THE PROCESS

To start we took time to brainstorm our different ideas and work to find some overlap where we might share interests. During our idea vetting process, we noticed we both liked the living hinge’s properties interesting, so we decided that we wanted to incorporate one into our design. The initial idea was to create a ripple mechanism, drawing inspiration from a previous student’s design that appears to undulate when cranked (seen below). Our addition would be a 2d living hinge draped on top but through a couple of test cuts, we found although the 2d living achieved its purpose of flexibility in 2 dimensions, it did so very slightly, and not enough to follow the path of the ripple.

Therefore, we switched gears to a translational wave in one direction and found the living hinge to be much more flexible. Our idea was to incorporate the use of staggered cams and dowels to raise and lower the living hinge strategically to animate a wave.

Sketches

In our initial sketches, we chose mechanisms #1, and #96, which were the use of a band/chain to rotate two (or more) axes in the same direction, and the use of cams and dowels, respectively. Looking at a previous project that had used mechanism #96, we noticed that a plate was necessary to hold the dowels in place over the cams to prevent them from just falling out, so that was included in these designs. We later realized, for our uses, 2 plates were required, since the dowels had a tendency to fall off of the cams, and having two plates spaced slightly apart prevents any movement of the dowel other than up and down. With this in mind, we began working on our low-fidelity prototype.

Initial Adobe Illustrator Designs

Low Fidelity Prototype

For our low-fidelity prototype, we used a combination of cardboard, laser-cut wood, wooden dowels, and rubber bands. We decided to use laser-cut wood for our dowels and band restraints because we noticed that when we initially made them out of wood, given the fragile interior structure of cardboard, it would have been impossible to push the dowels up. In the low-fidelity prototype, we wanted to show proof of concept for the oval cams, but we realized that when all the ovals are lined up coplanar, given the dimensions we had developed for the box, and the placement of the axels, they run into each other, and therefore couldn’t rotate properly. Because of this, we switched to an offset design in the medium-fidelity prototype. In this prototyping step, we also tested the band concept, using a rubber band, which worked well (but we later realized this success didn’t translate to success with the higher fidelity elastic band). Finally, we were also able to show that offset dowels could produce the image of a wave in the living hinge, although we weren’t able to achieve any movement of the dowels in this step––just resting the living hinge on stagnant dowels.

Mid Fidelity Prototype

For our medium/high fidelity prototype, we used a combination of laser-cut wood, bearings, and an elastic band. In this step, we were testing the placement and integration of bearings into the design, as well as the staggering cam formation. We also developed the two plates that direct the dowels but didn’t implement them in this step just yet.

We had to figure out a way to easily insert and remove both plates, as well as the living hinge into the design to help with prototyping and iteration. With the two plates, this was easy enough, as we could just attach 3 pairs of slats to the side panels of the box, which the panels could slip between. Keeping the living hinge in place was more of a challenge because although the slats would hold the hinge at first, the moment pressure was applied from below by the dowels, it would slip out and become detached. Our solution to this was a key-like slot, and this allowed the living hinge to be locked both up and down, and in and out.

It was during this iteration of the design that we realized the elastic band failed to properly spin the middle two dowels. We reasoned that the outer two dowels have at least 50% coverage by the band since the band wraps around a large part of the dowels’ circumference, while the middle two dowels likely had less than 25% coverage since the band was barely dragging the top and bottom of the dowels, which wasn’t enough to pull the dowels around. This prompted a pretty drastic change to use gears instead of the high-fidelity prototype. To eliminate the use of the elastic band in totality, we also shifted to integrate the handle on one of the four main dowels, instead as a separate dowel that was connected to the main ones.

High Fidelity Prototype

For our high-fidelity prototype, we used laser-cut wood, laser-cut acrylic, bearings, plasma-cut aluminum, vinyl, and super glue. The jump between the mid-fidelity and high-fidelity prototypes was a large one––changing both the method of turning our dowels, the shape of our cams, and newly the implementation of plates attached to the dowels so that they smoothly could be pushed up and down (which we were having trouble with during our presentation). This iteration also included the metal and vinyl cut as a boat, which moves on the wave, as the dowels slide up and down.

The first change we made was the gears. We realized the band was ineffective, so we measured the length between our axles, then spoke with friends and classmates who had struggled with their gears in the low and mid-fidelity prototypes about how to best dimension them. A classmate mentioned that in reality, the gears won’t mesh together perfectly, as they do on the gear generator software, so adding some wiggle room between each gear was essential to making them move fluidly.

