About my final project
(unlike previous posts, I've put all of the documentation into one video above. below are I explain my thoughts, challenges, and learnings.)
I started out this semester with an ambitious goal to make a jig that was simulataneously adjustable from a computer interface bike design software, and could be used in reverse to
where a user could use the jig itself to design a bike by moving around the parts so they move on the screen. However, as the semester went on, I realized that two constraints limited
my ability to make this into reality. The first was time and access to all the tools and equipment. Even though the section is pretty well stocked, finding enough time on a machine or with
certain equipment is tough. Secondly, and more importantly, I found that I have a lot to learn with regards to electronics and programming. Having only
had limited experience with HTML before entering this class and needing to recall sixth grade to remember how a light switch works, I quickly decided to
focus on something more achieveable. And even then, I was challenged.
I decided to add a bike rack to my bike. And, having repeatedly forgotten to turn on my lights as I ride home in the evening, I decided it would be fun to design a phototransistor circuit that
would tell a string of LEDs when it was dark outside, and the LEDs would turn on automatically. I also had a vision of installing solar panels into the bamboo so that the system was not only automatically run
but also automatically powered but that proved to be a bit much.
Ever since the first week, I've been curious about how I could incorporate bamboo into the weekly projects. I had tried to laser cut bamboo in the second week, but failed. Nevertheless, I came up with a new strategy
to press fit bamboo together into a bike rack. Because the bamboo is round and not a perfect 'round' at that, I decided to cut out the pieces that needed to be precise for the pressfit, and saw out the rest with a Japanese
bamboo saw that was lying around the Arch shop. I could only laser cut about 1.5cm of the bamboo poles due to the curvature but that was enough. In cutting the pressfit parts, I decided to leave about 2mm of "wiggle room" because
I assumed that the round bamboo which is not perfectly straight would be tough to press together if everything was precise down to .1mm. This ended up being a good idea, and the play of the interlocked bamboo pieces, I would latter constrain by wrapping the pieces together with carbon fiber.
I also have been very curious about how to bend bamboo. So, I laser cut a basic flexure pattern in the wall of the bamboo. And I would chop out the rest of the bamboo. My hope was to bend the frame of the rack to meet at the seat tube.
The flexure actually worked quite nicely bending about 5 degrees which was enough curvature to make the form I wanted. Unfortunately, and accident snapped it before I had time to steam the bamboo into the shape I wanted. So, I needed to come up with another way of attaching.
By far the hardest thing for me this semester has been electronics and programming. The two influence each other a great deal, and because of that I never know if I'm designing circuit incorrectly, soldering it incorrectly, or programming incorrectly. But no matter what, I'm doing something incorrectly.
I haven't got a circuit board to work all semester. So, I spent a lot of time designing a simple board with the ATTiny45 that would sense light and turn on LEDs when it got dark out. The first challenge came because I forgot which direction the LEDs needed to go in. (The dot indicates the anode not the cathode)
Then I couldn't program the board from my computer or the Arch shop avr, so I decided to try another board which ended up working. Then the programming... I got a handle on programming with Arduino back in Week 8, but I could not get my computer to talk the ATTiny through Arduino. So I tried using Atmel Studio briefly
which I couldn't get to program the board although it did recognize the programmer. I also tried programming using Neil's make file, but that didn't work because the virtual copy of Linux I was running couldn't find the AVR. Finally, a kind soul lent me her computer which could program with an AVR and ATTiny45, and I actually programed the board I had made!
The next problem was that even though the board was programmed it was not responding to changes in light. I spent a LOT of time trying to figure this out, and only because of the generous time of a fellow classmate did I learn that I was not calling the ATTiny's pins by the particular Arduino names (which are reversed) so nothing was workshop.
Another challenge came with using the composites. I actually have a lot of experience hand-wrapping carbon fiber with epoxy, but I had stupidly mixed my ratios backward this time (2 parts hardener to 1 part epoxy!), and because I was not only trying to add carbon fiber composite to stiffen the rack but also protect the electronics under a layer of cured epoxy,
all of my hardwork was one giant sticky mess. After 24 hours, I thought that perhaps it was just too cold out, so I stuck the rack in the oven. But, when that didn't work, I had to come to grips with either it was a bad batch of epoxy or I had mixed it incorrectly. The latter seemed more likely to me (this has happened to me once before while leading a bamboo bike workshop and finding that someone had mislabled the
hardener and epoxy and we had to start from scratch). With very little time before the project is due for display and the electronics still not installed into the rack, I'm currently waiting for a re-epoxied rack to come out of the oven. Ideally, I would have started over, but because of time I decided to cut off all of the carbon fiber from the first wrap and rub off as much resin too, and then recoat everything. We'll see how it comes out....
- what does it do?
- Bamboo bike rack that turns lights on when it gets dark out.
- who's done what beforehand?
- I've made bamboo bikes before but never a bike rack.
- what did you design?
- I designed the rack structure which was laser cut and then fitted together with some woodworking. I designed the circuit and some simple code to make the lights turn off and on.
- what materials and components were used?
- bamboo from leftovers in backyard
- carbon fiber from China
- epoxy from Entropy resins
- phototransistor from arch shop
- LEDs from arch shop
- wires and circuit components from arch shop
- p-clamps from hardware store
- how much did they cost?
- what parts and systems were made?
- I made everything with the materials listed above except for the p-clamps. I made 3 different circuits to control the light: one from copper sticker, one on a PCB adapted for two LED extensions, and the HTM standard board.
- what processes were used?
- laser cutting flexures and pressfit bamboo, milling, 3d design, carbon fiber composites, vinyl cut circuits, embedded programming of light output and light sensor, 3D printed rack attachment, Eagle circuit deisng
- what questions were answered?
- I learned that laser cutting bamboo poles is possible but very difficult and time consuming. Nevertheless it can be useful for pressfit systems. Flexures how are not a good idea as the laser cause the bamboo to caronize and become brittle. I also learned a great deal about how to program a board which has been a constant struggle for me.
- how was it evaluated?
- I rode the bike with the rack, and the lights turn on right around dusk which is what it was designed for. The biggest challenge was find the correct power source. I originally played around with solar cells that charge a battery during the day, but couldn't get that done in time.
- what are the implications?
- The biggest implication for me is with regards to laser cutting pressfit bamboo. If a I can get my hands on 3-axis laser cutter that can cut bamboo poles while coninually adjusting focus to account for the topography of the bamboo, there's a lot that could be done.