The root of all engineering products is a problem that needs to be solved. This problem can vary from improving the quality of life to subduing threats to making things more accessible to a wider range of people. Once the designing, modeling, and prototyping is completed, evaluation of the product occurs; this is used as a metric for success. Evaluation of the product is determined by a few factors such as if the product works and how well it solves the problems it aimed to tackle. Take Space X for example; Elon Musk, the CEO of the company, recently and successfully tested the Falcon Heavy, a rocket that aimed to solve a couple problems: to create a system that could place heavier instruments into Earth orbit, fly interplanetary missions, and lower the cost of launching things into space. And after the first launch, it can safely be said that the company is very successful. At this point in my college career (a first semester sophomore), I have never gotten the opportunity to walk through the steps of making a product to solve a problem. The project for this class allowed me this experience as I made a product to solve a problem, went through all the steps of the design and manufacturing process, and completed an evaluation to determine the success of the product.
Project Goals: The major goal of this project was to work as a group to create a prototype of a product that could solve a problem for a client. Once my group had an idea, we would all get to work over a two month period to build the prototype using materials and machinery offered to us by the Engineering Product Innovation Center (EPIC) at Boston University.
Learning Objectives: Throughout the process of completing this project, I had to employ common industry practices and basic engineering skills in order to successfully create the prototype. These skills are as follows:
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Problem Statement
Today, 70% of adults in the US own cellphones, and for many it is a primary means of communication. However, once those cellphone batteries die, these adults become isolated in the midst of these natural disasters. With these incentives in mind, the following problem statement was established: to engineer a low-cost, portable and durable device that can convert human driven work into energy that can fully charge a cellphone in less than 15 minutes of human work time. During debilitating weather conditions, the only simple alternative is using human power to generate electricity. Therefore, the goal of this project is to utilize this human power in order to charge a smart phone. |
Project Objectives
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The Design
Three basic designs were considered for the product, each one based off of a different machine already in existence: a rowing machine, a treadmill, and a crank mechanism(i.e. flashlight crank or bike). In determining which design to continue with, the effectiveness of each design was evaluated based on factors including functionality, efficiency, cost and power generation. The information of this evaluation was tabulated in the following Morph Chart and Internal Aspects-Chart:
Three basic designs were considered for the product, each one based off of a different machine already in existence: a rowing machine, a treadmill, and a crank mechanism(i.e. flashlight crank or bike). In determining which design to continue with, the effectiveness of each design was evaluated based on factors including functionality, efficiency, cost and power generation. The information of this evaluation was tabulated in the following Morph Chart and Internal Aspects-Chart:
The treadmill appeared flawless in its function means ability, but when it came to the internal aspects of the device, it was extremely flawed. The treadmill design provided minimal portability and durability, and it wasn't safe for elderly people to use in the current design. Additionally, manufacturing would be disastrous simply due to the absurd estimated cost of the device. Of the remaining designs, the rowing machine-based design was chosen based on the fact that the power that could be generated by a rowing motion was determined to be greater and more efficient than a pedaling motion. The basis of these results came from the power output on standard rowing machines and treadmill equipment found at a local gym. With each set at the lowest resistance, on average, someone using a rowing machine (without the use of legs) could produce around 50-60 Watts whereas someone using a stationary bike could only generate 40-50 Watts.
Modeling
Once the design was chosen, it was time to start modeling the prototype. In essence, this product would be a modified, shrunken rowing machine found at a gym that would generate power, convert and store that energy in a battery, and charge a phone via a charging circuit. To begin, a function chart was made in order to conceptually model the machine:
Once the design was chosen, it was time to start modeling the prototype. In essence, this product would be a modified, shrunken rowing machine found at a gym that would generate power, convert and store that energy in a battery, and charge a phone via a charging circuit. To begin, a function chart was made in order to conceptually model the machine:
Following the completion of the function chart, it was easy to create a machine that would perform all of these functions. First, a CAD model was created that showed off the mechanics of the machine. While designing this product, my group had to figure out a way to shrink the internal mechanism of a rowing machine into a smaller space. This was achieved via a system of rollers, chains, and elastic bands. This all interacted with a fly wheel mounted on a ratchet; as the user pulled on the cord, the flywheel spun and preserved that momentum which was transferred to a motor. This motor would later be attached to a circuit that would charge an internal battery and provide a safe current and voltage in order to charge a standard cell phone. The charging circuit was also modeled via a program called LTSpice.
