Thesis (M.A.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 72-79). Also available via Humboldt Digital Scholar.

The purpose of this study was to investigate the survival and movements of newly metamorphosed Northern Red-legged frogs (Rana aurora aurora) as they emigrated from two ephemeral breeding ponds. Quantifying survival and movement rates will be important to our understanding how changes to terrestrial and aquatic systems affect behavior and population dynamics. I manipulated food availability for a subset of uniquely marked metamorphic frogs and then analyzed temporal and spatial aspects of their recapture in forest pitfall traps relative to body size and date of metamorphosis. The probability of surviving and emigrating increased strongly with increasing body size and declined for frogs metamorphosing later in the season. Larger body size was associated with earlier emigration and greater correlation of movements with rainfall events. Within a pond, the time elapsed between metamorphosis and emigration was not affected by the pond drying. My results demonstrate that conditions during the tadpole stage which affect body size and the timing of metamorphosis may have a dramatic impact on the performance of frogs during their initial transition into the terrestrial environment. / Graduation date: 2004

No description available.

Existing state-of-the-art legged robots often require complex mechanisms with multi-level controllers and computationally expensive algorithms. Part of this is owed to the multiple degrees of freedom (DOFs) these intricate mechanisms possess and the other is a result of the complex nature of dynamic legged locomotion. The underlying dynamics of this class of non-linear systems must be addressed in order to develop systems that perform natural human/animal-like locomotion. However, there are no stringent rules for the number of DOFs in a system; this is merely a matter of the locomotion requirements of the system. In general, most systems designed for dynamic locomotion consist of multiple actuators per leg to address the balance and locomotion tasks simultaneously. In contrast, this research hypothesizes the decoupling of locomotion and balance by omitting the DOFs whose primary purpose is dynamic disturbance rejection to enable a far simplified mechanical design for the legged system. This thesis presents a novel single DOF mechanism that is topologically arranged to execute a trajectory conducive to dynamic locomotive gaits. To simplify the problem of dynamic balancing, the mechanism is designed to be utilized in a quadrupedal platform in the future. The preliminary design, based upon heuristic link lengths, is presented and subjected to kinematic analysis to evaluate the resulting trajectory. To improve the result and to analyze the effect of key link lengths, sensitivity analysis is then performed. Further, a reference trajectory is established and a parametric optimization over the design space is performed to drive the system to an optimal configuration. The evolved design is identified as the Bio-Inspired One-DOF Leg for Trotting (BOLT). The dynamics of this closed kinematic chain mechanism is then simplified, resulting in a minimal order state space representation. A prototype of the robotic leg was integrated and mounted on a treadmill rig to perform various experiments. Finally, open loop running is implemented on the integrated prototype demonstrating the locomotive performance of BOLT. / MS / Existing state-of-the-art legged robots often require complex mechanisms with multi-level controllers and computationally expensive algorithms. Part of this is owed to the multiple degrees of freedom (DOFs) these intricate mechanisms possess and the other is a result of the complex nature of dynamic legged locomotion. The underlying dynamics of this class of non-linear systems must be addressed in order to develop systems that perform natural human/animal-like locomotion. However, the number of active DOF is merely a designers choice. To simplify the problem at both levels: design and controls of dynamic locomotion, we developed a novel mechanism that incorporates the benefits of higher DOF legs while accommodating the simplicity of single DOF leg. The preliminary design of the mechanism was designed with parameters (lengths of the femur,tibia) that were directly derived from a domestic dog. Synthesis of the mechanism suggested that the design was not suitable for an intended running-trot gait observed in biological counterparts. However, to gain a deeper understanding of the mechanism, it was necessary to perform a sensitivity analysis, as a result we arrived at a mechanism whose performance was better than the initial but still not satisfactory.With the insight gained through the analysis and an ideal gait design exercise, then an optimization on the design space was performed with carefully tuned bounds. The final result is a novel mechanism identified as Biologically inspired One DOF Leg for Trotting (BOLT) that is topologically arranged to execute a running-trot gait. Finally, the design choice presented with a challenge that has not been actively addressed. The dynamics of the mechanism can not be modeled using traditional methods due to presence of constraints that characterize the closed loops of the mechanism. We present an adaption of the Singularly perturbed dynamic model for systems that are hybrid in nature. The resulting dynamics are simplified, resulting in a minimal order state space representation, which is more amenable to model based control development in future. A prototype of the robotic leg was integrated and mounted on a treadmill rig to perform various experiments.Finally, open loop running is implemented on the integrated prototype demonstrating the locomotive performance of BOLT.

Thesis (M.A.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 76-85). Also available via Humboldt Digital Scholar.

