The 1953 U.S. Navy training film (MN-6783a) Basic Mechanisms In Fire
Control Computers, Part 1: Shafts, Gears, Cams and Differentials
discusses some of the mechanisms that are required for the Fire Control
Computer to function. The film opens with a Navy crew surrounding a Fire
Control Computer (
00:48),
which solves fire control problems—including the ship’s location,
direction, speed, and the enemy ship’s location, direction, and speed—in
a matter of seconds so that the ship’s guns may fire accurately and
effectively. Though the computer processes the information in seconds,
it cannot do its job without the work of Navy men. Men operate the
director (
01:34), which provides target range and bearing information that is then entered into the computer (
01:38).
Part 1 of the film uses graphics to show the mechanical operations of
shafts, gears, cams, and differentials, all vital mechanisms inside the
computer (
02:20). Shafts are used to carry values throughout the computer, where a revolution of a shaft corresponds to a numerical value (
03:00). Gears are used to transfer values from one shaft to another (
04:30); different sizes in gears can change the value of the ratio of shafts for more complex computations. Cams (
04:55) are used as computing mechanisms in the computer. They have a working surface and a follower (
05:25;
07:25).
The film reviews the function of cams and the different types,
including a reciprocal cam, square cam, tangent cam, time of flight cam,
and barrel cam (
10:36). The latter is used to calculate trajectory for firing guns. Differentials (
12:50)
are the final mechanisms covered in Part 1. They are used in computers
to continuously obtain the algebraic sum of two quantities, keeping up
with the rapid changes of inputs of two quantities. A bevel gear
differential (
13:23)
is commonly used in Fire Control Computers. The film discusses how this
differential functions with its spider gears, spider shaft, and end
gears. Simplifying the concept of a bevel gear differential, the film
concludes with graphics that explain how the bevel gear differential
works using two racks and a pinion.
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