Gimbal lock can occur in devices that move in multiple directions, such as gyroscopes. Gyroscopes aid in navigation and maintain a horizontal orientation, but can experience gimbal lock. This can also occur in telescopes and radar antennas. Pilots performing stunts manually lock the gyro instruments to avoid gimbal lock. In space navigation, gyroscopes maintain a known landmark, but can experience gimbal lock, which can be solved by adding a fourth degree of freedom.
Gimbal lock can occur in gyroscopes, telescopes, and other devices that move in multiple directions, and is caused when the gimbals, or mounts, align in ways that prevent the device from moving in the desired direction. A gyroscope is a spinning wheel supported within a series of cages or mounts and is used in aircraft and ships to aid in navigation. Each cage provides movement in one of three directions, allowing the gyro to be mounted on a moving ship or aircraft while maintaining a horizontal orientation.
Gyroscopes were first discussed in literature in the 18th century and practical instruments for ships built in the 19th century. Elmer Sperry built the first gyroscope to control aircraft autopilots in the early 20th century. The benefit of using gyros for navigation is that the spinning gyro wheel maintains a horizontal orientation regardless of ship or aircraft movement. Connecting the gyroscope to instruments can provide an “artificial horizon” or instrumental view of the level even during sea storms or aircraft turbulence.
All objects in space can be described by a combination of three angles defined by a mathematical formula called Euler angles. These three angles are often described by the terms x, y and z. A device is said to have three degrees of freedom when it can move up or down, left or right, in or out. Gyroscopes mounted in three cages, each rotating at one of three angles, can in theory rotate in any direction needed for navigation.
The gimbal lock effect can be seen in a gyroscope, but can occur in less complicated devices. For example, a viewer tracking an overhead satellite with a telescope will reach a point where the telescope is pointing straight up. At this point, the viewer rotates the telescope 180° and can continue to follow the satellite as it moves towards the horizon in the opposite direction.
Gimbal lock occurs if the object being pursued, such as an aircraft, moves overhead and then changes direction 90° and away. At that point, the telescope cannot turn sideways, because the mounts or gimbals prevent movement in that direction. The tool must be rotated, or rotated on its base, to overcome the problem.
Humans can adapt to these situations, because they can recognize that the telescope cannot continue to track the aircraft unless the telescope is rotated 90°. The problem is that tracking of the object is often lost until the observer finds it again in the telescope’s eyepiece. This can also occur with radar antennas used to track aircraft that spin when over the antenna. Computer software must be written to compensate for the loss of tracking due to gimbal lock.
In gyroscopes, there are different angles where gimbal lock can occur as the cages align, preventing the gyroscope from rotating. As with the telescope example, the gyro now cannot move freely and is said to be “gyro locked”. Aircrafts that perform stunts, or veer and wheel in unusual directions, can cause this behavior in their navigation instruments. Pilots performing these maneuvers will often manually lock the gyro instruments prior to stunts to avoid gimbal lock and stress on the gyros.
Space navigation uses gyroscopes to maintain a known landmark. There is no horizon in space, and the location must be determined by its position relative to specific stars, a technique called celestial navigation. When a spacecraft falls or changes direction, gyroscopes that maintain “level” orientation can lock the gimbal and cause a loss of reference.
The astronauts had to visually reference the navigation stars and reset the gyroscope to prevent navigation errors. One way this problem was solved was to add a fourth degree of freedom, another cage, that was mounted at a different orientation or angle from the other cages. This provided movement even though two cages were gimbal-locked, thus allowing the instrument to continue sailing.
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