site: reviews — Kawran Bazar, Elevators, Cycloidal Gearbox (graduate from finds)

src/content/find/2026/08/cycloidal-gearbox/index.mdx

@@ -6,6 +6,7 @@ shortlist: true
 link: "https://github.com/tom-ilan/cycloidal_gearbox"
 linkText: "GitHub"
 source: "Hacker News — Show HN"
+promotedTo: cycloidal-gearbox
 topics: [gadgets-and-toys, learning-and-reference]
 tags: [3d-printing, cad, open-source, engineering]
 description: "Three versions of a 3D-printed cycloidal drive — including the failed one — plus the Fusion 360 script that generates the tooth profile from scratch."

src/content/find/2026/08/elevators/index.mdx

@@ -6,9 +6,10 @@ shortlist: true
 link: "https://john.fun/elevators"
 linkText: "john.fun"
 source: "Hacker News — Show HN"
+promotedTo: elevators
 topics: [web-tools, learning-and-reference]
 tags: [interactive, algorithms, explainer, free]
 description: "An interactive explainer on elevator scheduling — SCAN, LOOK and multi-car dispatch, all running live in the page at up to 25× speed."
 ---
 
-The SCAN algorithm was patented in 1961: ride to the top, reverse, collect everyone on the way down. LOOK stops at the highest floor actually requested, which is the behaviour you already expect from a lift. Both run live in the page at 1×, 5× or 25×, and a button drops five fresh calls into the shafts so you can watch the assign-it-to-the-nearest-car rule come apart in front of you.
+The piece dates SCAN to a 1961 patent: ride to the top, reverse, collect everyone on the way down. LOOK stops at the highest floor actually requested, which is the behaviour you already expect from a lift. Both run live in the page at 1×, 5× or 25×, and a button drops five fresh calls into the shafts so you can watch the assign-it-to-the-nearest-car rule come apart in front of you.

src/content/find/2026/08/kawran-bazar/index.mdx

@@ -6,6 +6,7 @@ shortlist: true
 link: "https://www.atlasobscura.com/places/kawran-bazar"
 linkText: "Atlas Obscura"
 source: "Atlas Obscura"
+promotedTo: kawran-bazar
 topics: [travel-and-places, food-and-drink]
 tags: [markets, dhaka, night, street-food]
 description: "Dhaka's central wholesale market runs hardest in the middle of the night and has vanished by mid-morning, when the same block turns back into a business district."

