Nicholas Moy, Amy Ngo, John Robinson, Terence Tan

MU 2801 | Making Music with Machines | A-Term 2021

The initial idea behind this project was to replicate a human strum on a ukulele. Unlike a piano, a chord played on a Ukulele is played one note at a time due to the motion of the pick/finger with each note coming slightly after the first. We wanted to replicate these delays by replicating the path of a pick/finger. We also wanted this device to assist people playing the Ukulele with limited use of their Right strumming hand rather than a device that plays by itself outright.

Our goal is to end up with a mechanism that can mimic the right hand and be played along with a human fretting the fretboard. This mechanism could also be the first component to a larger device that can fret and dampen the strings as well, although we will not have time to build all of those mechanisms. The largest focus that the machine will have in being more than a simple mechanism will be the ability to control the velocity of its motion. By being able to manipulate the speed of the strumming in both preset and real-time, we will also be able to add in the possibility of different volumes and patterns. In other words, the machine will be able to advance from playing simple rhythms to more complicated song melodies.

Planning & Modeling

The path of human strumming on a ukulele was first mapped in order to determine whether or not such strumming could be easily replicated by a machine (given the time constraint of the project). If the depth of the strumming is unaccounted for, then the motion of the strumming is relatively linear and therefore could be mimicked by the path of a linear actuator. Depth was determined to be a component that was not necessary at the moment and could be experimented on in the future.

3D Renderings of the individual components were created using Solidworks in order to examine how they would all interact in regards to size, fit, and motion.

CAD rendering of the ukulele along with the additional components of the strumming mechanisms.

Mechanics

The basis of movement within the system is a stepper motor that drives a belt connected to our pick carriage.

The pick moves back and forth on precision rods via 2 linear bearings and a 3-d printed mount. The pick holder is spring-loaded in the upward strumming direction and rigid for the downward strumming direction. This was designed intentionally to mimic the difference between a typically accented downstroke and a softer upstroke. Although the stepper motor can figure out its angular position and therefore the linear position of the pick, we attached 2 limit switches to the robot chassis, so that it can zero itself out every time it hits a limit switch. This made the code much simpler.