Once we added the gears, we moved on to assembly of the slats that hold the dowels in place, but we soon realized that the dowels, instead of being pushed up by the oval cams, were translated to right/left given the rotation induced. This problem was a result of too steep an angle on the ovals, preventing the dowels from having enough surface area to catch onto in time to move upwards with the force from the turn. To deal with this, we had the idea to add two crescent bodies to each oval, completing a 3-inch diameter circle to act as our new cams. This worked well to prevent this sideways translation instead of upwards movement, but we ran into yet another problem with our dowels slipping off of the cams.

To tackle this problem, we used a design we noticed in our classmates’ project, which was to use a hook-like module at the base of the dowel, which was to lead the dowel strictly on top of the cam (this was the method showcased during the presentation in class).

However, the problem with this method for our mechanism is that it created unwanted friction between the sides of the hooks, and the cams, which is how we discovered that our mechanism was stuck not because of the gears, but because of these attachments. When we switched to the second and final rendition of an attached module to the dowel, a flat circle, we found that the mechanism rotated freely and smoothly, as documented in the first video below. The move to the circle attachment was the last change we made, and we were finally able to fully assemble a working model.

 

 

REFLECTION

As I mentioned above, there were many major changes to our project during the high-fidelity prototype. I had mentioned in class that sometimes we run into problems during the mid/high-fidelity prototypes that we couldn’t anticipate during the low and middle-fidelity ones, and I think that was the largest contributing factor. I had felt that we were pretty consistently on pace with the check-ins during class, but in the past few days, as we began to assemble the final pieces, many problems popped up. I think one of our biggest mistakes as a team was improper testing in the middle-fidelity prototype. Instead of fully testing the slats, dowels, and cams together during the middle fidelity, we assumed that since all the components worked well independently, they would assemble and do so perfectly in the high-fidelity prototype.

I would say that our time management as a group was pretty good. That is to say, until the last few days––I felt that due to the extremely long queues for the laser cutter, we were spending hours and hours at the OEDK without making sufficient progress. I felt like it was a sprint to the finish line, despite having kept a pretty good pace throughout the whole project.

We did a good job of managing teamwork and independent work, always trying to be as efficient with our time as possible. We had great communication throughout the process, and we both were well-versed in the workings of the project at every step of the way.

Although we weren’t able to assemble a working model in time for class, we came back right after dinner and were able to troubleshoot the problems we were facing, which I’m very proud of. I was rather disappointed in the way the mechanism turned out for the class presentation, but we both decided that we wanted to make our mechanism work if we could and I’m glad that we committed to that.

Douglas mentioned at the end of class that we should all be very familiar with and comfortable working with the laser cutter and other 2d prototyping techniques, and I didn’t even notice until that point that he was right. In all the frenzy and rushing around these past few days we were so caught up with our work, that the prototyping techniques became second nature. This project was very rewarding for our group, especially right at the end. If I were to do this project again, I would remind myself about the final-day frenzy, and do a better job of testing during the lower and middle fidelity prototyping stages, since that was our team’s biggest weakness this time around.

 

COST ESTIMATE

Raw Materials

• ~4 square feet 1/4 cardboard (including scrap) =  $2 ($25.99/50/11″x14″)
• ~12 square feet 1/4 inch wood (including scrap) = ~ $80 ($20/3/12″x12″)
• ~10 in^2 steel plate= ~ $1.45 ($21/12″x12″)
• ~20 in^2 vinyl sheet = ~$0.19 ($1.40/12″x12″)
• 10 bearings = ~$3.03 (7.57/20)

Labor

• 35 hours = $262.5 ($7.50/hour)

Overhead

• Laser cutter operation (4 hours) = ~ $100 (Assuming laser cutter operation costs $25/hour)
• Plasma cutter operation (30 minutes) = ~ $10 (Assuming plasma cutter operation costs $20/hour)
• Angle grinder operation (30 minutes) = ~ $10 (estimate)
• Vinyl cutter operation (10 minutes) = ~ $5 (estimate)

Total Cost = $474.17

This project came at a pretty steep price. I think given slightly more time, we could have perfected the concept, and a number that high might be worth a perfectly functioning model. I didn’t include all of the idle time waiting around for the laser cutter, but it did inadvertently cut into our work time, which I did account for. I think that if we were to create a model, knowing what we know now about all the mechanisms, we would be able to skip the low and middle-fidelity prototypes, and could cut down on at least 75% of the time we spent on this model. A lot of our time went towards troubleshooting all the different problems that continued to pop up, but given we have found a solution that works, we could spend significantly less time on the prototyping, and instead working on first perfecting the mechanisms at play, and then recreating the first model.

VIDEO(S) OF THE WORKING MODEL

IMG_2779 (Working model: isolated dowels and cams)

IMG_0499 (Working model: fully constructed)

SLIDESHOW

https://docs.google.com/presentation/d/1K8qmX5DV-taR7QQ_jKp4cmpjHe5b6DJ_KA3OG-phJjA/edit?usp=sharing