No description available.

No description available.

No description available.

No description available.

No description available.

Gap crossing is a regular locomotor activity for arboreal animals. The distance between branches likely plays a role in determining whether an animal is capable of crossing a given gap, and what locomotor behavior it uses to do so. Yet, despite the importance of gap distance as a physical parameter influencing gap crossing behavior, the precise relationships between gap distance and movement kinematics have been explored in only a very small number of species. One particularly interesting group of arboreal inhabitants are the flying snakes (Chrysopelea). This species is able to use a dynamic "J-loop" movement to launch its glides, but it is not known whether it is also capable of using such jumps to cross smaller gaps between tree branches. This dissertation addresses this knowledge gap, and investigates the influence of gap distance on crossing behavior and kinematics in three closely-related species of snake: Chrysopelea paradisi, a species of flying snake, and two species from the sister genus, Dendrelaphis, neither of which can glide. Chapter 2 is a literature review of the biomechanics of gap crossing, specifically focusing on the role played by gap distance, and establishes the context for the rest of the work. Chapter 3 presents a detailed study of how increasing gap size influences the behavior and kinematics of gap crossing in C. paradisi, showing that this species uses increasingly dynamic movements to cross gaps of increasing size. Chapter 4 explores the same relationships between gap size and kinematics in D. punctulatus and D. calligastra, revealing remarkable similarities between the three species, suggesting the possibility that dynamic gap crossing may have evolved prior to gliding in this clade. Finally, chapter 5 addresses the role played by gap distance in limiting the non-dynamic, cantilever movements used by these species to cross small gaps, comparing observed stopping distances to those predicted by various torque-related limitations. / Doctor of Philosophy / To successfully cross a gap, an animal must be able to reach or jump from one side to the other. Animals who live in trees must do this quite frequently, as they live among the branches and there are often not connected paths from one place to another. But we don't know very much about how the distance between two structures (the "gap distance") affects the ways an animal moves between them. In this dissertation, I explore how gap distance changes the way a few special species of snakes cross a gap. The species I am studying are special because one species, the paradise tree snake, can glide. Because this 'flying' snake launches its glides by doing a big jump, it is possible that the snake can also jump between tree branches, but this question has never been examined before. We also don't know how the ability to do big jumps evolved, so I studied how distance affects the way two very closely related species of snake, the common tree snake and the northern tree snake, cross gaps. By looking at all of these species, we can understand more about what kinds of behavior are specific to the flying snakes, and which are present in related species. Finally, I also explore how gap distance limits the way the snakes cross gaps when they are not jumping. When the snakes do not jump, they have to hold themselves out straight off the end of a branch. This requires a lot of muscular effort, which means they can't go as far. The fact that the non-jumping behavior is distance-limited might help explain why the snakes need to jump. Altogether, the projects in this study help us understand how gap distance influences what behavior an animal chooses to cross the gap, and increases our knowledge of how flying snakes and their relatives cross gaps in particular.

It is often assumed that more realism is always desirable. In particular, many techniques for locomotion in Virtual Reality (VR) attempt to approximate real-world walking. However, it is not yet fully understood how the design of more realistic locomotion techniques influences effectiveness and user experience. In the previous VR studies, the effects of interaction fidelity have been coarse-grained, considering interaction fidelity as a single construct. We argue that interaction fidelity consists of various independent components, and each component can have a different effect on the effectiveness of the interface. Moreover, the designer's intent can influence the effectiveness of an interface and needs to be considered in the design. Semi-natural locomotion interfaces can be difficult to use at first, due to a lack of interaction fidelity, and effective training would help users understand the forces they were feeling and better control their movements. Another method to improve locomotion interaction is to develop a more effective interface or improve the existing techniques. A detailed taxonomy of walking-based locomotion techniques would be beneficial to better understand, analyze, and design walking techniques for VR. We conducted four user studies and performed a meta-analysis on the literature to have a more in-depth understanding of the effects of interaction fidelity on effectiveness. We found that for the measures dependent on proprioceptive sensory information, such as orientation estimation, cognitive load, and sense of presence, the level of effectiveness increases with increasing levels of interaction fidelity. Other measures which depend more on the ease of learning and ease of use, such as completion time, movement accuracy, and subjective evaluation, form a u-shape uncanny valley. For such measures, moderate-fidelity interfaces are often outperformed by low- and high-fidelity interfaces. In our third user study, we further investigated the effects of components of interaction fidelity, biomechanics and transfer function, as well as designers' intent. We learned that the biomechanics of walking are more sensitive to changes and that the effects of these changes were mostly negative for hyper-natural techniques. Changes in the transfer function component were easier for the user to learn and to adapt to. Suitable transfer functions were able to improve some locomotion features but at the cost of accuracy. To improve the level of effectiveness in moderate-fidelity locomotion interfaces we employed an effective training method. We learned that providing a visual cue during the acclimation phase can help users better understand their walking in moderate-fidelity interfaces and improve their effectiveness. To develop a design space and classification of locomotion techniques, we designed a taxonomy for walking- based locomotion techniques. With this taxonomy, we extract and discuss various characteristics of locomotion interaction. Researchers can create novel locomotion techniques by making choices from the components of this taxonomy, they can analyze and improve existing techniques, or perform experiments to evaluate locomotion techniques in detail using the presented organization. As an example of using this taxonomy, we developed a novel locomotion interface by choosing a new combination of characteristics from the taxonomy. / Ph. D.

