Retrotechtacular: Fire Control Computers In Navy Ships

October 28, 2014 by Kristina Panos 29 Comments

Here is a two-part Navy training film from 1953 that describes the inner workings of mechanical fire control computers. It covers seven mechanisms: shafts, gears, cams, differentials, component solvers, integrators, and multipliers, and does so in the well-executed fashion typical of the era.

Fire control systems depend on many factors that occur simultaneously, not the least of which are own ship’s speed and course, distance to a target, bearing, the target’s speed and course if not stationary, initial shell velocity, and wind speed and direction.

The mechanisms are introduced with a rack and pinion demonstration in two dimensions. Principally speaking, a shaft carries a value based on revolutions. From this, a system can be geared at different ratios.

Cams take this idea further, transferring a regular motion such as rotation to an irregular motion. They do so using a working surface as input and a follower as output. We are shown how cams change rotary motion to linear motion. While the simplest example is limited to a single revolution, additional revolutions can be obtained by extending the working surface. This is usually done with a ball in a groove.

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Using Echoes Of Light To Turn Walls Into Mirrors

June 23, 2014 by Mathieu Stephan 21 Comments

[Matthias] recently published a paper he worked on, in which he details how his group managed to reconstruct a hidden scene using a wall as a mirror in a reasonably priced manner. A modified time-of-flight camera (PMD CamBoard Nano) was used to precisely know when short bursts of light were coming back to its sensor. In the picture shown above the blue represents the camera’s field of view. The green box is the 1.5m*1.5m*2.0m scene of interest and we’re quite sure you already know that the source of illumination, a laser, is shown in red.

As you can guess, the main challenge in this experience was to figure out where the three-times reflected light hitting camera was coming from. As the laser needed to be synchronized with the camera’s exposure cycle it is very interesting to note that part of the challenge was to crack the latter open to sniff the correct signals. Illumination conditions have limited impact on their achieved tolerance of +-15cm.