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.
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| From right to left: different handle attachment, ball stopper, plate stopper |
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| Some early ball models |
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| 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.
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| A very early prototype using a racquetball |
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| Pugh chart after testing various balls
Final Design
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| Velcro incorporated into final design |
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| Testing our final model at CRI |
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| 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:
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.
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