Article

# Pump drill: A superb device for converting translational motion into high-speed rotation

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## Abstract

Pump drill is an easily constructed ancient device that has been used for centuries to start fires and bore holes. It can effectively transfer rhythmic translational motions into vibratory, bi-directional rotary insertions. Here we explore, both experimentally and theoretically, the kinematics, dynamics, and potential applications of pump drills. The theoretical model, validated by experimental measurements, enables us to obtain the optimal structural geometries (e.g., the thread length and the crossbar span) of pump drills that maximize the mechanical responses such as the winding angle of the threads. Furthermore, the dependence of its rotational speed and piercing force on the loading conditions is investigated. Finally, manually powered devices, including an electric generator and a centrifugal separator, are developed based on the pump drill. This study paves a way towards promising applications of the pump drill in, for instance, energy harvesting and centrifugation.

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... [16] and [17] and the many references cited therein). Recent contributions to the literature on the mechanics of helical rods include [18][19][20][21][22]. With respect to this recent literature, the main differences of our research consist in the type of structure analyzed, and in the generality of the allowed deformations, i.e., rods are not assumed to remain circular helices a priori and can deform into helical shapes with nonconstant curvature and torsion. ...
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... The theoretical model presented in this work can help design and optimize a general class of helical structures, which has a promise in analyzing and predicting the unique mechanical behavior of high-performance thread materials and devices, for example, the artificial muscles and actuators, 2,41 the buzzer prototype, 42 and the pump drill. 43 Finally, it is noteworthy that the deformation of real hierarchical helical structures is usually complicated, and there are many factors that may influence their mechanical responses. Some limitations of the model have to be mentioned. ...
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An analytical method is presented for studying the influence of fiber migration on the mechanical properties of a yarn with two-level helical structures. The theory of ideal migration is applied to the seven-ply yarn, which results in the exchange of the interior structure of the yarn. A bottom-up method for analyzing the internal forces and stresses of the yarn under axial tension and torsion is developed. The influence of fiber migration is demonstrated by making contrast between the mechanical responses of carbon nanotube yarns with and without fiber migration. The numerical results show that there is a periodical non-monotonic variation in both the internal forces and the stresses with the length of yarn. A stress concentration is revealed around the half-cycle migration point and the one-cycle migration point. It is shown that the chirality, initial helix angle, and the fiber migration pattern can be used to control the mechanical performance of yarns.
... Numerical simulations and physical prototyping validate the theoretical prediction. This study holes great promise in the application of designing advanced aeronautics [26], electronic [30], optics [31], MEMS, and rotating device [33,34]. ...
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Mosquitoes are exceptional in their ability to pierce into human skin with a natural ultimate painless microneedle, named fascicle. Here the structure of the Aedes albopictus mosquito fascicle is obtained using a Scanning Electron Microscope (SEM), and the whole process of the fascicle inserting into human skin is observed using a high-speed video imaging technique. Direct measurements of the insertion force for mosquito fascicle to penetrate into human skin are reported. Results show that the mosquito uses a very low force (average 18 μN) to penetrate into the skin. This force is at least three orders of magnitude smaller than the reported lowest insertion force for an artificial microneedle with an ultra sharp tip to insert into the human skin. In order to understand the piercing mechanism of mosquito fascicle tip into human multilayer skin tissue, a numerical simulation is conducted to analyze the insertion process using a nonlinear finite element method. A good agreement occurs between the numerical results and the experimental measurements.
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Many motile species of bacteria are propelled by flagella, which are rigid helical filaments turned by rotary motors in the cell membrane. The motors are powered by the transmembrane gradient of protons or sodium ions. Although bacterial flagella contain many proteins, only three-MotA, MotB and FliG-participate closely in torque generation. MotA and MotB are ion-conducting membrane proteins that form the stator of the motor. FliG is a component of the rotor, present in about 25 copies per flagellum. It is composed of an amino-terminal domain that functions in flagellar assembly and a carboxy-terminal domain (FliG-C) that functions specifically in motor rotation. Here we report the crystal structure of FliG-C from the hyperthermophilic eubacterium Thermotoga maritima. Charged residues that are important for function, and which interact with the stator protein MotA, cluster along a prominent ridge on FliG-C. On the basis of the disposition of these residues, we present a hypothesis for the orientation of FliG-C domains in the flagellar motor, and propose a structural model for the part of the rotor that interacts with the stator.
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Although 'diseases of affluence', such as diabetes and cardiovascular disease, are increasing in developing countries, infectious diseases still impose the greatest health burden. Annually, just under 1 million people die from malaria, 4.3 million from acute respiratory infections, 2.9 million from enteric infections and 5 million from AIDS and tuberculosis. Other sexually transmitted infections and tropical parasitic infections are responsible for hundreds of thousands of deaths and an enormous burden of morbidity. More than 95% of these deaths occur in developing countries. Simple, accurate and stable diagnostic tests are essential to combat these diseases, but are usually unavailable or inaccessible to those who need them.
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Flagellated bacteria, such as Escherichia coli, swim by rotating thin helical filaments, each driven at its base by a reversible rotary motor, powered by an ion flux. A motor is about 45 nm in diameter and is assembled from about 20 different kinds of parts. It develops maximum torque at stall but can spin several hundred Hz. Its direction of rotation is controlled by a sensory system that enables cells to accumulate in regions deemed more favorable. We know a great deal about motor structure, genetics, assembly, and function, but we do not really understand how it works. We need more crystal structures. All of this is reviewed, but the emphasis is on function.
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The Energy Harvesting Eel (Eel) is a new device that uses piezoelectric polymers to convert the mechanical flow energy, available in oceans and rivers, to electrical power. Eel generators make use of the regular trail of traveling vortices behind a bluff body to strain the piezoelectric elements; the resulting undulating motion resembles that of a natural eel swimming. Internal batteries are used to store the surplus energy generated by the Eel for later use by a small, unattended sensor or robot. Because of the properties of commercially available piezoelectric polymers, Eels will be relatively inexpensive and are easily scaleable in size and have the capacity to generate from milli-watts to many watts depending on system size and flow velocity of the local environment. A practical Eel structure has been developed that uses the commercially available piezoelectric polymer, PVDF. Future Eels may use more efficient electrostrictive polymer. Every aspect of the system from the interactions between the hydrodynamics of the water flow and structural elements of the Eel, through the mechanical energy input to the piezoelectric material, and finally the electric power output delivered through an optimized resonant circuit has been modeled and tested. The complete Eel system, complete with a generation and storage system, has been demonstrated in a wave tank. Future work on the Eel will focus on developing and then deploying a small, lightweight, one-watt power generation unit, initially in an estuary and then subsequently in the ocean. Such Eels will have the ability to recharge batteries or capacitors of a distributed robotic group, or remote sensor array, thus extending the mission life indefinitely in regions containing flowing water
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