Dear Rob,
Sorry to take a time to reply, but I don't usually browse 'Tech Forums' as much as 'Wannabes'.
Types of Gyro. There are 2 types of gyro (3, if you include the Rate Integrating as a separate type). These are:
Displacement Gyro. Used in DGI and Art Horizon. Measures displacement from an initial datum. Output is in degrees.
Rate Gyro. Used in Turn Indicator. Measures instantaneous angular rate. Output is in degrees/second.
Rate Integrating Gyros, which are most often used in INS, are sometimes treated as a separate case, but are in fact displacement gyros. They measure displacement from an initial datum.
Degrees of Freedom. The 'definition' of degrees of freedom has changed with the introduction of JAA. We used to use the old British nomenclature, in which displacement gyros have 3 degrees of freedom and rate gyros have 2 degrees of freedom. If you read Pallett, he still uses this convention. However, JAA Instrumentation is set by the French, so it's all changed. Under the French system, the number of degrees of freedom is the number of gimbals (we don't count the frame as a gimbal). So, for the JAA exams, displacement gyros (DGI, Art Horizon) have 2 gimbals and 2 degrees of freedom and rate gyros (Turn Indicator) have 1 degree of freedom and 1 gimbal. I don't know who you are studying with or how up-to-date their notes are, so it can be confusing, but the French usage is the one that the JAA want to see.
Hope this helps,
All the best,
Paul
[ 17 January 2002: Message edited by: Paul Hickley, Gen Nav Spec, Oxford ]
[ 17 January 2002: Message edited by: Paul Hickley, Gen Nav Spec, Oxford ]
[ 17 January 2002: Message edited by: Paul Hickley, Gen Nav Spec, Oxford ]</p>