Everything You Ever Wanted to Know About Gyroscopes
At first glance, gyroscopes are pretty strange objects. They move in peculiar ways and seem to defy gravity. The special properties of these devices have made them an invaluable asset in airplanes, space stations, and a variety of other technologies that have to deal with spin.
A typical airplane often has an entire array of them, including the all-important compass. The Mir Space Station actually used 11 of them to keep it oriented relative to the Sun, and the Hubble telescope has a batch of them too.
What is the definition of a gyroscope?
According to the English Oxford Dictionary, a gyroscope is a "device consisting of a wheel or disc mounted so that it can spin rapidly about an axis which is itself free to alter in direction. The orientation of the axis is not affected by the tilting of the mounting."
While this definition is great, it doesn't really explain how they work or why they are so important (granted we've trimmed the definition a little). To get a better understanding of this, we will first need to have a look at their "strange behavior."
Tricks of the trade
Gyroscopes, in their most basic form, are a spinning wheel or disk on an axle. More complex examples will also be mounted on a metal frame or a set of moveable or immovable frames (or gimbals) for increased precision of the apparatus.
Although they seem like simple objects on the surface, they can perform some very strange tricks.
When the wheel isn't spinning, gyroscopes are effectively over-engineered paperweights. If you try to stand one up, it will simply fall over (obviously). The key to them is in their spin.
Perhaps you've played with gyroscopes as a child? Maybe you have a fidget spinner? If so, you'll remember how they can perform lots of interesting tricks. You can balance one on a string or your finger whilst it is in motion, for example.
Another noticeable property of them, if you've ever held one, is that it will try to resist attempts to move its position.
You can even tilt it at an angle when suspended from a stand, and it will appear to levitate, albeit whilst orbiting the stand. Even more impressively, you can lift up a gyroscope with a piece of string around one end.
How do gyroscopes work?
The explanation for this phenomenon is tricky to understand intuitively. Their ability to seemingly defy gravity is a product of angular momentum, influenced by torque on a disc, like gravity, to produce a gyroscopic precession of the spinning disc or wheel.
This phenomenon is also known as gyroscopic motion or gyroscopic force, and it has proved to be very useful indeed for us humans. These terms refer to the tendency of a rotating object, not just a gyroscope, to maintain the orientation of its rotation.
As such, the rotating object possesses angular momentum, as previously mentioned, and this must be conserved. Because of this, the spinning object will tend to resist any change in its axis of rotation, as a change in orientation will result in a change in angular momentum.
Another great example of precession occurs with the planet Earth too. As you know, the Earth's rotational axis actually lies at an angle from the vertical which, owing to its angle, traces a circle as the rotational axis itself rotates.
While not entirely relevant to this article, the reason for Earth's odd tilt is actually pretty interesting.
This effect is enhanced the faster the disc or wheel is spinning, as Newton's Second Law predicts. This seems pretty obvious to anyone with a basic knowledge of physics.
The main reason they seem to defy gravity is the effective torque applied to the spinning disc has on its angular momentum vector. The influence of gravity on the plane of the spinning disc causes the rotational axis to "deflect".
This results in the entire rotational axis finding a "middle ground" between the influence of gravity and its own angular momentum vector. Now, remember that the gyroscope apparatus is being stopped from falling towards the center of gravity by something in the way -- like your hand, the frame/gimbals, or a table, for example.
Now, factoring in the fact that the gyroscope is being stopped from falling towards the center of gravity by something in the way leads to the fascinating properties we see in these devices.
A picture -- well video -- is worth a thousand words, so we'll delegate a more in-depth explanation to the following video:
Gyroscope vs. accelerometer: What is the difference between the two?
In order to fully answer this question, we need to assess how each device works. Since we have already covered the gyroscope in some detail above, let's check out what an accelerometer is and how it works.
Great, but that doesn't really give us much information. Accelerometers, in their most basic sense, are electromechanical devices that measure acceleration forces -- hence the name.
