Figure 4-11.--A. Simple gyroscope. B. Modified gyroscope.

Figure 4-11.--A. Simple gyroscope. B. Modified gyroscope.

how we use the apparent rotation of the gyro rotor to

between the simple base and the phantom is that the

phantom is turned by a servomechanism to follow the

make the modified gyroscope north-seeking. In figure

horizontal plane of the rotor's axle, while the simple

4-12, point A, the gyro axle is parallel to the earth's

base remains fixed in its position. The phantom ring

surface; however, as the earth rotates, the earth rate

allows the outer gimbal (vertical ring) (fig. 4-11, view

effect causes the gyro rotor axle to tilt in relation to the

A) the freedom to turn and to tilt. These modifications

earth's surface, and the weight that we attached to the

enable the gyroscope to maintain its plane of rotation as

bottom of the vertical ring now applies a force to the

long as it spins and nothing touches it. We have modified

bottom of the gyro. As we discussed earlier, precession

the basic suspension system to enable us to convert the

occurs in the direction of rotation, but 90 away from

gyroscop to a gyrocompass. Now, we must make it seek

the point of application; therefore, the weight applies a

out and point to true north.

force to the bottom of the gyro but is felt about its

For the purposes of this explanation, true north is

horizontal axis, which causes the gyro to turn. As the

the direction along the meridian from the point of

gyro turns, the phantom follows the rotor axle. As you

observation to the North Pole.

follow the gyro through one rotation on the earth's

surface, you can see that the gyro rotor follows an

To become a gyrocompass, a gyro must be modified

elliptical path around the meridian. It actually points

so it can

north twice in the ellipse; in other words, it has become

1. align its axis on the meridian plane,

north-seeking. The period of oscillation is actually much

less than the 24 hours required of an unmodified gyro;

2. align its axis nearly horizontal, and

the actual time is determined by the speed and weight

3. maintain its alignment both horizontally and on

of the rotor and the size of the pendulous weight. The

the meridian, once it is attained.

next step, logically, is to make the north-seeking

gyroscope north-indicating.

In figure 4-11, view B, a weight (pendulous weight)

has been added to the bottom of the vertical ring, which

As you have seen, we made the gyroscope

makes it bottom heavy, or pendulous. The weight exerts

north-seeking by adding a pendulous weight, which

a force on the gyro whenever the rotor is not level with

caused the gyroscope to oscillate about north. To make

the earth's surface.

it north-indicating, we must somehow dampen these

oscillations. To do this, we must add another smaller

In previous discussion, we talked about precession

weight, Wz, on the cast side of the rotor. Both weights,

and vertical and horizontal earth rates. Now, we will see

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