GYROSCOPIC STABILIZATION
Authors :- Mrunmayee Kulkarni, Neel Madane, Hussain Magar, Prachi Mahajan, Shreyas Mahajan & Neel Malwatkar
Gyroscopes
Most people’s familiarity with gyroscopes comes from playing with a string-operated gyroscope or top as a child. However, gyroscopes are an amazingly common part of people’s lives, with applications in transportation and even consumer electronics. Today, modern gyroscopes come in three general varieties: mechanical gyroscopes, gas-bearing gyroscopes and optical gyroscopes. Mechanical and gas-bearing gyroscopes work on the principle of conservation of angular momentum to detect movement, though some use other principles.
Types of Gyroscopes :
Mechanical Gyroscopes
Mechanical gyroscopes are perhaps the most common or familiar type of gyroscope. Children’s toy gyroscopes fit into this category, which includes any gyroscope that relies on a ball bearing to spin. These types of gyroscopes are used in navigation of large aircraft and in missile guidance and control. Since they are typically noisier than other forms of gyroscopes, they are often replaced with more modern forms of gyroscopes.
Gas-Bearing Gyroscopes
In gas-bearing gyroscopes the rotor is suspended by pressurized gas, reducing the amount of friction between moving parts. These types of gyroscopes were used by NASA in the development of the Hubble Telescope. According to NASA, the gas-bearing gyroscopes are much quieter than other forms of gyroscopes and also have greater accuracy. In fact, NASA states the gyroscopes aboard the Hubble Telescope are among the most accurate in the world.
Optical Gyroscopes
Unlike mechanical or gas-bearing gyroscopes, optical gyroscopes do not rely on a rotating wheel or bearing. Optical gyroscopes are not based on the conservation of angular momentum. These gyroscopes use two coils of fiber optic cable spun in different orientations. According to the Sagnac Effect, when the device is tilted, the two beams of light will travel different distances, which can be measured. Since there are no moving parts, fiber optic gyroscopes are very durable and are used in modern rocketry and spacecraft.
Gyroscopic Stabilization
In a nutshell, Gyroscopic stabilizer is a control system that reduces tilting movement of a ship or aircraft. It senses orientation using a small gyroscope, and counteracts rotation by adjusting control surfaces or by applying force to a large gyroscope. This entire process of stabilization is called Gyroscopic Stabilization.
In other words, due to the nature of the kinematics, the particles in the wheel experience acceleration in such a way that the force of gravity is able to maintain the angle θ of the gyroscope as it processes. This is the most basic explanation behind the gyroscope physics.
Gyroscope Instruments in Airplanes
Gyroscopes are an essential component of any instrument rig used for altitude, heading, turning, and navigation. Technological inventions created gyroscopes that work using a variety of theories. Each type of gyro is best suited for particular situations based on the type of information needed and the effect of drift. Three types of gyros are common in aviation.
Mechanical Gyro — We’re probably all familiar with this type. It is basically a spinning top suspended by gimbals. Rigidity in space is the primary operating principle of mechanical gyros. The gyros stay in place and the aircraft rotates and pitches around them.
MEMS Gyro — Micro-Electro-Mechanical Systems gyros work based on the Coriolis force. As the MEMS chip is subjected to angular acceleration, Coriolis forces impart a displacement of a vibrating plate. This force is translated into electrical signals. At the high end, these are found in many aircraft AHRS, and at the low end in many consumer electronics.
Laser Gyro — This group includes ring laser (RLG) and fiber optic (FOG) gyros. In these devices lasers are shot through a triangle (RLG) or other shaped (FOG) course. Rotation of the device will cause a light wave phase shift of the laser due to the Sagnac effect. The amount of light shift indicates rate of acceleration. These highly accurate and stable gyros are found in inertial navigation systems.
Gyroscopic Principles
The principal characteristic of a gyro which makes it suitable for use in attitude instruments is Rigidity in Space. A secondary gyroscopic principle which must be understood and compensated for, as necessary, is Precession. Explanation of the terms is as follows:
Rigidity in Space
The primary trait of a spinning gyro rotor is rigidity in space, otherwise known as gyroscopic inertia. As stated in Newton’s First Law, “a body in motion tends to move in a constant speed and direction unless acted upon by an external force”. The spinning rotor inside a gyroscopic instrument maintains a constant attitude in space so long as no external forces act to change its motion. This stability will increase in proportion to any increase in mass or speed of the rotor. As a consequence, the rotors in gyroscopic aircraft instruments are constructed of heavy materials and are designed to spin at rates in the order of 10,000 to 15,000 revolutions per minute (RPM).
Attitude and heading indicators use gyros as an unchanging reference in space; that is, once the rotor is spinning, it maintains a constant position with respect to the horizon or the direction. The rotor of a universally mounted gyro remains in the same position even as the surrounding circular frames or gimbals are moved. For all intents and purposes, this allows the aircraft to rotate around the gyro without changing the position of the rotor. The aircraft attitude or heading can thus be compared to the rotor to enable the instrument to display the actual attitude or direction.
Precession
Precession is the tilting or turning of the rotor axis as a result of external forces. When a deflective force is applied to a stationary gyro rotor, the rotor will move in the direction of the force. However, when the same force is applied to the rim of a spinning rotor, the force causes the rotor to move as though the force had been applied to a point 90 degrees around the rim in the direction of rotation. This turning movement or precession places the rotor in a new plane of rotation which is parallel to the force.
Precession is caused by both friction within the gyro and by aircraft maneuvering inclusive of turns, acceleration and deceleration. Precession causes a slow “drift” in the gyro and results in erroneous readings. Cross Checking the heading indicator or directional gyro with the magnetic compass and making the appropriate corrections should be accomplished on a regular basis.
