I PIGA: Pendulous Integrating Gyroscopic Accelerometer

AI Thread Summary
The PIGA accelerometer operates by utilizing a gyroscope that behaves like a pendulum when at rest on Earth's surface. When the gyroscope is not spinning, it falls under gravity, mimicking the motion of a non-spinning pendulum. Once the gyroscope activates the torque motor, it generates torque that causes the pendulum to rise, counteracting the gravitational pull. A feedback loop maintains the pendulum in a horizontal position, allowing the angular velocity of the torque motor to correlate with acceleration along the flight axis. This mechanism effectively measures acceleration by translating gravitational forces into rotational motion.
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Wiki describes the PIGA, https://en.wikipedia.org/wiki/PIGA_accelerometer. I want to see if I have a basic intuitive understanding of how it works.

https://en.wikipedia.org/wiki/PIGA_accelerometer#/media/File:PIGA_accelerometer_1.png
PIGA_accelerometer

PIGA_accelerometer_1.png

Lets imagine that the device, as shown, is at rest on the Earth's surface, with the "direction of flight" on the diagram being upwards. Let us also imagine that the motor on the top of the instrument is powered off. What I think should happen is that the gyroscope simply acts as pendulum, and falls downwards at the end of the pivot arm due to the Earth's gravity. While the gyroscope attempts to precess in a direction given by the right hand rule between the axis of rotation of the gyroscope and the applied torque due to the Earth's gravity, the mounting of the gyroscope prevents precession in this direction and the pendulum essentially falls in the same manner as it would if the gyroscope were not spinning.

Let us now imagine that as the gyroscope falls, it activates the torque motor. The resulting torque, assuming the motor is wired to rotate in the right direction, causes the pendulum to rise due to the cross product of the spin axis and the applied torque.

Thus, as Wiki describes, if a feedback loop holds the pendulum in the horizontal position, the angular velocity of rotation of the torque motor is proportional to the acceleration along the axis of flight, in this case that is the Earth's gravity.
 
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