src/content/reviews/cycloidal-gearbox/index.mdx

@@ -0,0 +1,30 @@
+---
+name: "Cycloidal Gearbox"
+subtitle: "A fifteen-year-old's 3D-printed 1:9 drive, published with the version that failed and the numbers that prove it"
+date: 2026-08-02
+category: making
+topics: [gadgets-and-toys, learning-and-reference]
+tags: [3d-printing, cad, open-source, engineering, fusion-360]
+link: "https://github.com/tom-ilan/cycloidal_gearbox"
+linkText: "GitHub"
+description: "Three iterations of a printed cycloidal drive for a NEMA 17, with measured torque and efficiency, plus a Fusion 360 script that generates the rotor profile for any ratio."
+source: "Hacker News — Show HN"
+fromFind: "cycloidal-gearbox"
+---
+
+import { Image } from 'astro:assets';
+import hero from './hero.png';
+
+<Image src={hero} alt="A CAD render of the open gearbox seen from above: a yellow nine-lobed cycloidal rotor with a ring of output holes sits inside a black cylindrical housing lined with ten pins, a bearing at the centre, a stepper motor just visible underneath." />
+
+> A printed cycloidal drive that turns a NEMA 17's 0.21 N·m into 1.28 N·m, documented with the ratio, the tolerances, the measured efficiency, and the version that did not work.
+
+Most published maker projects show you the one that worked. This repository is organised around three versions, and the second one is a failure kept on purpose: a micro cycloidal drive shrunk to the same footprint as the stepper driving it, which a 3D printer could not hold to the tolerances a small cycloidal drive needs. Version three gives up the footprint, gets the clearances it wants, and runs.
+
+The specification is unusually complete for a project posted by a teenager on a Saturday. **1:9 reduction from ten housing pins and a nine-lobed rotor. 90mm outer diameter. PLA. Four M3×8 screws and two 6704 bearings. A +0.15mm profile offset applied all round for print clearance.** And then the part almost nobody publishes: measured output torque of 1.28 N·m against the bare motor's 0.21 N·m, with an efficiency of 66 percent — that is, a ninefold reduction delivering about six times the torque, and the missing third accounted for rather than quietly rounded away.
+
+The gearbox is the demonstration; the tool is the point. The repository's real payload is a Python script that generates the rotor profile from first principles — pins, pitch radius, eccentricity, outer pin radius — with the geometric constraints enforced rather than assumed, including a check against the undercut limit. Change the pin count and you get a different ratio, since the reduction is simply one to *N* minus one. It is derived from a published SOLIDWORKS walkthrough and reimplemented as a parametric generator, which is the honest and more useful version of "I followed a tutorial."
+
+**Two things to know before you clone it.** The generator runs as a Fusion 360 script, launched from Scripts and Add-Ins — so no Fusion, no generator, and the CAD in `cad_models/` is what you get. And this is a printed PLA demonstrator: 1.28 N·m is a real number for a printed part and not a number to design a robot arm around. The author says as much between the lines, listing the upgrades that would change it — MR128 bearings in place of the plain housing pins to cut friction, M2 screws with metal sleeves for the output pins.
+
+What lifts it above a nice print is the discipline. A ratio, a tolerance, a torque figure with an error bar, and a failed version left standing where it can be learned from.

src/content/reviews/elevators/index.mdx

@@ -0,0 +1,32 @@
+---
+name: "Elevators"
+subtitle: "An interactive case that the fancy elevator kiosk is making you wait longer"
+date: 2026-08-02
+category: learning
+topics: [web-tools, learning-and-reference]
+tags: [interactive, algorithms, explainer, free, simulation]
+link: "https://john.fun/elevators"
+linkText: "john.fun"
+description: "A browser explainer that simulates elevator dispatch — SCAN, LOOK, Otis RSR and destination dispatch — and shows the destination-dispatch kiosk usually losing to plain up and down buttons."
+source: "Hacker News — Show HN"
+fromFind: "elevators"
+---
+
+import { Image } from 'astro:assets';
+import hero from './hero.png';
+
+<Image src={hero} alt="A schematic of six elevator shafts drawn on pale graph paper, floors numbered one to four, with dark blue cars sitting at different levels and small orange dots marking waiting calls inside them." />
+
+> Every algorithm in this piece runs live on the page, which is how it gets away with an argument you would not otherwise believe: the destination-dispatch kiosk in the smart building is probably making your wait worse.
+
+The find sold this short. SCAN and LOOK — go to the top and reverse, versus go only as high as anyone asked — are the first two paragraphs. What follows is applied statistics with the simulator wired into every claim.
+
+It starts by refusing the obvious metric. Nobody remembers their average wait; they remember the morning the lift took forever. So the piece works in **p50 and p90**, and shows both moving with traffic shape — the morning rush upward from the lobby, the evening flip, the lunch mix, interfloor. Morning is the worst, and you can watch it be the worst.
+
+Then it builds up Otis's **RSR** dispatcher, which scores every car for every call: time to reach you, plus a penalty for how loaded it already is, plus an anti-bunching penalty if another car is already heading to your floor in the same direction, minus bonuses for matching your direction, sitting idle within two floors, and running light. Crucially, RSR re-optimises every five seconds — the car coming for you can be swapped for a different car mid-journey.
+
+Two results earn the whole thing. First, **RSR does not always win**: at high traffic, when every car is full and stopping everywhere anyway, plain LOOK catches up and passes it, and LOOK also does better in small buildings with few cars per bank. Second, **destination dispatch — the kiosk that assigns you a car before you board — is generally worse**, and the reason is exactly the five-second re-optimisation it gives up. Telling the system where everyone is going sounds like more information; committing each passenger to one car is less flexibility, and the flexibility is worth more. Only very tall buildings with eight-plus cars per bank flip it back.
+
+**One date to treat carefully.** The piece opens by dating SCAN to a 1961 patent; Wikipedia's treatment of the elevator algorithm names no patent and puts the earliest published description in Knuth. The 1961 thread leads somewhere better anyway: to Leo Port, an Australian engineer credited with conceiving destination dispatch, who died in 1978 — decades before anyone built one, and remembered for the idea this article spends its last section dismantling.
+
+It ends with the full simulator — floors, cars, flow rate, all three algorithms, histogram on — and the only correct closing line: the elevator did hear you, it just has a lot to think about.