The thesis shows how to achieve bipedal robotic walking on flat-ground, up-slope and rough terrain by using Human-Inspired control. We begin by considering human walking data and find outputs (or virtual constraints) that, when calculated from the human data, are described by simple functions of time (termed canonical walking functions). Formally, we construct a torque controller, through model inversion, that drives the outputs of the robot to the outputs of the human as represented by the canonical walking function; while these functions fit the human data well, they do not apriori guarantee robotic walking (due to do the physical differences between humans and robots). An optimization problem is presented that determines the best fit of the canonical walking function to the human data, while guaranteeing walking for a specific bipedal robot; in addition, constraints can be added that guarantee physically realizable walking. We consider a physical bipedal robot, AMBER, and considering the special property of the motors used in the robot, i.e., low leakage inductance, we approximate the motor model and use the formal controllers that satisfy the constraints and translate into an efficient voltage-based controller that can be directly implemented on AMBER. The end result is walking on flat-ground and up-slope which is not just human-like, but also amazingly robust. Having obtained walking on specific well defined terrains separately, rough terrain walking is achieved by dynamically changing the extended canonical walking functions (ECWF) that the robot outputs should track at every step. The state of the robot, after every non-stance foot strike, is actively sensed and the new CWF is constructed to ensure Hybrid Zero Dynamics is respected in the next step. Finally, the technique developed is tried on different terrains in simulation and in AMBER showing how the walking gait morphs depending on the terrain.

No description available.

This thesis is about control and balance stability of leggedlocomotion. It also presents a combination of tools that makesit easier to design controllers for large and complicated robotsystems. The thesis is divided into four parts. The first part studies and analyzes how walking machines arecontrolled, examining the literature of over twenty machinesbriefly, and six machines in detail. The goal is to understandhow the controllers work on a level below task and pathplanning, but above actuator control. Analysis and comparisonis done in terms of: i) generation of trunk motion; ii)maintaining balance; iii) generation of leg sequence andsupport patterns; and iv) reflexes. The next part describes WARP1, a four-legged walking robotplatform that has been builtwith the long term goal of walkingin rough terrain. First its modular structure (mechanics,electronics and control) is described, followed by someexperiments demonstrating basic performance. Finally themathematical modeling of the robot’s rigid body model isdescribed. This model is derived symbolically and is general,i.e. not restricted to WARP1. It is easily modified in case ofa different number of legs or joints. During the work with WARP1, tools for model derivation,control design and control implementation have been combined,interfaced and augmented in order to better support design andanalysis. These tools and methods are described in the thirdpart. The tools used to be difficult to combine, especially fora large and complicated system with many signals and parameterssuch as WARP1. Now, models derived symbolically in one tool areeasy to use in another tool for control design, simulation andfinally implementation, as well as for visualization andevaluation—thus going from equation to action. In the last part we go back to“equation”wherethese tools aid the study of balance stability when complianceis considered. It is shown that a legged robot in a“statically balanced”stance may actually beunstable. Furthermore, a criterion is derived that shows when aradially symmetric“statically balanced”stance on acompliant surface is stable. Similar analyses are performed fortwo controllers of legged robots, where it is the controllerthat cause the compliance. <b>Keywords</b>legged locomotion, control, balance, leggedmachines, legged robots, walking robots, walking machines,compliance, platform stability, symbolic modeling

<p>This thesis is about control and balance stability of leggedlocomotion. It also presents a combination of tools that makesit easier to design controllers for large and complicated robotsystems. The thesis is divided into four parts.</p><p>The first part studies and analyzes how walking machines arecontrolled, examining the literature of over twenty machinesbriefly, and six machines in detail. The goal is to understandhow the controllers work on a level below task and pathplanning, but above actuator control. Analysis and comparisonis done in terms of: i) generation of trunk motion; ii)maintaining balance; iii) generation of leg sequence andsupport patterns; and iv) reflexes.</p><p>The next part describes WARP1, a four-legged walking robotplatform that has been builtwith the long term goal of walkingin rough terrain. First its modular structure (mechanics,electronics and control) is described, followed by someexperiments demonstrating basic performance. Finally themathematical modeling of the robot’s rigid body model isdescribed. This model is derived symbolically and is general,i.e. not restricted to WARP1. It is easily modified in case ofa different number of legs or joints.</p><p>During the work with WARP1, tools for model derivation,control design and control implementation have been combined,interfaced and augmented in order to better support design andanalysis. These tools and methods are described in the thirdpart. The tools used to be difficult to combine, especially fora large and complicated system with many signals and parameterssuch as WARP1. Now, models derived symbolically in one tool areeasy to use in another tool for control design, simulation andfinally implementation, as well as for visualization andevaluation—thus going from equation to action.</p><p>In the last part we go back to“equation”wherethese tools aid the study of balance stability when complianceis considered. It is shown that a legged robot in a“statically balanced”stance may actually beunstable. Furthermore, a criterion is derived that shows when aradially symmetric“statically balanced”stance on acompliant surface is stable. Similar analyses are performed fortwo controllers of legged robots, where it is the controllerthat cause the compliance.</p><p><b>Keywords</b>legged locomotion, control, balance, leggedmachines, legged robots, walking robots, walking machines,compliance, platform stability, symbolic modeling</p>

Thesis (M.S.)--Humboldt State University, 2007. / Includes bibliographical references (leaves 38-42). Also available via Humboldt Digital Scholar.