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While numerous gait families have been defined and studied for legged systems traversing level ground (e.g. walking, running, bounding, etc), formal distinctions have yet to be developed for dynamic gaits in the vertical regime. Recognition and understanding of different gait families has clear implications to control strategy, efficiency, and stability. While several climbing robotic systems have been described as achieving 'running' behaviors on vertical surfaces, the question of whether distinct dynamic gaits exist and what differentiates these gaits has not been rigorously explored. In this paper, by applying definitions developed in the horizontal regime to simulation and experimental data, we show evidence of three distinct dynamic climbing gaits families and discuss the implications of these gaits on the development of more advanced climbing robots.

Running with compliant curved legs involves the progression of the center of pressure, the changes of both the leg's stiffness and effective rest length, and the shift of the location of the maximum stress point along the leg. These phenomena are product of the geometric and material properties of these legs, and the rolling motion produced during stance. We examine these aspects with several reduced-order dynamical models to relate the leg's design parameters (such as normalized foot radius, leg's effective stiffness, location of the maximum stress point and leg shape) to running performance (such as robustness and efficiency). By using these models, we show that running with compliant curved legs can be more efficient, robust with fast recovery behavior from perturbations than running with compliant straight legs. Moreover, the running performance can be further improved by tuning these design parameters in the context of running with rolling. The results shown in this work may serve as potential guidance for future compliant curved leg designs that may further improve the running performance.

As mobile robots become more commonly utilized in everyday applications, the tasks they are given will often require them to quickly traverse unprepared and varied environments. While traditional mobile platforms may falter under such conditions, animals utilize distinct locomotion modalities such as running, jumping, or climbing, to adroitly negotiate a wide variety of challenging and changing terrains. Due to limitations including available on-board power, legged robots have struggled to match the speed of these animals, even in a single mode of transport. In this paper we experimentally investigate the synergies and trade-offs in developing a dynamical legged robot capable of both running and climbing. We utilize bio-inspired 'templates' or reduced-order models of motion to identify how the dynamics change from running to climbing and seek to identify a minimal set of robotic adjustments necessary to switch locomotion modalities. This template-based design methodology is explained and the resultant robot behavior in each domain is characterized. We show that using a trotting gait, the platform demonstrates running speeds of up to 0.67 ms(-1) on level ground and climbing speeds of up to 0.43 ms(-1)on near-vertical surfaces (and up to 0.16 ms(-1) on vertical surfaces) while exhibiting dynamical behaviors comparable to that of the inspirational models.

Animals have demonstrated the ability to move through, across and over some of the most daunting environments on earth. This versatility and adaptability stems from their capacity to alter their locomotion dynamics and employ disparate locomotion modalities to suit the terrain at hand. As with modalities such as running, flying and swimming, dynamic climbing is commonly employed by legged animals, allowing for rapid and robust locomotion on vertical and near-vertical substrates. While recent robotic platforms have proven effective at anchoring reduced-order, dynamic climbing models, its adoption as a common modality for multi-modal, legged platforms remains nascent. In this work, we explore several of the open questions related to the physical implementation of dynamic climbing, including investigation of substrate inclinations for which dynamic climbing is suited, mitigation of destabilizing out-of-plane dynamics and improvement of attachment reliability in the presence of dynamic effects. The results from these inquiries provide several mechanisms and approaches for increasing the reliability and versatility of dynamic climbing as a dynamic legged modality. With these and other developments into legged locomotion modalities, future multi-modal platforms will begin to approach the expertise of biological creatures at moving through a complex and challenging world.

The ability to traverse unknown, rough terrain is an advantage that legged locomoters have over their wheeled counterparts. However, due to the complexity of multi-legged systems, research in legged robotics has not yet been able to reproduce the agility found in the animal kingdom. In an effort to reduce the complexity of the problem, researchers have developed single-legged models to gain insight into the fundamental dynamics of legged running. Inspired by studies of animal locomotion, researchers have proposed numerous control strategies to achieve stable, one-legged running over unknown, rough terrain. One such control strategy incorporates energy variations into the system during the stance phase by changing the force-free leg length as a sinusoidal function of time. In this research, a one-legged planar robot capable of implementing this and other state-of-the-art control strategies was designed and built. Both simulated and experimental results were used to determine and compare the stability of the proposed controllers as the robot was subjected to unknown drop and raised step perturbations equal to 25% of the nominal leg length. This study illustrates the relative advantages of utilizing a minimal-sensing, active energy removal control scheme to stabilize running over rough terrain.