  The robotic field has been witnessing a progressive departure from classic
robotic systems composed of serial/stiff links interconnected by simple rigid
joints. Novel robotic concepts, e.g., soft robots, often maintain a series-like
structure, but their mechanical modules exhibit complex and unconventional
articulation patterns. Research in efficient recursive formulations of the
dynamic models for subclasses of these systems has been extremely active in the
past decade. Yet, as of today, no single recursive inverse dynamics algorithm
can describe the behavior of all these systems. This paper addresses this
challenge by proposing a new iterative formulation based on Kane equations. Its
computational complexity is optimal, i.e., linear with the number of modules.
While the proposed formulation is not claimed to be necessarily more efficient
than state-of-the-art techniques for specific subclasses of robots, we
illustrate its usefulness in the modeling of different complex systems. We
propose two new models of soft robots: (i) a class of pneumatically actuated
soft arms that deform along their cross-sectional area, and (ii) a piecewise
strain model with Gaussian functions.
