“Greg’s Harp” is an extraordinary mechanically and robotically musical device with 3 strings excited in 3 different ways that generate some wonderfully unearthly sounds.
Instrument maker Frank Piesik has developed a playable robotic stringed instrument for his friend Gregor. It’s an evolution of a previous single-stringed machine called the Pythagotron. With Greg’s Harp the idea is to be able to play chords from a MIDI keyboard or sequencer.
Each string has a number of motorised frets that use a dedicated servo and driver to push up against the string. With 4 of these “moFrets” on each string covering 5 semi-tones they could play every possible triad. The strings are tuned in major thirds which overlap by a tone and when the notes come in a software algorithm analyses them and puts them into a range the moFrets can play. That’s very clever.
To excite the strings Frank came up with 3 different ways. The first uses a “Kickup” that he had designed for another project that uses a solenoid to strike the string from below. This is the yellow block with the 3 screws in the top. The second way is using a magnetic field actuator like an e-bow for infinite sustain. Lastly, there’s a little motor that spins a tape propeller that clatters against the strings.
The sound is collected through a regular piezo pickup and little preamp circuit.
The hardware control is taken care of by two Arduino Nanos while the audio routing, DSP and MIDI interface is delivered by a Teensy. The Teensy interprets the incoming data and tells the Nanos what to do.
The result is both an amazing thing to look at and a wonderful thing to hear. I hope Gregor is very pleased with it.
- Frank Piesiks website.