This paper is about a novel robotic guitar that establishes shared control between human performers and mechanical actuators. Unlike other mechatronic guitar instruments that perform pre-programmed music automatically, this guitar allows the human and actuators to produce sounds jointly; there exists a distributed control between the human and robotic components. The interaction allows human performers to have full control over the melodic, harmonic, and expressive elements of the instrument while mechanical actuators excite and dampen the string with a rhythmic pattern. Guitarists can still access the fretboard without the physical interference of a mechatronic system, so they can play melodies and chords as well as perform bends, slides, vibrato, and other expressive techniques. Leveraging the capabilities of mechanical actuators, the mechanized hammers can output complex rhythms and speeds not attainable by humans. Furthermore, the rhythmic patterns can be algorithmically or stochastically generated by the hammer, which supports real-time interactive improvising.