src/content/reviews/kawran-bazar/index.mdx

@@ -0,0 +1,30 @@
+---
+name: "Kawran Bazar"
+subtitle: "Dhaka's wholesale market runs hardest at 2am — and the city has been trying to move it since 2024"
+date: 2026-08-02
+category: places
+topics: [travel-and-places, food-and-drink]
+tags: [markets, dhaka, night, street-food, bangladesh]
+link: "https://www.atlasobscura.com/places/kawran-bazar"
+linkText: "Atlas Obscura"
+description: "A wholesale market in central Dhaka that peaks in the small hours, empties by mid-morning into a district of newspaper offices, and is under a relocation order a visitor should check before going."
+source: "Atlas Obscura"
+fromFind: "kawran-bazar"
+---
+
+import { Image } from 'astro:assets';
+import hero from './hero.jpg';
+
+<Image src={hero} alt="Traders working by lamplight at Karwan Bazar at night: two men crouched over a spread of onions tipped from a red mesh sack, a caged electric fan running beside them, a woven basket of onions and two brass scale pans with chains in the foreground." />
+
+> A wholesale market in the middle of Dhaka that does its real business between midnight and dawn, then disappears by lunchtime — and that the city corporation has been trying to relocate since 2024.
+
+Most markets you visit are performing for you. Kawran Bazar is not open late for anyone's benefit; it is open late because that is when a city of twenty million gets its vegetables. Trucks arrive in the dark, fruit goes to auction at two in the morning, fish are descaled by hand, and the meat section keeps livestock that is slaughtered on purchase. By mid-morning the whole apparatus is gone and the same blocks are a business district — the head offices of *Prothom Alo*, *The Daily Star*, and four television channels, plus a hospital, a mall and a university campus.
+
+The detail that stays with people is the railway. Tracks run alongside part of the bazar, and traders lay their goods out across them, then lift everything clear each time a train comes through and put it back after. It is not a stunt; it is the rent being paid on the only flat, empty ground available.
+
+**One number in the popular description does not check out, and it is the headline one.** The claim that the market handles 57 percent of Dhaka's daily vegetable supply is offered by Atlas Obscura itself as coming from "one source," and no reference work reachable from here carries it. What *is* documented is more concrete anyway: as of 2024 the Dhaka North City Corporation counted four markets on the site across roughly 24 bighas, 1,789 permanent shops and 180 temporary ones, turning over about 50 million taka a day.
+
+The history is close but not exact either. The market is named for Karwan Singh — a Marwari trader who came to Dhaka in the early years of British rule in Bengal and set up a market here in the late eighteenth century — though there was trade on the site well before that.
+
+**And then the caveat that decides whether the trip is worth taking.** Since March 2024 the city has been relocating Karwan Bazar to Gabtoli: the corporation's own regional office moved out first, then shops from a building declared unsafe. Bangladesh has been announcing this move for decades and has never finished it, which is why the market was still being written about as fully operational in mid-2026 — but it means the honest advice is to check what is actually trading before booking a 2am rickshaw. Go for the hour, not the guidebook entry.