ME360- Product Design Portfolio Spring 2021
ME360 Product Design is a junior level mechanical engineering course in which students build upon prior knowledge and apply engineering principles to solve problems, design, and build projects throughout the semester. This course focuses on improving generic design skills such as sketching and CAD modeling, utilizing FEA simulations, integrating electromechanical systems, and hands on construction and prototype testing of products. The following portfolio entries are quick entries to build upon these skills.
Entry No. 1: Snowy Solution
In a quick 10 minute exercise, students were tasked with creating a sketch of a solution to the following scenario: Salt and dirt dragged indoors by soiled shoes damages floors and carpets Sketch a solution! The purpose of this exercise was to work on problem solving and quick sketching to convey ideas.
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My thought process focused on solving two simple tasks. I first needed a way to remove the snow, salt, and dirt from the shoes, and I next needed to make sure the shoe is dried so it does not track anything indoors. One consideration is whether this device is to be used indoors or outdoors, and I opted for an outdoor device for easy clean up.
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The design includes a cement block with an elliptical cavity in the top. The block is heavy enough so that it stays in place, and it is placed on top of a generic outdoor doormat with bristles. The cavity's surface is covered in rubber textured spikes, so that the
user can place their foot inside this cavity and wipe it around to remove the snow and other debris. The user can then proceed to wipe the bottom of their shoe dry on the bristled doormat under the cement block in order to dry it. The bottom of the cavity has a hole drilled in it that then protrudes to the side for drainage and cleanup purposes. The user can simply pour water in the device after many people have used it and the dirt will wash and drain out of the cavity and away from the mat through a tube.
Assignment 1: Ideation- Equipment for the Classroom
Complete Problem Statement: Currently, students at Boston University and colleges nationwide feel uncomfortable attending class in-person in the middle of a pandemic. Although there are social distancing practices encouraged in classrooms, they are rarely enforced leading many students to bunch together to chat during breaks, and walk in and out of class in groups. Due to students' fear of catching the virus in a classroom setting, many students opt to attend lectures remotely despite the fact that there is an in-person option. This is detrimental to students’ education because students learn more effectively in an in-person classroom environment compared to a zoom lecture. The objective of the product is to notify students if they are a safe distance from other students, and provide updated real-time feedback as they adjust positions. The
goal with implementing this device is to encourage students to attend classes in-person by allowing them to feel safer around other students and providing a method of enforcing social distancing practices in order to provide a safer, improved learning experience to all students. The product is intended for use by college students, but it could be extended to other levels of education or the general public. It must be worn by all students in order to be effective, as it only detects another person if they also have the charged device.
Product Idea and Sketches: My idea to combat this problem is to design a wearable device that alerts users if they are breaking safe social distancing protocol in the classroom. The device will utilize an ESP32 chip with integrated wifi and Bluetooth to detect the distance the device is away from another device, and notify the student via LED colored lights on their safety adherence shown to the right.
Design 1: Watch/ Wristband: This idea takes inspiration from a watch, and uses a similar watchband, but instead of the watch face there is an LED light. Alternatively, the device could have a strip of LEDs running around the band as shown in the bottom figure. Of the two watch ideas, the top one with only one LED is the best because it is more sleek and less distracting.
Design 2: Keychain:
The chip, circuitry, and LED will be encased and attached to a keychain. This is a simple design that is easily portable, but one limitation is that students would have to be carrying their bag on them at all times which may be unrealistic.
Design 3: Phone Case:
The circuitry components are encased in the back of the phone case, and the low power bluetooth chip can be charged while the phone is being charged. This is easily portable and accessible, however phones are often put away inside bags, and having them out in a classroom is distracting and should be discouraged.
Pugh Chart and Design Selection
Important considerations when selecting the design of this product are centered around the behavior and mindset of college students, thus criteria such as wearability, level of distraction, likelihood of always having it on them, fashion, and implementation are key considerations. Ultimately, the best design for the purpose of this device is the wristband, mainly because will always be on the student and it is less distracting than a phone. The main downside of the key chain design was the fact that it would most likely be attached to a backpack or bag, and it is important to stay a safe distance away from other students even when they aren't carrying bags around the classroom. The main downside of the phone case was the fact that it would require students to always have their phone out and be looking at it, causing a major distraction in a learning environment.
