1,721,109 research outputs found
An Experimental Investigation of Digging Via Localized Fluidization, Tested With RoboClam: A Robot Inspired by Atlantic Razor Clams
No full textThe Atlantic razor clam, Ensis directus, burrows underwater by expanding and contracting its valves to fluidize the surrounding soil. Its digging method uses an order of magnitude less energy than would be needed to push the clam directly into soil, which could be useful in applications such as anchoring and sensor placement. This paper presents the theoretical basis for the timescales necessary to achieve such efficient digging and gives design parameters for a device to move at these timescales. It then uses RoboClam, a robot designed to imitate the razor clam's movements, to test the design rules. It was found that the minimum contraction time is the most critical timescale for efficient digging and that efficient expansion times vary more widely. The results of this paper can be used as design rules for other robot architectures for efficient digging, optimized for the size scale and soil type of the application
Shape and Form Optimization of On-Line Pressure-Compensating Drip Emitters to Achieve Lower Activation Pressure
No full textThis study presents the design and validation of on-line pressure-compensating (PC) drip irrigation emitters with a substantially lower minimum compensating inlet pressure (MCIP) than commercially available products. A reduced MCIP, or activation pressure, results in a drip irrigation system that can operate at a reduced pumping pressure, has lower power and energy requirements, requires a lower initial capital cost, and facilitates solar-powered irrigation systems. The technology presented herein can help spread drip irrigation to remote regions and contribute to reducing poverty, particularly in developing countries. The activation pressures of drip emitters at three flow rates were minimized using a genetic algorithm (GA)-based optimization method coupled with a recently published fluid-structure interaction analytical model of on-line PC drip emitter performance. The optimization took into account manufacturing constraints and the need to economically retrofit existing machines to manufacture new emitters. Optimized PC drip emitter designs with flow rates of 3.3, 4.2, and 8.2 lph were validated using precision machined prototype emitters. The activation pressure for all was ≤0.2 bar, which is as low as 16.7% that of commercial products. A limited production run of injection molded 8.2 lph dripper prototypes demonstrated they could be made with conventional manufacturing techniques. These drippers had an activation pressure of 0.15 bar. A cost analysis showed that low MCIP drip emitters can reduce the cost of solar-powered drip irrigation systems by up to 40%
Design and Preliminary Testing of a Prototype for Evaluating Lower Leg Trajectory Error as an Optimization Metric for Prosthetic Feet
Get PDFThis work presents the design and preliminary testing of a prosthetic foot prototype intended for evaluating a novel design objective for passive prosthetic feet, the Lower Leg Trajectory Error (LLTE). Thus far, all work regarding LLTE has been purely theoretical. The next step is to perform extensive clinical testing. An initial prototype consisting of rotational ankle and metatarsal joints with constant rotational stiffness was optimized and built, but at 2 kg it proved too heavy to use in clinical testing. A new conceptual foot architecture intended to reduce the weight of the final prototype is presented and optimized for LLTE. This foot consists of a rotational ankle joint with constant stiffness of 6.1 N·m/deg, a rigid structure extending 0.08 m from the ankle-knee axis, and a cantilever beam forefoot with bending stiffness 5.4 N·m2. A prototype was built using machined delrin for the rigid structure, three parallel extension springs offset along a constant radius cam from a pin joint ankle, and machined nylon as the beam forefoot. In preliminary testing, it was determined that, despite efforts to minimize weight and size, this particular design was still too heavy and bulky as a result of the extension springs to be used in extensive clinical testing. Future work will focus on reducing the weight further by replacing linear extension springs with flexural elements before commencing with the clinical study.Massachusetts Institute of Technology. Tata Center for Technology and DesignMassachusetts Institute of Technology. Department of Mechanical Engineerin
Passive Prosthetic Foot Shape and Size Optimization Using Lower Leg Trajectory Error
