This article provides a history of robotic guitars and bass guitars as well as a discussion of the design, construction, and evaluation of two new robotic chordophones, with a focus on different techniques to extend the expressivity of robotic guitars. Swivel and MechBass, two new robots we built, are discussed. Construction techniques likely to interest other musical roboticists are included. These robots use a variety of techniques, both new and inspired by prior work, to afford composers and performers the ability to precisely control pitch and string-picking parameters. Both new robots are evaluated to test their precision, repeatability, and speed. The article closes with a discussion of the compositional and performative implications of such levels of control, and how it might affect humans who wish to interface with the systems.