  Nanoelectromechanical systems (NEMS) are devices integrating electrical and
mechanical functionality on the nanoscale. Because of individual electron
tunneling, such systems can show rich self-induced, highly non-linear dynamics.
We show theoretically that rotor shuttles, fundamental NEMS without intrinsic
frequencies, are able to rectify an oscillatory bias voltage over a wide range
of external parameters in a highly controlled manner, even if subject to the
stochastic nature of electron tunneling and thermal noise. Supplemented by a
simple analytic model, we identify different operational modes of charge
rectification. Intriguingly, the direction of the current depends sensitively
on the external parameters.
