We describe the design features that underlie the operation of iSprawl, a small (0.3 kg) autonomous, bio-inspired hexapod that runs at 15 body-lengths/second (2.3 m/s). These features include a tuned set of leg compliances for efficient running and a light and flexible power transmission system. This transmission system permits high speed rotary power to be converted to periodic thrusting and distributed to the tips of the rapidly swinging legs. The specific resistance of iSprawl is approximately constant at 1.75 for speeds between 1.25 m/s and 2.5 m/s. Examination of the trajectory of the center of mass and the ground reaction forces for iSprawl show that it achieves a stable, bouncing locomotion similar to that seen in insects and in previous (slower) bio-inspired robots, but with an unusually high stride frequency for its size.

This paper describes the inspiration for, design, analysis, and implementation of, and experimentation with the first dynamical vertical climbing robot. Biologists have proposed a pendulous climbing model that abstracts remarkable similarities in dynamical wall scaling behavior exhibited by radically different animal species. We numerically study a version of that pendulous climbing template dynamically scaled for applicability to utilitarian payloads with conventional electronics and actuation. This simulation study reveals that the incorporation of passive compliance can compensate for the scaled model’s poorer power density and scale disadvantages relative to biology. However, the introduction of additional dynamical elements raises new concerns about stability regarding both the power stroke and limb coordination schemes that we allay via mathematical analysis of further simplified models. Combining these numerical and analytical insights into a series of design prototypes, we document the correspondence of the various models to the scaled platforms and report that our final prototype climbs dynamically at vertical speeds up to 0.67 m/s (1.5 body-lengths per second, in rough agreement with our models’ predictions).

The design of legged robots has long drawn on nature for inspiration. However, few of these robots exhibit the speed and robustness seen in even the simplest of animals. This paper presents the design and fabrication of a novel class of six-legged running robots based on biologically- inspired functional principles. We first describe recent findings in biological research that motivate our robots' design, leg configuration, and control structure. We then describe an emerging layered-manufacturing technology that allows us to fabricate the robots with passive mechan- ical properties like those found in nature. Finally, we present preliminary tests over different terrains and condi- tions which show speed and robustness approaching the performance of small animals.

Humans and animals adapt their leg impedance during running for both internal (e.g., loading) and external (e.g., surface) changes. To date, the mechanical complexity of designing usefully robust tunable passive compliance into legs has precluded their implementation on practical running robots. This work describes the design of novel, structure-controlled stiffness legs for a hexapedal running robot to enable runtime modification of leg stiffness in a small, lightweight, and rugged package. As part of this investigation, we also study the effect of varying leg stiffness on the performance of a dynamical running robot.

The spring loaded inverted pendulum template has been shown to accurately model the steady locomotion dynamics of a variety of running animals, and has served as the inspiration for an entire class of dynamic running robots. While the template models the leg dynamics by an energy-conserving spring, insects and animals have structures that dissipate, store and produce energy during a stance phase. Recent investigations into the spring-like properties of limbs, as well as animal response to drop-step perturbations, suggest that animals use their legs to manage energy storage and dissipation, and that this management is important for gait stability. In this paper, we extend our previous analysis of control of the spring loaded inverted pendulum template via changes in the leg touch-down angle to include energy variations during the stance phase. Energy variations are incorporated through leg actuation that varies the force-free leg length during the stance phase, yet maintains qualitatively correct force and velocity profiles. In contrast to the partially asymptotically stable gaits identified in previous analyses, incorporating energy and leg angle variations in this manner produces complete asymptotic stability. Drop-step perturbation simulations reveal that the control strategy is rather robust, with gaits recovering from drops of up to 30% of the nominal hip height.

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.