“The idea came to me while I was listening to a great Seattle fingerpicking guitarist, the late Klaus Lendzian, at a favorite local restaurant. I’d been hearing him play at various venues around town since the 1980s.
As I watched him play, I thought, “He’s really good. Lyrical, a great sense of timing. Wow, I wish I could play like that. What makes it all work is his right hand, his picking hand. It’s like a machine.”
Why Build a Guitar Picking Robot?
Here are a few of my reasons, in no particular order:
- I’ve been playing guitar, off and on, for over 40 years. At this point, I’m a semi-competent flatpicking guitarist. But I’ve always been interested in the sound of fingerpicking. I’m 65 years old. Do I have 40 more years to learn fingerpicking?
- I wanted to be able to play patterns on the guitar that would be difficult or impossible for me to play. Or for almost anyone to play. (John McLaughlin or Yvette Young notwithstanding.)
- I’m a writer and software developer. I type a lot, and my hands and wrists are getting worn out.
- My sense of rhythm is poor.
What does all of that mean? I need help playing guitar. So I’m building a prosthesis to help me do that, just as I wear glasses to improve my nearsightedness.
Why didn’t I simply switch to using MIDI instruments? There are perfectly good guitar simulations available, after all. That wasn’t what I wanted.
What I want is the sound of the guitar string, vibrating in air, under the influence of other vibrations, and my fingers, in a room, from an amplifier, through the body and neck of the guitar.
At the same time, I wanted something I could interact with, an extended instrument. Not just something that would play a given song at the press of a button. I think that would be boring. I think that interaction and improvisation are where music happens, and I’m not particularly interested in “songs.”
When my friend Jon Singer speaks of a current obsession of his (building organic dye lasers, or glow-in-the-dark ceramics, for example), he says, “It’s got me by the throat.” This project has had me “by the throat” for a long time.
I haven’t kept rigorous track of how many versions of the guitar robot I’ve built. At least 20, over 16 years.
Software and Circuit Design
Over the years, I’ve used Microchip PIC microcontrollers and various Arduino platform devices to control the robot, but I’ve recently switched to a Pimoroni Servo 2040 — this board combines a RP2040 microcontroller and servo controllers. I’m using CircuitPython to program the board.
The program is very simple — when a MIDI note comes in, pick the string. I’m using the range from E-1 (MIDI note 16) for the low E string to A-1 (21) for the high E string. The actual note that gets played depends on whatever fretting I do with one or more hands.
Mechanical Design
The software design is simple — it’s the hardware side (both design and fabrication) that’s taken up most of my time on this project.
The challenge, all along, has been to find actuators (solenoids, motors, or servomotors) that are:
• Small enough that six of them will fit on the guitar. The space between strings on a Telecaster bridge is around 11mm, so if the actuators are no wider than that, they can be positioned six-abreast behind the bridge of the guitar.
• Powerful enough: It takes a fair amount of force to push a pick past a guitar string. I’ve found that 3kg/cm of force is about the minimum for this design.
• Fast enough: I wanted, at a minimum, the ability to pick 32nd notes at 120 beats per minute (bpm). This means the time it takes the actuator to pick the string (swing the pick from one side of the string to the other) needs to be ~63 milliseconds (ms) or less (see the box below).
• Relatively inexpensive: My initial budget was $2.00 or less per actuator (keep in mind that I need to buy six for each design). I bought solenoids, stepper motors, and gearmotors from electronics surplus shops. This was an unrealistic requirement — I think “laughable” is the correct term. My current actuators cost around $20, and I’m now looking longingly at ~$70 servos. “