Pedal-driven Guitar Strummer

Guitar strummer made for a guitarist with right-side hemiplegia who can no longer strum his guitar normally.
The pedal allows him to use his functioning left foot for strumming.

If you know of anyone who could benefit from a similar device, don’t hesitate to get in touch!

Design

Materials

The mechanism is mainly 3D printed in PLA with few bits in NinjaFlex.
The gantry rides on top of IGUS anodized aluminum shafts with IGUS iglidur® J4 polymer bearings to minimize weight and noise.
The pedal is based on a B-Stock, Millenium DCH-SET01 Cable Hi-Hat which was a horrible mechanical design so I have rebuilt the insides almost entirely to decrease friction, lower noise and to better control the pedal-angle to cable translation ratio.
Cable is a standard bike breaking cable.
Assembled with m3 nuts and bolts

Specifications

Who is it for:
- For anyone who has lost the function of the right side of their body and wants to return to – or learn to play – the guitar.
Key Features:
- introduces the foot as an alternate limb for playing a two-handed instrument
- users press a floor pedal to strum the guitar
- only down-stroke strumming
- a flexible cable attached to a sliding mechanism holds the pick in position over the strings
- can be attached to a wide range of guitar styles and shapes
- designed to ensure minimal foot fatigue and leg strain
- light-weight
- good sound
- low noise

Design Solution Overview

The mechanism consists of a guitar mount with 2 rods on which a gantry is mounted with linear bearings. The gantry is attached with elastics in one end and is pulled in the other direction through a cable mechanism, controlled by a foot pedal.
The gantry consists of a base that attaches to the rods, a plector arm with a plector attached at the end. The plector arm hinges at the top of the gantry base and is held in place by a spring. When the gantry is moved down across the guitar strings, the plector arm pushes directly against the gantry base and cannot move which forced the strings to displace, strumming the guitar. When the gantry moves up, the force is in the opposite direction so the plector arm pushes against the spring and moves out of the way, without strumming the guitar.
The mechanism is attached to the guitar with a wide fabric band with velcro and a bit of elasticity.

Challenges

While the overall mechanics are rather simple, I spent about 80% of the time refining the sound and playability, and I believe it was a success.

Main challenges were:

Avoid the up-stroke strumming without adding unnecessary friction
Minimize noise of mechanism
Low variation in strumming volume of each string despite fretboard radius
Low variation in strumming volume when pushing down strings
All while creating a good strumming sound

All work was done in my 3x4m office using only a caliper, screwdrivers, nuts and bolts, needle and thread, scissors, a Dremel for cutting the aluminum rods and my Prusa i3 MK3 3D printer. While some parts definitely could have been manufactured cheaper and faster using other tools and techniques, I believe this is a testament to the flexibility and versatility of 3D printers. I would have needed a much bigger room and many more tools had it not been for the printer.