FINAL POST

Abstract

Over the course of the semester, we (Nasreen and Alex) worked on making an erg chain stopper for CRI. When we originally visited CRI, the coaches noted that when changing between the standard handle and the one handed handle, there was a tendency for the chain on the erg to snap back into the machine. After many designs and tests, we found that a ball shape was the best way of making a successful erg chain stopper because no matter how the ball is oriented on the chain or when it hits the machine, it is the same shape. In the final weeks of the project, we found that there is a lot of variety in ball sizes and shapes and, ultimately settled on a wiffle ball. We decided to use a wiffle ball for our final model because of its low cost and ability to come back into shape most of the time.

Problem Statement

This semester we worked for Community Rowing Inc.’s adaptive rowing program. Many of the products that they use are not commercially made because of the specific nature of adaptive rowing. Jaden and Jenny showed us the one handed handle and commented on how difficult it is for the two handles to be changed out efficiently. Their biggest concern was the erg chain snapping back into the machine, which would require much more work to fix and not allow for the handle to be changed out quickly and efficiently.

Design Specifications

Easy to remove (<20 sec)

Want anyone to be able to use the product quickly and have minimal training

Does not damage the erg

Do not want to cause any damage in anyway

Does not weigh down the chain

Can be used during the duration of the workout if needed, if something weighed down the chain it could influence the form of the rowers or make it more difficult to erg

Staying in place for greater than 4 drop tests

Don’t want the coach to have to come around every time someone drops the handle, also if a coach is changing out the handles, they should know that the ball will not fall off after the first or second drop.

We selected this final design because it had the best results when testing and was inexpensive.

A detailed description of your design, including reasons for your design decisions. Include pictures, drawings, and calculations as needed to fully describe your design such that an outside party could both fully operate your product and create replicas.  An appendix with an instruction manual is appropriate. Note that making a document that allows for full replication is exceedingly difficult and take great care to do so.

When assigned this project, the first thing we did was brainstorm. We came up with three main ideas, a different handle attachment to the chain, a ball chain stopper, and a plate like stopper.  

From right to left: different handle attachment, ball stopper, plate stopper

Some early ball models

Magnetized stoppers that would clip to the erg chain

We settled on a ball shape after talking with Jaden and discussing pros and cons. The other designs were not sturdy enough to handle the weight of a dropped erg handle and would easily fall off the chain. There was no easy way to prevent this from happening without making the design too heavy.

We then began testing everything from dog toys to racket balls to wiffle balls to decide on our final model.

A very early prototype using a racquetball

Pugh chart after testing various balls

Final Design

Velcro incorporated into final design

Testing our final model at CRI

The size of the hole is a crucial element to the design

The design we ended up with was a wiffle ball with a piece of velcro wrapped around the outside. Our wiffle ball is two and a half inches in diameter. There is a hole drilled in the top and bottom. We created the hole by using a step drill up to the step that measures .29 inches in diameter. Then we used an olfa knife to cut from the top hole to the bottom hole in a straight line. We then attached the velcro around the outside of the wife ball with hot glue. We put a lot of hot glue where we planned on putting the velcro and pushed down on the velcro so the hot glue would  come out of the sides. We then used an olfa knife to cut the dried glue off the sides of the velcro.

The ball is attached to the erg chain by:

1. Unfastening the velcro and squeezing the upper and lower halves of the ball.
2. Positioning the ball around the erg chain so that the chain sits comfortably in the holes.
3. Making sure the ball is at least one foot from the erg handle.
4. Re-fastening the velcro.

Methodologies and results of tests you performed in designing and refining your prototype.

When testing our product, we looked at the grip and strength. We tested many types of balls, but quickly came to the conclusion that the Wiffle Ball was the strongest. We still however, had problems with grip. Commonly, a ball out be really easy to put on but would fall off very quickly. If a ball was very sturdy and hard to put on/take off, it would pass the drop test. After seeing that our best ball (the Wiffle ball) would still fall off after the second or third drop test, we added the velcro around our ball. It was a last resort since we initially did not want to ruin the simplicity of having the ball alone. This velcro allowed for the ball to retain its shape when hitting the erg machine.

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Discuss the extent to which your final design meets the design specifications, and if there are shortfalls, indicate how these might be addressed in the future.

Our final design meets most of the design specifications. The product does not weigh down the chain, is easy to place and remove from the chain, and does not damage the erg. Although our product can usually withstand multiple drop tests, it sometimes slides onto the U-bolt that holds the erg handle to the chain. This may be addressed in the future by focusing on the internal structure of the wiffle ball, such as adding some sort of foam or rubber core since we did not have time to test any internal structures during the semester. Another complaint we had was that the Wiffle ball collapsed when it hit the erg, although it does quickly spring back to shape. It would be nice to incorporate a rubber-like texture to the outside of the Wiffle ball to give the illusion of the strength and malleability of a rubber ball.

