We propose an autonomous monoparametric optomechanical mechanism that exploits nonlinearities to convert a constant energy current into a nonconservative mechanical force. This force self-sustains the generation of phonons whose frequency is much lower—by several orders of magnitude—than that of the photonic degrees of freedom. We identify conditions under which the maximum mechanical power extracted becomes invariant and uncover a new form of self-induced robustness, where power production remains stable in the presence of imperfections and external noise in the drive.