Construction of GYROSCOPE
- There is a thick wheel known as gyro wheel (which is made to rotate at high speed )
- It is mounted on a circular ring by its axil.
- To make the disc rotate in every direction 3 rings are used as shown in the above gif
- Basically, all the 3 discs are connected at 90 degrees, this allows a full 360 movement of a disc in any direction.
- It gives a 3-degree freedom which means
- It can spin on its axis .
- It can tilt about on its Horizontal plane .
- It can turn about its vertical axis .
PROPERTIES OF A FREE GYRO
1) rigidity of a space
when the disc is made to spin on its axis it is continuously pointing to a fix direction has the same direction as it was started it will not change the direction, although the supporting base is moved or tilted this unique property of a spinning free gyrascope is called rigidity of a space.
when the free gyroscope made to spin on its Axis it is continuously pointing to a fixed direction as the same direction as it was started. Assuming it is directed to a distance imaginary point in the space as referred to Cairo compass it is called gyrostar .
The axis of rotation has a tendency to turn at right angle to the direction of applied force.
1)Tilt -this is the angle by which the spin axis of gyro has apprently moved up and down from the horizontal plane.
2)Tilting- This is the apprent motion of gyro axel on the vertical plane. it may be upward and downward depending on factors which is causing it.
Rate of tilting per hour = 15 cos (latitude) * sin (azimuth).
3) Drift – This is the angle by which gyro axel has drifted and moved away from the original direction in the horizontal plane.
4) Drifting – This is the apparent motion of Gyro axel on the horizontal plane.
rate of drifting per hour = 15 *sin (Lat)
Operational errors of a gyrocompass
- Latitude error (Damping error or setting error).
- Course, Latitude & speed error (Steaming error).
- Ballistic Deflection
- Ballistic Tilt
- Rolling Error
- Inter Cardinal Rolling Error
- Rolling error
Gyro compass fitted on a ship also senses the accelerations present within the vessel at the time of rolling and pitching. The errors resulting due to that are known as rolling errors.
- Speed and latitude error
It is caused by force generated by a combination of Earth’s rotation and Ships movement.
- If the ship course is northerly the error is westerly and if the course is southerly the error is easterly.
- These errors are corrected by adjustment of latitude and speed corrector located on the gyroscope body.
- Ballistic deflection
This error occurs whenever the ship’s speed and the course is rapidly changed. If a vessel is going on N course and then changes its course by 90 degrees there will be a surge of mercury (Hg) from S part to N part ( As governed by Newton’s first law of motion).
How is the Gyro Compass System made North Seeking?
- In order to damp unwanted oscillation, we need to achieve damping in tilt.
- This is done by means of offset slightly to the east of vertical, resulting in
component of the same force producing the required torque.
- The magnitude and direction of this force is pre-calculated to achieve the required
- The amplitude of each oscillation is reduced to 1/3rd of previous oscillation.
- The spin axis reaches equilibrium and settles in a position at which drifting is
counteracted by control precession & the damping precession counteracts tilting.
- Finally, the gyro settles in the meridian & becomes north seeking.
Various Types of gyro-compasses used on Merchant Ships
- Admiralty Sperry type
- Arma Brown compass
Procedure starting and stopping of gyro compass and routine maintenance of gyro compass
Starting a Gyro Compass.
1) refer to the manufacturer’s manual and follow the procedure.
2)make a preparation of at least four hours before the compass is required for service
3) check that all supply switches are open
4) adjust the latitude and speed setting accordingly
5) Switch on an alternator and wait for 10 seconds until it gains full speed.
the compass will settle faster in Port then at sea also depends on how much the gyro axel was out of Meridian.
6) test the alarm switch on the alarm panel.
Stopping gyro compass.
1) open repeater switch.
2) open the azimuth motor switch.
3) switch off the alternator and lock the rotor.
1) check repeater with a master compass to ensure that repeater is functioning properly if Power fails repeater may have to be reset.
2) check the compass error by azimuth
3) speed and latitude characters should be reset as necessary
4) inspect the compass to guard against any abnormal condition of operation.
a) Check the alarm buzzer.
b) Clean and oil any part as indicated in the manufacturer’s manual.
c)General cleanliness should be checked repair and maintenance should only be carried out by a professional.