Figure 10-31.--Schematic drawing symbol for a differential.

designed to drive heavy loads. The outputs from such

differential (as is illustrated in fig. 10-30). Whichever

mechanisms often merely control the action of

proves the most convenient mechanically may be

used.

servomotors. The motors do the actual driving of the

loads to be handled. The device that makes it possible

for the comparatively weak output from a computing

BASIC COMPUTER

mechanism to control the action of a servomotor

MECHANISMS

is called a follow-up control. In this device, the

differential is used to measure the difference, or error,

So far, we have discussed the various gears and

in position between the input and the output. The input

what they can accomplish, and the gear differential,

is geared to one side of the differential. The servo

which is a simple analog computer. Next, we will

output is used to do two things: (1) to position

discuss basic computer mechanisms. As in all

whatever mechanism is being handled, and (2) to drive

complex machines, focus on the simple mechanisms

that comprise the complex machine. An understanding

of the simple mechanisms will enable you to

understand how they enable the complex machine to

perform its function.

The differentials used in analog computers are

gear differentials similar to those we discussed

previously, unlike the automotive differential, which

receives two inputs and combines them to provide a

single output. Most differentials used in computers

are quite small, between 2 inches x 2 1/2 inches in

size, and are designed for relatively light loads. Fig-

ure 10-31 illustrates the symbol used to indicate the

differential in schematic drawings.

Figure 10-32 shows one of the many applications

of the gear differential in a computer. In this case, the

differential is being used as an integral part of a

Figure 10-31.--Schematic drawing symbol for a differential.

follow-up control. Computing mechanisms are not

Figure 10-30.--Differentia1 hookups.

10-16