  Superconductivity is a result of quantum coherence at macroscopic scales. Two
superconductors separated by a metallic or insulating weak link exhibit the AC
Josephson effect - the conversion of a DC voltage bias into an AC supercurrent.
This current may be used to activate mechanical oscillations in a suspended
weak link. As the DC voltage bias condition is remarkably difficult to achieve
in experiments, here we analyse theoretically how the Josephson effect can be
exploited to activate and detect mechanical oscillations in the experimentally
relevant condition with purely DC current bias. We unveil for the first time
how changing the strength of the electromechanical coupling results in two
qualitatively different regimes showing dramatic effects of the oscillations on
the DC current-voltage characteristic of the device. These include the
apperance of Shapiro-like plateaux for weak coupling and a sudden
mechanically-induced retrapping for strong coupling. Our predictions,
measurable in state of the art experimental setups, allow the determination of
the frequency and quality factor of the resonator using DC only techniques.
