Towards a terramechanics for bio-in spired locomotion in granular environments

Granular media (GM) present locomotor challenges for terrestrial and extraterrestrial devices because they can flow and solidify in response to localized intrusion of wheels, limbs and bodies. While the development of airplanes and submarines is aided by understanding of hydrodynamics, fundamental theory does not yet exist to describe the complex interactions of locomotors with GM. In this paper, we use experimental, computational, and theoretical approaches to develop a terramechanics for bio-inspired locomotion in granular environments. We use a fluidized bed to prepare GM with a desired global packing fraction, and use empirical force measurements and the Discrete Element Method (DEM) to elucidate interaction mechanics during locomotion-relevant intrusions in GM such as vertical penetration and horizontal drag. We develop a resistive force theory (RFT) to account for more complex intrusions. We use these force models to understand the locomotor performance of two bio-inspired robots moving on and within GM. The sponsor was DARPA/SPAWAR N66001–05-C-8025. For further information, visit Kod*lab

Desert RHex Technical Report: Jornada and White Sands Trip

Researchers in a variety of fields, including aeolian science, biology, and environmental science, have already made use of stationary and mobile remote sensing equipment to increase their variety of data collection opportunities. However, due to mobility challenges, remote sensing opportunities relevant to desert environments and in particular dune fields have been limited to stationary equipment. We describe here an investigative trip to two well-studied experimental deserts in New Mexico with D-RHex, a mobile remote sensing platform oriented towards desert research. D-RHex is the latest iteration of the RHex family of robots, which are six-legged, biologically inspired, small (10kg) platforms with good mobility in a variety of rough terrains, including on inclines and over obstacles of higher than robot hip height. For more information: Kod*La

Transport in granular systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 93-98).There are many situations in which a continuum view of granular systems does not fully capture the relevant mechanics. In order for engineers to be able to design systems for transporting granular materials, there needs to be an understanding of the mechanics of granular systems and how their non-continuous behavior affects their dynamics. This thesis takes an example of a granular system from nature and uses this system to analyze the way granular materials interact with flexible boundaries. This thesis focuses on digging in granular materials. Pinto bean plant roots were used as a model biological system, and experiments using photoelastic grains were performed to quantify the effect of the inhomogeneous forces in the substrate on the root growth. It was determined that the pinto bean roots grew between grains when the force between those grains was less than 0.5 N. This value was time-dependent and showed a previously-unquantified strengthening of the roots over time. Also, while the roots were growing in the granular substrate, they altered the forces between grains by an average of 110 mN. An analytical model of digging energy was developed to investigate the differences between diggers that are much larger than the grain size and diggers that are much smaller than the grain size. Based on this model, a design tool was created so that designers could quickly identify promising technologies for digging based on the size scale of the grains and the desired size of the digger. Finally, two elements of the plant roots, mechanical flexibility and an actuated tip, were used to create robotic diggers to quantify the associated savings in digging energy. Increasing the mechanical flexibility of the digger was shown to result in energy savings of more than 50% when decreasing the bending modulus by one order of magnitude. However, large variations in the data were observed as a result of the inhomogeneity of the granular system. These variations were quantified and were consistent with previous literature regarding forces in granular systems. Also, a numerical model was created that demonstrates that the increase in digging efficiency can be attributed to the flexibility of the digger. Experiments with diggers whose tip orientation cycled from side to side show that it is more energy-efficient to dig with this active tip only if the energy used to create the changing tip orientation is less than 2.5 x 10-⁵ J per mm dug.by Dawn Marie Wendell.Ph.D

Biological, simulation, and robotic studies to discover principles of swimming within granular media

The locomotion of organisms whether by running, flying, or swimming is the result of multiple degree-of-freedom nervous and musculoskeletal systems interacting with an environment that often flows and deforms in response to movement. A major challenge in biology is to understand the locomotion of organisms that crawl or burrow within terrestrial substrates like sand, soil, and muddy sediments that display both solid and fluid-like behavior. In such materials, validated theories such as the Navier-Stokes equations for fluids do not exist, and visualization techniques (such as particle image velocimetry in fluids) are nearly nonexistent. In this dissertation we integrated biological experiment, numerical simulation, and a physical robot model to reveal principles of undulatory locomotion in granular media. First, we used high speed x-ray imaging techniques to reveal how a desert dwelling lizard, the sandfish, swims within dry granular media without limb use by propagating a single period sinusoidal traveling wave along its body, resulting in a wave efficiency, the ratio of its average forward speed to wave speed, of approximately 0.5. The wave efficiency was independent of the media preparation (loosely and tightly packed). We compared this observation against two complementary modeling approaches: a numerical model of the sandfish coupled to a discrete particle simulation of the granular medium, and an undulatory robot which was designed to swim within granular media. We used these mechanical models to vary the ratio of undulation amplitude (A) to wavelength (λ) and demonstrated that an optimal condition for sand-swimming exists which results from competition between A and λ. The animal simulation and robot model, predicted that for a single period sinusoidal wave, maximal speed occurs for A/ λ = 0.2, the same kinematics used by the sandfish. Inspired by the tapered head shape of the sandfish lizard, we showed that the lift forces and hence vertical position of the robot as it moves forward within granular media can be varied by designing an appropriate head shape and controlling its angle of attack, in a similar way to flaps or wings moving in fluids. These results support the biological hypotheses which propose that morphological adaptations of desert dwelling organisms aid in their subsurface locomotion. This work also demonstrates that the discovery of biological principles of high performance locomotion within sand can help create the next generation of biophysically inspired robots that could explore potentially hazardous complex flowing environments.PhDCommittee Chair: Daniel I. Goldman; Committee Member: Hang Lu; Committee Member: Jeanette Yen; Committee Member: Shella Keilholz; Committee Member: Young-Hui Chan

Biophysically inspired development of a sand-swimming robot

© 2011 MIT PressPresented at Robotics: Science and Systems (RSS) 2010, held at the University of Zaragoza in Spain, from June 27 to June 30, 2010.Previous study of a sand-swimming lizard, the sandfish, Scincus scincus, revealed that the animal swims within granular media at speeds up to 0:4 body-lengths/cycle using body undulation (approximately a single period sinusoidal traveling wave) without limb use [1]. Inspired by this biological experiment and challenged by the absence of robotic devices with comparable subterranean locomotor abilities, we developed a numerical simulation of a robot swimming in a granular medium (modeled using a multi-particle discrete element method simulation) to guide the design of a physical sand-swimming device built with off-the-shelf servo motors. Both in simulation and experiment the robot swims limblessly subsurface and, like the animal, increases its speed by increasing its oscillation frequency. It was able to achieve speeds of up to 0:3 body-lengths/cycle. The performance of the robot measured in terms of its wave efficiency, the ratio of its forward speed to wave speed, was 0:34 0:02, within 8 % of the simulation prediction. Our work provides a validated simulation tool and a functional initial design for the development of robots that can move within yielding terrestrial substrates