Bipedal robotic locomotion based on passive dynamics is a field that has been extensively researched. By exploiting the natural dynamics of the system, these bipedal robots consume less energy and require minimal control to take a step. Yet the design of most of these bipedal machines is inherently unstable and difficult to control since there is a tendency for the machine to fall once it stops walking. This thesis presents the design and analysis of a novel three-legged walking robot for a single step. The STriDER (Self-excited Tripedal Dynamic Experimental Robot) incorporates aspects of passive dynamic walking into a stable tripedal platform. During a step, two legs act as stance legs while the other acts as a swing leg. A stance plane, formed by the hip and two ground contact points of the stance legs, acts as a single effective stance leg. When viewed in the sagittal plane, the machine can be modeled as a planar four link pendulum. To initiate a step, the legs are oriented to push the center of gravity outside of the stance legs. As the body of the robot falls forward, the swing leg naturally swings in between the two stance legs and catches the STriDER. Once all three legs are in contact with the ground, the robot regains its stability and the posture of the robot is then reset in preparation for the next step. To guide the design of the machine, a MATLAB simulation was written to allow for tuning of several design parameters, including the mass, mass distribution, and link lengths. Further development of the code also allowed for optimization of the design parameters to create an ideal gait for the robot. A self-excited method of actuation, which seeks to drive a stable system toward instability, was used to control the robot. This method of actuation was found to be robust across a wide range of design parameters and relatively insensitive to controller gains. / Master of Science

Microorganisms swimming in their natural habitat interact with debris and boundaries, which can modify their swimming characteristics. However, the boundary effect on swimming microorganisms have not been completely understood yet, and is one of most active areas of research. Amongst microorganisms, unicellular ciliates are the fastest swimmers and also respond to a variety of external cues. We choose Paramecium multimicronucleatum as a model system to understand the locomotion of ciliates. First, we explore the effects of boundaries on swimming modes of Paramecium multimicronu- cleatum by introducing them in 2D films and 1D channels. The geometric confinements cause the Paramecia to transition between: a directed, a meandering and a self-bending behaviors. During the self-bending mode the cell body exerts forces on the walls; which is quantified by using a beam bending analogy and measuring the elasticity of the cell body. The first inves- tigation reveals the complicated swimming patterns of Paramecium caused by boundaries. In the second study we investigate the directed swimming of Paramecium in cylindrical capillaries, which mimics the swimming of ciliates in the pores of soil. A finite-sized cell lo- comoting in extreme confinements creates a pressure gradient across its ends. By developing a modified envelop model incorporating the confinements and pressure gradient effects, we are able to predict the swimming speed of the organisms in confined channels. Finally we study how Paramecium can swim and feed efficiently by stirring the fluid around its body. We experimentally employ "-Particle Image Velocimetry to characterize flows around the freely swimming Parameicum and numerically use Boundary Element Method to quantify the effect of body shapes on the swimming and feeding process. Results show that the body shape of Paramecium (slender anterior and bulky posterior) is hydrodynamically optimized to swim as well as feed efficiently. The dissertation makes significant advances in both experimentally characterizing and the- oretically understanding the flow field and locomotion patterns of ciliates near solid bound- aries. / Ph. D.

Emergency first responders are the great heroes of our day, having to routinely risk their lives for the safety of others. Developing robotic technologies to aid in such emergencies could greatly reduce the risk these individuals must take, even going so far as to eliminate the need to risk one life for another. In this role, humanoid robots are a strong candidate, being able to take advantage of both the human engineered environment in which it will likely operate, but also make use of human engineered tools and equipment as it deals with a disaster relief effort. The work presented here aims to lessen the hurdles that stand in the way through the research and development of new humanoid robot technologies. To be successful in the role of an emergency first responder requires a fantastic array of skills. One of the most fundamental is the ability to just get to the scene. Unfortunately, it is at this level that humanoid robots currently struggle. This research focuses on the complementary development of physical hardware, digital controllers, and trajectory planning necessary to achieve the research goals of improving the locomotion capabilities of a humanoid robot. To improve the physical performance capabilities of the robot, this research will first focus on the interaction between the hip and knee actuators. It is shown that much like the human body, a biped greatly benefits from the use of biarticular actuation. Improvements in efficiency as much as 30% are possible by simply interconnecting the hip roll and knee pitch joints. Balancing and walking controllers are designed to take advantage of the new hardware capabilities and expand the terrain capabilities of bipedal walking robots to uneven and non-stationary ground. A hybrid position/force control based balancing controller stabilizes the robot's COM regardless of the terrain underfoot. In particular two feedback mechanisms are shown to greatly improve the stability of bipedal systems in response to unmodelled dynamics. The hybrid position/force approach is shown through experiments to greatly extend humanoid capabilities to many types of terrain. With robust balancing ensured, walking trajectories are defined using an improved linear inverted pendulum model that incorporates the swing leg dynamics. The proposed method is shown to significantly reduce the control authority (by 50%) required for satisfactory trajectory following. Three parameters are identified which provide for quick manual or numerical solutions to be found to the trajectory problem. The walking and balance controller were operated on four different terrains successfully, strewn plywood, gravel, and high pile synthetic grass. Furthermore, SAFFiR is believed to be the first bipedal robot to ever walk on sand. The hardware enabled force control architecture was very effective at modulating ground reaction torques no matter the ground conditions. This in combination with highly accurate state estimation provided a very stable balance controller on top of which successful walking was demonstrated. / Ph. D.