Gimbal
From Wikipedia, the free encyclopedia
A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain vertical regardless of the motion of its support. For example, gyroscopes, shipboard compasses, stoves and even drink holders typically use gimbals to keep them upright with respect to the horizon despite the ship's pitching and rolling.
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[edit] Inertial navigation
[edit] Marine
In inertial navigation, as applied to ships and submarines, a minimum of three gimbals is needed to allow an Inertial Navigation System platform (stable table) to remain fixed in inertial space, compensating for the ship's Yaw (direction) as well as its Pitch and Roll. In this application, the Inertial Measurement Unit is equipped with three orthogonally mounted gyros to sense rotation about all axes in three dimensional space. The gyro outputs drive motors controlling the orientation of the three gimbals as required to maintain the orientation of the IMU. In turn, angular measurement devices, called "resolvers" mounted on the three gimbals provide the nine cosine values for the direction cosine matrix needed to orient the ship.
[edit] Aerospace
In aerospace inertial navigation systems, gimbal lock may occur when vehicle rotation causes two of the three gimbal rings to align with their pivot axes in a single plane. When this occurs, it is no longer possible to maintain the sensing platform's orientation. To avoid this problem, a fourth gimbal must be employed, driven so as to keep the other three at substantial angles to each other. Modern practice is to avoid the use of gimbals entirely by mounting the inertial sensors directly to the body of the vehicle strapdown system and integrating sensed rotation and acceleration digitally using quaternion methods to derive vehicle orientation and velocity.
[edit] Rocket engines
In spacecraft propulsion, rocket engines are generally mounted on a pair of gimbals to allow a single engine to vector thrust about both Pitch and Yaw; or sometimes just one axis is provided per engine. To control Roll, twin engines with differential Pitch or Yaw control signals are used to provide torque about the vehicle's Roll axis.
[edit] Fishing
In big-game fishing, a two axis gimbal may be used as a fixed pivot for the butt of the rod, with the gimbals mounted in a "fighting belt" or a "fighting chair". In either case, this is a considerable advantage to the angler. Inside the gimbal there is usually a horizontal pin that the fishing rod locks into, preventing rotation about the long axis of the rod, making it easier to reel. This is demonstrated in the 1975 film Jaws, where the character Quint uses a "fighting chair" & "fighting belt/harness" to attempt to catch the shark they were pursuing.
