Strumli

Strumli is a Completely Free! and open source musical project with the design files included so you can build and modify your own. The Design files are freely available to the public but if you're feeling generous a "support" purchase can be made here.

Quick Links for the Impatient:

Printables: https://www.printables.com/model/597330-strumli-a-single-string-meme-strument

Cults3D: https://cults3d.com/en/3d-model/gadget/strumli-a-single-string-meme-strument

Thangs: https://than.gs/m/940094

Necessary hardware can be purchased through my affiliate links

Bearings: https://amzn.to/48vOaoN

Strings: https://amzn.to/467jPex

Screws and Washers: https://amzn.to/46eHKJ9

Backstory and Product Definition

Firstly, the absolute original nugget of this design was first thought of after seeing the TuneFast harp.

This appears to be a project done by either Adam Kumpf, Maura Atwater, or both. Strumli obviously shares the same fundamental concept, and really the only change is that _they_ chose to target a scale (similar to a harp) while I chose the much less useful option of targeting specifically a single songs at a time. Adam or Maura, if you by some chance land on this page, hit me up! I would love to connect/collaborate!

Online Piano Interface

I started this project knowing literally nothing about HTML, JavaScript, or CSS, thankfully the internet exists and it has never been easier to teach yourself stuff. I found this tutorial by the user CodingNepal which pretty accurately matched what I had in my head. With a little bit of tweaking I was able to get it to display all the relevant information, and play music when you clicked on the notes. Once I had it working on/with a local server I googled a bit and found Netlify which promised simple JavaScript web app hosting. If anyone knows better or has suggestions please don't be a stranger, I barely know more than when I started :D. All code can be found on the Github Page for this project.

Physical Design

Thankfully this is actually the part I am most competent in. I knew from the start that I wanted an interchangeable soundboard so the song's could be swapped out. Originally I had plans of making this a little pull back car type toy where the user would pull back on it and let it go and the device would drive itself forward while playing the song over an over again. After a handful of prototypes I decided that was WAY to bulky and realistically too big of scope creep. After that I focused on making a functional prototype before the scope creep goblin could get me to add more to the project (The goblin did get me when I decided to make the web app but the fight was valiant.) Once I had a working prototype of a soundboard I attempted to wrap it in a halfway aesthetic housing. There were a few false starts and dead ends but with the assistance of my partner I landed on the final "Pill Shape"

Sound board Design and Assembly

The Actual soundboard has some geometry on the back to connect the base and the soundboard, as well as features to hold the shafts and guitar tuner.

As I mentioned in the video the spacing between the strings is fixed by the V groove bearings. The bearings help transmit the tension between the various string segments, without the bearings you're dealing with the capstan equation, which makes this whole thing not work. The bearings sit on screws and are lifted off the actual soundboard by small washers. I project the sketch and enter the string lengths necessary for the song, zig zagging the notes back and forth to generate a continuous string.. Generally the song can't be more that 7 or 8 individual notes. The limiting factor is the string length that's available for guitars. If one wanted to source just raw music wire they theoretically could make a much longer sound board ( but the tension is multiplied by the number of notes so be warry of.)

Once all the string lengths are laid out place a circle on the midpoint of the line segment connecting two adjacent notes. This will represent the center of the bearing support screw. Simply copy the dimensions of the reference design STEP file I provided with project files. Make sure to include an extra bearing at the beginning to loop the one end of the guitar string around, and the guitar tuner hole at the opposite end.

Build Instructions

The assembly is fairly straight forward for this project. Start by threading all of the m3 bolts with a V groove bearing and a single washer. Then one at a time, you can insert the bolt into the holes of the Strumli, securing with a nut from the underside of the sound board. Once all of the V groove bolts are in place you can install the guitar tuner which is used to tension the string. The guitar tuners typically come in pack of 6 and have left and right handed tuners. Make sure the tuners bolt hole lines up properly.

Optionally you can glue in some small magnets in the recesses in both the soundboard and main body to make the connection a little more secure.

Once that's done you can string the instrument and begin tensioning it. Thread the end of the guitar string through the eyelet hole in the base and hook the loop that is created around the "anchor" bearing. string the instrument in a zig zag fashion to set the appropriate distances between the strings. Once you reach the guitar tuner loop the end of the guitar string through the hole in the guitar tuner and begin turning the knob on the tuner. The string will eventually kink and self lock onto the tuner, pluck one of the strings and set the tension by using a normal guitar tuner.

**Important Tip!:** I found using a high E string works the best, any thicker and the soundboard REALLY starts struggling to hold a tune. I think this has to do with the overall force being exerted on the plastic. Going to a softer material will also help such as nylon guitar strings

Current State of Project

The project is currently Complete, I encourage people to add to the library of sound boards though!

Future Plans

I don't have any active plans to add sound boards with any consistency. I do encourage people to submit new soundboard designs, I can an will add them to the Repo.

How to Contribute

The best way to contribute is going to be through discord, Please join the discord server and reach out with your examples. I'd be happy add them to be base design.

Where and how to ask for Help

Again Discord is likely the best place to reach me and the community.

PLEASE post and show any and all designs you make!

Feel free to take the concept and embed it in other shapes as well, I chose something that would work on a shelf but the ridiculousness/hilarity could certainly be turned up a notch.