The Final Product
The prototype was crafted out of cheap materials such as wood and a re-purposed rowing machine parts. In the end, we were successful in shrinking the internal structure of the rowing machine into a smaller volume. Further, we were able to mount all of the circuitry such that it was out of the way of the moving parts. This was complete with a door that allowed access to the inside of the machine in case it needed to be serviced. Above all, the machine was able to charge the internal battery, and at the flick of a switch, the battery was able to charge my cell phone without completely destroying it. Images of the final product are shown below:
The prototype was crafted out of cheap materials such as wood and a re-purposed rowing machine parts. In the end, we were successful in shrinking the internal structure of the rowing machine into a smaller volume. Further, we were able to mount all of the circuitry such that it was out of the way of the moving parts. This was complete with a door that allowed access to the inside of the machine in case it needed to be serviced. Above all, the machine was able to charge the internal battery, and at the flick of a switch, the battery was able to charge my cell phone without completely destroying it. Images of the final product are shown below:
Evaluation
The completed human-powered phone charger performed well overall, meeting many of the objectives and requirements. Mechanically, our product worked as expected, with the linear motion from the pulling of the handle generating the required rotational motion to spin the flywheel, and hence, the motor. Without pulling too hard, our prototype could generate an average of 8 volts, although a much stronger and faster pull could generate upwards of 15 volts. Using the average of 8 volts for our calculations, we computed that our charger outputs 1.26 amps of current, and 10.08 Watts of electrical power. From this, we determined that to fully charge a phone from a dead battery, it would take 1.1 hours of activity, while to fully charge the battery pack, it would take 2.14 hours of activity. In addition, 15 minutes of pulling would generate enough energy to power roughly 12 percent of a phone.
The completed human-powered phone charger performed well overall, meeting many of the objectives and requirements. Mechanically, our product worked as expected, with the linear motion from the pulling of the handle generating the required rotational motion to spin the flywheel, and hence, the motor. Without pulling too hard, our prototype could generate an average of 8 volts, although a much stronger and faster pull could generate upwards of 15 volts. Using the average of 8 volts for our calculations, we computed that our charger outputs 1.26 amps of current, and 10.08 Watts of electrical power. From this, we determined that to fully charge a phone from a dead battery, it would take 1.1 hours of activity, while to fully charge the battery pack, it would take 2.14 hours of activity. In addition, 15 minutes of pulling would generate enough energy to power roughly 12 percent of a phone.
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Although we did not meet the 15 minutes of activity for a full charge requirement, we concluded that our prototype was still successful, as this time requirement is simply near impossible to reach without damaging the phone. With 15 minutes of activity, one could charge a dead phone up to 12 percent, enough to make calls, texts, and then some.
Improvements could be made to the physical design. Although we used wood for the frame, as it was both cheap and readily available, in our prototype, it is heavy and unaesthetic. Were we given more time and money to build this, we could have used a transparent plastic, such as acrylic or polycarbonate, which is lightweight, easy to machine, and provides the user an inside view of our product. The same material could be used to create a protective casing for the exterior part of the flywheel. Currently, the flywheel is sticking out of the frame and when spinning at very high speeds, is extremely dangerous. A hemispheric plastic casing would easily solve the problem. In addition, we could cut down the size of our device, especially its length. Though it is not too large and is already able to fit in a closet or on a shelf, it is possible to shorten the length by more than a foot in order to make our device even smaller and more portable. Furthermore, we could improve the small hatch on the side of the box that allows the user to maintain and/or fix parts of the machine. With these modifications and additions to our prototype, our human-powered phone charger can become more effective, more aesthetically pleasing, more user friendly, and an overall better product for our client.
Improvements could be made to the physical design. Although we used wood for the frame, as it was both cheap and readily available, in our prototype, it is heavy and unaesthetic. Were we given more time and money to build this, we could have used a transparent plastic, such as acrylic or polycarbonate, which is lightweight, easy to machine, and provides the user an inside view of our product. The same material could be used to create a protective casing for the exterior part of the flywheel. Currently, the flywheel is sticking out of the frame and when spinning at very high speeds, is extremely dangerous. A hemispheric plastic casing would easily solve the problem. In addition, we could cut down the size of our device, especially its length. Though it is not too large and is already able to fit in a closet or on a shelf, it is possible to shorten the length by more than a foot in order to make our device even smaller and more portable. Furthermore, we could improve the small hatch on the side of the box that allows the user to maintain and/or fix parts of the machine. With these modifications and additions to our prototype, our human-powered phone charger can become more effective, more aesthetically pleasing, more user friendly, and an overall better product for our client.