Mechanisms: Rotational Motion to Nearly Linear/Linear Motion

For this assignment, we were asked to look at different methods of converting rotational motion to linear-ish motion. Exploring the Kinematic Models for Design from Cornell, I found quite a few fascinating mechanisms.

Slider-Crank Mechanism - Inversion

http://kmoddl.library.cornell.edu/model.php?m=20
https://www.youtube.com/watch?v=3zpDGtiJoaM

I was initially attracted to this mechanism because of the unprovided in-motion image and the description from Cornell's digital library stating that it was "one of the most useful mechanisms in modern history." I went to other sites to explore the mechanism and found many applications and a quick, informative video of its basic movement, which I thought was fascinating.

In this mechanism, there are four bodies (rods) connected by three cylindrical joints and a long, rectangular sliding joint. Two of the bodies are located the in front and two in the back. In the front, there is a joint connecting the shorter and longer bodies together, which I imagine would be the same for the two bodies in the back. Near the bottom, there is the a cylindrical joint connecting the bottom and front of the mechanism together, as well as the third one connecting the short bodies from front to back. The fascinating aspect of this mechanism is that it entirely flexible, and as the name implies, the rotation can be inverted if desired. Since the site where I found the image did not have a small clip showing how this mechanism moved, I assume the movements would be similar to the Youtube clip I searched. The cylindrical joint of both the back and the front where the short body and the long body meet would be fixed, as well as the long bodies to the cylindrical joint at the bottom. The sliding joint (the central piece of the mechanism) could have a thin, oval cut out at the bottom to allow the cylindrical joint to cross through to the back, as well as allow itself to move up and down as that cylindrical joint is fixed. As this sliding joint moves only in an up and down motion, restricted by the small oval cut out and the length of the connecting two bodies, the smaller of the rods (connected to the sliding joint with a joint that is loose enough to allow its rotation) is forced to move up and down as well, but in the image of a rotating radius with a permanent center, oscillating. Slightly protruded to the side and securely connected to the longer rod when at rest, the shorter rod allows the longer rod to be given the image of being shot upwards and downwards as it rotates, creating an different angles. The longer rod, however, consistently moves in the motion of a inverted pendulum, swinging side to side without losing energy, and is given this image of being shot upwards and down because it is the sliding joint that confuses the eye on the relative position of the longer rod. Both of these rods would be in fixed moving positions. This is the same for the back of the mechanism, and this way, they are both forever going in opposite directions. I imagine, like the mechanism example shown in the Youtube clip, the back and the front can set into motion in the opposite direction than it was originally, depending on where the protruding cylindrical joint (connecting smaller and larger rods) is placed at rest. 

According to the Cornell's Digital Library website, four different inversions of this kinematic chain are possible, depending on which body is fixed: the crank, the connecting link, the sliding link, and slot link. In the D-4 model shown above, it is the slot link that is fixed, meaning that the connecting rods (bodies) are fixed, producing an oscillatory motion. There are so many applications when deciding which component to fix, and depending on the decision, this slider-crank mechanism can be used in engines, pumps, and more, which I find lovely, complicated, and paradoxically simple. 

Windlass Day(s): 2/6/15 - 2/20/15

My first try at compiling everything in one blog! Hopefully, this will be less wordy than my last posts.

2/6/15 & 2/10/15: Windlass Project

My new partner, Angel, and I started on our new project: the windlass for a well. The device had to span over a 12cm "well" (just a gap between two tables), and use a hand-powered crankshaft to lift a "bucket of water" (1 liter of soda). We drew multiple sketches of what our windlass might look like and took a pause many times, adjusting to the unfamiliarity of the term. These are our compilations of our main sketches.

Our initial favorite idea was the third sketch from the top. We could stack up all the Delrin pieces We started measuring out all the pieces of structure from a 500cm^3 sheet of Delrin we were limited to, and realized we had to change our plans. It used up too much material, especially since each Delrin piece was 1/8'' thick and we had a target height of 15cm. We ended up with making (or attempting to make) a Styrofoam model of the 3rd sketch from the top: the trapezoidal stands with a rod running through them. It seemed like a sturdy structure and would hold the 1 liter bottle well.