Get PDFA method is presented to optimize the shape and size of a passive prosthetic foot using the Lower Leg Trajectory Error (LLTE) as the design objective. The LLTE is defined as the root-mean-square error between the lower leg trajectory calculated for a given prosthetic foot by finding the deformed shape of the foot under typical ground reaction forces and a target physiological lower leg trajectory obtained from published gait data for able-bodied walking. In previous work, the design of simple two degree-of-freedom analytical models consisting of rigid structures, rotational joints with constant stiffness, and uniform cantilevered beams, have been optimized for LLTE. However, prototypes built to replicate these simple models were large, heavy, and overly complex. In this work, the size and shape of a singlepart compliant prosthetic foot keel made out of nylon 6/6 was optimized for LLTE to produce a light weight, low cost, and easily manufacturable prosthetic foot design. The shape of the keel was parameterized as a wide Bézier curve, with constraints ensuring that only physically meaningful shapes were considered. The LLTE value for each design was evaluated using a custom MATLAB script, which ran ADINA finite element analysis software to find the deformed shape of the prosthetic keel under multiple loading scenarios. The optimization was performed by MATLAB's built-in genetic algorithm. After the optimal design for the keel was found, a heel was added to structure, sized such that when the user's full weight acted on the heel, the structure had a factor of safety of two. The resulting optimal design has a lower LLTE value than the two degree-of-freedom analytical models, at 0.154 compared to 0.172, 0.187, and 0.269 for the two degree-of-freedom models. At 412 g, the optimal wide curve foot is nearly half the mass of the lightest prototype built from the previous models, which was 980 g. The design found through this compliant mechanism optimization method is thus far superior to the two degree-of-freedom models previously considered.Massachusetts Institute of Technology. Tata Center for Technology and Desig
Designing a Low Activation Pressure Drip Irrigation Emitter With Constraints for Mass Manufacturing
Get PDFThis work discusses the modeling and optimization of a drip irrigation emitter for reducing activation pressure. Our model formulation focuses on analytically characterizing fluidstructure interactions in an existing 8 liters per hour (lph) pressure-compensating online emitter. A preliminary experimental validation of the resulting model was performed for three different emitter architectures. This model was used as a basis for a genetic algorithm-based optimization algorithm that focused on minimizing activation pressure. The design variables considered in our formulation include, geometric features of the emitter architecture, and practical constraints from manufacturing. We applied our optimization approach to four emitters (with flow rates of 4, 6, 7 and 8.2 lph) and were able to lower activation pressure by more than half in each case. The optimization results for all four emitters were experimentally validated in lab-studies. We performed a more exhaustive validation study for the 8.2 lph emitter with an emitter manufacturer. Results from these experiments (which followed ISO standards) showed that the optimized 8.2 lph emitter had a 75% lower activation pressure when compared to the original emitter design.Jain Irrigation System Ltd
Why the Developing World Needs Mechanical Design
No full textThe dramatic and often unjust difference between life in the developed versus developing parts of the world is striking. For example, roughly 3 billion people still burn biomass to cook their meals; more people in the world have a mobile phone than have a toilet; Dallas Cowboy Stadium (AT&T stadium) requires three times the electrical power than the entire country of Liberia can produce; and a 73 s shower (using an EPA approved low-flow shower head) uses all of the daily clean water available per person in Rwanda. These conditions and others have given rise to an interesting area of design and research that spans multiple engineering disciplines and is called Engineering for Global Development (EGD). Work in this area is also often referred to as design for the developing world, design for development, and humanitarian engineering
Stakeholder and Constraint-Driven Innovation of a Novel, Lever-Propelled, All-Terrain Wheelchair
Get PDFThe Leveraged Freedom Chair (LFC) is a low-cost, all-terrain, lever-propelled wheelchair designed primarily for use in developing countries. LFC technology was conceived because 70 percent of wheelchair users in these markets live in rural areas and no currently available mobility aid enables them to travel long distances on rough terrain and maneuver in tight, indoor confines. Because developing world markets impose constraints on cost, durability, and performance, a novel solution was required to satisfy stakeholder requirements. The key innovation behind the LFC is its single speed, variable mechanical advantage lever drivetrain. The user effectively changes gear by shifting his hands along the levers; grasping near the ends increases torque, while grasping near the pivots enables a larger angular displacement with every stroke, which increases speed. The drivetrain is made from low-cost bicycle parts found throughout the developing world, which enables the LFC to be sold for $200 and be repairable anywhere.
