Leg force interference in poly-pedal locomotion

Abstract

The examination of gaits and gait-changes have been the focus of movement physiology and legged robot engineering since the first emergence of the fields. While most examinations focussed on bipedal and quadrupedal designs many robotic implementations rely on the higher static stability of three or more pairs of legs. Nevertheless, examinations of gait-changes in the biological models, i.e. poly-pedal arthropods such as insects or arachnids, are rare. Except for the well-known change from slow feedback controlled walking to a fast, feedforward controlled running gait, no changes are known or are deemed to be of low significance.\n\nHowever, recent studies in fast moving spiders, mites and cockroaches have revealed an additional gait change also for the transition from intermediate to high running speeds. This change is similar to gait transitions as found in quadrupedal vertebrates.\n\nAccordingly, the present approach aims to extend available theory to poly-pedal designs and examines how the number of active walking legs affects body dynamics when combined with changing duty factors and phase relations. The model shows that higher numbers of active leg pairs can prevent effective use of bouncing gaits such as trot and their associated advantages because significantly higher degrees of leg synchronisation are required. It also shows that small changes in the leg coordination pattern have a much higher impact onto the COM dynamics than in locomotor systems with fewer legs. In this way, the model reveals coordinative constraints for specific gaits facilitating the assessment of animal locomotion and economization of robotic locomotion.\n\nSignificance StatementThe present model approach enables to assess the impact of different numbers of walking legs onto movement dynamics and gait choice in terrestrial legged locomotion. The models results are indicatory for research in legged locomotion regardless whether biological examples or legged walking machines are considered. The approach is suitable for all numbers of pairs of walking legs larger than two and is focussed on symmetrical gaits as found in straight and continuous locomotion. The model fills a gaping gap as the impact of phase shifts among the legs in the coordinated sets of legs typical for poly-pedal animals and robots on overall body dynamics are not considered sufficiently in existing dynamic model approaches.