Mechanisms

As an assignment, I needed to find a mechanism that converts rotational motion to linear-ish motion. I chose a mechanism called a multiple straight line drive or a hypocycloid gear straight line mechanism. It looks like this.

Any point on the circumference of the inner gear will form a straight line when the smaller gear moves around in the outer gear ring. This is because the inner gear's diameter is half the length of the outer gear's diameter. Therefore, as the inner gear moves around the outer gear the piston will move up and down in accordance to the position of the inner gear. Thus rotational motion of the inner gear is translated into linear motion of the piston. This mechanism does not allow for much force to be exerted on the piston, however.

I initially chose this mechanism because it reminded me of a piston in a car's engine. I thought it was applicable to something I have used a lot. I think it can be useful in the engines of cars, though I am not sure if it would provide enough force. I was also interested in this mechanism because the linear motion of the piston is very fluid. As I was watching the video of the mechanism and thought about how it worked, I concluded that it would not be convenient to use this mechanism if the piston needed to move a large distance. This is because the height the piston moves is exactly the diameter of the larger gear. In order for the piston to move a large distance, the diameter of the larger gear would need to be that large distance, which would take up a lot of space.

Well Windlass

For our second project, my partner, Tiffany, and I had to build a well windlass that could span 12cm. We needed to be able to hoist a 1 liter bottle of water 10cm above the top of the tables with one hand. The structure had to be stable and be able to lift the load easily. We were also only allowed to use 500 cm^2 of delrin, 50cm of delrin rod, and 120cm of string

We started the project by brainstorming various well-windlasses that would work.

There were various ideas, but we decided on this one.

The idea, called Crank, is that there are two triangular bases on both sides of the table. The delrin rod goes through two of the bases and has a handle attached to it. The delrin could then be rotated so that the string would wind around the delrin and pull up the bottle.

However, we soon realized many flaws with the plan. The delrin rod was not going to be able to support the weight and the bases were going to use too much delrin. Instead, we modified our idea to have rectangular bases, with only two of the sides actually in place and we added a rectangular delrin casing for the delrin rod for added support. In addition, we made the handle longer on both sides for easier turning. Our final model looked like this.

Our next step was to make a physical mock-up out of foam core.

We changed the handle to a rod eventually because we found that it would be easier to turn the handle with one hand that way as opposed to a circular handle. After, we needed to make each piece of our design in solidworks. We started by drawing out all of dimensions we would need, including test pieces.

We then made up all of the pieces we needed in solidworks. When everything was to our specifications, we made a drawing of the solidworks.

We started by cutting out test pieces to make sure all of our notches would fit into each of our holes. When we got the test pieces to fit correctly

We printed out our final project. The first thing we noticed is that our notches in the bases were too small to fit the delrin rod casing, so we changed the dimensions on solidworks and printed out new delrin bases. We also noticed that some of the pegs in our delrin rod casing did not fit into the holes. This was because the laser cutter needed to make two passes to cut the delrin, so part of the delrin would melt. We fixed this by sanding down the pegs and then the rod fit together very nicely. We put the delrin pieces together.

My lovely partner demonstrating our Well Windlass!

We tried it out, and it worked (thought it was a little shaky)! It lifted the piece without too much difficulty. 

Engineering Analysis

We picked this design because we thought that the delrin rod casing would prevent the delrin beam from bending and allow for the delrin rod to pick up more weight. We also tried to make the base wide enough to support the height of the base without using too much delrin. We attached delrin squares in between the two sides of the base to strengthen them. These design implements were important since we could not control the material that we used.

However, the windlass was not as sturdy as we hoped it to be because the notches that held the delrin rod casing in place to the base was not tight. Therefore it did not hold on to the rod casing tight enough to make the rod casing stay in place

Materials Usage

Delrin Rod Casing: 2cm x 22cm x 4 pieces = 176 cm^2

Bases: 12cm x 4 cm x 4 pieces= 192 cm^2

Base Connecting Pieces: 4cm x 4 cm x 2 pieces= 32 cm^2

Handle: 1.5cm x 20cm= 30 cm^2

Total Derin: 430 cm^2

Delrin Rod: 27 cm

We used Delrin of width 3/16 and inch.