During three user trials in East Africa, Guatemala, and India, stakeholder feedback was used to refine the chair between trials, resulting in a device 9.1 kg (20 lbs) lighter, 8.9 cm (3.5 in) narrower, and with a center of gravity 12.7 cm (5 in) lower than the first iteration. Survey data substantiated increases in performance after successive iterations. Quantitative biomechanical performance data were also measured during the Guatemala and India trials, which showed the LFC to be 76 percent faster and 41 percent more efficient during a common daily commute, and able to produce 53 percent higher peak propulsion force compared to conventional, pushrim-propelled wheelchairs. The LFC offers comparable performance at less than one-twentieth the cost of off road wheelchairs available in the rich world. Stakeholder feedback and the highly-constrained environment for which the LFC was created drove the technology towards a novel, innovative solution that offers a competitive advantage in both developing and developed markets. The paper concludes with a description of how the LFC is a “constraint-driven innovation.” This idea ties together the theories of “disruptive innovation” and “reverse innovation,” and may be used as a design tool for engineers striving to create technologies that have global impact.Singapore University of Technology and DesignInter-American Development BankNational Collegiate Inventors and Innovators AllianceD-Lab (Massachusetts Institute of Technology)Clinton Global InitiativeMassachusetts Institute of Technology. Office of the Dean for Graduate Education (Hugh Hampton Young Memorial Fellowship)Massachusetts Institute of Technology. Department of Mechanical EngineeringMassachusetts Institute of Technology. Public Service CenterMassachusetts Institute of Technology. Edgerton CenterMassachusetts Institute of Technology. Undergraduate Research Opportunities ProgramCalifornia Environmental Protection Agency. Air Resources Boar
Village-Scale Electrodialysis Desalination: Field Trial Validation
Get PDFThis paper presents the design and initial testing of a villagescale photovoltaic (PV) powered electrodialysis reversal (EDR) desalination system for rural India. The system was built by the authors and tested at the Brackish Groundwater National Desalination Research Facility in New Mexico. EDR has the potential to be more cost effective than currently installed village-scale reverse osmosis (RO) systems in offgrid locations due to the lower specific energy consumption of EDR versus RO at high recovery ratios. Lower energetic demand leads to lower solar power system costs for off-grid areas. The system tested in this study is designed to validate that energetic, product water quality, and water recovery requirements can be met. An analytical model of the system that accounts for the composition of natural groundwater is presented and compared to initial experimental results. Additionally, results from the USAID Desal Prize are presented showing the system's performance in regards to recovery ratio and product water quality. This paper presents the design methodology, resulting system parameters, and experimental results for an initial village-scale PV-EDR field trial.Jain Irrigation Systems Ltd.Massachusetts Institute of Technology. Tata Center for Technology and DesignMassachusetts Institute of Technology. Undergraduate Research Opportunities Progra
Validating a Method for Turbocharging Single Cylinder Four Stroke Engines
Get PDFThis paper presents a method for turbocharging single cylinder four stroke internal combustion engines, an experimental setup used to test this method, and the results from this experiment. A turbocharged engine has better fuel economy, cost efficiency, and power density than an equivalently sized, naturally aspirated engine. Most multi-cylinder diesel engines are turbocharged for this reason. However, due to the timing mismatch between the exhaust stroke (when the turbocharger is powered) and the intake stroke (when the engine intakes air), turbocharging is not used in commercial single cylinder engines. Single cylinder engines are ubiquitous in developing world offgrid power applications such as tractors, generators, and water pumps due to their low cost. Turbocharging these engines could give users a lower cost and more fuel efficient engine. The proposed solution is to add an air capacitor, in the form of a large volume intake manifold, between the turbocharger compressor and the engine intake to smooth out the flow. This research builds on a previous theoretical study where the turbocharger, capacitor, and engine system were modeled analytically. In order to validate the theoretical model, an experimental setup was created around a single cylinder four stroke diesel engine. A typical developing world engine was chosen and was fitted with a turbocharger. A series of sensors were added to this engine to measure pressure, temperature, and power output. Our tests showed that a turbocharger and air capacitor could be successfully fitted to a single cylinder engine to increase intake air density by forty-three percent and peak power output by twenty-nine percent.Massachusetts Institute of Technology. Tata Center for Technology and DesignNational Science Foundation (U.S.). Graduate Research Fellowship (Grant No. 1122374
Design of Agricultural Waste Charcoal Cooking Fuel for Developing Countries
Get PDFCharcoal made from agricultural waste (AWC), intended for use in developing countries, has the potential to be a cooking fuel with health, economic, and environmental benefits. Investigations were undertaken to integrate the technical understanding of the fuel with the real-world context in which it may be produced and used. Multiple formulations of AWC were studied to understand the impact of raw material variation on charcoal briquette emissions. A key finding is the viability of manure as a binder, which should improve AWC production costs and proliferation. In Nicaragua, AWC emissions, end user interest, and producer economic viability was examined. Emissions of AWC appear to be similar to or less than wood and wood charcoal. End user interest seems moderate, a positive outcome given the lack of charcoal usage in the region studied. Based on the outcomes of pilot production, development of the manufacturing system must account for local preferences.Massachusetts Institute of Technology. Tata Center for Technology and Design (Fellowship 2012)Martin Family Society of Fellows for Sustainability (Fellowship 2009-2010)SUTD-MIT International Design Centre (IDC) (2011-2012)Legatum Center for Development & Entrepreneurship (Massachusetts Institute of Technology) (Fellowship 2008-2009)Xerox Fellows Program (Massachusetts Institute of Technology) (Fellowship 2007-2008
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