads.
• Global – Availability of gasoline/oil mixture.
• The cylinder head has no aesthetic purpose; it is covered by a shroud.
• The component is silver, from the manufacturing process.
• Smooth surface finish from manufacturing, not functional or aesthetic.

Manufacturing Methods

The engines cylinder head is made using several manufacturing processes. This is the most likely method to assume due to the seam down the middle of the head and the feel of the surface finish. To gain the overall shape, the Aluminum would have to be melted down to liquid and cast in a die. Although the head’s edge is lined with many cooling fins, their basic geometry make them simple enough for a die. After the basic shape is cast, the head is machined so that it has blind holes to mount external sub-components too, and through holes for the intake and exhaust ports, and the spark plug. After the holes are made, each is tapped if necessary.

Although the material choice did not have a significant impact on the method that was used to produce the head, using metal over plastic rules out the possibility of injection molding or rapid prototyping processes. However, the engine’s head’s shape played a definitive roll in which manufacturing process was to make it. Because of the cooling fins, which surround the head on all sides, in addition to other asymmetrical features, the head could not be extruded. Also, because of the general three dimensional shape, it would not be possible to forge the head. The last factor influencing the manufacturing of the engine’s cylinder head is economics. This factor eliminates the possibility of investment casting, which would be entirely reasonable to use, except that it is significantly more expensive than die casting, and offers no significant advantage for this use.

Component Complexity

The cylinder head is a 2 on the complexity scale due to is variation on the geometry of a simple cylinder but the lack of subcomponents prevents the head from getting a higher complexity rating.

Wheel

Component Function

The function of the wheel is to provide an efficient method of movement by rotation along its axis. The component is tied to two different systems, each utilizing a different wheel. The front wheel is connected to the braking system as the brake pad will upon human signal from the brake handle, apply pressure and friction to the wheel, thus slowing the Goped. The rear wheel is connected to the engine and directly via the spindle. The spindle rotates and turns the wheel providing propulsion. Both wheels are completely exposed and are both housed in the front and rear forks of the Goped.

Component Form

• Shape: Circular
• Notable properties: groves cut out on both sides of the braking surfaces
• Three dimensional
• 6.3 in diameter, .79 in wide
• Shape is round to create a smooth rolling surface
• Roughly weights 3lbs
• Made out of rubber
• Manufacturing influenced the design by utilizing injection molding to create the tire.
• Traction is specific material property needed for the tires to grip the road.
• Societal- Hard rubber means the user isn’t going to deal with popped tires. It also creates easier maintenance when the tires are worn.
• Ridges are on both sides of the tire to improve braking surface.
• The color of the tire is black, from the material used, rubber.
• Smooth finish to provide optimal grip between the rubber and the road surface.

Manufacturing Methods

The wheel on the Goped is comprised of two separate components: the wheel itself (which, although is not technically a “rim,” will henceforth be referred to as such for the sake of clarity) and the tire. The rim is injection molded, which is evident due to the marks left on its outside from where it was punched out of the mold. The tire is also made by injection molding, which can be determined because of the seam around the middle of the “tread”. Although this is not necessarily obvious on a used tire because the rubber becomes worn down, the seam can be clearly seen. Once the rim and tire are manufactured, they are assembled by fitting the tire around the edge of the rim.

Component Complexity

The wheel rates a 2 on the complexity scale due the variation in geometry due to the ridge design on the side of tire. If the tire were a pure cylinder without ridges in a regular pattern then it would rank a 1 for using regular geometry with no variation and no sub-components.

Solid Modeled Assembly

The main component chose was the front wheel assembly. The group felt that it was a good set of components to illustrate because from a first glance, the system seems very basic and one might assume there is only the wheel and axle. There are however several parts involved in this assembly that someone might not know without inspecting the Goped. The explosion created makes each part visible and gives the reader a proper visualization of what components are involved.

The CAD program Autodesk Inventor was chosen to create the components because of its user-friendly interface. Inventor has a much better UI than its counterpart, AutoCAD, which allows the user to create the components accurately with ease. The creation of assemblies is also made very intuitive and simple, allowing for animations of the explosion and assembly to be made.

