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- IEEE robotics automation letters
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- National Science Foundation
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Walking on natural terrain like soil and rock is a challenging problem that has been approached from a variety of strategies such as using sophisticated control methods, compliant legs, and compliant feet. In this paper we explore how to modify granular jamming feet for walking applications by adding stabilizing internal structures. Previous work has explored how granular jamming technology can be used to create compliant and stiffness changing feet that enable locomotion over a diverse range of natural terrain by allowing robot feet to conform around 3D multicomponent terrain such as wood chips and gravel and stiffen, preventing slip. To date, no work has been done to tune granular jamming feet for the specific application of walking. We show that adding internal structures to granular jamming membranes can increase the force they are able to resist without slipping by 1.5x while maintaining their ability to conform around obstacles. When attached to a robot, we see increases in speed of up to 1.4x, decreases in the duty cycle necessary to reach desired foot trajectories of up to 5%, and increases in traction force of up to 1.2x over a diverse set of natural terrain.
Robotic navigation on land, through air, and in water is well researched; numerous robots have successfully demonstrated motion in these environments. However, one frontier for robotic locomotion remains largely unexplored—below ground. Subterranean navigation is simply hard to do, in part because the interaction forces of underground motion are higher than in air or water by orders of magnitude and because we lack for these interactions a robust fundamental physics understanding. We present and test three hypotheses, derived from biological observation and the physics of granular intrusion, and use the results to inform the design of our burrowing robot. These results reveal that (i) tip extension reduces total drag by an amount equal to the skin drag of the body, (ii) granular aeration via tip-based airflow reduces drag with a nonlinear dependence on depth and flow angle, and (iii) variation of the angle of the tip-based flow has a nonmonotonic effect on lift in granular media. Informed by these results, we realize a steerable, root-like soft robot that controls subterranean lift and drag forces to burrow faster than previous approaches by over an order of magnitude and does so through real sand. We also demonstrate that the robot can modulate itsmore »
Soft robots employ flexible and compliant materials to perform adaptive tasks and navigate uncertain environments. However, soft robots are often unable to achieve forces and precision on the order of rigid-bodied robots. In this paper, we propose a new class of mobile soft robots that can reversibly transition between compliant and stiff states without reconfiguration. The robot can passively conform or actively control its shape, stiffen in its current configuration to function as a rigid-bodied robot, then return to its flexible form. The robotic structure consists of passive granular material surrounded by an active membrane. The membrane is composed of interconnected robotic sub-units that can control the packing density of the granular material and exploit jamming behaviors by varying the length of the interconnecting cables. Each robotic sub-unit uses a differential drive system to achieve locomotion and self-reconfigurability. We present the robot design and perform a set of locomotion and object manipulation experiments to characterize the robot's performance in soft and rigid states. We also introduce a simulation framework in which we model the jamming soft robot design and study the scalability of this class of robots. The proposed concept demonstrates the properties of both soft and rigid robots, andmore »
This paper describes a new type of compliant and configurable soft robot, a boundary-constrained swarm. The robot consists of a sealed flexible membrane that constrains both a number of mobile robotic subunits and passive granular material. The robot can change the volume fraction of the sealed membrane by applying a vacuum, which gives the robot the ability to operate in two distinct states: compliant and jammed. The compliant state allows the robot to surround and conform to objects or pass through narrow corridors. Jamming allows the robot to form a desired shape; grasp, (a) manipulate, and exert relatively high forces on external objects; and achieve relatively higher locomotion speeds. Locomotion is achieved with a combination of whegs (wheeled legs) and vibration motors that are located on the robotic subunits. The paper describes the mechanical design of the robot, the control methodology, and its object handling capability.
Synopsis Locomotion in most tetrapods involves coordinated efforts between appendicular and axial musculoskeletal systems, where interactions between the limbs and the ground generate vertical (GV), horizontal (GH), and mediolateral (GML) ground-reaction forces that are transmitted to the axial system. Snakes have a complete absence of external limbs and represent a fundamental shift from this perspective. The axial musculoskeletal system of snakes is their primary structure to exert, transmit, and resist all motive and reaction forces for propulsion. Their lack of limbs makes them particularly dependent on the mechanical interactions between their bodies and the environment to generate the net GH they need for forward locomotion. As organisms that locomote on their bellies, the forces that enable the various modes of snake locomotion involve two important structures: the integument and the ribs. Snakes use the integument to contact the substrate and produce a friction-reservoir that exceeds their muscle-induced propulsive forces through modulation of scale stiffness and orientation, enabling propulsion through variable environments. XROMM work and previous studies suggest that the serially repeated ribs of snakes change their cross-sectional body shape, deform to environmental irregularities, provide synergistic stabilization for other muscles, and differentially exert and transmit forces to control propulsion. The costovertebralmore »