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An active flexural hinge has been developed and incorporated into the transmission of a prototype flapping-wing robot. The multilayered flexure, which is constructed from a shape memory polymer and a polyimide film, showed controllable stiffness under change in temperature. At room temperature, the flexure had a bending stiffness of 572 mN·mm; when warmed to 70°C, the stiffness was 11 mN·mm. The resulting single-wing flapping system demonstrated up to an 80% change in generated lift without modification of the waveform of the main driving piezoelectric actuator. Such active stiffness tunable flexure joints could be applied to any flexural miniature mobile robot and device mechanisms.