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Awesome art project. Where did you get 53 years from? I think, for longevity as a design criteria, including the documentation including design files is the bes

• kragen 2y ago
  thanks! your ideas are mostly pretty good i agree that the machine should be fully self-describing, like darius bacon's 'book in itself'. of course, that won't help you if it won't turn on... rather than just conformal coating and seals, i'm thinking i'll not just conformally coat the boards, but also pot the whole assembly in something like silicone or toilet-ring wax, so that the potting material can be removed, but otherwise it's trivially ip68. except for the keyswitches, but the keyswitches can be a magnetic type that doesn't have any exposed electrical contacts or any springs solar-powered devices generally don't have to worry too much about cooling, though. or if they do it's from the heat they passively absorb from the sun, not from anything they dissipate internally. if your solar panels are 10% efficient (the best you can get out of amorphous silicon, which is the only kind that works under indoor lighting) and cover 30% of your device, they only harness 3% of the illuminance, which is later converted to heat in the circuitry. the other 97% is either reflected or converted into heat immediately. so the heat produced internally is only about 5% of the heat it has to deal with. now think about how much heat you feel on your skin from indoor illumination; we're talking about 5% of that socket-mounted chips tend to induce a lot of unreliability, so i don't favor them. desoldering surface-mount chips is a bit of a pain but still done routinely in cellphone repair shops around the world. but i want it to make it to its design lifetime without replacing components, and one reason for that is that i don't want to depend on the economy. (consider what components were commonplace in 01971 and how many of them are hard to obtain nowadays — and that was 53 years of relative peacetime. imagine trying to get parts today in moscow.) unlike batteries, chips do have a long shelf life, so you could conceivably stockpile chips today for future repairs. but if you're going to do that, probably the best place to stockpile them is on circuit boards inside the device, so you don't have to solder anything to fail over to them. that's not applicable for every device, but fortunately things like voltage regulators have very low failure rates, and you can still probably build in redundancy at a higher level. that's what we did when i worked on satellite systems: of n identical systems onboard, we only needed one to survive to run the satellite. there were even multiple power buses, so that even a failure that shorted a voltage rail to ground would only disable part of the satellite as i understand it (not having taken the measurements yet myself) over-rating is especially important for bypass capacitors in this context — not because they're prone to failure (unless you're using tantalums) but because capacitors have enormously higher leakage near their rated voltage if you want to build such a thing and have a mechanical charging option, i think a pullstring like 20th-century children's windup toys is the best option. it's compact, the spring constrains how much force you can apply to the generator and runs it at a predictable speed, and the pullstring grommet constrains the direction of force applied to the mechanism so that kofi annan can't break it by applying side-loading to your crank handle like he did with olpc. but i don't think electromechanical generators are likely to fit into the reliability budget for screws, i think protruding screws would catch on my pockets. but there are lots of ways to fasten things together in reopenable ways, especially if you don't need seals. if you did want to use conventional milled-head screws, well, i filed a flathead screwdriver out of a bolt a few months ago. i used a file, a vise, and a steel bolt. but exposed screws would tend to rust unless you made them out of titanium or something, which isn't an option for me a metal case has advantages and disadvantages. being able to take input power inductively (qi style) or communicate over rf could be useful, which you can't do with an all-metal case. metals are not very chemically stable, except for gold, silver, platinum, iridium, palladium, lead, nickel, aluminum, titanium, tin, and chromium. most of these have major disadvantages of their own, though titanium would be a pretty good option. many plastics are very chemically stable, including polypropylene, polyester terephthalate, silicones, and epoxy resins, and the epoxies in particular can be glass-fiber reinforced up to steel-like strengths and stiffnesses. so that was my plan why 53? i just like 53
  • contingencies 2y ago
    Pocketable wasn't in my mental spec, agree this is a good idea. You can also inset them. Marketing a portable as Kofi-proof is a neat marketing angle ;) Depending on your radio frequency perhaps you could put your RF behind your screen to get signal out, or use a slot as the antenna, or have a fold-out or telescopic antenna, or have a screw-on antenna port exposed when you open the thing, or some combination thereof. Aluminium's fine for cases, cheap, light, castable, extrudable, cheaply machined, and readily anodized. Steel won't rust for ages if it's of a decent chemistry and either treated and/or oil is used when the thread is mated. Even steel that appears heavily rusted after many decades of total abuse can be restored quite easily to a good state in many cases. I mean people had multi hundred year old wooden structures ... I don't think an embedded steel thread with an oil surface coating is going to disappear overnight. As a learning project I recently restored a 1980s drill press, that's basically 40 years old which is ~most of your target length, it had apparently been left with exposure to moisture for 20+ years, and was mostly intact. The net result of the learning was it's not worth restoring old drill presses, but I sure learned a lot! For maximum chip shelf life, you want to store them in nitrogen or some similar inert gas. With Wikipedia and survivalist content modules you could market this to the prepper crowd. Of course long distance radio would be an add-on. As would the radio direction finding hardware, encryption, etc. I still like the pneumatic idea. 100% of existing bicycle pump hardware becomes your viable charging interface. Speaking of which, a low profile wheel based generator would be a good add-on module.
    • kragen 2y ago
      those are good ideas about antennas i hadn't actually considered machining it out of an aluminum billet. you might be right that it would be adequately stiff, even if it's much less stiff than glass-fiber-reinforced epoxy. it's much heavier than epoxy, but only slightly heavier than glass, and of course most of its grades are enormously less brittle
    • kragen 2y ago
      oh, i don't know why i didn't answer the stuff about steel and preppers and pumps; maybe it was a brain fart or maybe you edited it in later. i'll try to answer later