This paper presents a simplistic passive dynamic model that is able to create realistic quadrupedal walking, tölting, and trotting motions. The model is inspired by the bipedal spring loaded inverted pendulum (SLIP) model and consists of a distributed mass on four massless legs. Each of the legs is either in ground contact, retracted for swing, or is ready for touch down with a predefined angle of attack. Different gaits, that is, periodic motions differing in interlimb coordination patterns, are generated by choosing different initial model states. Contact patterns and ground reaction forces (GRFs) evolve solely from these initial conditions. By identifying appropriate system parameters in an optimization framework, the model is able to closely match experimentally recorded vertical GRFs of walking and trotting of Warmblood horses, and of tölting of Icelandic horses. In a detailed study, we investigated the sensitivity of the obtained solutions with respect to all states and parameters and quantified the improvement in fitting GRF by including an additional head and neck segment. Our work suggests that quadrupedal gaits are merely different dynamic modes of the same structural system and that we can interpret different gaits as different nonlinear elastic oscillations that propel an animal forward.
Passive Dynamics Explain Quadrupedal Walking, Trotting, and Tölting
Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF COMPUTATIONAL AND NONLINEAR DYNAMICS. Manuscript received February 10, 2015; final manuscript received May 7, 2015; published online August 26, 2015. Assoc. Editor: Javier Cuadrado.
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Gan, Z., Wiestner, T., Weishaupt, M. A., Waldern, N. M., and David Remy, C. (August 26, 2015). "Passive Dynamics Explain Quadrupedal Walking, Trotting, and Tölting." ASME. J. Comput. Nonlinear Dynam. March 2016; 11(2): 021008. https://doi.org/10.1115/1.4030622
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