~sound in the advent of the phonograph and,
subsequently, the loudspeaker largely led to the demise
of the increasingly complex automated instruments.
During the 1970's, artists created to the field of
musical robotics by integrating the pre-loudspeaker
automatic music techniques with contemporary
electronics. These artists, including still-active workers
Trimpin and Godfried-Willem Raes, found in musical
robots a way to express computer music through media
other than loudspeakers. This interest in utilizing
computer music techniques with mechatronic apparatus
is still active in contemporary musical roboticists who
use state-of-the-art techniques to endow their machines
with AI-driven musicianship [1].
While much musical robotic research focuses on
percussive instruments such as drums and marimbas [5,
10], the past two decades have seen several notable
robotic guitar systems. These instruments served as key
inspirations to the new work described in this paper.
William Baginsky's The Three Sirens ensemble uses a
mechatronically-complex robot guitar, dubbed
Aglaopheme, which plays music based on the output of
an artificial neural network.
A second influential robotic guitar is GuitarBot,
built by Singer in 2003. GuitarBot features four
vertically mounted strings that remain in permanent
contact with their sliding fretter. GuitarBot, shown in
Figure 1, was most notably used in concert with guitarist
Pat Metheny in 2010.
Groundbreaking sound sculptors Trimpin and
Godfried-Willem Raes have also contributed to the
subfield of robotic guitars: Trimpin's 2001 sculpture
Krautkontrol features an array of solenoid-actuated
guitars (shown in Figure 1) capable of floating bridgemediated pitch bends [2]. The Logos Foundation,
created by Godfried Willem Raes [7], built the
Synchrochord monochord string instrument in 2012.
While existent robotic guitars have varying degrees
of musical expressivity available to performers and
composers, a goal in the design of Swivel was to create
a system that affords artists high-resolution control over
parameters such as pitch and loudness. The next section
details the design, fabrication, and evaluation of these
subassemblies.
The following subsections focus upon the design,
implementation, and construction of Swivel's
subassemblies. The mechanisms of action of each
subassembly are discussed, and design and construction
techniques are detailed.
3.1. Fretting Mechanism
Figure 3. Swivel's fretting mechanism
Swivel's fretting assembly consists of a fretter arm,
which is attached to a stepper motor via a pivot arm.
The system is diagrammed in Figure 3. The stepper
motor positions the fretter arm along the string; upon
reaching the desired position, the solenoid-actuated
fretter arm clamp brings the fretter arm into contact with
the string. By eschewing traditional linear motion-based
fretter systems in favor of a rotary mechanism, it was
hoped that higher speed could be attained and simpler
construction techniques be used. This rotary mechanism
has been built using rapid prototyping techniques: 3D
printing techniques were used to create the pivot arm.
3.2. Plucking Mechanism
F Pickwheel
Stepper Motor
Vllll
3. SWIVEL: A SYSTEMS OVERVIEW
Volume Adjustment Servo
Figure 4. Swivel's plucking mechanism
A rotary plucking mechanism, diagrammed in Figure 4,
is used for string actuation. Guitar picks are mounted
radially around a laser cut acrylic clamp. The pick
clamp is attached to the shaft of a stepper motor: upon
actuation, the stepper motor rotates and brings the picks
into contact with the string. To vary the power of the
Figure 2. Swivel, with its sub-assemblies indicated.
446 2013 ICMC
