2021-10-25 7 min read


Notes, 2021-10-25.

Last week I disassembled my two year old iPhone 11 for the second time. The first time was about a month ago, when I replaced a damaged Lightning cable jack - a project that’s obscure enough that iFixit’s guide is just an embedded video from a prolific Russian YouTuber, and complicated enough that once I had glued the screen back on and powered the phone up, I discovered that I had left the wireless charging coil unplugged. From a functionality standpoint this was not exactly a deal breaker (my first wireless charging experience was just a week or two prior), but the mistake hurt my pride enough that I was convinced to double down on my repair effort, opening the phone back up to reconnect the charging coil and also replace the battery while I was at it.

The second repair went as planned; it was by any measure a success. And so I joined a rare class of dorks: those whose phones display a persistent and more or less meaningless Important Battery Message - a perpetual reminder of my transgression into iOS’s hardware ecosystem.

I’ll admit, the little notification badge definitely gets under my skin. But I also see it as a badge of honor - a sign that, if nothing else, I tried my best to make a useful tool last a little longer.

-Spencer Wright

The most clicked link from last week's issue (~13% of opens) was a video of an undulating nine-segment RC plane. In the Members' Slack, we've been chatting about the perfect EE workbench and scheming on a group project to make a custom pellet extruder capable of laying down 1 kg/hr.

Planning & Strategy.

Making & Manufacturing.

  • From Sheldon Brown et al, a good technical description of the “electro-forging” process that Schwinn used to make the iconic Varsity “ten speed” bike. Varsities came to life through true vertically integrated mass production: The entire frame was made from coils of 1010 steel strip, which was stamped, rolled, and welded together in a crude process that mimicked the appearance of a fillet brazed frame. “To produce a typical [electro-forged] frame joint, the ends of two tubular frame components were held nearly together and clamped in copper jaws, which acted as anodes and cathodes...Then a high electric current was applied across the two parts, jumping the small gap between them. The relatively thin edges of the tubes became molten and the two parts were pushed together by hydraulic rams, amid a shower of sparks. This left heavy slag around the joint...The actual welding took only a few seconds compared to several minutes to weld or braze each conventional joint.”

    Built in staggering quantities between 1960 and 1986, the Varsity remains ubiquitous - and widely reviled - today. Varsities are heavy, annoying to work on, and rarely well cared for. As Tom Shaddox later wrote, “for a quarter century the easiest way to show you were a sophisticated, discriminating cyclist has been to make disparaging remarks about the Schwinn Varsity.” And Schwinn’s strategic commitment to electro-forging, which required lots of engineering and up-front tooling costs, was probably a key factor in the company’s demise.

    Anyway: Before it became Schwinn’s albatross and the bane of bike mechanics in college towns everywhere, the Varsity was a good product. And I can’t help but appreciate the scale - and the production efficiency - that Schwinn aimed for during the Varsity years.
  • In the NYTimes, a sumptuous Christopher Payne photo essay from a roller skate factory. My favorite machine here is the swing arm clicker press, which uses dies to quickly cut parts out of sheets of leather. Old clicker presses like this Herman Schwabe 25 ton have an amazing look, but modern little presses like this 15 ton Tippmann are pretty neat too.
  • A somewhat odd product marketing video for Mesdan yarn splicers, which use a blast of compressed air to splice two pieces of overlapping thread or yarn.
  • In Stratechery (paywalled, sorry), an interesting point about Apple’s new Macbook Pro lineup: Now that Apple owns their own line of chips, they get to (have to?) sell a broader range of processor configurations so that they can utilize chips even when they contain a high number of defects. In other words, Apple is binning its processors and selling a different laptop configuration for each bin - “an interesting manifestation of how owning the whole widget means owning all of the complexity as well.”

    Related, my favorite binning link from the archives of this newsletter: The video of the LED binning process in the Inspection, Testing & Analysis section of 2019-10-07 ;)

Maintenance, Repair & Operations.

