Synthesis of the Body Swing Rotator Joint Aligning Mechanism for the Abductor Joint of a Novel Tripedal Locomotion Robot

Abstract

The unique three-legged walking robot STriDER (Self-excited Tripedal Dynamic Experimental Robot) utilizes a novel tripedal gait which incorporates aspects of passive dynamic walking into a stable tripedal platform to walk efficiently, and is also capable of changing directions. This unique tripedal gait, however, requires three abductor joints to align two of the three body swing rotator joints in the body, depending on the direction of the step the robot takes. In an earlier prototype of STriDER, the three abductor joints were independently actuated using three DC motors to align the rotator joints which made the robot heavy and inefficient. In this paper, we present the synthesis, analysis, and mechanical design of a novel mechanism for actuating the three abductor joints of this unique three-legged walking robot to generate the required motion using only a single actuator. The mechanism utilizes an internal gear set to generate a Hypotrochoid path curve and uses pin-in-slot joints to coordinate the motion of the three abductor joints to guide them through the four sets of positions required to enable the robot to walk efficiently. A brief description and background of the tripedal locomotion robot STriDER is presented first, followed by the design constraints and requirements of the abductor joint mechanism. Synthesis and kinematic analysis of the mechanism is presented with a study of the force transmission characteristics for a quasi-static case. A description of the detailed mechanical design, results from the experiments, and a conclusion with a discussion for future work is presented next.