Gyroscope is a sensor which maintain orientation and also measure angular rate. It is based on angular momentum principle. It has two gimbals, inner and outer gimbal. And a spinning wheel.
It needs an initial angular velocity and of course the orientation. Once it spinning around the axis, gyroscope will maintain its orientation. It's wonderful that it can maintain the orientation.Gyroscope is very useful in aeroplane and spacecraft, to sense the orientation.
See this video to know how it works.
How is the video?! Bravo!
I start learning this thing from aerospace course... huft... a tough course for me. But, I found something interesting,, which is Gyroscope.