  • The White House’s location was selected by George Washington in 1791, but the building that we now know dates to the eighteen-teens, when it was rebuilt after having been burned during the war of 1812. In 1948, three years into Harry Truman’s presidency, its interior underwent “a comprehensive dismantling and rebuilding,” during which time Truman’s family and the entire executive apparatus was relocated across the street. Photos of the renovation are stunning, from the North Portico’s excavation, to the gutted second story oval study, to the cavernous interior filled with heavy construction equipment.
  • Another recent repair project of mine: A full teardown of a Shimano Alfine 11 internally geared hub, which had underwent multiple oil changes and cable adjustments and still slipped under load. The project did not result in a functional hub, but I *definitely* learned something about bikes - and made some realizations about how easy derailleurs are to service - in the process. I didn't document the project, but this old forum post shows a similar project.

Distribution & Logistics.

Inspection, Testing & Analysis.

  • Some *really* rad video footage of paper airplanes flying through a fog machine, creating perfect wingtip vortices. A form of turbulence, wingtip vortices produce induced drag, slowing airplanes (paper and otherwise) down. Today most modern airplanes have winglets - roughly vertical extensions on the end of the wings that reduce wingtip vortices and (as this NASA blog post describes it) “trick an aircraft’s wings into acting as though they were longer.”

    Winglets were conceptualized in the late 1800s by Frederick Lanchester, a British aerodynamicist and automotive engineer, but they didn’t gain popularity until the 1970s, when Dr. Richard Whitcomb, an engineer at NASA Langley, showed that they could produce fuel savings of between 6% and 9%. As described in this 2002 article from Boeing’s own (now defunct) Aero Magazine, winglets are now standard on the Boeing Business Jet, and are available as an option on 737s. Boeing sells them through a joint venture with Aviation Partners, which also has options for Gulfstream jets and is apparently working on loop-shaped winglets called Spiroids. Airbus offers similar options; this 🔥 2015 video of an A320neo wing being torn down and retrofitted gives a decent sense of how straightforward the upgrade (which takes ten days to complete) is. See also these partially exploded views of the winglet extensions that a company called Tamarack makes for Cessna CJs.

    Very tangentially related, and yes I know I’m like four years late on this: This America’s Cup AC75 technology overview video is wild; the Luna Rossa team goes into the engineering of their hydrofoil wings here.
  • A technical teardown video of the Tesla Model S Plaid battery, which contains 7,920 18650 lithium ion cells. After having taken apart a few battery packs myself, I’ve seen the electronic world as increasingly built upon 18650s, which are less space efficient than pouch cells (18650s look like extra large AA batteries and don't nest particularly well, whereas pouches can be kind of whatever size and shape you want) but are also cheaper per unit storage capacity and are less prone to being damaged than pouches.

    But the 18650 is not a fully standardized building block: Its dimensions (18 mm in diameter, 65 mm long) are more or less common across the industry, but cell chemistry, discharge properties, manufacturing tolerances and other features (18650s made for the consumer market can include micro USB ports and integrated charging circuits) vary from brand to brand. I suppose in this respect 18650s resemble gasoline, though to be fair there’s a hundred and twenty standards in ISO's committee on petroleum products and IEC's specs on rechargeable batteries (I'm aware of 61960 and 62133, though there may be others) are mostly focused on naming, overall dimensions, and safety.

    As a side note, someone in The Prepared’s Members’ Slack is looking for a good book on batteries; send any recommendations you’ve got here. Thanks also to Saket, Robert, Carl, Sebastian, Nathan, Michael, and Anthony for context on working with 18650s in The Prepared’s Members’ Slack.
  • Under the 1982 UN Convention on the Law of the Sea, territorial waters extend up to 12 nautical miles from a nation’s coast and are treated as sovereign territory. Outside of territorial waters are exclusive economic zones, which extend up to 200 nautical miles from the coastline and grant special exploration, resource extraction, and energy production rights. The US’s exclusive economic zone is the second largest in the world; it’s larger than the land area of all fifty states combined. And, NOAA says that 53% of it is unmapped.


  • The design of the “phone connector,” which you make know of as a “TRS/TRRS connector” or “¼ inch audio connector,” dates to 1877 🤯
  • The Capitol Hill Babysitting Co-op is a cooperative in Washington, DC that uses a form of currency called “scrip” to exchange babysitting responsibilities. Its economy has experienced a range of crises over the years (recession! liquidity trap!) and has been the topic of fairly serious study from macroeconomists.

From the Wikipedia page for circlips:

The term "Jesus clip" comes from the propensity of the clip's spring action to launch the clip at a high velocity when removing or installing, leading to remarks such as, "Oh Jesus, where did it go?"

NASA's guide to anthropometry and biomechanics.

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