Bicycles are typically seen as moving but quiet things and musical instruments are typically stationary. Over the past two weeks, our group aimed to subvert both of those ideas with the music box bike. When in motion, the music box bike uses the motion from the back wheel to spin a series of gears attached to the bike frame. The final gear, a whole bicycle wheel, spins a studded cylinder which plays the kalimba attached to the back of the bicycle.
We were given the challenge of making a bike that played music when we rode it. More specifically, our group was tasked with making the bike a plucked or stringed instrument. We got our original inspiration for this idea through a video of a man riding a bike that then played a music box like instrument. He did this through gear reduction and a plucking mechanism. After seeing this we thought that we could do it better by having all of the gear reductions contained on the moving bike, instead of sprawled out in a room like the guy in the video. After getting our inspiration we came up with a complicated plan to complete this project. Our main idea was to attach a music box to the back of the bike, and use the motion from the back wheel to rotate the cylinder. We planned on doing this by slowing down the rotational speed of the cylinder by creating a huge gear reduction through connecting the smallest gear on the bike to several other gears on the rear basket frame. After connecting a few gears together, one of them would turn another bike wheel that we fastened to the back of the bike, and that would turn a cylinder that would pluck our instrument.
Our plan was to make a bike that played a music box. In order to play the music box at a reasonable tempo, we needed to slow the rotation speed of the bike gears down. We did this through gear reduction that we created by connected smaller gears to larger gears, thus slowing the rotational speed. First, we took some bike chain and a large gear from a different bike and used the chain to connect the smallest gear on our bike the larger gear that we took. The larger gear was connected to the bike. The connection from the small gear to the large gear did slow down the rotational speed, but in order to slow it down further, we had to add another component to the system. We fixed a small spool to the large gear that ran a bike tube that spun a bike wheel that we took and connected to the back of our bike. Now we have two gear reduction that end with a bike wheel spinning very slowly. We took out the axle of the bike wheel and replaced it with threaded rod. We could screw on our plucking cylinder to that threaded rod, so when the whole mechanism spun, the cylinder would turn and pluck our music box. The music box ended up just being a wooden box with popsicle sticks as teath. At the end of our project we had a bike that when you peddled, it turn a bunch of gears and wheels that spun a cylinder that plucked our music box to make noise.
The first iteration of the music box teeth was a steel pipe with steel bicycle spokes welded onto it. First we used a tuner and a ruler to measure the length of a bicycle spoke when it made the note G, and then we figured out G an octave lower. We mathematically found out the rate of change in the spokes for a chromatic scale, and then we calculated the angle the pipe had to be at to make the spokes level. Ultimately, this iteration was scrapped because of how little sound the steel spokes made. We were basing this design off a contraption that Kirk made, two titanium pipes welded together with titanium spokes welded into that. At time, we did not know that the spokes in our predecessor were titanium. The material of our version contributed largely to its failure.
To make the final version, we first designed a box in Rhino and laser cut it. From there we had three other main components: the tines (popsicle sticks), the nut (to suspend the tines above the box), and the bridge (to apply pressure to the tines). When making the final product we had to add an additional screw in the middle of the bridge because the bridge was too loose and could not make any sound.This is less of a music-box-teeth type design and more of a kalimba.
The cylinder was less of a challenge, but we had issues nonetheless. The first iteration was cardboard, a foot long, and was divided into 24 ½-inch sections. The concept was that the circular ½-inch sections would be divided into . I decided to make it out of cardboard at first because it was easy to work with, inexpensive, and the cylinder for the music did not have to resonate. The main issue with this iteration was that the cylinder actually did have to be strong to support its own weight and not crumple.
The final iteration was made of PVC. It had two wooden caps with holes in the center of each. Over the holes are nuts on each side that allow the pipe to screw on and off the axle. When tightened, the nuts apply enough pressure to keep the pipe firmly attached to the axle. The PVC is more difficult to hammer fingers (to pluck the kalimba) into. For fingers, we used cut-off, filed-down nails. In the end, we also greatly reduced the number of horizontal fingers and notes.
On our last day of building, we were testing our design and the gear mechanism fell apart. The tube was not feeding correctly, the gear was unaligned, and in the process of fixing it, we snapped the spool. We had little time to fix the problem but in the end we made the design better. While we reglued the spool back together, we found wood locking nuts that would much more efficiently hold the mechanism together and keep things in alignment. After the fix, we had a much better arrangement of the gears and spool, because of the addition of spacers, and the design had not broken since.
After the spoke model failed, we tried a variety of other materials and methods for the teeth. The recurring problem with these trials was that none of the materials could produce a note, resonate and sustain in the right way. The only material that had ideal results was titanium, but that was not viable to due to cost and lack of access. It would also be a hard metal metal to work because of its strength. First we tried a laser-cut wooden plank with teeth measured out by the bar length website. It did not have enough resonance, so we scrapped it. We also tried to make teeth out of sheet metal, but sheet metal was of limited access, so we only had one piece of sheet metal. That piece was too thin, and the entire sheet resonated when one tooth was stuck, so that idea is not viable either. We ended up going with popsicle sticks, which I was hesitant about at first, but the sticks had a good sound, and were easy to work with and access.
We spent most of a day designing the cylinder/axle connection. The problem was to make the axle firmly attach to the cylinder, but also make it interchangeable. The first idea was to make two caps with nuts in the center and bolt those to the cylinder. This would mean tightening the nuts tightens the cylinder around the axle, and can later be unscrewed. A later idea was to make two felt-lined wheels that attach to the axle with two locknuts each. The wheels would have threaded holes, and when the cylinder was slid onto the wheels, you would be able to screw the cylinder to the wheels, and unscrew it when you were done. In the end, we went with a variation of the first idea, because the threaded holes did not seem reasonable.