GYRO

GYROBy Lt NS Wickramasinghe Bsc (E & E Eng) hones

True North and Magnetic North

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

True NorthMagnetic North

True NorthMagnetic North

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What is GyroGyro is an instrument used for finding the course of ship orcraft and also feeding the course data to various devices forcomputation purpose and for taking reference

Gyroscope 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'.

Three Degree of FreedomThe 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

YYZZXXThe point where the all the three axis of gyroscope intersects is knows as point of gyroscope suspensionPoint of Suspension

Properties of Gyro 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 turnedThe factors on which the gyroscopic inertia of a spinning body depends Its speed

Its mass

The distribution of the mass

Properties of Gyro 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 bodyThe effect of the external force applied to the gimbals rings of the gyroscope is experienced 90 ahead in the direction of rotation of gyroscope

Rules for Spinning BodyCurve 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

Geographic Grid

Directional Error in a Gyro mechanical drift Unbalance-The static balance of the gyro is upset when its center of gravity is not at the intersection of the three major axes

Bearing friction-Friction in the gimbals and rotor bearings results in loss of energy and incorrect gimbals positions

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 - Effect of the Earth's rotation due to angular motion and coriolis forces.

Viewpoint Out in Space

Viewpoint on Earth

Effect of Earth Rotation

Effect of Earth RotationThe 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 isthis 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.

Effect of Earth RotationWhen 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

Effect of Earth RotationAt 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.

Coriolis ForceDifferent parts of the face of the Earth are actually moving through space at different speeds.

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 hourA point on the equator of the Earth moves about 24,000 miles in 24 hours, or about 1000 mph.

The Gyroscope as a CompassThe 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

Effect of Weights on the Gyroscope

Vertical RingGyroSphereWeight WPhantomAssume external means provided to turn phantom so as to follow the Gyro in AzimuthSpinning VectorWeight ForceRotate Around Vertical AxisWeight W causes precession

Effect of weights on the gyroscopeThe free gyroscope has now become a gyrocompass, able to settle only on the meridian (pointing north) and level

W1, also causes the gyro to precess towards a more level position, which limits the effect of precession caused by weight WThe excursions from level continue, but the dampening effect of weight W1 causes each successive oscillation to be reducedThe only position of rest for the gyro axle is level and on the meridian.

Gyro ErrorsSpeed error

Ballastic Deflection Error

Quadrant error (rolling error)speed error, latitude error, ballistic deflection error, ballistic damping error, quadrantal error, and gimballing error

Speed errorThe magnitude of the speed error is dependent upon the speed, course, and latitude of the ship in which the compass is installedA

CANNB1000 kmph36kmph

Cosine of latitude Earth Radius

Ballistic Deflection ErrorD - True MeridianA - Direction of gyroscope axis at the end of maneuversDA

Initial CourseThis 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 errorThe 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 positionThis occurs due to the change in speed or course experienced by the gyrocompass following a constant straight course

Consider a ship following northward course at a speed V1 and then accelerates until the speed becomes V2. The acceleration exerts a force F, which is applied to the centre of gravity of the sensitive element and is directed opposite to the acceleration25

Quadrantal ErrorThis 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