Rice University engineering students design new capo for guitars


A capo is a clamp-like device that acts as a sixth finger across the strings. But what's the problem with most?

"Sometimes capos hurt," guitar-playing Rice engineering student A.J. Fenton said. "When you play this F major 7, it presses against your index finger and it's quite uncomfortable, especially if you want to wrap your thumb all the way around."

"Most people figure out how to make do and curse a little bit while they play, but it's pretty awkward," Rice trustee and alumnus John Jaggers added.

Jaggers, managing general partner of a Dallas venture capital firm, plays in an acoustic duo with his friend and fellow picker Matthew Carroll in his spare time. Jaggers said he and Carroll started talking about capos and decided changes were in order, so he approached the students about coming up with a better capo design.

"I've been fairly involved in Rice and a big believer in the OEDK [Oshman Engineering Design Kitchen]," Jaggers said. "I thought, 'Wow, this is a mechanical design challenge.'"

He noted that he and Carroll are not mechanical engineers.

"And frankly, we don't have a lot of time to sit around designing capos. So I thought this might be a great project," he said.

A team of students -- Fenton, Eric Stone, Lisa Sampson, Nicki Chamberlain-Simon and Amber Wang -- took four months this spring to design and build a series of prototypes that flatten out the capo, sweeping the mechanical elements back and out of the way of flying fingers while retaining all the qualities good commercial capos offer: versatility, speed of placement and the convenience of being able to clip it onto the headstock when not needed.

And there are problems the guitar poses for a capo maker. The device acts as the barre, taking the place of the index finger that spans the neck in a barre chord and depressing the strings just enough to create solid contact with the frets but not so much as to throw the tones off-pitch. That lets a player change the key of a song to match one's vocal range without changing the basic chord shapes.

The capo also has to be versatile in order to accommodate a variety of guitar necks, which not change from guitar to guitar as well as along the neck of a single guitar. Finally, it shouldn't dig into the woodwork of a guitar.

There are a lot of nuances we didn't think about before we started, like the curvature of the guitar neck or the materials we had available," Wang said. "Every single part of the prototype we had to make ourselves. So we had to be creative."

The students' final prototype has a two-piece, spring-loaded plastic framework created on a 3-D printer with a hard rubber strip that contacts and gently clamps the strings. While it's not yet perfect -- the capo has to be placed just so -- the teammates feel they've come a long way in four months toward the guitarists' goal. They expect the capo project will continue next year, perhaps with a new team of students.

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