Mechanisms and things

After further exploration into the idea of developing a mechanism to automate the bowing of a piano soundboard, I realized that the project would require longer-term project development and wasn’t really the ideal final project.  

I initially wanted to build a hurdy-gurdy, which is a sort of mechanical violin.  There’s a wheel, which is operated by a crank, functioning as the violin bow, which the strings of the instrument run over to create the sound.  Piano-like keys on the side of the instrument create different pitches by pressing the strings down in various locations, like a violin.  Upon further investigation, this instrument is extremely complicated.  Although I found many building schematics and die-hard hurdy-gurdy builders, the sketches and building suggestions were incomplete and confusing.   Here’s a video of a hurdy-gurdy in action: http://www.youtube.com/watch?v=xLlIbMA6VFA 

So, I started to brainstorm other ways to create a crankable instrument.  Since I’ve always been fascinated with music boxes, and worked on one for my final project in pcomp last semester, I decided my instrument would be a music box.  I thought of building a theremin (an electronic instrument controlled by the performer’s hand motions, played without touching the instrument) (here’s a video of theremin: http://www.youtube.com/watch?v=Wd5l_FHGWfE&feature=related) but found out that this was really expensive.  

I came across a diagram for a mini optical theremin- basically just an oscillator chip with a photosensor.  It was just small enough to turn into a music box.  Since we had just learned about linkages, I decided to build a linkage to control the shadows passing over the photosensor.   And I painted it bright colors.  

Making the linkage was pretty tricky, much to my surprise.  I have been playing with the cardboard cutout kits from flyingpig.com, building paper gears and things (to moderate success), and so I initially constructed my linkage out of paper, using the same shapes and sizes I intended to use for the final creation.  I wanted to make the linkage out of various geometric shapes, which obviously created some difficulty.  However, I managed to make it work with the paper.  Translating this to 3D objects was quite a different matter.  With Dustyn’s advice, I used Legos to prototype the linkage. I appreciated this experience, since I came to the class late in the semester and unfortunately missed out on the initial Lego assignment.

After figuring out how to make a linkage using rectangular Lego shapes, I decided to shave down the wooden geometric shapes I had to make it work, and used loose bolts and nuts to fix them all together.  I glued the linkage onto the theremin music box, to control the pitches.I wish the sound could have been a little louder, but all in all I think it was a successful project. 

I worked with Joe on this contraption.  Unfortunately I mistakenly deleted the pictures I took of the car before throwing it away… But I’ll do my best to describe it.  Using four CDs, we constructed a rather large vehicle with a foam body.  I did actually buy some bearings, but they were the wrong ones.  I bought needle-roller bearings, which for some reason I thought were just plain old ball bearings.  I was wrong.  We ended up using them anyway, but more just as joiners than bearings.  We put the mousetrap on the car and fixed it to a long wooden dowel with a long string at the end, which attached and wound around the front axel.  When the mousetrap tripped, the dowel pulled up on the string and moved the car.  It went pretty fast, but it fared much better in distance than speed.  In hindsight, we should have made a much smaller car, built for speed.  However, I was very happy with the car, since I do not have the brain for engineering and it took a long time for me to figure out how to make this work at all.  Also, it moved in a straight line.  :) 

My initial idea was to make a wire mobile based on the Rapunzel fairy tale.  I wanted to have a bunch of bulky men hanging in equilibrium off of Rapunzel’s hair.  While I still like this idea, I decided instead to make an attempt at building a mechanism relevant to my life.  I’ve recently been really fascinated with bowing the piano- this is done with lengths of fishing string passed through the strings of the piano’s sound board.  Here’s what it sounds like: bowedpiano ensemble. My pianist and composer friends rarely use this sound in their compositions because of its one glaring setback- the pianist can only achieve this sound at the sacrifice of all others, plus a delay in getting in the piano and back out.  A mechanism which would allow the pianist to bow the string from a distance (from the piano bench) would open up the world of bowed piano.  I had several problems in the design of this mechanism.  My first thought was to use motors, specifically servo motors on each end of the bowing string, with both ends spooled on pulleys, which would receive messages from a microcontroller through a switch operated by the pianist.  Alternately, a single spool of fishing wire could be controlled by a DC or servo motor.sorry about the lousy drawings!After giving this design some thought, I realized a serious flaw- the sound of the bowed piano is an extremely quiet one, and the sound of any motor I could afford would drown it out.  I decided to work with a lever instead, operated by a church-bell like action.bowedpiano21.pdfI changed the design a little bit through the construction process to make it more aesthetically pleasing and to simplify matters.  I wanted the base of my construct to be a simple machine, a first-class lever.  While initially I had planned on the lever holding both ends of the bow, I found that this design did not allow for a sufficient amount of pressure on the string.  Also, I had initially wanted to use a piano string for this prototype, but I quickly found out that this was a really bad idea, because to exert the amount of force I would need to in order to sufficiently tighten the string would shatter any structure I could build to hold the string.  I switch to a violin string and bowhair, instead of piano string and fishing line.  I’ve had some serious problems acquiring bowhair- I initially took the hair off an old bow we had lying around, but because of the way bows are haired, it was extremely difficult to keep the hairs taut and together at the cut end.  I ordered some… two weeks ago… three-day delivery… and I’m still hoping right now, 8 hours before class, that DHL will actually deliver.  I suspect they won’t.  I ordered several reams of hair, which are combined on both ends, thus preventing my fraying problem.  I really enjoy Calder’s bright colors in his wall sculptures- -and I used these as inspiration for the colors of my bowed piano mechanism. Also I enjoy making wire sculptures, and in an attempt at artistic-ness I made a couple of hanging wire people to operate the lever and pulley.

I’ve been struggling with a couple ideas- I’ve wanted for a while now to create a mechanism that would allow a pianist to bow the inside of the piano while maintaining close proximity to the keyboard, to allow for quick changes between sounds and further versatility.My initial thought was to use servo motors and arduino to create a circuit which would be completely by a touch switch, imitating a key press on the piano.  The servos would be attached to spools of fishing wire- the traditional tool of bowing the piano- and upon circuit completion, the Arduino would send forward and reverse messages to the servos, causing the spool to wind and unwind, thereby bowing the string.  However, upon further deliberation, I realized this would not be effective, as the noise from the motors would interfere with the sound of the piano.  I’ve decided to create a Calder-like mechanism relying on equilibrium.  A lever hold a single length of fishing wire (bowing the string) will be balanced on either end by a small weight.  One of the weights will be free, and attached to a pulley.  The other end of the pulley string will hang in front of the performer, and when she wishes to bow the piano, she will pull the string, lifting the weight off the lever, upsetting the equilibrium of the lever.  The performer will mimic the motion of church bell ringing, replacing the weight onto the lever with each release of the string.  When she wishes to cease the bowing, she will simply release the string and the lever will find equilibrium after a short decay.bowedpiano2.pdf

here is a fbd of a bookend.  I don’t think I did it right.  fbd.pdf