Scooter Design Portfolio
Introduction:
The goal of this project was to design and build a fully functional scooter almost entirely constructed out of PVC. We designed our scooter to meet specific criteria, including:
• Weight – to not exceed 12 lbs.
• Deflection – no visible static deflection
• Dimensions – able to fit in a 36” x 36” x 24” envelope
• Strength – survive a 10” jump without breaking
• Materials - nearly all members are fabricated out of PVC, including connections (minus
bolts, small hardware, wheels)
• Safety - no excessive deformation, sharp or jagged corners, dragging of components on
ground, loose connections, or other safety hazards
• Braking – fully functional handbrake or a redundant braking system
• Desirability – would a college student be interested in owning this scooter?
The project was broken up into a design phase, a manufacturing phase, and a testing phase. Designing the scooter started with team brainstorming of various scooter deck and fork designs. Hand calculations, SolidWorks FEA, and manufacturability assessments were done on each idea, narrowing our ideas to a single design. After acquiring our materials, the scooter was built in the Cal Poly machine shops where we performed various turning, milling, drilling, welding, and affixing operations. Testing our scooter involved measuring for design criteria fulfillment, racing the scooter against other teams’ prototypes, and most excitingly, riding our scooter off a 10-inch jump.
Solution Description:
Our deck design consisted of three 1.5-inch diameter PVC tubes spanning the length of the deck, encased in paneling. The tubes were affixed with two 3D printed end caps and one 3D printed housing piece in the center of the deck that the pipes ran through. Water jet cut PVC panels were put in-between the 3D printed blocks, giving the deck its “striped” appearance.
We created two connection points between the deck and the fork using various ABS fittings, one coming straight out of the center deck pipe, and the other branching off of the center deck pipe at a 45-degree incline. All PVC pipe to ABS fitting connections were both JB Welded and bolted. The ABS fitting diameters connected to the steering column were slightly larger than that of the column, allowing the column to rotate with minimal friction and thus allowing the rider to easily steer the scooter. Caster wheels were bolted to the base of the steering column and to the rear of the deck. The steering column was a 30” long, 1.5” diameter PVC pipe, connected to 1.5” diameter handle bars through an ABS T-fitting. We chose all our fittings to be ABS material because it was much lighter than PVC without compromising strength, given the loads applied to our scooter.
The brake consisted of a curved piece of steel that cupped the backside of the rear wheel. A tube was welded to the end of the brake and affixed to hinges mounted to the underside of the deck, just above the wheel. This gave the brake an axis to rotate about. A hollow steel tube was welded further down the curved steel piece and brake cables were drawn through this tube and welded together. The cable was attached to a hand brake, harvested from an old bicycle, which was then attached to one of the scooter’s handle bars. A rubber band was attached to the underside of the deck and to the brake, which kept the brake off of the wheel when not in use. Additional rubber bands were wrapped around the brake to increase contact friction.
Analysis:
We designed our scooter knowing that the greatest stress it would experience would be from going off of the 10” jump. During the design phase, we figured out what this load was going to be by jumping off a 10” curb with an accelerometer. The accelerometer indicated that the deceleration from a 10” drop was approximately eight times the acceleration of gravity. Assuming a rider weight of 200 lbs, we modeled this force as a point load on all of our potential deck designs and calculated by hand the maximum displacement, factor of safety with respect to bending, and factor of safety with respect to shear. We also performed an FEA analysis in SolidWorks to get a better visualization of how both the static and dynamic loads affected each deck design. Our final design yielded a factor of safety of 4.89, a maximum displacement of 0.08 inches, and a section modulus of 4 cubic inches. We also calculated the critical buckling load and factor of safety for a steering column of only 1 inch in diameter, a third smaller than what we actually used. Our calculations yielded a critical buckling load of 27,418 lbf. We assumed that the rider would put a maximum of 25% of their body weight on the scooter fork. This equates to an impact force of 10,304 lbf for a 200 lb rider, which produces a factor of safety with respect to buckling of 2.66. However, we decided to use a 1.5-inch pipe for our steering column, increasing the safety and rigidity.
Conclusion:
Our scooter performed well at the testing day “scoot-off”. Our scooter had no visible deflection under a static load, easily fit within the required dimensions envelope, and weighed less than 12 lbs. The brake didn’t generate quite enough friction force on the rear wheel for the scooter to stop in a reasonable distance, but this could easily be modified by making the brake cables more taught. The idea to add the bolts to each tube-to-fitting connection site didn’t come until after the scooter fork broke during the race. This was because we initially only JB Welded each connection, but after quickly inserting the bolts our scooter seemed indestructible. Our scooter easily survived going off the 10” jump multiple times.
This project was the first time I had designed something to meet specific criteria, manufactured a fully functional prototype of the design, and then tested it to see how it met that criteria. I learned a lot about the importance of designing for manufacturability. PVC only comes in certain sized pipes and sheets, so our design had to take that into account. The challenge was designing the scooter to meet the specifications given our available materials, manufacturing resources, and limited time frame. This is what real engineering design is all about and not only did this project give me valuable experience in engineering design, it also gave me affirmation that becoming a designer is something that I am very interested in.
The most challenging aspect of the project was designing a fork to connect the deck and the steering column that made for easy manufacturing but was also strong enough to withstand the jump. The fork is the weakest section of the scooter due to the numerous connections, and this was made apparent when it broke while I was riding it in the race. Out of all of the parts of the scooter, the fork underwent the most design evolutions because throughout both the design and manufacturing phases we ran into several obstacles. The last evolution was repairing it in the middle of the race by reinforcing all the connection sites with bolts. My proudest moment of the whole project was watching my teammate successfully take our scooter off the 10” jump, as that was the last criterion we needed to meet, thus making our scooter a total success.
