1. Magnetic compasses indicate magnetic north using the Earth's magnetic field, while gyro compasses indicate true north by measuring the Earth's rotation and are unaffected by magnetic fields. 2. A gyroscope maintains its orientation in space regardless of movement by relying on the principle of gyroscopic inertia. It has three degrees of freedom and its orientation remains fixed due to precession caused by external torques. 3. Errors in gyrocompasses like speed error and ballistic deflection error occur due to the Earth's rotation and changes in a ship's speed or course, but can be compensated for through electrical adjustments and a dual rotor design.

1. By Lt NS Wickramasinghe Bsc (E & E Eng) hones

3. True North
Magnetic North
Compasses are instruments for
indicating the direction of
the
North. They fall in two main
categories.
Magnetic Compasses which are controlled by the
earth's magnetic field and indicate the direction
of magnetic north.
The Navigator onboard ship has these
instruments to determine his center.
two
True North
Magnetic
North
Gyro Compasses which are
controlled by the rotation of
the
earth
and
indicate
the direction of true North.

4. Gyro is an instrument used for
finding the course of ship or
craft and also feeding the
course
data
to
various
devices for
computation purpose and for
taking reference

5. A Gyroscope is a well defined
balanced rotor, spinning at a high
speed, and mounted so as to
posses
three
degrees
of
freedom.
Only the center of gravity of
the rotor is fixed, the rotor
itself being free to move in
any direction
about this
point, such a gyroscope is
referred to as a `Free Gyro'.

6. The three degrees of freedom consist
the ability of the rotor
 to spin about the spin axis
-X
 to tilt about the horizontal axis - Y
 to turn about the vertical axis
-Z

7. Z
The point where the
the
three
axis
gyroscope intersects
knows
as
point
gyroscope suspension
all
of
is
of
Y
X
X
Y
Z

8. 
Gyroscopic inertia or rigidity in space
property
of
a
free
gyroscope which causes it to
maintain its direction regardless of
how the supporting frame is tilted
or turned
The factors on which the gyroscopic
inertia of a spinning body depends

Its speed

Its mass

The distribution of the mass

9. 
Precession
The precession is associated only
with spinning bodies and is the resultant
motion due to a couple or torque being
supplied to such a body
The effect of the external force
applied to the gimbals rings of the
gyroscope is experienced 90 ahead in
the direction of rotation of gyroscope

10. Curve the fingers of your right hand in the
direction in which the rotor is turning as if
you intended to grasp the rotor. Your thumb
will point in the direction of the spin vector
Arrange the thumb, forefinger, and middle
finger of your right hand mutually
perpendicular to each then thumb points in
the direction of the precession vector, your
middle finger points in the direction of the
torque vector, and your forefinger points in
the direction of the spin vector

12. 
mechanical drift


Bearing friction -Friction in the gimbals and rotor
in loss of energy and incorrect gimbals positions


Unbalance
-The static balance of the gyro is upset
when
its center of gravity is not at the intersection of
the three major axes
Inertia of gimbals -Energy is lost whenever a gimbals rotates because
of the inertia of the gimbals and greater the mass of the gimbals, the
greater the drift
apparent drift
bearings results
- Effect of the Earth's rotation due to angular motion
and coriolis forces.

16. The spin axis of a gyro
remains aligned with a
fixed point in space,
while your plane of
reference
changes,
making it appear that
the spin axis has moved
Apparent precession is
this apparent movement
of the gyro spin axis
from its initial alignment
further it calls vertical
earth rate. It varies as
per the Sine value of
latitude.

17. When a gyro is placed at equator and observed from earth, the gyro
appears to rotate about its horizontal axis, but in opposite direction
to the rotation of earth, this effect or feeling is known as Horizontal
Earth Rate It varies as per the Cosine value of latitude

18. At points between the poles
and the equator the gyro
appears to turn partly about
the horizontal axis and partly
about the vertical, because it is
affected by both the horizontal
component and the vertical
component of the earth's
rotation.
The
horizontal
component of the earth's
rotation causes the north end
of the axle to rise. The vertical
component causes it to turn to
the east.

19. Different parts of the
face of the Earth are
actually
moving
through
space
at
different speeds.
A point on the equator of
the Earth moves about
24,000 miles in 24 hours, or
about 1000 mph.
On the other hand, a piece of
ground 4 feet from the North Pole
moves only 24 feet in 24 hours
about speed of 1 foot per hour

20. The first stage in
making
gyroscope
a
gyrocompass is
to make the gyro
seek
the
meridian. To do
this, a weight W
is added to the
bottom of the
vertical ring and
W1 to the sphere

21. Vertical Ring
Gyro
Sphere
Rotate Around
Vertical Axis
Spinning
Vector
Weight W
Phantom
Weight
Force
Assume external
means provided to
turn phantom so as to
follow the Gyro in
Azimuth
Weight W causes precession

22. W1, also causes the gyro to precess towards a more level position, which
limits the effect of precession caused by weight W
The excursions from level continue, but the
dampening effect of weight W1 causes each
successive oscillation to be reduced
The only position of rest for the gyro
axle is level and on the meridian.
The free gyroscope has now become a gyrocompass, able to settle only
on the meridian (pointing north) and level

23. Speed error
Ballastic Deflection Error
Quadrant error (rolling error)
speed error, latitude error, ballistic deflection error, ballistic damping error,
quadrantal error, and gimballing error

24. The magnitude of the speed error is dependent upon the speed, course,
and latitude of the ship in which the compass is installed
N’
N
Cosine of latitude
θ
36kmph
A’
A
Earth Radius
C
B
1000 kmph

25. This occurs due to the change in speed or course experienced by the
gyrocompass following a constant straight course
A
A - Direction of
gyroscope axis at
the end of maneuvers
This will occur the time
for change of course is
less than 2 minutes
This will take 1.5 to 2
hours to die out this
error
D
D - True Meridian
The ballistic deflection error is
electrically
prevented
in
the
gyrocompass by varying the speed of
the gyro rotors in accordance with the
cosine of the latitude of the vessel's
position
Initial Course

26. This error occurs due to the rolling of the ship
This error is compensated by the use of two rotors in a single sensitive
element. In this way, swinging of the compass in the east and west
direction is prevented, giving both east and west stabilization as
well as north and south