While numerous gaits in the horizontal regime (e.g. walking or running) have been defined for legged systems on level ground, no dynamically grounded definitions have been developed for dynamic vertical running. Gaits have clear implications to robotic control strategy, efficiency, and stability. However, while several climbing robotic systems have been described as achieving `running', the question of whether distinct dynamic gaits exist and what classifies these gaits has not been rigorously explored. In this paper, by applying definitions developed in the horizontal regime, we show evidence of three distinct gaits as well as discuss the implications of these gaits on the development of dynamic climbing systems.

Robots are often used to perform similar tasks on vastly different scales. When utilizing traditional design approaches, this typically requires a full redesign and optimization at each specified size, a costly and time intensive process. In this work, we propose an alternative approach based on the principle of dynamic similarity. With this method, an initial design may be conceived at any size and scaled to any other without needing to re-optimize either physical or control variables. In the following study, we derive a generalized scaling method for this application that not only preserves system performance, but also affords flexibility in the scaling process. The preservation of dynamic similarity is validated in simulation. We further explore the application for robot-to-robot scaling, flexibility afforded by an additional free parameter, and the implications of scaling on both power requirements and structural loading. With these insights, we provide an improved methodology for the efficient and cost-effective development of scaled robotic systems.

As the use of mobile robots expands to more diverse and challenging environments, improved mobility methods are required to provide these platforms with the ability to reliably negotiate these terrains. In this paper, we investigate SCARAB, a quadrupedal platform designed to rapidly traverse level, vertical, and inclined surfaces. This study extends previous work in which SCARAB's climbing performance was analyzed to demonstrate its ability to run effectively on level ground. We detail several modifications made to the platform to improve its capacity to both climb and run. This updated platform was used to investigate the influence of leg configuration and leg phasing on running performance and shows that SCARAB is able to run at speeds upward of 40cms-1. Furthermore, analysis of the dynamic characteristics shows similarity between those of the robot and the Lateral Leg Spring model, particularly for configurations that produce the highest running speeds. These results make SCARAB the first platform to effectively demonstrate horizontal plane dynamics quantitatively similar to this model, as well as the first to utilize two distinct dynamical locomotion modalities.

The ability of biological locomotors to rapidly and stably traverse unstructured environments has inspired the development of numerous legged robotic platforms. While strides have been made in negotiating terrains cluttered with obstacles, dealing with surface property variations has received less consideration. This work presents a leg stiffness control strategy that estimates the surface compliance and adjusts the leg stiffness in order to maintain a nominal locomotion behavior while allowing for stable transitions between surfaces of up to three orders of magnitude differences in ground compliance. Implementation of this technique with high-bandwidth variable stiffness actuators that are currently being developed will expand the range of legged robotic platforms to environments with sudden and significant changes in terrain characteristics.

This paper describes the development of a horizontal-plane dynamic running robot based on a reduced order locomotion model, the Lateral-Leg Spring (LLS) model. Contributions include the development of a scaled, actuated, distributed mass simulation of the model, control approaches to compensate for physical and motor limitations, and the design and fabrication of bipedal running robot that instantiates the horizontal plane dynamics of the LLS model.