The Rotary Harp

Musical Robotics, B 2025

Robert Branchaud, Nathan Gravelle, David Penney

Description

The Rotary Harp is an automated instrument which plays a set of 24 strings about a cylindrical rotating turret called the harp core. The strings are all nickel wound and use different gauges to achieve different tunings, these gauges range from 0.08 to 0.28. This allows the harp to be tuned chromatically from C3 to B4 while having a consistent scale length of 16 inches. The harp core is printed out of carbon fiber petg with a hollow steel rod that runs through the middle, these materials were chosen to resist the large amount of tension exerted by the 24 strings. A set of arms are attached to a gear underneath the harp core which rotates about the center to pluck strings using stepper motors. The arms are printed out of regular petg as they do not experience much stress. Using bearings both of these pieces are attached to a stick which runs through the middle of the harp. This piece is the main load bearing component of the harp so it is printed out of carbon fiber nylon. To pluck a note both the harp core and closest arm spin to meet each other in a middle point and then spin one of the two motors on the arms. This was done so that we could cut down on the travel time between notes. All of the motion of the harp is driven by stepper motors which we are running at 24v for better performance as opposed to 12v. The entire electrical system consists of 4 stepper motor drivers and a pico pi w which we use to control the harp and provide a 5v source to the stepper motor drivers. Signals can be sent to the pico pi w through both serial communication and wifi, and midi data is transmitted from Ableton Live using a Max patch.