Gimbal Rings
The gyro rotor is held in place by rings or better known as gimbal rings. These allow for freedom of motion in three dimensional planes as required by the instruments of the aircraft. Not all instruments will need all planes of movement at the same time, this depends on their function.
Gyro Stabilizer for Boats
Gyro stabilization is becoming increasingly common on boat builds and refits. The flying bridge, tuna tower, and mezzanine are maybe three of the most important characteristics in the history of the sport-fishing boat, aside from hull design. However, a fourth factor is now influencing the game: gyro stabilization. If a boat builder wants to sell a new boat these days, he or she must include a gyro. Gyros may be handled by vessels of various sizes, including small boats with stabilizers.
History of Gyro Stabilizers
The first experimental gyros were developed in the late 1860s and into the early 1900s, with less than desirable results. Several large ships used the technology, including USS Henderson, a military transport ship, in 1917, which had two 25-ton units, and an Italian cruise liner that utilized three large units in 1930. The cost and weight of the systems were prohibitive, and other forms of stabilization became more readily available. External fin stabilization, which used the speed of the vessel to help create anti-roll stabilization, became more popular, but by no means more practical — especially in sport-fishers.
How Does a Gyro Stabilizer Work?
The gyro stabilizes the boat through the energy it creates spinning a flywheel at high revolutions per minute. The subsequent angular momentum, or stabilizing power, is determined by the weight, diameter, and RPM of the flywheel and measured in Newton meters — a unit of torque. The output rating in Newton meters is the amount of power the unit is capable of generating to stabilize the boat. The more output, the more anti-rolling torque generated by the gyro to stabilize the boat. Several companies make gyros for sport-fishing boats, and they have units to fit almost any application in the sport-fishing industry. Seakeeper, the fastest-growing brand, offers units for practically every size sport-fishing boat made today.
Mitsubishi Gyro Stabilizer
Mitsubishi also designed anti-roll gyros for the sport-fishing market. Now called the Tohmei Anti Rolling Gyro stabilizer, manufactured by Mohmei, its unit only requires bolting to the boat and plugging in. Its unit is completely self-contained, with no external moving parts and no need for raw-water cooling. Tohmei Anti Rolling Gyros come in four models: the ARG50T/65T, the ARG175T, the ARG250T/250T-1, and the ARG375T.
Each company’s recommended installation procedure must be adhered to for the units to work properly. The torque generated by the flywheel requires the units to become an integral part of the boat and be tied into the main stringers and strengthened areas of the boat. This makes retrofits difficult. Only the original builder or an experienced boatyard should do this kind of work because they have the capability to integrate the mounting system into the structure of the boat. However, a large portion of Seakeeper’s business is retrofitting, so the opportunity is readily available.
Active Gyro Stabilization
Gyro stabilization works by mounting a state-of-the-art FOG (Fiber Optic Gyroscope) or MEMS (micro-electro-mechanical systems) gyroscope to the camera base that measures for any movements that might occur. When the gyroscope senses movement, it then sends a command to the pan/tilt unit to counteract that movement by applying the opposite rotation to the camera.
This keeps the image on target, even with massive shifts in movement (up to the rotation limits of the pan/tilt). Performance is then dependent on the accuracy of the gyroscope, the latency in the system, and the speed and precision of the pan/tilt motors. These components can quickly become expensive, which is why we custom configure your camera for the needs of your situation. It is important to look at the specs of the pan/tilt before purchasing a gyro stabilized system as it must be able to perform quickly and accurately enough to stabilize the image. Not all gyro stabilization systems are created equal. What type of system you require will depend on its intended usage.
Some may wonder why gyro stabilization is needed when the cameras they use like a cellphone or a GoPro produce usable images without it. This is because the need for stabilization is proportional to the camera’s field of view. An iPhone for example has a wide field of view (60°) and a GoPro has an extra wide field of view (120°). If the camera is bumped and consequently shakes by two degrees, this means an iPhone’s image shifts by 3% while a GoPro’s image only shifts by 1.5%. These are fairly mild fluctuations to account for, but Infiniti’s long-range zoom cameras often have fields of view that are less than 1°. A camera with a 1° field of view would experience an immense image shift of 200% from that same small vibration.
The Limits of Digital Stabilization
With digital stabilization becoming more popular on smartphone cameras, video editing software and even a one-click YouTube option, it’s understandable that many people may think that advanced digital stabilization could then solve any stabilization problems, but for long-range images it’s simply not possible. Digital stabilization works by comparing the frames of the video and watching for sudden shifts in the overall scene.
When these shifts occur, the algorithm digitally moves the image back to where it would be if the camera had remained stable. This means the edges of the video now have areas where there is no information. To compensate for this, the final video image is cropped to eliminate those jittery black edges. When the image is shifting by one or two percent, this method can work quite well, but when the image is shifting by over 100%, this is impossible as there is no overlapping image to track.
How Gyro Stabilization Works
Gyro stabilization works by mounting a state-of-the-art FOG (Fiber Optic Gyroscope) or MEMS (micro-electro-mechanical systems) gyroscope to the camera base that measures for any movements that might occur. When the gyroscope senses movement, it then sends a command to the pan/tilt unit to counteract that movement by applying the opposite rotation to the camera. This keeps the image on target, even with massive shifts in movement (up to the rotation limits of the pan/tilt). Performance is then dependent on the accuracy of the gyroscope, the latency in the system, and the speed and precision of the pan/tilt motors. These components can quickly become expensive, which is why one should configure their camera for the needs of the situation.
It is important to look at the specs of the pan/tilt before purchasing a gyro stabilized system as it must be able to perform quickly and accurately enough to stabilize the image. Not all gyro stabilization systems are created equal. What type of system you require will depend on its intended usage.