2/11/15 & 2/13/15: Styrofoam Modeling and SolidWorks

However...

The cut outs of these squares have remained in this bag since (almost) the beginning of their creation. Angel and I came in to cut out a Styrofoam model, and we were never able to stably put all the pieces together. After learning the multiple ways of attaching Delrin, we thought that we could use the piano wire and the drill press to attach them more easily when we actually cut them out in Delrin. We were advised not to complete this model, and thankfully, we didn't. It would not have been an efficient way to use or materials, or time.

We revisited our models, and came up with the first sketch! A build-on from our previous sketches, we wanted a simple model in which we could still run a rod through it and have our little wheel. The triangle would also be more stable than the rectangle because it would not topple over easily. The pulley itself needed space for the string, so we thought of stacking the inner circles together to create more space, using a total of 4 separate circular disks. Keeping in mind the multiple ways of attaching Delrin, we made tabs at the bottom of our triangular foundations to connect on a horizontal base, so that it wouldn't wobble under pressure. Not only would this structure be much more time efficient than the first model, but it would also use much less Delrin (approximately 400cm^2)!
We spent most of class time cutting out our Styrofoam model...which had adjustments of its own.

Hinges and plates! We originally wanted our triangular structures to be secured by a tab, but what it wiggled back and forth? Side to side? We created four hinges for our model and the blank squares were additional cut outs from the Styrofoam to represent the plate we would make in SolidWorks. As for where the bushings would go, we would want them on both sides of the wheel and both sides of each of the triangular foundations. The handle also needs to be secured, but since we would piano wire the handle to the rod, bushings wouldn't be necessary. The hinges and the attachment of the wheels would also be secured by piano wires.

Moving on to the SolidWorks, we created each piece and saved them. The next day, we would be printing out test pieces and using Assembly to complete our design.

2/14/15 & 2/16/15: From SolidWorks to Product

These were rough snowy and laser cutting days. We designed our SolidWorks parts already and used some time the next afternoon to link them through the Assembly portion of the SolidWorks. The pieces had fit together and all the measurements were accurate in the design, but as we know from learning how to connect Delrin together, we would need to print out test pieces slightly smaller in dimensions in order to achieve tight and loose bushings on the rod, and tightly fitting tabs and notches. After a few runs (and much waiting!), we finally had successful tight tabs and notches, and loose and tight bushings. We tested the tab and notches twice, and tested the bushings three times before we obtained a tight fit. The loose "bushings" were needed to figure out the radius of the holes at the top of the triangles, because we didn't want them too tight. They needed to be stationary and not be spun by the rod when it rotates. Besides the triangles, everything else would need to have a tight fit.

Ready to print! We were able to use the laser cutter on Monday to print out our first product on one sheet of Delrin (1/8''). We decided we would only need two hinges (to lessen the materials), and added more holes to the triangles to run more of the rod through it. We wanted to create a more stable and stronger structure by adding the rods. Although we printed a total of 12 bushings with the idea of using all of them for extra support for the handle, wheels, triangle, we didn't end up using all of them.

Though, not only in part because we didn't need them, but also because we couldn't use them. Unfortunately, the laser cutting was not perfect with its cuts and we had to force out some of the parts. We got out some sandpaper afterwards and tried to sand away all the ragged edges, but some of them were thick or the sides were bent. Thankfully, all of the parts of our main designs made it through safely, and we had enough bushings that were able to fit tightly on the rod. After we put our product together, we were happy that parts had all fit nicely together, but there were functions that weren't quite working.

2/16/15, 2/17/15, 2/20/15: Improvements

The key function of the windlass is to lift up the one liter bottle, and our initial product needed some modifications. None of our attachments were permanent, so we were able to dissemble the parts easily. The two primary issues with the product were 1) the wheel and 2) the handle. We had yet to piano wire the handle to the rod, and our attempts to lift the heavy one liter bottle made the wheels turn in the opposite direction as the rod. We needed to figure out a way for the wheels to remain completely intact with the rod.

At first, we were hesitant to attach the materials with piano wire. If we did, we would be running the piano wire vertically through the thickness of the Delrin into the rod. After successfully running the piano wire through an extra bushing on a rod however, we came up with two ways to secure the whole wheel together: 1) to attach a small rod through another set of holes in the disks and 2) to piano wire the two smaller circles directly onto the rod. The small rod fit perfectly after we printed out the set of circular disks, and we were able to piano wire both of the small circular disks onto the rod. The larger ones would be held together with the small ones with the short, extra rod running through all of them. At either end of the larger circular disks, we placed tight bushings to securely hold the wheel in place on the rod.

We left a bit of the wire sticking out from the smaller disks because we decided we could tie a small noose on the string and secure it on this piece of piano wire so it would not fall out.  

As for the handle, piano wiring was slightly more difficult (even when it already is!). We tried piano wiring our initial handle, and it cracked. Printing out another handle and being more cautious of the position of the drill, we were able to successfully connect our handle to the rod. The beginnings of the piano wire process was shaky because the piano wire kept falling out of the hole, but since matching the drill bit to the correct piano wire size, the process ran more smoothly!

Best of all...our product works! It was able to lift up the bottle pretty sturdily!

2 Plates: 3x7 cm^2 x 2
2 Triangles: 14.5x3 cm^2 x 2
2 Large Circles: Pix5^2 cm^2 x 2
2 Small Circles: Pix3^2 cm^2 x 2
1 Handle ~ 16 cm^2 
6 Bushings (Pix2^2 - Pi) ~ 56 cm^2

Total: approximately 415 cm^2 of 1/8'' Delrin sheet

Engineering Analysis: The primary rod of our windlass at the top was subjected to beam bending, and we were careful not to have it too long. The physics of beam bending determines the amount of stress the "beam" or in our case, the rod, can handle, and takes into account the Moment of Inertia (I), Young's Modulus (E), the weight of the load, and the length of the rod (d). The longer the rod, the more likely the beam is to bend, which is the only variable we can control, since we are restricted to Delrin and our objective is to lift the one liter bottle. The triangles were also subjected to beam bending, since they experience the stress at the top from the rod, but we were careful not to have them too short either, because the structure would become unstable if the triangle is narrow. Overall, our structure was very sturdy, since there were supporting plates and tabs at the bottom, extra rods running through the triangles, an appropriate width for each triangle, and an almost even distribution of weight across the rod.

Concluding Reflection: We realized that we did not need more rods to go through the triangles in our structure, because it was already sturdy enough. They would be nice to ensure stability of our structure though, and as for the hinges, they did not make it to our improved product. They hadn't made it to our initial product either, because we were not able to piano wire it to the plate. We had technical issues with the drill bit when we first started putting our product together, and if we had more time, we could have included the hinges to ensure the stability of our windlass when we use our handle. It was also inconvenient to crank the handle as well, because we had to continuously apply pressure in order to crank the bottle upwards. If there was time, we could have created a long, rectangular handle, or heat staked another piece of Delrin to our existing handle to create a crank. To add additional support (although it is already sturdy), we could have distributed the load evenly throughout our design by making our triangles arches instead. Our design could have been made more convenient to use, but in conclusion, it is efficiently functional in completing the task.

2/10/15: Lesson - Fastening & Attaching

Connecting Delrin!

In class we rotated through stations with our partners to learn about four different ways to attach two pieces of Delrin together. 

1) Heat Staking 

To heat stake Delrin pieces together, we started with a t-shaped piece already placed loosely into a peg. It was able to melt the T-stub right on top of the peg. Heat staking requires one piece inserted into the other with a stub sticking out on the other end to melt the stub onto the other. This is a permanent method for attaching Delrin pieces together and would be an excellent way to fully join two pieces together, especially pieces that are foundational and perpendicular to each other, because that is where the most pressure will be applied. However, heat staking should be used with caution because it cannot be undone, and if there are mistakes made afterwards with building the structure, all the pieces might have to be created over again. In addition, the material of the pieces matters when melting them together, because two pieces of different materials might not actually stick.


2) Piano Wiring

We practiced with piano wiring through joining two pieces of Delrin together to create a hinge. Lining up two teethed pieces that fit loosely into the other, we used a clamp on the drill press to secure the overall piece in place while bringing the drill bit downwards. After creating a hole into both of the pieces, we pushed the piano wire into the hole, connecting the two pieces and allowing the hinge to swing freely. Piano wiring is excellent for creating movable and immovable hinges, and the piano wire can be pulled out if the process needed to be undone. The process itself can be difficult to master though. Since the piano wire is very thin and the thickness of the Delrin (3/16'' or less) would often drilled through to create the hinge, the drill bit could move to the side as it drills. This piano wire would consequently not go through the desired path, which we encountered when making our hinge. The wire could bend or not move through the entire length of the desired path as well. The multitude of steps, from the necessary precision of the drill bit's path through the Delrin to the measurement of the matching piano wire to drill bit, makes piano wiring inefficient. 


3) Notches & Pegs 

The method allows for one piece of Delrin to be inserted into a peg shaped piece perpendicularly, loosely or tightly. This is non-permanent attachment of two pieces of Delrin and is not entirely secure if the two pieces are pulled apart with pressure. The tolerances between loose and tight fit can be adjusted as needed for the structure's objective, making this a flexible method for joining two pieces together. This method would be an excellent, impermanent way to allow a single sheet to hold pieces up vertically. To connect the pieces using notches and pegs for a tight fit or loose would be take time to reach though, because there are many tolerances and measurements to take into account with each sheet of Delrin, and from SolidWorks to print. On the plate of Delrin with different sized notches according to SolidWorks, we measured that the tolerance differences for loose or tight fit were around .2 to .3 of a millimeter, and the differences between the tab and a tight fit were around .01 - .02 of a millimeter.  


4) Bushings

As we measured with the Calipers, the tolerances for the notches and pegs are the same for the bushings, where approximately .02 of a millimeter is needed for a tight fit and the tolerances for the difference between loose and tight fit is approximately .2 of a millimeter. Bushings are important to hold pieces of Delrin on a rod, and are flexible when trying to secure them tightly or loosely. Tight bushings would cause the Delrin piece stuck between to be immovable, which is especially important when the rod is rotating, because immovable Delrin would with the rotation of the rod. Loose bushings would still hold the Delrin piece in place, but it would permit the piece to remain stable as the rod rotates. Structures with foundational pieces held together by a rod will need loose bushings in order for the pieces to stay in place, but not rotated along with the rod.


Discrepancy Between Model and Product with the Laser Cutter

The discrepancy that we documented between the dimensions specified in SolidWorks and measuring with a Caliper is approximately 0.01 inch, where the actual size (measured by the Caliper) is larger than the dimensions specified. To use bushings and notches and pegs, multiple trials with the laser cutter on the same sheet on Delrin would be necessary to find the right fit (loose or tight). The tolerances differ from real part and the model because of the Delrin thickness and the laser cutter. The thicker the sheet of Delrin, the more over lapses the laser cutter would have to go through on the design. The velocity of the laser cutter also determines whether or not more or less of the Delrin is melted: the slower the velocity, the more melted Delrin, but the Delrin is cut through more thoroughly, and the faster the velocity, the increased risk of the Delrin rapidly melting back together,  but the cut would be thin.

To print out sheets of Delrin, or any material in the future, we will want to think about trial runs and making measurements on SolidWorks millimeters less than the its theoretical. We will need to be careful with our precision and accuracy when measuring parts for our structure.

Bottle Opener Finale: 2/6/2015

Bottle Opener Presenting Day! 

Our bee opener successfully opened the bottle cap (as messy as it was)! Some of the soda ended up spilling across the table because I wasn't holding the bottle properly on the table...sorry table. It was very nerve-racking to test out a product in front of classmate, and I am glad our product didn't fail us on presenting day. The bottom part of the bee's mouth had already chipped away from testing, and it was difficult to gain a good grip on the cap's ridges.

Analysis of Bee Bottle Opener 

As I mentioned in my last post, the whole bee serves as a lever to open the bottle cap. By holding the bee vertically, we would push upwards and allow the fulcrum (top of the bee's mouth) to roll towards the other end of the cap. Meanwhile, the bottom of the bee's mouth pushed outwards and pulled the ridges up, loosening the cap and eventually opening the bottle. The torque we created on the bee from 1) exerting force ourselves (controllable) and 2) its distance away from the pivot point (fixed), was enough so that the fulcrum would move slowly and allow the bee's bottom mouth to pull the cap's ridges out.

Applying the cantilever equation, , where deflection = (FL^3)/(3EI), that Amy gave us
at the start of class, we can apply this to our bee. We couldn't change E (Young's Modulus) because we were asked to work with only Delrin, nor I, the area moment of inertia, because were were working in 2D on a sheet of Delrin. The force F that it would take to open the bottle cap wasn't controllable either, since it would take a set amount of force to pry open each bottle cap. However, we could control the length of our bottle opener, which is why our bee fits in the palm of our hands. The smaller the deflection, the less likely it would bend and break, and thankfully, our bee bottle opener did not crumble at the sight of soda bottle.

Reflection 

Over the course of this project, we had many iterations until we finally came up with the bee. My blog posts from earlier describes the process (with photos) that Olivia and I had gone through to reach our bee. If I could go back in time, I would have stopped ourselves from making so many mistakes in our iterations, so that we wouldn't used as much Delrin. :( If we could change our final design, I would 1) use the 1/4'' thick Delrin so that our bee could serve its function longer, and 2) enlarge the bee's wings so that it could be used as a handle to make it easier to hold.

Thank you for reading my blog (or skimming it if it was too long)! I'm glad that our first project is completed! 

Bottle Opener Day(s) 2.5: 2/4/2015 - 2/6/2015

Evolution: From Jellyfish to Bee

Over the past few days this week, we worked on our Jellyfish model.  With much help from Larry, our machinist, we were able to get our designs printed out. Continuing from my last post, Olivia and I had left the lab confused as to why the laser cutter was not printing out our designs. After our first attempt, Larry went back to check our DXF and SolidWorks files and emailed a photo of our product to us. Apparently, we were not too careful about setting up units in SolidWorks--the reason why the squiggles weren't displayed on the first attempt!

The head definitely fits over the entire bottle cap and the size of the Jellyfish is larger than it should be. We did not set any units in our first DXF file, and Corel couldn't read it entirely. Over the next few hours, I worked on lowering the head and setting the dimensions on SolidWorks. After a while...

Attempt #2: The Old Phone Jellyfish

 

I am definitely not proud of this second attempt. We cut this one, and all other attempts after, out of the 3/16'' sheet of Delrin. The pointy end has no function, and although I want to say that I have forgotten what I wanted to do with the pointy end, I still do remember. Could I possibly pry the bottle cap open with a sharp end? Naaah. If I wanted to fully develop a product with such a function, there would need to be another end from the top to stabilize the bottle and act as a fulcrum. It was a silly add-on idea, but it was nice to learn more functions on SolidWorks to create the sketch. The half oval itself was also a disappointment though; although I had set the dimensions for sketch and measured some of the parameters, I was not careful enough. I did not know of the existence of the "Measure" function on SolidWorks yet, and had been eye-balling the dimensions from the ruler above. The semi-oval from this product was exactly the same size as the semi-oval from the first product! :( 

Attempt #3: The Tragic Jellyfish

Lucky number three wasn't lucky at all. Cutting the Jellyfish out from the 3/16'' sheet of Delrin again, we collided with empty space from another person's cutout...so, our Jellyfish lost some of its ovalness. This attempt turned out to be a little too small. Although I measured the width and length (3.1 cm by 2 cm), the thickness of the Delrin made it impossible for the straight edge to fit underneath the bottle cap and for the conic section to rest on top. 

Attempt #4: The Almost Perfect Jellyfish

This was our final attempt before switching to a new model. The dimensions were finally right! The straight edge just barely fit underneath and the conic section rested on top of the cap. I pushed upwards and... realized that the cap wasn't going to give at all. Instead, the metal ridges of the cap stripped away at our straight edge. I tried filing down the sharp edges of the straight edge in hopes that it would get under the bottle cap a bit more and cover more under the curve, but the bottle cap kept stripping away at the straight edge.  The two resting points on the conic curve did not help much at all, because the concentrated force mainly relied on the tangent point that the cap made with the straight edge to open the bottle cap. If the bottle cap kept stripping at the straight edge, it wasn't going to make enough contact with the curve at all.

So, goodbye Jellyfish, swim back to your ocean, but we could no longer use you to open our bottle caps... 

Attempt #5: Bee Successful

Bee Successful! :) Mission complete: the bee bottle opener works! The night before Thursday, we designed another model in SolidWorks in case our original design did not function. To do this, we had gone back to our original sketches and found one of the models where we could 1) hold vertically instead of horizontally and 2) would serve as a lever. 

Originally, the sketch of our "bee" looked like this. After Olivia drew the figure out in SolidWorks though, she saw that the main function of the figure, its "mouth", could possibly be the mouth of a bee, and changed its shape. The engineering design process for this was slightly backwards, but we cut out a Styrofoam model of our bee after creating our SolidWorks model. The next morning, after our unfortunate Jellyfish still did not complete the task, we went to check the dimensions and printed out our bee Friday morning. 

It was so exciting to finally produce a functional bottle cap opener! It was even more thrilling that it continued to work and that we could easily apply a constant and significantly less force to push to the bottle cap over. The top of the bee's mouth to serve as a rolling fulcrum and stabilizer for keeping the cap in place, while the lower part of the bee's mouth went underneath the bottle cap that pulled up the cap's edges. Holding the bee vertically as we exert a force in an upwards motion, the bottom of the bee's mouth to exerts an upwards force underneath the ridges of the cap, opening the bottle.

We are ready to show our product to the class.

This was quite a long process! Thank you Larry for helping us print out our designs!

Bottle Opener Day 2: 2/3/2015

Laser Cutter: The Birth of the Jellyfish (Alien?) Bottle Opener 

Olivia had already started our model of the Jellyfish on SolidWorks when I entered the classroom. After various and multiple attempts, confusion, a few Youtube videos, and much trial and error, we managed to have a final, 2-D DXF copy of our Jellyfish. It was a grueling process, since we both didn't have SolidWorks experience, but we are happy that we learned the basics of creating a 2-D sketch and extruding parts of the model. 

The birth of our Jellyfish still didn't go exactly as planned. It was on hold, because when we presented our DXF copy to the computer linked to the laser cutter, Corel could not read our decorations. The main part, the half-oval head, and its body were outlined, but the small curves would not show. We volleyed back and forth between our primary computer and the laser cutter computer for a while, taking the flash drive back and forth as we tried to figure out why the DXF file would not completely portray our Jellyfish. Near the end of class, we decided to just print out our model in its current, basic state. We needed to test whether its primary function as a bottle opener works. 

Today was my first time working with a laser cutter, but wow, it was a process. It was exciting to see the laser cutter in action and to have our first model! Above is a clip of part the cuts, but it definitely wasn't working the way it was supposed to either. Larry, our machinist, asked us if we had multiple lines on top of our drawing stacked up on top of each other, and shook our heads. The laser cutter kept retracing the lines over and over on our existing model, and we had to cancel the order so that it wouldn't just continue cutting on forever and ever... 

Yay! We have a product at last! 

And the best part is...

It works! :) Success!

Except...only temporary. We definitely need improvements! We had cut out our Jellyfish from a 1/8'' thick Delrin sheet, and our piece was too thin. It was heart-wrenching to open the Coca Cola bottle cap above--we took much care to not break the opener (it was bending!) and held it very close to the head in order to apply most of the pressure to force open the bottle cap ourselves. After a couple of more tries, we found it was just generally too difficult push up caps with our opener. The head even slipped over the entire cap and got stuck around the neck a few times! We will be working over the week to improve, or even change the entire design. Even if we get our contact points and the angle to work, we need to rethink whether pulling the bottle cap from underneath with a straight edge would work out well at all.

Bottle Opener Day 1.5: 2/1/2015

Introducing...the Jellyfish Keychain!

To finish the first part of our project, Olivia and I came in to the We-Lab to cut out Styrofoam prototypes of what we might want our product to look like. We brought out the razors and Styrofoam and started cutting out a few of our sketches that we liked. In the end, we chose a seemingly simple and cute design...that we present as the Jellyfish! We couldn't cut out the tiny bubbles that were part of the decorations, but hopefully, they will be easier to make on SolidWorks.

In theory from our Styrofoam demo, the head of the Jellyfish, or the half oval, is supposed to rest its circular frame against the 2 sides of the bottle cap from the top and the diameter of the oval should be lifted upwards under the bottle cap to force it open.