Summary

1) Brainstorming many different ideas

2) Choosing the best idea

3) Making the piece out of foam core

4) Iterations while making the foam core- We realized that it would be impossible to make pieces fit or sturdy enough in 3d.

5) Making the pieces and test pieces in solidworks

6) Laser-Cutting Delrin test pieces- We used smaller pieces of delrin to make sure the holes and pegs would fit together correctly

7) Iterations to the test pieces- We had to keep changing the dimensions of the pieces until they fit snugly together

8) Print out the whole piece

9) Reprinting out some pieces- We realized that some pieces didn't fit together, so we needed to change the dimensions and try again

10) Putting the piece together- This involved filing down some pieces as they melted in the laser cutter.

11) IT WORKS!!

Results: In class, the Well Windlass lifted the bottle, but it was pretty shaky while doing so. I believe this is because the Delrin rod casing was fit too loosely into the notches on the bases. It might have been better to heat stake or piano wire the pieces together to make them sturdier. I might have also improved the design by making the delrin rod casing smaller so the delrin rod would have fit better in the casing.

I also would like to experiment with completely different ideas as they seemed very sturdy in class.

Fastening & Attaching

The other day in class, I learned different methods of attaching pieces of delrin to other pieces of delrin. My partner, Tiffany, and I rotated through different stations were we learned how to heat stake two pieces together, use piano wire to connect pieces, and use notches/pegs to connect delrin.

Heat Staking
Heat staking is a process where one leg of a t-shaped piece of delrin is fit into a hole in another piece of delrin. The delrin is then melted together. This method is beneficial if the pieces need to be permanently attached to each other. The only way the pieces could come apart after they are connected in this way is to break the piece. This is useful for making objects that need to stay together, like toys for children.

Piano Wire
This process is good for putting two pieces of delrin together in a hinge. It allows for movement of the two pieces. It is good if the point is for the pieces to be able to move together. The drawbacks of this process is that it is not useful if the pieces need to stay together at a rigid angle. It is not as permanent or stable as the heat staking process.

Notches/Pegs
The benefit of this process is that it allows two pieces to stay together pretty tightly, but it is still possible for the pieces to come apart if needed. This would work well if there was something inside that would need to be taken out to be fixed or upgraded at a later time, while still retaining a tight bond. This process is not as permanent as heat staking, but if the tolerances are right, it could be very hard to take the pieces apart. The drawback to this method is that it can take a couple tries to get the sizing right on the notches and pegs. If the sizing is too loose, the two pieces won't hold together.

Tolerances

A Width of Sheet of Delrin: 3.15mm
Width of Notch:................... 3.16mm-Tight Fit
                          ....................3.33mm-Loose Fit
B Width of Sheet of Delrin: 3.33mm
Width of Notch:....................3.34mm-Tight Fit
                          ....................3.52mm-Loose Fit

For the A, the dimensions specified in solidworks for the width of the notch were
Tight Fit: 3.175mm (.125 inches)
Loose Fit: 3.429mm (.135 inches)

The tolerances differ in solidworks as compared to what really came out because the laser cutter is not exact. It will cut a piece a couple times before it cuts all the way through the material. The tolerances will also differ for different material thickness because it takes more power and possible more passthroughs to fully cut the piece. This means that it is necessary to test the measurements of the notches and pegs on the laser cutter in a smaller piece before building the entire part. The measurements may not be correct the first time the piece gets cut out.

Bushings

Tight Bushings are necessary for keeping a piece in a specific place on a rod while loose bushings are necessary for enforcing the strength of a rod.

Measurements-diameters

Rod....................6.35mm
Loose Bushings:6.52mm
Tight Bushings: 6.37mm

Bottle Opener

For our first project, Sarah and I  had to design a two dimensional bottle opener. The bottle opener had to be capable of opening a non-twist-off soda bottle, be made from a single piece of Delrin plastic, and could not be bigger than 6'' in any dimension. To start the project, Sarah and I went through a brainstorming session. Many ideas came out of the session.

