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Originally Posted by nobtiba
Let take an imagine experiment: if you have a laser pointer mounted on a rotation board. At starting point, the laser pointer lights a point on the wall (or any target). Mark this point on the wall. Now turn an alpha angle. All I have to do is turn the table back so that the pointer lights exactly in the marked point on the wall.
In fact, robot or airplane also have the same mission when they need to keep straight direction. So how they to do that with this ADXRS150 gyro ?
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First, about the laser: You should have no trouble getting the laser pointer back to your point using the ADXR150, a 10-bit A/D, and a PID control loop. We have been able to have great accuracy with the ADXR300 with a 10-bit A/D. The key is to have a fast-enough sample rate (< 1 ms).
2nd, about the airplane:
Airplanes do not use solid-state angular rate sensors - they use mechanical gyroscopes with sensors to measure the angle of the gymbals. These gyros have anti-precession mechanisms built in, but in the case of precession, there is a pilot "trim" knob in which the pilot can remove the precession of the gyro.
Also, airplanes will not use a gyro when precision navigation is required. They use a navigation system to provide the heading input (and therefore the bank input) to the autopilot. The navigation system tells the auto-pilot if it needs to turn right or left and how much to turn. The auto-pilot then banks accordingly. For enroute navigation, the autopilot can use GPS (if the airplane is equipped) or VOR inputs. For approaches, the autopilot can switch over to an ILS localizer or it can stick with the GPS if the GPS is approach certified.
So, to answer the airplane question: if the airplane needs to hit a precise point from far away, it will use ground or satellite navigation, not a gyro. (However, before the days of GPS, you could use inertial navigation systems (gyros and accelerometers) to get across the ocean until you could pick up ground-based navigation systems.)