Stakeholder and Constraint-Driven Innovation of a Novel, Lever-Propelled, All-Terrain Wheelchair

The 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

Designing a Low Activation Pressure Drip Irrigation Emitter With Constraints for Mass Manufacturing

This 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

Passive Prosthetic Foot Shape and Size Optimization Using Lower Leg Trajectory Error

A 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

A Theoretical Investigation of the Critical Timescales Needed for Digging in Dry Soil Using a Biomimetic Burrowing Robot

RoboClam is a bio-inspired robot that digs into underwater soil efficiently by expanding and contracting its valves to fluidize the substrate around it, thus reducing drag. This technology has potential applications in fields such as anchoring, sensor placement, and cable installation. Though there are similar potential applications in dry soil, the lack of water to advect the soil particles prevents fluidization from occurring. However, theoretically, if the RoboClam contracts quickly enough, it will achieve a zero-stress state that will allow it to dig into dry soil with very little drag, independent of depth. This paper presents a theoretical model of the two modes of soil collapse to determine how quickly a device would need to contract to achieve this zero-stress state. It was found that a contraction time of 0.02 seconds would suffice for most soils, which is an achievable timescale for a RoboClam-like device.Massachusetts Institute of Technology. Department of Mechanical Engineerin

Design and Preliminary Testing of a Prototype for Evaluating Lower Leg Trajectory Error as an Optimization Metric for Prosthetic Feet

This 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

Determination of Resistance Factor for Tortuous Paths in Drip Emitters

Drip irrigation has the potential to decrease water consumption and increase crop yields and profit. Globally, drip irrigation has had low adoption rates. There are several major barriers to adoption, including the cost of the system and its energy consumption. Mathematical models describing the behavior of drip emitters can provide insights on the performance of drip systems. The models and procedures developed in this paper can be used as a tool for the design of improved drip irrigation systems. This paper presents a method of combining a CFD model that characterizes flow through the tortuous paths of emitters with an analytical model describing pressure-compensating behavior. The CFD model detailed in this paper was verified for three commercially available emitter designs. The model fell within acceptable variation bounds when compared to experimental data. The results of CFD analysis are represented in a resistance factor that can be used in a hybrid analyticalcomputational model. This method requires significantly less processing than using computational models alone. Future work on this topic will detail an analytical model that accurately predicts the behavior of inline PC drip emitters of varying geometries and an optimization of the geometry to lower activation pressure and material costs. Analytical models to predict the flow behavior of a range of tortuous path designs given a prescribed geometry will also be developed.Jain Irrigation System Ltd.National Science Foundation (U.S.). Graduate Research Fellowship Progra

A Hybrid Computational and Analytical Model of Inline Drip Emitters

This paper details a hybrid computational and analytical model to predict the performance of inline pressure-compensating (PC) drip irrigation emitters. The term inline refers to flow control devices mounted within the irrigation tubing. Pressure-compensating emitters deliver a relatively constant flow rate over a range applied pressure to accurately meter water to crops. Flow rate is controlled within the emitter by directing the water through a tortuous path (which imposes a fixed resistance), and then through a variable resistor composed of a flexible membrane that deflects under changes in pressure, restricting the flow path. An experimentally validated computational fluid dynamics (CFD) model was used to predict flow behavior through tortuous paths, and a pressure resistance parameter was derived to represent the pressure drop with a single variable. The bending and shearing mechanics of the membrane were modeled analytically and refined for accuracy by deriving a correction factor using finite element analysis. A least-squares matrix formulation that calculates the force applied by a line load of any shape, along which there is a prescribed deflection applied on a rectangular membrane, was derived and was found to be accurate to within one percent. The applicability of the assumption of locally fully developed flow through the pressure compensating chamber in a drip emitter was analyzed. The combined hybrid computational-analytical model reduces the computational time of modeling drip emitter performance from days to less than 30 minutes, dramatically lowering the time required to iterate and select optimal designs. The model was validated using three commercially available drip emitters, rated at 1.1, 2, and 3.8 L/hr. For each, the model predicted the flow rate with an error of twenty percent or less, as compared to the emitter performance published by the manufacturer.Jain Irrigation Systems Ltd.National Science Foundation (U.S.). Graduate Research FellowshipMassachusetts Institute of Technology. Tata Center for Technology and Desig

Validating a Method for Turbocharging Single Cylinder Four Stroke Engines

This 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

Energetic and Socioeconomic Justification for Solar-Powered Desalination Technology for Rural Indian Villages

This paper provides justification for solar-powered electrodialysis desalination systems for rural Indian villages. It is estimated that 11% of India’s 800 million people living in rural areas do not have access to an improved water source. If the source’s quality in regards to biological, chemical, or physical contaminants is also considered, this percentage is even higher. User interviews conducted by the authors and in literature reveal that users judge the quality of their water source based on its aesthetic quality (taste, odor, and temperature). Seventy-three percent of Indian villages rely on groundwater as their primary drinking supply. However, saline groundwater underlies approximately 60% of the land area in India. Desalination is necessary in order to improve the aesthetics of this water (by reducing salinity below the taste threshold) and remove contaminants that cause health risks. Both technical and socioeconomic factors were considered to identify the critical design requirements for inland water desalination in India. An off-grid power system is among those requirements due to the lack of grid access or intermittent supply, problems faced by half of Indian villages. The same regions in India that have high groundwater salinity also have the advantage of high solar potential, making solar a primary candidate. Within the salinity range of groundwater found in inland India, electrodialysis would substantially reduce the energy consumption to desalinate compared to reverse osmosis, which is the standard technology used for village-level systems. This energy savings leads to a smaller solar array required for electrodialysis systems, translating to reduced capital costs.Massachusetts Institute of Technology. Tata Center for Technology and DesignMassachusetts Institute of Technology. Undergraduate Research Opportunities Progra