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Page Title: Figure 4-11.--A. Simple gyroscope. B. Modified gyroscope.
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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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