Strategy for Implementation
The use of this product would be favored to students and professors at BU in the Boston area. Similar to the way lab kits are distributed by mail, the wristband technology would be sent to students who opt into the in-person class preference, encouraging them to attend their classes on campus and foster a safe and improved learning experience. Similar to the current method for entering campus buildings by showing the green ‘cleared’ badge on patient connect, students could only be allowed in campus buildings if they are wearing the wristband. Other implications of the device include wearing them in other crowded areas of campus such as the dining hall and the library.
Benchmarking
A software product with a similar goal as my product is Apple and Google’s exposure notification technology that they co-created. The objective of this technology is to notify people who have been in a close range to someone who has tested positive for COVID, and this is tracked by using bluetooth radio signals between cell phones. Similarly, my wristband uses bluetooth signals to track the distance between devices, but the difference is that it provides real time feedback on your distance between people rather than waiting for someone to test positive before notifying the user. Another product related to the ideas of my product is called VergeSense, and it is an indoor occupancy tracking company. It utilized various sensor technologies, but one of them is Beacon/ BLE that utilized bluetooth to measure occupancy and distance between people.
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https://vergesense.com/product
https://www.google.com/covid19/exposurenotifications/
http://bit.ly/2Ma7tyK
ME360 Assignment 2- Skateboard Deck Design
Goal- The goal of this project is to design and select the material for the deck of a skateboard that satisfies the project’s constraints.
Constraints
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Support users weighing up to 180 lbs
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Suitable for users with a shoe size of 12
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The deck must deflect a vertical displacement less than 0.375 inches
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Ensure a safety factor of at least 3
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Assume the board is supported by revolute joints (hinges above the front and back truck axels)
In order to be able to design a deck that works for users defined by the constraints, a bit of research had to be conducted about skateboarding. Information that is relevant to the project is summarized below:
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Skateboards are generally chosen based on width, not length
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For size 12 feet, the deck should be at least 8’’
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Average length is 28-32'', longer decks help tall users keep balanced
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The area of a medium width size 12 shoe is 48 square inches if it is simplified to be a rectangle
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Most skateboard decks are made of glue and wood
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Cheap plywood is typically a softwood, such a pine and the plies are made from small pieces of wood that are epoxied together
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Curving of the board on front and the back is there for gain leverage for tricks, to put your foot on it while riding, and to pop it up and stand on it/ stop yourself while riding
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Boards are generally curved down in the center of the board where feet go in order to offer more control to users while riding
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All boards flex a little- they bend a bit under forces, if they didn't have flex they would be brittle and snap (yield) more often
Different style skateboards that are used for different purposes are shown to the left. I opted to design a deck that mimicked the 'regular' style because it is the most popular, common, and versatile design.
Design Decisions
The board that I designed in SolidWorks took on the general shape of the regular skateboard deck. Because the design must work for a size 12 shoe, I made the skate deck 8.25’’ which is a popular size for that shoe size. No specifications were given for height of the user, but because a slightly longer board can benefit a taller user, I opted to make the board on the longer side at 31.5” inches in length. Size 12 feet is fairly large, so I made the assumption that the user might be tall and could benefit from a board with these dimensions. The user weight could be up to 180 lbs, so I made sure when conducting finite element analysis to use this upper limit as the weight, and I distributed it over the area of a size 12 foot. The ‘worst case scenario’ would be having all the weight on one foot rather than spread between two, so I analyzed the board with this scenario. I added small supports sticking off the board with a hole extruded through that acts as a fixed hinge joint and is analyzed as this type of fixture. Because the board is curved, I could not put a hole through the board, and this scenario would be unrealistic in comparison to truck axels. The last two design decisions were the thickness and the material selection which were optimized to create the lightest board that still met all the project constraints. The SolidWorks CAD model showing the shape of the deck is shown below.
