Basilisk Lizard Inspired Methods for Locomotion on Granular and Aquatic Media with Robotic Applications

abstract: The Basilisk lizard is known for its agile locomotion capabilities on granular and aquatic media making it an impressive model organism for studying multi-terrain locomotion mechanics. The work presented here is aimed at understanding locomotion characteristics of Basilisk lizards through a systematic series of robotic and animal experiments. In this work, a Basilisk lizard inspired legged robot with bipedal and quadrupedal locomotion capabilities is presented. A series of robot experiments are conducted on dry and wet (saturated) granular media to determine the effects of gait parameters and substrate saturation, on robot velocity and energetics. Gait parameters studied here are stride frequency and stride length. Results of robot experiments are compared with previously obtained animal data. It is observed that for a fixed robot stride frequency, velocity and stride length increase with increasing saturation, confirming the locomotion characteristics of the Basilisk lizard. It is further observed that with increasing saturation level, robot cost of transport decreases. An identical series of robot experiments are performed with quadrupedal gait to determine effects of gait parameters on robot performance. Generally, energetics of bipedal running is observed to be higher than quadrupedal operation. Experimental results also reveal how gait parameters can be varied to achieve different desired velocities depending on the substrate saturation level. In addition to robot experiments on granular media, a series of animal experiments are conducted to determine and characterize strategies exhibited by Basilisk lizards when transitioning from granular to aquatic media.Dissertation/ThesisMasters Thesis Mechanical Engineering 201

A Terradynamics of Legged Locomotion on Granular Media

The theories of aero- and hydrodynamics predict animal movement and device design in air and water through the computation of lift, drag, and thrust forces. Although models of terrestrial legged locomotion have focused on interactions with solid ground, many animals move on substrates that flow in response to intrusion. However, locomotor-ground interaction models on such flowable ground are often unavailable. We developed a force model for arbitrarily-shaped legs and bodies moving freely in granular media, and used this "terradynamics" to predict a small legged robot's locomotion on granular media using various leg shapes and stride frequencies. Our study reveals a complex but generic dependence of stresses in granular media on intruder depth, orientation, and movement direction and gives insight into the effects of leg morphology and kinematics on movement

Force Measurement of Basilisk Lizard Running on Water

abstract: Basilisk lizards are often studied for their unique ability to run across the surface of water. Due to the complicated fluid dynamics of this process, the forces applied on the water’s surface cannot be measured using traditional methods. This thesis presents a novel technique of measuring the forces using a fluid dynamic force platform (FDFP), a light, rigid box immersed in water. This platform, along with a motion capture system, can be used to characterize the kinematics and dynamics of a basilisk lizard running on water. This could ultimately lead to robots that can run on water in a similar manner.Dissertation/ThesisMasters Thesis Mechanical Engineering 201

Feedback Control as a Framework for Understanding Tradeoffs in Biology

Control theory arose from a need to control synthetic systems. From regulating steam engines to tuning radios to devices capable of autonomous movement, it provided a formal mathematical basis for understanding the role of feedback in the stability (or change) of dynamical systems. It provides a framework for understanding any system with feedback regulation, including biological ones such as regulatory gene networks, cellular metabolic systems, sensorimotor dynamics of moving animals, and even ecological or evolutionary dynamics of organisms and populations. Here we focus on four case studies of the sensorimotor dynamics of animals, each of which involves the application of principles from control theory to probe stability and feedback in an organism's response to perturbations. We use examples from aquatic (electric fish station keeping and jamming avoidance), terrestrial (cockroach wall following) and aerial environments (flight control in moths) to highlight how one can use control theory to understand how feedback mechanisms interact with the physical dynamics of animals to determine their stability and response to sensory inputs and perturbations. Each case study is cast as a control problem with sensory input, neural processing, and motor dynamics, the output of which feeds back to the sensory inputs. Collectively, the interaction of these systems in a closed loop determines the behavior of the entire system.Comment: Submitted to Integr Comp Bio

Beyond jamming grippers: granular material in robotics

Robot grippers based on the jamming of granular material have been studied widely in previous years. Recently, also other benefits and challenges of granular material have emerged for robotics. We discuss various functions of granular matter in robotic actuation, sensory processing, locomotion, and manipulation. We also provide a review of the design and methods of robots for moving in or on challenging granular environments. Drawing on the properties of granular material and their potential applications, we propose our unique perspectives and innovative ideas for future research and development in this field

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

Dynamics of magnetoelastic robots in water-saturated granular beds

We investigate the dynamics of a magnetoelastic robot with a dipolar magnetic head and a slender elastic body as it performs undulatory strokes and burrows through water-saturated granular beds. The robot is actuated by an oscillating magnetic field and moves forward when the stroke amplitude increases above a critical threshold. By visualizing the medium, we show that the undulating body fluidizes the bed, resulting in the appearance of a dynamic burrow, which rapidly closes in behind the moving robot as the medium loses energy. We investigate the applicability of Lighthill\u27s elongated body theory of fish locomotion, and estimate the contribution of thrust generated by the undulating body and the drag incorporating the granular volume fraction-dependent effective viscosity of the medium. The projected speeds are found to be consistent with the measured speeds over a range of frequencies and amplitudes above the onset of forward motion. However, systematic deviations are found to grow with increasing driving, pointing to a need for further sophisticated modeling of the medium-structure interactions. © 2023 American Physical Society

Experimental Methods To Support Robot Behavior Design For Legged Locomotion On Granular Media

Most models of legged locomotion assume a rigid ground contact, but this is not a reasonable assumption for robots in unstructured, outdoor environments, and especially not for field robots in dry desert environments. Locomotion on sand, a highly dissipative substrate, presents the additional challenge of a high energetic cost of transport. Many legged robots can be adapted for desert locomotion by simple morphological changes like increasing foot size or gearing down the motors. However, the Minitaur robot has direct-drive (no gearbox) legs which are sensitive enough to measure ground properties of interest to geoscientists, and its legs would lose their sensitivity if they were geared down or the footsize increased substantially. This thesis has two main contributions. First, a controller for jumping on sand with a direct-drive robot that saves significant energy in comparison to a nominal compression-extension Raibert-style controller without sacrificing jump height. This controller was developed by examining the complex interaction between the jumping leg and the ground, and devising a force to add to the leg controller which will push the robot’s foot into a more favorable state that does not transfer as much energy to the ground. The second contribution is a ground emulator robot which can be programmed to exert ground force functions of arbitrary shape. With the ground emulator, it is possible for a robot on a linear rail to jump dozens of times per experiment, whereas traditional experiments on granular media would require the ground to be reset between individual jumps. Results from the simulation experiments used to develop the controller and the ground emulator experiments used to test it on a physical robot leg are validated with experiments on a prepared granular media bed. Finally, the contributions of this thesis are contextualized in a broader project of building explainable artificially intelligent systems by composing robust, mostly reactive controllers