Chapter 4 - Gyroscopes Flashcards by Joseph Tidswell | Brainscape

Q

What are the categories of gyroscope?

A

Spinning gyroscope

Vibrating gyroscope

Optical gyroscope

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Q

Give two examples of optical gyroscopes.

A

Ring Laser Gyro

Fibre Optic Gyro

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Q

Note - Look up details of fibre optic gyros briefly in there’s time and if it might be needed.

A

At the end of the gyroscopes section in course manual.

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Q

What is the definition of inertia?

A

The resistance of an object to any change in its state of motion

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Q

What is the definition of momentum?

A

The product of an objects mass and velocity

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Q

What is the definition of angular velocity?

A

An object’s speed of rotation or spin

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Q

What is the definition of moment of inertia?

A

The product of the total mass of the spinning object and the moment arm (distance) from the spin axis that this mass is said to act

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Q

What is angular momentum?

A

The product of angular velocity and the moment of inertia, which defines the amount of force needed to oppose rotation

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Q

What is Conservation of Angular Momentum?

A

Angular momentum is the product of moment of inertia and angular velocity, if one increases the other decreases and vice versa to conserve the spinning object’s angular momentum.

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Q

What is Conservation of Angular Momentum?

A

Angular momentum is the product of moment of inertia and angular velocity, if one increases the other decreases and vice versa to conserve the spinning object’s angular momentum.

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Q

What is Conservation of Angular Momentum?

A

Angular momentum is the product of moment of inertia and angular velocity, if one increases the other decreases and vice versa to conserve the spinning object’s angular momentum.

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Q

What is Conservation of Angular Momentum?

A

Angular momentum is the product of moment of inertia and angular velocity, if one increases the other decreases and vice versa to conserve the spinning object’s angular momentum.

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Q

What is Conservation of Angular Momentum?

A

Angular momentum is the product of moment of inertia and angular velocity, if one increases the other decreases and vice versa to conserve the spinning object’s angular momentum.

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Q

What is Conservation of Angular Momentum?

A

Angular momentum is the product of moment of inertia and angular velocity, if one increases the other decreases and vice versa to conserve the spinning object’s angular momentum.

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Q

What is the first law of gyrodynamics?

A

If a rotating body is free to move in any axis through its centre of mass, then its spin axis will remain fixed in inertial space.

Expresses the gyroscopic property of RIGIDITY

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Q

What is the second law of gyrodynamics?

A

If a constant Torque is applied about an axis perpendicular to an unconstrained, symmetrical object’s spin axis, then the spin axis will precess steadily about an axis mutually perpendicular to both the spin axis and torque axis.

PRECESSION

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Q

What is secondary precession?

A

Can only occur if a gyro is already processing.

Occurs if another torque is applied, resulting in the gyro continuing to precess in the same direction.

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Q

What are the classifications of spinning gyroscope?

A

Rate gyroscope

Rate-integrating gyroscope

Displacement gyroscope

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Q

What do Rate gyroscopes measure?

A

The rate of Angular Displacement of a vehicle.

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Q

What do Rate-integrating gyroscopes measure?

A

The integral of an input with respect to time.

Q

What do Displacement gyroscopes measure?

A

Angular Displacement from a known datum.

Q

Explain what a rate gyroscope is?

A

A spinning gyroscope constrained with a SINGLE DEGREE OF FREEDOM.

Works using precession.

Q

Explain how a Displacement gyroscope works.

A

Has AT LEAST TWO DoF about its spin axis.

Allows the inertial axis to remain as a fixed inertial reference due to RIGIDITY.

Spin axis VERTICAL TO EARTH’S SURFACE = AI

Spin axis HORIZONTAL TO EARTH’S SURFACE = HSI

Q

Explain how a Rate-integrating gyroscope works.

A

One (or two?) degrees of freedom, using viscous restraint to damp the precessional rotation about the output axis.

Similar to a rate gyroscope but uses a viscous fluid as a restraint instead of springs. Aka a floating gyro.

Q

What errors can affect gyroscopes?

A

Wander - Real Wander or Apparent Wander

Real Wander - Real Drift or Real Topple

Apparent Wander - Apparent Drift or Apparent Topple

Gimbal Error - Gimbal lock

Q

What is the cause of real wander?

