A Microstructural View of Burrowing with RoboClam

RoboClam is a burrowing technology inspired by Ensis directus, the Atlantic razor clam. Atlantic razor clams should only be strong enough to dig a few centimeters into the soil, yet they burrow to over 70 cm. The animal uses a clever trick to achieve this: by contracting its body, it agitates and locally fluidizes the soil, reducing the drag and energetic cost of burrowing. RoboClam technology, which is based on the digging mechanics of razor clams, may be valuable for subsea applications that could benefit from efficient burrowing, such as anchoring, mine detonation, and cable laying. We directly visualize the movement of soil grains during the contraction of RoboClam, using a novel index-matching technique along with particle tracking. We show that the size of the failure zone around contracting RoboClam, can be theoretically predicted from the substrate and pore fluid properties, provided that the timescale of contraction is sufficiently large. We also show that the nonaffine motions of the grains are a small fraction of the motion within the fluidized zone, affirming the relevance of a continuum model for this system, even though the grain size is comparable to the size of RoboClam

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

Analysis of Rollover Shape and Energy Storage and Return in Cantilever Beam-Type Prosthetic Feet

This paper presents an analysis of the rollover shape and energy storage and return in a prosthetic foot made from a compliant cantilevered beam. The rollover shape of a prosthetic foot is defined as the path of the center of pressure along the bottom of the foot during stance phase of gait, from heel strike to toe off. This path is rotated into the reference frame of the ankle-knee segment of the leg, which is held fixed. In order to achieve correct limb loading and gait kinematics, it is important that a prosthetic foot both mimic the physiological rollover shape and maximize energy storage and return. The majority of prosthetic feet available on the market are cantilever beam-type feet that emulate ankle dorsiflexion through beam bending. In this study, we show analytically that a prosthetic foot consisting of a beam with constant or monotonically decreasing cross-section cannot replicate physiological rollover shape; the foot is either too stiff when the ground reaction force (GRF) acts near the ankle, or too compliant when the GRF acts near the toe. A rigid constraint is required to prevent the foot from over-deflecting. Using finite element analysis (FEA), we investigated how closely a cantilever beam with constrained maximum deflection could mimic physiological rollover shape and energy storage/return during stance phase. A constrained beam with constant cross-section is able to replicate physiological rollover shape with R[superscript 2] = 0.86. The ratio of the strain energy stored and returned by the beam compared to the ideal energy storage and return is 0.504. This paper determines that there is a trade off between rollover shape and energy storage and return in cantilever beam-type prosthetic feet. The method and results presented in this paper demonstrate a useful tool in early stage prosthetic foot design that can be used to predict the rollover shape and energy storage of any type of prosthetic foot.MIT Tata Center for Technology and DesignMassachusetts Institute of Technology. Department of Mechanical EngineeringMIT International Science and Technology Initiatives (India Innovation Fund

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

Method for Turbocharging Single Cylinder Four Stroke Engines

This paper presents a feasibility study of a method for turbocharging single cylinder, four-stroke internal combustion engines. Turbocharging is not conventionally used with single cylinder engines because of the timing mismatch between when the turbo is powered, during the exhaust stroke, and when it can deliver air to the cylinder, during the intake stroke. The proposed solution involves an air capacitor on the intake side of the engine between the turbocharger and intake valves. The capacitor acts as a buffer and would be implemented as a new style of intake manifold with a larger volume than traditional systems. In order for the air capacitor to be practical, it needs to be sized large enough to maintain the turbocharger pressure during the intake stroke, cause minimal turbo lag, and significantly increase the density of the intake air. By creating multiple flow models of air through the turbocharged engine system, we found that the optimal size air capacitor is between four and five times the engine capacity. For a capacitor sized for a one-liter engine, the lag time was found to be approximately two seconds, which would be acceptable for slowly accelerating applications such as tractors, or steady state applications such as generators. The density increase that can be achieved in the capacitor, compared to air at standard ambient temperature and pressure, was found to vary between fifty percent for adiabatic compression and no heat transfer from the capacitor, to eighty percent for perfect heat transfer. These increases in density are proportional to, to first order, the anticipated power increases that could be realized with a turbocharger and air capacitor system applied to a single cylinder, four-stroke engine.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