adam.setapen...how.to.make.(almost).anything

.: final project.electrello :.

Electric Cello

We may be coming to a new golden age of instrument making.
--Yo-Yo Ma

Technical Tasks

  • Cello Body
    • 3D Design
    • Order parts
    • Cut Mahogany body and sides
    • Route wiring ports
    • Drill wire holes
    • Glue body halves
    • Glue neck fasteners
    • Sand body
    • Carve slot for neck
    • Glue neck to body
    • Epoxy casts to wood
    • Sand body
    • Carve tailpiece lip
    • Glue tailpiece lip
    • Finish wood
    • Mold for body and side accents
    • Cast body and side accents
    • WaterJet leg supports from aluminum
    • WaterJet cavity covers from aluminum
    • Attach legs to body
    • Laser-cut leg fastener
    • Epoxy leg pins into body
    • Attach endpin
    • Attach tailpiece
    • Sand bridge to fit body
    • Electrical wiring
  • Cello Bow
    • Design case
    • Design board
    • 3D Print case
    • Mill board
    • Stuff board
    • Software for capacitive sensor + accel
    • Do something interesting with the data...
  • Pickup
    • Wiring
    • Build fab-able pre-amp with off-the-shelf op-amps
  • Screen in cello
    • Equalizer based on microphone
    • Display accelerometer visualization
  • Output servo
    • Connect to bow positions and capacitive sensor

Hardware

  • ShopBot
  • OMax WaterJet
  • Universal Laser
  • 3D Printer
  • Modela
  • Bridgeport mill
  • Sandblaster

Software

  • SolidWorks - Solid body design
  • Rhino - Surface design
  • Adobe Illustrator - 2D part design
  • Eagle - PCB Design
  • Processing - visualization

Items repurposed from old cello

  • Fingerboard and Neck
  • Bow
  • Pegs
  • Fine tuners
  • Endpin
  • Tailpiece
  • Bridge
  • Strings

Cost

References



Design

I did the design in SolidWorks. It took FOREVER.

Mockup of Electric Cello Electric Cello with sides retracted Electric Cello with sides retracted
Mockup of Electric Cello Electric Cello with sides retracted Mockup of Electric Cello
Electric Cello with sides retracted

The Process

Body accents

For the composites week, I made some accents for the body of the cello. First I created a mold:

Electric Cello with sides retracted

Then, I chopped it up and filled it with SmoothCast 326 and PMC121-30:

Composites and Joining

The casts turned out pretty well after some TLC. A plastic cast (after sanding):

Composites and Joining

and a rubber cast (before trimming):

Composites and Joining

I sewed black stretchy fabric around the casts (thanks Natalie!):

Composites and Joining

and dipped them in SmoothCast 326 + black pigment. The result is the accents for the body of my cello:

Composites and Joining

Materials

I ordered the used cello parts from Paul Perley Cellos, and got a sheet of mahogany from Boulter plywood. Everything else I ordered online.

Cello neck

Electric Cello with sides retracted

Mahogany for body

Electric Cello with sides retracted

Cutting the body

I used the ShopBot to cut the mahogany, and it worked beautifully!

Mahogany on ShopBot

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Mahogany test cuts:

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Milling body

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Body parts in block:

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Body parts removed:

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Ready for routing

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Gluing neck block

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Joining body (wood glue):

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Gluing neck block to body:

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Body routed! Huge thanks to Tom and John!

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Other view:

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Test endpin holes:

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Testing how to drill a big hole into a small hole:

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My solution

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Hole drilled

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Endpin gets the dowel out!

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Sanding endpin (~1 hour):

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Leg mounts cut from .25" aluminum on the WaterJet

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Sandblasting my aluminum leg mounts. Thanks to Matt Blackshaw for showing me how to use the sandblaster!

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Sandblasting before and after:

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Flexifits take a few tries:

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Time to epoxy the composites onto the wood. This was much messier than I expected...

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The cello with all the composites epoxied on

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Piezo PVDF film being wrapped in copper tape for magnetic shielding

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WaterJet and sandblasted 1/16" aluminum for cavity covers on back of cello

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Epoxying screws into wood to hold legs on (for good!)

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I strung the cello up to test if everything would hold. Voila!

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This led to a 2 hour jam session, which was a much needed break from fabbing

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Carving the neck

I was told this is the hardest part of making a cello. I bought some nice sharp German-engineered chisels, and got to work...

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I traced the neck on cardboard and made a stencil:

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And slowly carved out the profile

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The hardest part was making the slanted grooves so the neck couldn't pop out the top:

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I glued the neck in, and voila!

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Making the wood pretty

First I sanded the wood. I used 6 types of grits in order, from 60 to 400.

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Then it was time to protect the wood and bring out the rich color of the mahogany. I chose tung oil, as it is easy to use and doesn't mar the natural qualities of the wood.

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Taking the necessary precautions while using the tung oil...

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My naked cello waiting for a coat of love.

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...after the first coat. I love the rich color that starts to become apparent in the mahogany at this point.

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I ended up doing 2 coats of Tung oil, but I might go back and do a few more when I have time.

Finally, I sanded the bridge to fit the contour of the fingerboard. I traced with a pencil, and then took off just enough so the action of the strings would be perfect for my taste.

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There are 5 pots and a switch, because I'd like to eventually add a magnetic pickup and be able to blend between the two signals. But I only had time to finish the piezo right now, so here is a volume+tone diagram I made for wiring up the cello:

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...which turned into this. I used shielded wire for everything, as one should do when working with pickups...

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Bow

The bow of the cello is outfitted with a capacitive sensor (detects when it is being held) and an accelerometer (detects the motion of the bow). For input devices, I made an accelerometer board. I redesigned it to make it modular and a bit smaller. Also, I used an XBee for wireless communication, because I'm familiar with this protocol and hardware.

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Next comes milling and stuffing. This wasn't my cleanest board, but I was pressed for time. It works flawlessly, but it's just a bit messy looking.

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Time to wire all the modular components together...

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...and program the accelerometer (with a few improvements from last time)

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Which results in this! A tiny self-contained accelerometer + capacitive sensor inside a cello bow case.

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Case closed!

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The capacitive sensor worked much better when there was a connection between the copper tape and the battery.

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The final bow with a working capacitive sensor and accelerometer over wireless!

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Finished electrello!

The cello turned out much better than I anticipated. A few minor snags, but I am extremely proud of the final product.

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Design files

Body

  • SolidWorks files (including assemblies) (.zip): download
  • CAM files (.zip): download

Bow

Code

  • bowBoard microcontroller code here (.zip): download
  • Processing visualization (.pde): download

Thanks!

Thanks to Neil for teaching this incredible class, to all the TA's for being patient and helpful, and to the students in the class for making it a truly unforgettable semester.