Finite Element Analysis (FEA) process
After modeling the skateboard deck in SolidWorks, I utilized the simulation ad-on to simulate the loading of a 180 pound person on the deck of the board and analyze the resulting displacement and stresses on the board. To do this, a material was applied uniformly to the part, and a static external load was defined as a pressure of 3.75 psi was applied over the area of the a size 12 shoe. This is equivalent to the force distribution of a 180 pound person. Additionally, the fixtures were defined to be fixed hinges that represented the revolute joint that a skateboard truck provides. The allowed for a one degree of freedom kinematic pair that supported flex of the deck in the vertical direction. After meshing the part and running the simulation, the results for stress, strain, and displacement could be viewed and analyzed.
Another aspect of the finite element analysis was optimizing the design with FEA by determining a smallest thickness of the board (and thus lightest weight) that still ensures a safety factor of 3. Two materials that I compared with the FEA optimization process were Bamboo and Pine. Both are common plywood materials used for skateboard decks because they are lightweight and allow for flex of the board.
The figure above shows the process for applying an external load to the deck of the board.
FEA with Pine
The figures to the right show the FEA run on a board made with Bamboo. The material's mechanical properties were defined by consulting Granta, a resource for material selection. The top figure shows the stress on the board, and the bottom figure shows the displacement of the board. The maximum stress is less than 1/3 of the yield strength, ensuring a safety factor of 3. The deflection is 1.4 mm, also meeting the displacement constraint.
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The figures to the left show the same FEA run on a board made of pine. Similarly, the safety factor is 3, and the displacement is less than the maximum allowance of 0.375 inches.
FEA with Bamboo
Optimization and Material Selection
To optimize the board to have the lightest weight, I optimized the thickness dimension to the smallest thickness possible while still allowing the board to have a safety factor of 3. This meant that the board was optimized to have the thinnest deck possible while the maximum stress on the board did not exceed 1/3 of the yield strength for the selected material. After optimizing the dimensions of bamboo board, the minimum thickness required was 0.515 in and the resulting weight of the board was 3.24 lbs. After optimizing the dimensions of the pine board with the maximum stress parameter, the minimum thickness was 0.53 inches thick, resulting in a board that only weighed 1.63 lbs!
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In comparison to metals, such as aluminum alloys, wood materials work better for skateboard decks. Selecting Aluminum 6061 for the material and optimizing the board with the parameters above, the board weighed a whopping 9.4 lbs!
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Ultimately, both bamboo and pine are good material selections for this skateboard deck design because the average skateboard deck on the market is 2-5 lbs. I decided the best lightweight material to use for this design would be Pine because it results in the lightest weight while meeting all the requirements outlined by the constraints. The material properties used for pine as defined by Granta and used by SolidWorks to run the FEA are shown right.
Project Conclusions and Future Work
In conclusion, this assignment allowed me creative freedom to explore mechanical design options and design an optimized skateboard deck that minimized weight, deflection, and stress on the material. Future applications include modeling the truck, axels, and wheels on SolidWorks and running FEA simulations with more realistic force distribution and interactions between the parts. Additionally, the modeled deck could be built using Pine (or a different wood) and woodwork machinery and tested in real life applications. FEA is a useful tool because it allows companies to optimize a design before spending time and money prototyping and testing it.
Sources
https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1077&context=matesp
https://www.skatedeluxe.com/blog/en/wiki/skateboarding/skateboard-wiki/decks/
ME360 Assignment 3- Pen Mechanism
Goal- Design a (1-DOF) linkage mechanism that positions a pen on a flat, horizontal surface and afterwards stores it inside a fixed cap that prevents it from drying. The end position after positioning the pen on the paper should lie 1 cm lower than the pen cap and mechanism mounted on a raised surface.
Design Considerations and Process
I decided to make a four bar linkage mechanism because it is a simple design and can be motorized to convert rotational motion to translational motion in order to reposition the pen. Utilizing a stepper motor would further allow precise positioning of the pen at 1 cm lower than the mechanism mounting surface. The 4 bar linkage is to have 2 longer bars of equal length and 2 shorter bars of equal length. The longer bar is to hold the pen, meaning it needs to be slightly longer than the pen itself so the tip can hang below the bar and there can be space for the linkages and sufficient motion to occur. Additionally, the pen needs to be mounted on a bar that is fully in front of the other bars so that it can move an entire semi circle arc without interference. The design sketches are shown right.
