Comparative experimental and theoretical approaches on multi-legged locomotion – Using fast running insect, arachnid, isopod and centipede species for examining leg coordination and body dynamics with increasing numbers of propulsive legs and running spee

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Robotic applications are becoming increasingly prevalent in our everyday life, and will soon include advanced self-propelled assistive technology. Since human environments are full of a wide range of obstacles, and legged systems excel on uneven terrain, many of these devices will, in addition to wheels, also rely on some sort of legged propulsive apparatus. Multilegged locomotor apparatuses intrinsically provide a high degree of static stability. Accordingly, it is high time for a better understanding of multilegged locomotion. Arthropods are natural models and prime examples for such polypedal structures. However, the impact of different leg numbers on body dynamics in fast moving polypedal animals is still underexplored. Consequently, this application aims at experimental and theoretical examinations of terrestrial locomotion in different arthropod species covering a range of leg numbers in the transition zone from few to many. Knowledge gained on these organisms’ locomotion biomechanics, peak performance and control will also advance our understanding on migratory processes and ecosystem dynamics. So far, available data covers only a handful of species. These example species, however, do not at all represent the entire wealth of locomotor apparatuses available in arthropods. Likewise, many mathematical models on arthropod locomotion disregard the real number of propulsive legs and focus exclusively on horizontal running dynamics. Recently, I have shown that insects and arachnids shift leg coordination when changing from intermediate to high running speeds. These changes impact body dynamics, energetics and running stability. Moreover, in a modelling study I was able to reveal the increasing impact of slight coordinative changes on body dynamics and energetics as the number of propulsive legs increases. Since such small coordinative changes have been neglected so far, naturally occurring gait changes are likely to have been overlooked in a large number of arthropod species. Consequently, the present proposal aims at gaining knowledge from biological models by examining steady locomotion, including peak performance, in a range of insect, arachnid, isopod and centipede species. The experimental species are all similarly sized, poikilotherms with exoskeletons, which reduces the impact of these features on the results. When running at speed, the species use 2, 3, 4, 7 and 14 pairs of legs. Their movements will be examined via high speed kinematics, semi-automated tracking techniques and previously developed analytical technology. By comparing the results of the intended experiments to the predicted outcomes of established models, it will be possible to test crucial predictions of those models. Furthermore, recently developed model concepts will be enhanced by implementing additional parameters such as noise and irregular ground reaction forces, which will enable the assessment of these parameters’ impact on multilegged locomotion.