A

Imperfections in the gyroscope mechanism

Q

What causes apparent wander?

A

The rotation of the Earth or transportation of the gyroscope from one point on Earth to another can give an indication of apparent wander with regards to the Earth’s surface, even though the gyroscope’s actual orientation remains fixed in inertial space.

Q

What are the two components wander can be resolved into?

A

Drift

Topple

Q

What is Drift?

A

Wander of the spin axis in the horizontal plane.

Q

What is Topple?

A

Wander of the spin axis in the vertical plane.

Q

How can apparent wander be corrected?

A

Apparent wander varies predictably, so can be corrected for by causing the gyroscope to precess at a rate nullifying the apparent wander for a given latitude.

Q

Where is apparent wander greatest for a gyro with its spin axis horizontal to Earth’s surface (e.g. HSI)?

A

At the poles

Q

Where is apparent wander greatest for a gyro with its spin axis vertical to Earth’s surface (e.g. AIs)?

A

At the equator

Q

How can topple be corrected/compensated for?

A

Gravity sensitive switch

Synchro case levelling device:

Senses movements away from vertical
Sends appropriate signals to a torque motor until the vertical is re-established

Q

What causes gimbal lock?

A

When the gimbal orientation is such that the spin axis becomes coincident with an axis of freedom.

When the gyro has lost one of its degrees of freedom and two axis’ aligned on the same axis.

Often caused by sudden/violent manoeuvres, particularly sudden pull ups into a climb.

Q

What is the main problem with gimbal lock?

A

Any attempted movement of the lost axis will result in REAL Wander.

Ability to measure direction in one axis is lost.

Q

How can we solve the problem of gimbal lock?

A

Use a motor to keep a fourth outer gimbal spinning constantly to counteract the tendency of the three ring system to lock.

Q

What type of gyroscope does the military use in modern strapdown INS systems and AHRS?

A

RLG - Ring Laser Gyroscope

Q

What gas fills the chamber of a RLG?

A

Inert gas - typically a mixture of Helium and Neon

Q

How does a RLG work?

A

Chamber filled with inert gas experiences a DC electrical discharge to ionise the gas and cause a lasing action.

Two beams of light produced in the cathode, flowing in opposite directions.

Mirrors are used to REFLECT the beams around the enclosed area.

If rotating about an axis, one beam will appear to speed up and the other will appear to slow down.

This leads to a phase shift between the two beams of light, the ‘SAGNAC Effect’.

A readout detector will detect this shift and calculate the angular velocity and acceleration about the defined axis. No moving parts + very accurate.

Q

What is the Sagnac Effect?

A

A frequency shift between two beams of light from the same source.

The frequency shift is directly proportional the the rotation rate of the ‘ring’ about which the beams of light travel.

Q

What are the advantages of a RLG?

A

Almost no ‘spin up time’

Performance is unaffected by high ‘g’

No moving parts, therefore high reliability + low maintenance requirements

Wide dynamic range

Very SMALL drift rates

Q

What are the disadvantages of a RLG?

A

Precision machining and polishing

Costly production of high quality mirrors and optical seals

Requires a carefully balanced mix of Helium and Neon, free of contaminants

Q

What is a FOG and what principle does it work on?

A

Fibre Optic Gyroscope

Sagnac Effect

Q

What is the advantage of a FOG and why/when might it be used?

A

Cheaper and more efficient (to produce) alternative to RLGs.

Useful in aircraft INS and AHRS, but particularly good for missile INS and AHRS where it is destined to be destroyed, saves destroying an expensive and more complex RLG.

Q

Note - Learn the FOG diagram in book

A

Learn now

Q

How does a Vibrating Structure Gyro work?

A

Uses a vibrating structure to determine the rate of rotation.

A vibrating object tends to continue vibrating in the same inertial plane, even if its support platform rotates.

The Coriolis Effect causes the vibrating structure, when rotated, to exert a force on its support.

By measuring this force, the rate of rotation can be determined.

Q

What is another name for a Vibrating Structure Gyro?

A

Coriolis Vibratory Gyro (CVG)

Q

What are some applications of Vibrating Structure gyros (aka CVG)?

A

Aircraft AHRS and AFCS (Automatic Flight Control System)

Mobile device orientation

Drone auto stabilisation and control

Self-driving cars

Image stabilisation