A gyroscope is a spinning wheel or disc in which the axis of rotation is free to assume any orientation by itself. When rotating, the orientation of this axis is unaffected by tilting or rotation of the mounting, according to the conservation of angular momentum, because of this, gyroscopes are useful for measuring or maintaining orientation. Due to their precision, gyroscopes are used in gyrotheodolites to maintain direction in tunnel mining. Gyroscopes can be used to construct gyrocompasses, which complement or replace magnetic compasses, a gyroscope is a wheel mounted in two or three gimbals, which are a pivoted supports that allow the rotation of the wheel about a single axis. In the case of a gyroscope with two gimbals, the gimbal, which is the gyroscope frame, is mounted so as to pivot about an axis in its own plane determined by the support. This outer gimbal possesses one degree of freedom and its axis possesses none. The inner gimbal is mounted in the frame so as to pivot about an axis in its own plane that is always perpendicular to the pivotal axis of the gyroscope frame. This inner gimbal has two degrees of rotational freedom, the axle of the spinning wheel defines the spin axis. The rotor is constrained to spin about an axis, which is perpendicular to the axis of the inner gimbal. So the rotor possesses three degrees of freedom and its axis possesses two. The wheel responds to a force applied to the axis by a reaction force to the output axis. The behaviour of a gyroscope can be most easily appreciated by consideration of the front wheel of a bicycle. If the wheel is leaned away from the vertical so that the top of the moves to the left. In other words, rotation on one axis of the turning wheel produces rotation of the third axis, a gyroscope flywheel will roll or resist about the output axis depending upon whether the output gimbals are of a free or fixed configuration. Examples of some free-output-gimbal devices would be the attitude reference gyroscopes used to sense or measure the pitch, roll, the centre of gravity of the rotor can be in a fixed position. Some gyroscopes have mechanical equivalents substituted for one or more of the elements, for example, the spinning rotor may be suspended in a fluid, instead of being pivotally mounted in gimbals. In some special cases, the outer gimbal may be omitted so that the rotor has two degrees of freedom. Essentially, a gyroscope is a top combined with a pair of gimbals, Tops were invented in many different civilizations, including classical Greece, Rome, and China
Gyroscope invented by Léon Foucault in 1852. Replica built by Dumoulin-Froment for the Exposition universelle in 1867. National Conservatory of Arts and Crafts museum, Paris.
A digital gyroscope module connected to an Arduino Uno board
Diagram of a gyro wheel. Reaction arrows about the output axis (blue) correspond to forces applied about the input axis (green), and vice versa.