A self-exciting controller for high-speed vertical running

Abstract

Traditional legged runners and climbers have relied heavily on gait generators in the form of internal clocks or reference trajectories. In contrast, here we present physical experiments with a fast, dynamical, vertical wall climbing robot accompanying a stability proof for the controller that generates it without any need for an additional internal clock or reference signal. Specifically, we show that this "self-exciting" controller does indeed generate an "almost" globally asymptotically stable limit cycle: the attractor basin is as large as topologically possible and includes all the state space excluding a set with empty interior. We offer an empirical comparison of the resulting climbing behavior to that achieved by a more conventional clockgenerated gait trajectory tracker. The new, self-exciting gait generator exhibits a marked improvement in vertical climbing speed, in fact setting a new benchmark in dynamic climbing by achieving a vertical speed of 1.5 body lengths per second. Abstract-Traditional legged runners and climbers have relied heavily on gait generators in the form of internal clocks or reference trajectories. In contrast, here we present physical experiments with a fast, dynamical, vertical wall climbing robot accompanying a stability proof for the controller that generates it without any need for an additional internal clock or reference signal. Specifically, we show that this "self-exciting" controller does indeed generate an "almost" globally asymptotically stable limit cycle: the attractor basin is as large as topologically possible and includes all the state space excluding a set with empty interior. We offer an empirical comparison of the resulting climbing behavior to that achieved by a more conventional clock-generated gait trajectory tracker. The new, self-exciting gait generator exhibits a marked improvement in vertical climbing speed, in fact setting a new benchmark in dynamic climbing by achieving a vertical speed of 1.5 body lengths per second.

CLASH: Climbing vertical loose cloth

“…Preliminary tests on CLASH with the four-bar foot design presented above reveal the robot is capable of climbing vertical loosehanging cloth at speeds up to 15 cm second −1 , or up to 1.5 body-lengths second −1 . To the authors knowledge, this is the first robot capable of climbing loose cloth, and its speed is comparable to DynoClimber which had set the current benchmark for vertical climbing when normalized by body length [6]. CLASH only requires the four-bar foot mechanisms on the front and middle legs in order to achieve climbing, and thus the rear hips can be equipped with stiff, oar-like legs originally used in the DASH design [7].…”

“…The fastest among the legged climbing robots is DynoClimber, which uses two legs to dynamically climb vertically-mounted, rigidly-backed carpet [6].…”

Dynamical trajectory replanning for uncertain environments

“…[1][2][3][4]) this paper focuses on a control scheme that places the reference dynamics in the feedforward pathway using a design akin tö…”

“…Over the past two decades, the field of robotics has given rise to many examples of notional [1][2][3][4] and arguably [5] or potentially [6,7] useful working physical machines whose behavioral goals are encoded by means of reference dynamics rather than the more traditional reference trajectory. In this paper we pursue a general framework for stably coupling dynamical reference generators to actuated mechanical systems last addressed in such abstracted (rather than robot-specific) form more than two decades ago [8].…”

“…In contrast, the focus of this paper is the question of what benefit can be achieved by modifying the reference trajectory r in the face of online exposure to the disturbances d. Specifically, we advance an architecture relevant to the growing class of robots [1][2][3][4][5][6] whose reference trajectories are dynamically generated by allowing disturbance induced tracking errors (2) to excite a transient "replanner" subsystem that alters the reference generator in a stable manner.…”