How your design has been received by your community partner, what follow up is needed (prototype delivery, etc.), and how that will be achieved: these plans should be explicitly discussed with with Prof. Banzaert and your community partner prior to writing the final report.

The design has been received positively by CRI. They viewed our prototypes as a better replacement for the current erg chain stopper, which is a cut PVC pipe. We made six Wiffle balls that were delivered to them for extensive testing. They should perform the same way they did during previous testing. CRI was not worried about the velcro and found it to be a necessary addition to the design. They still seemed eager to make more themselves in the future.

Acknowledgements: Thank you to Professor Banzaert who guided us the whole time. Thank you to our classmates for giving us feedback and bearing the sound of our countless drop tests. And thank you Larry, who was there every step of the way and helped wherever he could.Special thanks to CRI for providing us with valuable feedback and opening their doors to us.

Over the past few weeks..

We have finally finished testing all the different balls and trying different way of slicing the balls so that they stay securely on the chain.

Unfortunately, all the balls except the Wiffle ball had major issues staying on the chain and not popping off under the pressure of our "drop test".

Here is a Pugh chart that summarizes our conclusions:

We were therefore forced to add another component to our design - that kind of ruins the simplicity of the idea - which is velcro. The addition has helped the ball stay on the chain and so it actually works now, which is great.

We glued velcro on to the racquetball, bouncy ball, and Wiffle ball. We then took a trip to CRI for feedback. They seemed to like the Wiffle ball, but didn't think it would be sturdy enough to withstand repeated drops. They liked the pliability of the racquet and favored it. However, after further testing we confirmed that the racquetball was too easily ripped at the holes and would not work. 

Wiffle ball testing at CRI

We decided to run with the Wiffle ball, since it was the only one that could hold up. Since CRI didn't like the "feel" of the ball, we experimented with different textures to make the plastic Wiffle ball seem more like a rubber ball. However, the PlastiDip we used to coat the ball was messy and took away from the aesthetic of the original prototype.

We asked Larry about the best way to attach the velcro to the ball and he suggested we glob a bunch of glue-gun glue onto the velcro strip and then press it onto the ball until the glue squirts out the sides. Then when the glue dries, cut off the access with a Xacto knife. This method worked great, and we have clear edges now. 

Our presentation is ahead, and we are almost done making 6 replicas of our final prototype!

Final Prototypes + Meeting with Jaden

On Wednesday we finalized our ideas and came up with a couple of sacrificial concepts before our meeting with Jayden.

Also, the 3D printed part I modeled last week is finished printing, and we added in the bolts just to have a finished prototype even though we scrapped the idea. The size and spacing of the holes were pretty accurate which I was happy about, and I learned a lot about SolidWorks and modeling through the process.

Final HandleStopper permanent attachment prototype.

The second prototype we showed Jayden was a sacrificial idea. It made use of magnets and wood to keep the cord in place. The cord would be sandwiched between the two pieces of wood, holding it in place. This idea was not practical for a few reasons. First, it was really difficult to get the magnets to align properly. Secondly, even if they were aligned, they didn't have the strength to stop the momentum of a dropped chain.





Another idea that utilized magnetics was the prototype Alex had been working on for the past few weeks. After adding foam padding to the inside, it didn't fit over the cord as well as perform. It also didn't pass our "chain drop test".

We also went back to the original idea of simply slicing a sphere in half. We modified a red plastic ball and fitted it over the erg chain. It worked surprisingly well and didn't fall off even after we let go of the handle at full resistance (10) while sitting on the erg seat. Jayden liked the idea of the sphere the most out of all our prototypes, especially since CRI can make their own using balls such as tennis balls.

Sliced sphere prototype

 After our meeting we have decided to move further with the sphere concept. We ordered a bunch of spheres and will cut/drill, and test them over the next week. Our goal is to have a few viable ball options before our visit to CRI.

Variety of balls ready for testing

Prototyping Part 2

Alex and I have made good progress with the prototypes. We have sent both ideas to CRI for review. 

This past few weeks we have been ordering parts, making 3D models of our prototypes. So far we still have two different concepts we have been working on separately, but by next week, after we receive feedback from community rowing, we should know which concept we should invest all our time to.

Our first idea is to make a simple stopper that prevents the chain from snapping into the machine. Alex has created a prototype out of wood and magnets.