Brainstorming Session

From all of the ideas, we thought ten of them were the most feasible and we drew better mock ups of them. We organized them by variations on different shapes.

The Ledge Designs

The Inverted Circle Designs

Circular Designs

The first idea was the ledge design. We thought it could open the bottle by providing a lever for the bottle to be opened on with the smaller end under the bottle and the larger end on top. We thought the teeth in the last one could grip on the bottle better (and that it looked like a shark). Ultimately,  we didn't choose this design because we thought it would be easy for the side to get dull and not open the bottle.

Our second idea was the inverted circle. We thought the teeth could have helped grip the bottle or the shaped handle would make the opener more comfortable for the user. Ultimately, we did not choose this design because we thought it would need more force than possible to open the bottle.

Our third idea was the circular designs. We thought that since the opener was more compact, it could provide more force to open the bottle than our other ideas. We did not choose the donut or the oval because we thought that the measurements would need to be precise in order to work, which doesn't always work with a laser cutter. We thought the half-circles could open the bottle by having the straight edge on the underside of the bottle cap and the rounded edge on top of the bottle cap, providing the right leverage and force to open the bottle. We went with the circular half-circle because we thought the design was more fun than the hand shaped one.

Our next step was cutting the piece out of foam core.

Doesn't it look happy?

Our outside circle ended up having a 30mm radius with the middle half circle having a  20mm radius.

Then we needed to make the piece in solidworks. Neither Sarah or I had worked in solidworks before but we soon got used to it. Our piece looked like..

Solidworks piece of the foam core.

The final step was to send the piece to the laser cutter to print it out. There was some trouble finding the right file to make it print. When we got it to work, we printed the piece on 3/16'' delrin because we thought it would be thick enough to be stable, but thin enough to fit under the bottle cap. The final product came out.

Final Delrin Piece!

Engineering Analysis

Cantilever Beam Equation: 

delta=deflection

F=Force

L=Length

E=Young's Modulus (material stiffness)

                          I=Area moment of inertia (stiffness of cross-sectional area)

For this project, we had to use delrin as the material of our object so the Young's Modulus could not be influenced by the design of our bottle opener. It is also hard to tell the Force someone will put on the bottle opener so that could also not be influenced by the design of our opener. Our model was influenced by the Length (from the top of our head to the top of our mouth) and the area moment of inertia. We chose this design as opposed to one with a handle because the length from where the force is applied to were it opens the bottle was the shortest. We also made it a circle because we concluded that the area moment of inertia would be the largest. Therefore deflection would be small and it would be able to open the bottle cap.

Summary

1) Brainstorming-Create many different ideas

2) Top Ten Ideas- Look at all the ideas and pick the 10 most feasible ideas

3) Chose Best Idea to try- Circle because deflection would be small, would provide best leverage, and looked the best.

4) Cut piece out of foam core

5) Make piece in Solidworks

6) Laser Cut the Bottle Opener

7) Open the Bottle!- Our bottle opener worked the second time we tried it in class. When we were using the bottle opener before the presentation, we noticed that it would sometimes fail because the flat part could not get fully under the bottle.

If I had more time, I would experiment with sanding the flat part of the bottle opener down so that 

more of the part could get underneath the bottle cap. I would also try different sized half-circles in the middle of the design to see if it would change how easily the bottle cap would come off. If I had a lot more time, I would also want to experiment with different types of bottle openers to see which one works the best.

About Me!!

Hello!

I'm Sonja Cwik, a sophomore physics major and teaching studies minor. I am from Southern California and on the varsity cross-country and track teams here at Wellesley. I took this course because it looked interesting and I wanted to be in a class that involved working with my hands as opposed to taking tests or writing essays. I also want to learn various methods of making objects and the technique behind it so that I can be more competent making objects in the future.