The goal of this project was to design and build a fully functional scooter almost entirely constructed out of PVC. We designed our scooter to meet specific criteria, including:
• Weight – to not exceed 12 lbs.
• Deflection – no visible static deflection
• Dimensions – able to fit in a 36” x 36” x 24” envelope
• Strength – survive a 10” jump without breaking
• Materials - nearly all members are fabricated out of PVC, including connections (minus
bolts, small hardware, wheels)
• Safety - no excessive deformation, sharp or jagged corners, dragging of components on
ground, loose connections, or other safety hazards
• Braking – fully functional handbrake or a redundant braking system
• Desirability – would a college student be interested in owning this scooter?
The project was broken up into a design phase, a manufacturing phase, and a testing phase. Designing the scooter started with team brainstorming of various scooter deck and fork designs. Hand calculations, SolidWorks FEA, and manufacturability assessments were done on each idea, narrowing our ideas to a single design. After acquiring our materials, the scooter was built in the Cal Poly machine shops where we performed various turning, milling, drilling, welding, and affixing operations. Testing our scooter involved measuring for design criteria fulfillment, racing the scooter against other teams’ prototypes, and most excitingly, riding our scooter off a 10-inch jump.
Solution Description:
Our deck design consisted of three 1.5-inch diameter PVC tubes spanning the length of the deck, encased in paneling. The tubes were affixed with two 3D printed end caps and one 3D printed housing piece in the center of the deck that the pipes ran through. Water jet cut PVC panels were put in-between the 3D printed blocks, giving the deck its “striped” appearance.
We created two connection points between the deck and the fork using various ABS fittings, one coming straight out of the center deck pipe, and the other branching off of the center deck pipe at a 45-degree incline. All PVC pipe to ABS fitting connections were both JB Welded and bolted. The ABS fitting diameters connected to the steering column were slightly larger than that of the column, allowing the column to rotate with minimal friction and thus allowing the rider to easily steer the scooter. Caster wheels were bolted to the base of the steering column and to the rear of the deck. The steering column was a 30” long, 1.5” diameter PVC pipe, connected to 1.5” diameter handle bars through an ABS T-fitting. We chose all our fittings to be ABS material because it was much lighter than PVC without compromising strength, given the loads applied to our scooter.
The brake consisted of a curved piece of steel that cupped the backside of the rear wheel. A tube was welded to the end of the brake and affixed to hinges mounted to the underside of the deck, just above the wheel. This gave the brake an axis to rotate about. A hollow steel tube was welded further down the curved steel piece and brake cables were drawn through this tube and welded together. The cable was attached to a hand brake, harvested from an old bicycle, which was then attached to one of the scooter’s handle bars. A rubber band was attached to the underside of the deck and to the brake, which kept the brake off of the wheel when not in use. Additional rubber bands were wrapped around the brake to increase contact friction.
Analysis:
We designed our scooter knowing that the greatest stress it would experience would be from going off of the 10” jump. During the design phase, we figured out what this load was going to be by jumping off a 10” curb with an accelerometer. The accelerometer indicated that the deceleration from a 10” drop was approximately eight times the acceleration of gravity. Assuming a rider weight of 200 lbs, we modeled this force as a point load on all of our potential deck designs and calculated by hand the maximum displacement, factor of safety with respect to bending, and factor of safety with respect to shear. We also performed an FEA analysis in SolidWorks to get a better visualization of how both the static and dynamic loads affected each deck design. Our final design yielded a factor of safety of 4.89, a maximum displacement of 0.08 inches, and a section modulus of 4 cubic inches. We also calculated the critical buckling load and factor of safety for a steering column of only 1 inch in diameter, a third smaller than what we actually used. Our calculations yielded a critical buckling load of 27,418 lbf. We assumed that the rider would put a maximum of 25% of their body weight on the scooter fork. This equates to an impact force of 10,304 lbf for a 200 lb rider, which produces a factor of safety with respect to buckling of 2.66. However, we decided to use a 1.5-inch pipe for our steering column, increasing the safety and rigidity.
Conclusion:
Our scooter performed well at the testing day “scoot-off”. Our scooter had no visible deflection under a static load, easily fit within the required dimensions envelope, and weighed less than 12 lbs. The brake didn’t generate quite enough friction force on the rear wheel for the scooter to stop in a reasonable distance, but this could easily be modified by making the brake cables more taught. The idea to add the bolts to each tube-to-fitting connection site didn’t come until after the scooter fork broke during the race. This was because we initially only JB Welded each connection, but after quickly inserting the bolts our scooter seemed indestructible. Our scooter easily survived going off the 10” jump multiple times.
This project was the first time I had designed something to meet specific criteria, manufactured a fully functional prototype of the design, and then tested it to see how it met that criteria. I learned a lot about the importance of designing for manufacturability. PVC only comes in certain sized pipes and sheets, so our design had to take that into account. The challenge was designing the scooter to meet the specifications given our available materials, manufacturing resources, and limited time frame. This is what real engineering design is all about and not only did this project give me valuable experience in engineering design, it also gave me affirmation that becoming a designer is something that I am very interested in.
The most challenging aspect of the project was designing a fork to connect the deck and the steering column that made for easy manufacturing but was also strong enough to withstand the jump. The fork is the weakest section of the scooter due to the numerous connections, and this was made apparent when it broke while I was riding it in the race. Out of all of the parts of the scooter, the fork underwent the most design evolutions because throughout both the design and manufacturing phases we ran into several obstacles. The last evolution was repairing it in the middle of the race by reinforcing all the connection sites with bolts. My proudest moment of the whole project was watching my teammate successfully take our scooter off the 10” jump, as that was the last criterion we needed to meet, thus making our scooter a total success.
3 Teammates
