.: final project.electrello :.
We may be coming to a new golden age of instrument making.
--Yo-Yo Ma
Technical Tasks
Hardware
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Software
Items repurposed from old cello
Cost
References |
Design
I did the design in SolidWorks. It took FOREVER.
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The Process
Body accents
For the composites week, I made some accents for the body of the cello. First I created a mold:
Then, I chopped it up and filled it with SmoothCast 326 and PMC121-30:
The casts turned out pretty well after some TLC. A plastic cast (after sanding):
and a rubber cast (before trimming):
I sewed black stretchy fabric around the casts (thanks Natalie!):
and dipped them in SmoothCast 326 + black pigment. The result is the accents for the body of my cello:
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
Mahogany for body
Cutting the body
I used the ShopBot to cut the mahogany, and it worked beautifully!
Mahogany on ShopBot
Mahogany test cuts:
Milling body
Body parts in block:
Body parts removed:
Ready for routing
Gluing neck block
Joining body (wood glue):
Gluing neck block to body:
Body routed! Huge thanks to Tom and John!
Other view:
Test endpin holes:
Testing how to drill a big hole into a small hole:
My solution
Hole drilled
Endpin gets the dowel out!
Sanding endpin (~1 hour):
Leg mounts cut from .25" aluminum on the WaterJet
Sandblasting my aluminum leg mounts. Thanks to Matt Blackshaw for showing me how to use the sandblaster!
Sandblasting before and after:
Flexifits take a few tries:
Time to epoxy the composites onto the wood. This was much messier than I expected...
The cello with all the composites epoxied on
Piezo PVDF film being wrapped in copper tape for magnetic shielding
WaterJet and sandblasted 1/16" aluminum for cavity covers on back of cello
Epoxying screws into wood to hold legs on (for good!)
I strung the cello up to test if everything would hold. Voila!
This led to a 2 hour jam session, which was a much needed break from fabbing
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...
I traced the neck on cardboard and made a stencil:
And slowly carved out the profile
The hardest part was making the slanted grooves so the neck couldn't pop out the top:
I glued the neck in, and voila!
Making the wood pretty
First I sanded the wood. I used 6 types of grits in order, from 60 to 400.
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.
Taking the necessary precautions while using the tung oil...
My naked cello waiting for a coat of love.
...after the first coat. I love the rich color that starts to become apparent in the mahogany at this point.
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.
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:
...which turned into this. I used shielded wire for everything, as one should do when working with pickups...
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.
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.
Time to wire all the modular components together...
...and program the accelerometer (with a few improvements from last time)
Which results in this! A tiny self-contained accelerometer + capacitive sensor inside a cello bow case.
Case closed!
The capacitive sensor worked much better when there was a connection between the copper tape and the battery.
The final bow with a working capacitive sensor and accelerometer over wireless!
Finished electrello!
The cello turned out much better than I anticipated. A few minor snags, but I am extremely proud of the final product.
Design files
Body
Bow
- bowBoard v2: Schematic (Eagle .sch) | Layout (Eagle .brd) | Traces (png) | Holes (png)
- Bow enclosure: Body (.stl) | Top (.stl)
Code
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.