SolidWorks Simulation and Analysis
Each part was modeled in SolidWorks to simulate the motion of the prototype. This included the bars, a motor, makeshift pen cap, an object to fasten the pen to the bar, and a step file of a Sharpie that was downloaded from GrabCad (https://grabcad.com/library/sharpie-pen-2). These were modeled out of Aluminum 1020, which would be the best option although the prototype was created with cheaper materials. An assembly was created within SolidWorks representing the linkages and setup of the mechanism, and was then further animated to simulate the motion of the system resulting from the motor. This shows the oscillating nature of the stepper motor, that can be changed based on the number of times the mechanism is desired to move the pen. The simulation is shown below.
The motor speed of the simulation is set to 0.5 Hz so that the pen moves from one position to the other in 500 ms. The magnitude of the motor torque versus time as it undergoes multiple oscillations is shown below.
Prototype
The linkage bars were cut with an exacto knife from foam board. They are each 2 cm in width, and created with foam sheets that were provided that is 0.25 cm thick. Additionally, a hole was punched into the foam 0.25 cm from the end that allowed for the linkage with metal brads to be made, allowing for stability and rotation about the linkage. The stepper motor was used in combination with a motor driver and an Arduino to motorize the mechanism. In order to determine what angle to move the motor, the math is shown below. In the Arduino programming, the number of steps for a full revolution (360 degrees) is defined to be 2048, so 185.7 degrees would be 1,056
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steps (math shown). This number was used to program the Arduino, however, the pen’s pressure on the paper is adjustable based on this number. For example, by turning the motor 1,060 steps clockwise, the pressure of the pen against the paper is increased. The Arduino code used to turn the oscillating stepper motor is shown.
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The mechanism was mounted on top of 1 cm worth of foam boards, and the pen was moved to a paper 1 cm below. A video showing the physical prototype in action oscillating between the two positions is shown below.
ME360 Assignment 4- 2.5 Axis Motion System
Goal- Design and build the electro-mechanical interface of a 2.5 axis cartesian motion system. This involves creating a product prototype, and integrating the mechanical and electrical components to accomplish a certain task. This project was done in a group of four, and we decided to build a robotic clock that wrote the time on a whiteboard and erased it every minute.
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The components were designed with CAD prior to any of the actual building taking place. After designing each part and ensuring the assembly was correct, the components for 3-D printing were printed using PLA filament. The tolerances and fits of each part was important so that pieces could slide and stay together, and sometimes we would have to reprint parts to get the tolerance correct. An assembly and motion analysis were also created within SolidWorks to demonstrate the motion of the components relative to one another. The SolidWorks animation is shown right.
The end product is made of 80-20 Aluminum, 3-D printed parts, and controlled by two stepper motors, a stepper shield, 1 servo motor, an Arduino, and a linear belt. The end effector houses a marker and an eraser that are actuated with a servo motor that switches between the two. The 3 positions are eraser down, marker down, and a neutral position when the robot needs to lift up between numbers and does not want writing or erasing to take place. This is done with a function that is passed a zero, one, or negative one depending on the desired position of the end effector. This servo motor contributes to the motion in the z- direction.
The motion in the x-direction takes place when both the linear belts move in the same direction at the same time. The motion in the positive y-direction takes place when the belts move towards each other, and the motion in the negative y-direction takes place when the belts move away from each other. The motion and direction of the linear belts is controlled by the two stepper motors.
The time is sent over serial to the arduino using python. The time is then written to resemble 7-segment digital displays, this way all the lines are straight and only either in the x or y direction, making coding for each number easier. The lines for each of the 7 segments were created by programming the motors to move a certain number of steps in a specified direction. Therefore, after the motion to create each of the segments had been defined, a program was written to define which of the segments was necessary to write each digit 0-9. Code can be downloaded here: