Mechanisms: Reciprocating Rectilinear Motion

Reciprocating rectilinear motion gives the slow advance and quick return of a bar, as shown in the video above. A pin in a rotating disk changes position in a slotted arm causing this motion. A single reciprocation cycle is called a stroke. This type of mechanism converts circular motion to linear motion. This type of motion was used in early steam engines, propelling the vehicle. 

The fact that this type of motion converts to another type of motion which is able to do a different type of work is very interesting. The angular displacement, velocity, and accelerations become linear displacement, velocity, and acceleration. This type of motion can be caused by a crank, gears, or other simple mechanisms.

Well Windlass

Our original sketches.

Preliminary side sketch (with accurate measurements) of our well.

Sketches of our parts and their measurements.

Measurements for our bushings and the hole for our rods.

Foam well windlass prototype. We focused a lot on the height of the windlass in order to make sure that our windlass rose the full 10cm above the table.

Bushings parts in Solidworks

Side part in Solidworks.

Crank in Solidworks.

Test pieces of the top and bushings.

Complete set of test pieces for various parts.

Final windlass spanning the 'well'

Final measurements of how much Delrin our windlass used.

Engineering Analysis: Our windlass works using very tight press-and-fit notches at the top of the structure in order to keep our two flat pieces together. In order to keep the bottom of the sides from flattening out, we added extra supports on the sides. We made the support rods as tight as we could in order to prevent slipping, as well as adding bushings on the end of each. We put the rod as close to the table in order to spread out the weight and not put too much pressure on the top notches. We had to align the homes on each side in order to keep the rod straight and make them big enough to spin easily. We could control the width of the sides and the height of the structure but not the strength of the material (though it was fairly strong) and the thickness. Our structure was fairly sturdy due to the wide legs parallel to the gap. We also kept our structure as short as we could (while still maintaining the required height) which greatly reduced wobbling. 

Reflection: We began with many diverse ideas for our structure. Our actual decision-making process probably could've taken a shorter amount of time but we ended up going with the design the used a reasonable amount of material, seemed to be the sturdiest, and was simple enough to build. We then made the Solidworks drawing and foam prototypes, making some small measurement adjustments as needed in Solidworks. We then made many test pieces in order to make sure that our measurements for the notches and business were correct. Our first copy was warped and our sides were ruined because one of lines wasn't hairline for some reason. Our second cope fit together well, although if we were to redo anything, we would have designed and printed a new crank. 

Fastening and Attaching

Delrin, or Polyoxymethylene is a stiff thermoplastic that has high stiffness and low friction. These properties make it suitable for precision parts such as ski bindings and small gear wheels. Because of Delrin's low friction and water absorbance, glue doesn't work when binding pieces together. In class, we practiced three different ways of joining the Delfrin. First, by heat staking, where the Delfrin is melted together in an immobile joint. Heat staking is useful when you know exactly where you want the joint. Once a joint is heated, it becomes completely joined and unable to be taken apart. This is the strongest attachment. Piano wire joints are movable joints where a piece of wire holds together two pieces of Delrin. This is one of the weaker joints because the wire can come out fairly easily but it preferable when you need a hinge-like joint. Notches and pegs are a bit of a happy medium between the two joints. It is an immobile joint where one piece of Delrin fits snugly into another piece. It is possible to get the pieces apart but when measured tightly can be a fairly permanent joint. 

Tight bushings are useful when you need to keep a piece in place, specifically a rod. Loose bushings are useful when the rod needs to be mobile, such as the rod that pulls of the string attached to the water. For the bushings, the difference between a loose and tight fit was about 0.01 inches. 

The discrepancies between the dimensions were about 0.01 inches for the 0.135 inch notch. For the the 0.125 inch was about 0.012 inches larger. The tightest notch, the 0.115 inch notch was from 0.005 to 0.01 inches. The tolerances are the same for different thickness materials. In the future of laser cutting, a thinner laser would make the tolerance more accurate to the model. 

Bottle Opener

Engineering Analysis: A cantilever, which is defined as a beam anchored only at one end. While force is being applied to the bottle cap, the bottle opener has a full moment connection. One edge of the bottle opener is inserted under the metalwork and another point uses a fulcrum point on which to pivot when an upward force is applied to the handle. One main issue that we had with the final design was that the part of the opening that was inserted under the cap chipped off on the edge. This could have been fixed by making the height of the opener smaller. This would've put the bottom edge at a different angle from the cap, possibly fixing the chipping problem.

Design Process:

We began with many designs, but ended up deciding between a "Crown Cork" opener and our final, simple opener. 

Initial drawings of chosen design. 

The most important measurements we took were the ones for the actual opening of our bottle opener. We had to make sure that it would fit around the cap on the sides and that the pivot point on the top of the cap was as near to the center as it could be.

More detailed measurements to be transferred to foamcore prototype.

Cutting the foamcore prototype.

Checking the prototype on the bottle.

Final measurements to be transferred to Solidworks. 

Solidworks design before extrusion. 

One of our biggest challenges was learning how to use Solidworks. We had to figure out how to use all of the shapes in the right way in order to create our design. 

Laser-cut iterations (right opener was our final).  

Reflection: We decided on the design that we did because one of our worries with the "Crown Cork" design was that the tip would break off. We still had chipping issues with our opener but the edge wasn't nearly as thin as the tip of the other design's would have been. We began with over 30 designs, although many were variations of the final two that we decided between. When we chose our final general design, we combined it and altered it, drawing inspiration from other ideas. We decided on the teeth because we thought that they would provide a good surface with which to press on the cap ( and they were cute). The bottom of the "mouth" was rounded in order to make it slip under the cap. The rest of the design was just to go with our "monster" theme. After drawing it on paper, making a prototype, and drawing it in Solidworks (with a few mouth alterations along the way, including making the mouth a bit smaller and wider), we were ready to cut. The first cut was scaled too large and slipped right over our bottle cap so we made a second, smaller design. This one worked but (as mentioned above), still chipped at the bottom of the mouth which could've been fixed by changing the single of opening by making the mouth smaller. Besides that, other options for changes were taking away the handle which would have allowed for more freedom in the angle of opening and eliminated the possibility of the handle breaking off. 

Introductions

Hello World, my name is Magdalena Sowder. I'm a first-year at Wellesley College and I'm originally from Ann Arbor, Michigan (Go Blue!!). I am relatively undecided in my major although I am considering Computer Science. I love to hike and last summer I hiked in the Parc National de la Vanoise in France.
A few summers ago, I went to Liberia and worked with a group of University of Michigan students on several environmental engineering projects. That trip played a huge role in sparking my interest in engineering and the possibilities to help people through engineering. Through ENGR 160, I want to continue to explore engineering principles and begin to get a sense of what an engineer does and if that is something I wish to pursue. In this course, I want to challenge myself to go above and beyond in each of the projects.
I am looking forward to a great semester!