Prototype of Idea 1 in wood

The idea is that the two pieces will "clamp" the chain and act as a border so the chain doesn't retract and damage the erg.

Sketch of Idea 1

Before making the prototypes out of wood, Alex and I tried to 3D print them but we were having issues with that process. The built plate wasn't heating up properly so the plastic wasn't sticking. We aren't sure whether that's an issue with the printer settings or with the model.

3D models made in TinkerCAD

Our second idea was to create a cord stopper that also  made the process of replacing the handle easier. The stopper would stay on the machine and allow the handles to be interchanged without any tools. One side of the stopper would hold the chain and the other a bolt that can attach to any handle needed.

 

We 3D printed the model and it came out fine, but there were a few issues with the underside of it. We also had to scale it down to make it easier to print. We will be printing a final model this week.

Sketch of Idea 2

 

 Overall we are in good shape and it's just a matter of hearing CRI's feedback to that we can move forward with a final product.

Rob Wood Seminar

I really enjoyed Rob Wood's talk. I think the projects his lab are working on are interesting and I learned a lot of new things during the seminar. I didn't know that microrobotics had come so far, and didn't expect the variety of prototypes they had already built. The production process of folding or "snapping" the pieces into place with one gesture was, I thought, a really creative and ingenious idea. I wish he had more time to go into more detail about the design of the MEMS and the actuators. 

I remembered something that I had read during the discussion, which was about the relationship between quantum physics and transistors. I can't remember the details, but I read that transistors can only get so small before quantum physics comes into play, and they stop working (something about the electrons not being stopped by the "gate"). The theory was that when transistors became this small, Moore's Law would end and we'd have to come up with materials other than silicon to create transistors. The Schon scandal was related to this topic because Schon had claimed he made transistors out of organic dye. Although, I guess this is applicable to the nano scale and not micro scale. Either way, I'm curious to know if they have faced any similar difficulties at such small scales. 

I also found it interesting that so many different departments collaborated to make the projects possible, and that it has a lot to do with understanding the biology of whatever organism they are simulating.

Final Project Community Rowing

We want to create a cord stopper that will prevent the cord from retracting into the machine as the handles are being switched out.

Our design specifications are as follows:

- Easy to remove (<20 sec).

- Does not damage the erg.

- Is sturdy/reliable and holds the cord every time.

Materials: Heavy metals, rubber, magnets?

Parts list?

Schedule:

3/18 - parts list/materials

       - basic prototype/concept

       - meet up after exam, finalize materials list

3/30 - have prototype mostly done

       - meet up outside of class to see where we are with prototypes and what needs to be done between Monday and Friday

4/1   - finalize prototype, hopefully end the class with two or more prototypes almost/ready for presentation

       - test prototypes

4/3   - present to class

       - discuss critiques, identify weak points,

4/6 - commit to design, narrow down to one design

4/8 - begin final product, think of variations according to feedback

4/10 - continue working on final product, think of variations accoring to feedback

4/13 - test product

4/15 - prototype testing at CRI

4/17 - discuss critiques, identify weak points, work on final product

4/22 - make changes to final product design

4/24 - continue working on the final product, test product

4/27 - test product,

4/29 - (Ruhlman Conference) final adjustments

Testing plan:

- Figure out how to safely test without ruining the machine.

- Place stopper on the erg chain, check for correct width and strength of stopper/mechanism.

- Use erg with attachment in place to test for compatibility.

Prototyping Part 1

Alex and I are off to great start. We've decided to tackle the one-handed handle project. We both made sketches of handle ideas and then compared our ideas. We both had similar concepts and decided to work off of Alex's sketch, which was more clear.
 

Initial concept sketch

We then began the process of making a rough prototype out of sheet metal, scrap wood and foam board. The initial model is not accurate at all because at that point we were still vague on how we were going to exactly idealize the design. In order to get a better sense of our direction, we wrote up questions to ask CRI. We also sent them our initial sketch for their opinions.

Our next step was to take a trip to the KSC to take measurements of the erg machines. We also looked up different clamp designs to brainstorm how to attach the handle to the cord. We looked at rod-latch systems such as those found on camera mounts and music stands. Those types of latches tend to be very easy to mount/unmount. These are the clasps we found:

Clasp options

Some options are more refined products and others are pretty industrial looking. After testing them out, we can incorporate features from multiple products to create the ultimate clasps for our handle.

I'm working on learning SolidWorks so that we can create a better prototype that has features that will be reflected in the final design. We are trying to standardize the handle as best as possible, while also working with the curvature of the handle for a secure fit.