Characterization and Selection of Contractile Actuators for Soft Robotics Operating in the Quasistatic Regime

Contractile actuators are promising candidates for soft robotics, but selecting a suitable actuator for a specific mechanism requires the combination of performance metrics such as free stroke, blocking force, or work density. For a specific elastic actuator, the available stroke is strongly dependent on the force imposed by the intrinsic stiffness of the robot or the external structure. Here, we present a framework for characterizing and selecting contractile actuators typical uses operating in the quasistatic regime. To characterize the actuators, we use the longitudinal force–displacement curves, measured in the passive state via tensile test and in the active state via isometric or isobaric test. The force–displacement curves in these two states define the boundary of the operational range of achievable strokes. We demonstrate the framework on three representative and distinct contractile actuators: electrically stimulated thermal twisted‐and‐coiled polymer actuators, heat‐stimulated liquid crystal elastomer actuators, and McKibben‐type pneumatic actuators. To select actuators, we propose the incidence matrix formulation for actuator groups arranged in series and/or in parallel. We validate the approach experimentally in two design problems: an insect‐scale jumping robot with nonlinear buckling loads, and an antagonistic structure. This framework for actuator characterization and selection replaces trial‐and‐error with a predictive, materials‐agnostic design workflow, providing a foundation for the rational integration of emerging contractile actuators into soft robotics.