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Cake day: April 13th, 2024

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  • Using G.657.A2 fiber you could get away with 7.5 mm bend radius, or 15 mm diameter, for the innermost layer of the spool. That’s around 5/8 inch for freedom units.

    But then again if you went that tight you’d need like 56’000 windings for 10 km. That sounds like a fuckton, and like we can’t ignore the outer diameter being larger.

    Approaching it from the other side: The fiber diameter with coating but without any mantle is 0.25 mm. If you want to put 10 km on a 100 mm long spool you could put in 400 layers lengthwise, and each layer would have to be a spiral of 25 m (of course you’d spool it outside in, not layer by layer, but should be mathematically similar enough). Using this spiral calculator and some random changing of the values it looks like an outer diameter of 91 mm (3 & 5/8 inch), and inner of 15 mm and a thinkness of 0.25 mm would work for a 25 m spiral.

    Or if we go for 125 mm drum length, so 500 layers, with 20 m each we get 82 mm (3 & 1/4 inch) outer diameter.

    Or if we go for 150 mm drum length, so 600 layers, with 16.7 m each we get 75 mm (3 inch) outer diameter.

    So yeah I think your estimate was pretty spot on, if the 10 km length is the right assumption.


  • Today’s wires aren’t actually wires, they are optical fibers. It must be G.652 or G.657 from telecom use, since that’s commercially available en masse. I think most likely would be G.657.A2 because that can be bent tighter. Here’s an example data sheet from a random google search. I wrote it in a different comment already, but the core has 9 micrometer, the cladding 125 micrometer and the coating 250 micrometer diameter. For telecom applications you’d add at least a mantle, or more likely use a cable with many fibers in little pastic tubes wrapped around a metal core for stability, 12 x 12 is fairly standard. Here of course it’s just a single fiber without mantle being spooled off.





  • Those news are already not so new any more. We’ve had reports of those two months ago.

    Since fiber optic wire guided missiles exist it’s not that much of a leap to think it should work with drones too, so long as the weight works out.

    Fiber is really really thin. 9 micrometer core diameter and 125 micrometer cladding diameter (incl core) and 250 micrometer coating diameter (incl core, cladding). The 10 km spools we use in our lab for network equipment testing are boxes of only like 20x20x10cm, and those aren’t optimized to be extra small with bend insensitive fiber. I can totally believe the 1.2-1.4 kg for 10 km in the article.

    Edit: leak -> leap