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# Gyro

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basic gyro theory

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### Gyro

1. 1. By Lt NS Wickramasinghe Bsc (E & E Eng) hones
2. 2. 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.
3. 3. 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
4. 4. 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'.
5. 5. 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
6. 6. Z The point where the the three axis gyroscope intersects knows as point gyroscope suspension all of is of Y X X Y Z
7. 7.  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
8. 8.  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
9. 9. 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
10. 10.  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.
11. 11. 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.
12. 12. 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
13. 13. 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.
14. 14. 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
15. 15. 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
16. 16. 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
17. 17. 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
18. 18. Speed error Ballastic Deflection Error Quadrant error (rolling error) speed error, latitude error, ballistic deflection error, ballistic damping error, quadrantal error, and gimballing error
19. 19. 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
20. 20. 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
21. 21. 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