Figure 1. Wheel Assembly Explosion

Figure 2. Wheel

Figure 3. Wheel Bearing

Figure 4. Bearing Spacer

Figure 5. Axle Bolt

Figure 6. Washer

Figure 7. Lock Nut

Engineering Analysis: Force of Friction on Front Tire

Problem Statement: Determine the force needed to be applied to the brakes in order to bring the Go-ped from it's top speed to a stop.

Diagram:

Figure 8. Force of Friction Diagram

List of Equations:

fk =µkN

KE= 1/2mv^2

W=FD

Discussion: In the design stage it would be important to calculate the necessary force the front brakes need to stop the Go-ped from it's top speed, in order to select the necessary parts needed for adequate braking. This could be calculated by determining the normal force needed to counter the force kinetic friction of the caliper against the tire. Using the equation fk= µkN. Where µk is the coefficient of kinetic friction between the tire and the caliper, and N is the normal force due to the calipers. Assuming that it is an emergency stop, and all the weight is going to be shifted to the front wheel. The normal force is going to be equal to the mass of the rider and the mass of the scooter. N *µk is equal to the force of friction. To find the minimum distance required to stop, the kinetic energy, which is 1/2mv^2, is going to be equal to the force of friction times the distance. With kinetic energy known and the normal force known distance can be solved for.

Design Revisions

Gas Tank Cap

Figure 9: Gas Cap Picture

One design revision that would benefit the Goped would be to create better ventilation through the gas tank cap. Although the current design features a small pinhole in the center of the gap to allow airflow through the gas tank, it is not large enough to prevent the vacuum that can occur in the tank due to the removal of fuel. This design fault could possible cause fuel cutoff, which would result in stalling the engine. Therefore, the pinhole design poses a potentially serious performance issue.

A simple fix to this issue would be to modify the gas cap so that the ventilation hole is larger in diameter, thus allowing a higher air flow. In order to prevent spillage due to the larger vent, a one-way valve could be molded into the bottom side of the cap, where a vented cup housed a ball bearing of a larger width than the vent. If the tank were to tip, the bearing would fall into vent, thereby sealing it off from leakage.

One societal impact that this modification would make is that it would increase the reliability and performance of the Goped. When dealing with a product that is sold at the price point that the Goped is, our society has certain expectations about how it should perform, and the current design of the gas cap could seriously act against these notions. This proposed revision would eliminate the fuel cutoff problem without having any significant impact on cost, if any.

Brakes

Figure 10: Brake Calipers

One design revision that should be made to the Goped is the braking system. The current system has the brake caliper catch the rubber tire to stop the tire’s rotation, and thus stopping the linear motion of the Goped. The problem with this system is over time the rubber from tire at the brake contact point will wear away faster than the rest of the tire, if the consumer is not aware of this fact two things can happen, if enough material is removed then the tire may not be stable enough to ride on and fail while the Goped is in use potentially causing bodily injury. Also, when too much material is removed the brake may not be able to catch the wheel to stop it from rotating potentially causing more injury to the user.

Adding one simple piece to the wheel can prevent these potential failures. If a metal rim were added under each tire for the brake to catch and stop the wheel’s rotation, much like a bicycle, the rubber tire would remain intact. This would in turn make the Goped safer, a societal concern for many.

Rim Material

Figure 11: Stock Wheel

A design revision at the component level is changing the rim material from plastic to metal. The stock wheels are made out of injection molded plastic, these wheels have thin spokes that have failed during normal use. Through a previous experience with the Go-ped, the spokes on the front tire broke while riding over a crack in a sidewalk. This resulted in the loss of control of the scooter. If the spokes were made out of metal or more specifically, billet aluminum, they would be able to handle the stresses of normal riding. This would most likely raise the price of the Go-ped, as it would be more expensive to individually machine each wheel, as well as take longer to process. Many online retailers offer after wheels that cost approximately $60.00 for machined replacement wheels. If Patmont Motor Werks, the manufacturer of the product, included machined wheels instead of the stocked injection molded ones, it would reduce the risk of having them unexpectedly break at the spokes. This design change is based on a social factor, safety. Wheel failure could potentially cause major harm to the rider.