Add to ORKGInternational audienceTwo models of the grand piano key mechanism are presented: a single-degree-of-freedom model and a model based on 6 rotating bodies, 13 contact zones with nonlinear springs, 3 of them (hammer-jack, jack-escapement button, hammer-check) being also subject to Coulomb friction. The latter model introduces discontinuities on the velocities. The problems raised by the usual regular-dynamics formulation are discussed and a non-smooth dynamics approach is proposed. Based on the comparison between experimental and simulation results, it is discussed whether the simulation should be driven by the force exerted by the pianist or by the displacement of the key