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Mechanical Engineering

Engineering in the fun

May 31, 2018

Jonathan Spangler feels like he has played “Folsom Prison Blues” to more audiences than anyone in history.

He doesn’t have roadies or a tour van. He’s a patent lawyer and entrepreneur who packs his guitar with him on business trips in case he can find a new venue and melt some faces. Traveling with a guitar is annoying and stressful. You never know what the baggage handlers may do to your axe as they shove it under the plane and onto transport carts.

What if Jonathan could carry his guitar onto the plane and safely stow it in the overhead bin? Several companies have designed travel guitars and while some are intriguing, they all fall short for a few reasons:

  • They are still too long to fit in a small case
  • When deployed, they don’t look like a normal guitar
  • The transformation process is difficult (i.e., managing the strings or having to tune the guitar).

Design Concepts and CIARI clearly defined the requirements for the end product – it must be lightweight and fit in a backpack, it must control the strings throughout the transformation process, and it has to look and play like a normal guitar.

The solution? A neck that breaks in the middle so it folds exactly in half and backwards, keeping the strings under tension the whole time so they don’t turn into a rat’s nest.

This architecture required a complex over-center, spring-loaded mechanism to allow the strings to move as the neck folded and to lock the neck in place. Initially we addressed three major technical challenges:

  1. Design a mechanism that fit in the space and provided an ergonomic user interface for locking and unlocking the guitar. This required the creation of a kinematic model of the proposed over-center mechanism to estimate the forces the user would encounter.
  2. Create a CAD model of the ideal fret board profile that would provide the “action” required on the strings. This CAD model allowed us to determine how to correctly design and tolerance the hinges so the guitar played and sounded great.
  3. Balance friction and spring force to maintain tension on the strings during transformation while stressing the strings as little as possible to avoid kinking.

Plenty of blood, sweat and beers were spilled as we mitigated risk and figured out how to design and manufacture each component of the guitar. It was lots of work, but it brought a deep understanding of the design and allowed the team to enhance the experience of the guitar in a few key ways. In other words, we were able to engineer in a bunch of fun.

First, the mechanism turned into a work of art. The team decided to put a clear back on the guitar to show it off. We did a round of refinement of the mechanism to remove some extraneous parts and swap in some cool-looking fasteners. This fastener simplification had the added benefit of cost reduction.

Engineering in the fun hinges on one simple word: yes.

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