As I prepared for another round of testing this week, I was able to finish assembly of the new testing units, as well as review the appropriate ISO testing standards (soaking the joints in a liquid medium at X degrees Celsius for X hours, using a X mm/min pull rate for a X mm gauge length) to determine how to test the new units. This round of testing only consisted of 20 samples, which is significantly less than the 50 from the previous round. This decrease in samples needed (less scrap/resources utilized!) is all thanks to the fact that my coworker and I dedicated a solid chunk of time in the first round of testing to identify a more appropriate test method for analysis. The data collected from this test will more accurately characterize the joint.
For this round of unit assembly, there were two main things to take into consideration:
- The amount of adhesive used to connect the two drive cables together
- The length of thinner drive cable that is inserted into the thicker drive cable
These were two issues that were brought to light during the first round of testing. The results, load at break and % tensile strain, from the first few units of round one were pretty varied, and I was stuck wondering why this was. My coworker and I concluded that it had to do with the above two points. The amount of adhesive that is added to the joint would obviously affect the integrity of the joint, as more adhesive would make the joint stronger, and if a shorter segment of the thinner drive cable was inserted into the thicker drive cable, it would take less load to pull the unit to failure.
I sought to mediate these two main causes of variability by:
- Standardizing the amount of adhesive used per unit using an EFD dispenser
- Ensuring that the same length of thinner drive cable is inserted into the thicker drive cable per unit
After running these two assembly modifications by my supervisor, she deemed the first point to be unnecessary for the purposes of these pull tests. Down the line, the amount of adhesive added to the joint will be regulated; this amount will be determined by R&D and added to the manufacturing GOI in the future. However, since the device is still in the very early stages of development, the data from these pull tests are preliminary, and I should just address this cause of variability in the pull test technical report. The second bullet was an issue that I could resolve without having to significantly modify or change any portion of assembly. I made sure the same amount of thinner drive cable was inserted into the thicker drive cable for each unit by measuring how much of the thinner drive cable remained after insertion- my coworker called this gap analysis. Hilary, the (awesome) girl who helps me with assembly on the production floor, was able to get about 0.4-0.5 cm of the thinner drive cable inserted for each unit. Now that the units are completed and a test method has been better delineated, I am excited to re-test and analyze the new data to determine if there is a significant difference in results between the two tests.
For this weekend’s expedition, we stayed super local (Escazú and San José). I know I said this the weekend that we went to Irazú Volcano, but that “local” trip was relative to all the excursions we had embarked on before that point. We took a short “hike” in Bebedero, which didn’t turn out to be anything like I expected. Most of our time was spent aimlessly walking up and down random hills on a very narrow, but car accessible, roads that took us past many residential homes. It was kind of strange to think that I was walking through this unknown neighborhood (with difficulty- realized I’m super out of shape) as an adventure with no clear destination, but I will say that even though there were some moments in which we definitely made the wrong move (getting barked at by three protective guard dogs, walking up a very swampy, bug-infested hill only to find someone’s goat/chicken farm, turning around from many dead ends), every move resulted in something that was worth it- incredible views, cute dogs, and cool road art. I feel like I’ve said “incredible views” or something similar in every blog post, but I mean it every time I say it. Our Costa Rican adventures have been nothing short of breathtaking!