Path: SC/Sensor
% Models a gyro.
Input is a data structure with, at a minimum,
input.type 'hrg default' (for a default Hemispherical Resonating Gyro)
input.u eye(3) (for three orthogonal gyros)
You may fill in the rest of the data structure or use the built in defaults.
Optical and other solid-state gyros have the equations
dangle/dt = w + b + d.angleRandomWalk1Sigma*randn
db/dt = -d.beta*b + d.biasRandomWalk1Sigma *randn
y = angle + d.outputNoise1Sigma *randn
c = fix(d.scaleFactor*y/d.lSB)
Mechanical gyros have the equation terms in the output equation
y = (d.forwardGain/d.damping)(d.angularMomentum*angle
- d.torqueRebalanceGain*z)
+ d.outputNoise1Sigma*randn
and the additional state
dz/dt = y;
where beta is the correlation time constant for the bias drift.
On initialization, the scale factor and bias are set using
d.scaleFactor = d.scaleFactor + d.scaleFactor1Sigma*randn
d.bias = d.bias1Sigma*randn
Valid types are:
hrg default
fog default
Mechanical RIG default
Mechanical RG default
For failures the input is the index of the failed gyro.
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Form:
output = Gyro( action, input )
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Arguments
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action (1,:) Action
action is 'initialize'
input (1,1) Data structure
.type (1,:) Same as input string described above
.u (3,n) Unit vectors for the gyros
.lSB (1) LSB for the gyros (quantization)
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References: Farrenkopf, R.L., (1974). Generalized Results for
Precision Attitude Reference Systems Using Gyros.
AIAA Paper 74-903.
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SC: Attitude/RW2SDev SC: Sensor/Counter
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