  A simple model for a granular ratchet corresponding to a single grain
bouncing off a vertically vibrating sawtooth-like base is studied. Depending on
the vibration strength, the sawtooth roughness and the restitution coefficient,
horizontal transport in both the preferred and unfavoured directions is
observed. A phase diagram indicating the regions in parameter space where each
of the three possible regimes (no current, normal current, and current
reversal) occurs is presented.
