PeriscopeFilm
11 HN recommenders · recommended in 17 months, 2018–2026
19:43 · 225K views · May 10, 2018
A 1953 US Navy training film on the basic mechanisms in fire control computers: shafts, gears, cams and differentials. It shows how these mechanical parts compute ship and target firing solutions.
HN treats it as the classic demonstration of how analog mechanical computation works, especially the differential gear section.
17 comments from Hacker News
Two gems (among many)... Periscope Films (on YouTube): [LINK] Digitized 40-60s era reels. It still amazes me how effectively they presented complex topics then. E.g. mechanical naval gunnery computers: this video And this on-the-ground movie on the Columbia student occupation in 1968: [LINK]
So I've known about slide-rules for a while. What I didn't realize was that the mechanical principles of slide-rules were applied to fire-control computers on WW2-era Battleships. [LINK] These computers had slide-rule like cylinders that would rotate. As you aimed the gun sights "at" a target, the gun's coordinates were being mapped to a cylinder, which would move the gun a different direction (you have to aim the gun "higher" the further away the target is, to account for gravity "drooping" the bullet). In effect; the weirdly shaped cylinder inside the fire-control computer is a pre-computed solution that maps x/y coordinate inputs to a z-coordinate output (where "z" would be fed into the gun's raw aiming system). The different parameters of the gun were programmed in with gears and cranks, moving the cylinder around physically. For more details, see: this video Its a 20-minute video. The cylinder mechanism (of 2x inputs mapped to 1x output) is specifically talked about here: this video . Carefully crafted cylinders could be any pre-computed 2-input / 1-output function. --------- Mechanical computers are fun. Slide rules are but the simplest kind. People were using more complicated "mechanical computers" for very serious combat / rangefinding / etc. systems just a few decades ago, before the advent of modern digital computers.
From top of head I really enjoy: MAPMAKING PROCESS, THE [LINK] mechanism computer of fire control computer (a classic) this video Physical science documentary series whose exact title I can't recall. It has been a while. To find more, my method is to do the occasional PeriscopeFilm binge (on youtube that digitizes a lot of old media, with great descriptions), always find find something interesting I haven't watched. If style, delivery really good, there's usually something in description to point to more. Like "U.S. NAVY TRAINING FILM", which usually returns playlists, and videos in same era often share quality. The technical ones generally don't disappoint. Another one is The Best Film Archives with good military training playlists. Tangent for others: the one I wish to remember, is a deleted/banned channel, one of the original US archival footage channel, with I think 1000s of videos, that got wiped many years ago right when youtube started drm crackdown. It had a companion website with obsessive amount of detail and tags to find the perfect video. And from what I recall, it didn't feel like a business like periscopefilm, but a passion project. It was an incredible amount of work to have been wiped out.
This could use a lot more visual aids. Here's a film that goes over a lot of the basics: "BASIC MECHANISMS IN FIRE CONTROL COMPUTERS" [1]. It's a 1953 US Navy instructional film explaining how mechanical fire control computers worked. These machines took inputs giving the speed and direction the ship was traveling, the speed and direction the target was moving, the distance and direction to the target, the wind speed and direction, and other factors, and computed how to aim the guns to shell the target. [1] this video
If you want more information on how you can do computation with mechanical systems, try this video: U.S. NAVY BASIC MECHANISMS OF FIRE CONTROL COMPUTERS MECHANICAL COMPUTER INSTRUCTIONAL FILM 27794 this video