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Gyroscopes and Navigation

Gyroscopes

 

Forces acting through the center of gravity of the gyroscope are known as translation forces and do not change the angle of the plane of rotation but move the gyroscope as a unit. Thus a spinning gyroscope may be moved freely in space by means of its supporting frame without disturbing the plane of rotation of the rotor.

 

Gyroscopic Forces

The gyroscope's axis, like that of a top, will tend to remain fixed in space, but if it is perturbed by an external force it will move or precess at a right angle to the force exerted. The resistance to precession is directly proportional to the gyroscope's angular momentum which is the product of its mass and its rate of rotation.

 

Displacement Gyro

Rate Gyro

 

Gyrocompass

 

The gyrocompass uses a spinning gyroscope, pre-set to point north (or any other desired bearing) and it will maintain this reference bearing no matter what manoeuvres the vehicle in which it is mounted may make. Unlike the magnetic compass the gyrocompass is immune to the affects of nearby magnetic (iron) structures which can cause inaccuracies in the bearings indicated by the pointer in a magnetic compass.

 

 

Accelerometers

 

Many devices for measuring acceleration have been developed. The mechanical device shown here uses gyroscopic forces to determine acceleration.

PIGA Gyro

The PIGA device is essentially a rate gyro, constrained by the electrical torque motor, used to measure acceleration and speed by integrating the acceleration over time. It is also used to measure distance travelled by integrating the speed over time. This second integration was initially accomplished by mechanical integrators but is now performed electronically.

 

Stabilised Platform and Inertial Navigation

 

Inertial navigation systems are based on a stabilised reference platform consisting of three orthogonal gyroscopes which maintain a fixed reference orientation in space, independent of any motion of the vehicle in which they are mounted. Using accelerometers such as the PIGA sensor above, or electronic sensors, coupled with integrators, the position in space and orientation of the vehicle can be determined.

 

The main advantage of the inertial navigation system is that it operates independently of signals from the ground. However it is a dead reckoning system with accumulating errors which increase as the duration or distance of travel increases.

 

 

 

 

 

 

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