These forces can be either static (like gravity) or dynamic (caused by moving or vibrating the device). There are various ways to make an accelerometer with most using either the piezoelectric effect or through sensing capacitance.
The former tend to consist of microscopic crystal structures that become stressed by accelerative forces and generate a voltage in return. The latter makes use of two microstructures placed next to one another.
Each has a certain capacitance, and as accelerative forces move one of the structures, its capacitance will be changed. By adding some circuitry to convert from capacitance to voltage, and you will get a very useful little accelerometer.
There are even more methods, including the use of the piezoresistive effect, hot air bubbles, and light, to name but a few. So, as you can see, accelerometers and gyroscopes are very different beasts indeed.
In essence, the main difference between the two is that one can sense rotation, whereas the other cannot. Since gyroscopes work through the principle of angular momentum, they are perfect for helping indicate an object's orientation in space.
Accelerometers, on the other hand, are only able to measure linear acceleration based on vibration.
However, there are some variations of accelerometer that do also incorporate a gyroscope. These devices consist of a gyroscope with a weight on one of its axes.
The device will react to a force generated by the weight when it is accelerated by integrating that force to produce velocity.
What are optical gyroscopes?
Another form of the gyroscope is an optical gyroscope. This device has no moving parts and is commonly used in modern commercial jetliners, booster rockets, and orbiting satellites.
Taking advantage of something called the Sagnac effect, these devices use beams of light to provide a similar function to mechanical gyroscopes. The effect was first demonstrated in 1911 by Franz Harris, but it was French scientist Georges Sagnac who correctly identified the cause.
If a beam of light is split and sent in two opposite directions around a closed path on a revolving platform with mirrors on its perimeter, and then the beams are recombined, they will exhibit interference effects. In 1913, Sagnac concluded that light propagates at a speed independent of the speed of the source.
He also discovered that despite the beams both being within a closed-loop, the beam traveling in the same direction of rotation arrived at its starting point slightly later than the other one.
According to Encyclopedia Britannica, "as a result, a “fringe interference” pattern (alternate bands of light and dark) was detected that depended on the precise rate of rotation of the turntable".
The Right-Hand Rule
Scientists tend to use what is called the "right-hand rule" to visualize this.
To do this, take your right hand and make a right angle. Then you can stretch your fingers out along the radius of the wheel.
If you curl the end of your fingers in the direction of the spin your thumb will be pointing in the direction of the angular momentum. Basically, the axle of the wheel will be the direction that the entire spinning wheel "wants" to move in.
This video gives us a pretty simple explanation using a suspended bicycle wheel.
Applications of Gyroscopes
The interesting properties of gyroscopes have provided scientists and engineers with some fascinating applications. Their ability to maintain a particular orientation in space is fantastic for some applications.
Slap on some sensors and you've got a recipe for usefulness. With that in mind, here are some great examples of the use of gyroscopes in our modern world.
1. You'll find plenty of gyroscopes in aircraft
In modern aircraft, inertial guidance systems make good use of these relatively simple devices. They have a suite of spinning gyroscopes to monitor and control the orientation of the aircraft in flight. Spinning gyroscopes are kept in special cages that allow them to keep their orientation, independently of the orientation of the aircraft.
The gyroscope cages have electrical contacts and sensors that can relay information to the pilot whenever the plane rolls or pitches. This lets the pilot and guidance systems "know" the plane's current relative orientation in space.
2. The Mars Rover has a couple of gyroscopes, too
The Mars Rover also has a set of gyroscopes. They provide the Rover with stability as well as aid with navigation. They also have applications in drone aircraft and helicopters, in providing stability and helping with navigation.
3. Cruise and ballistic missiles use gyroscopes as well
Another interesting application of gyroscopes is for the guidance systems of cruise and ballistic missiles. Used to automatically steer and correct roll, pitch, and yaw, gyroscopes sensors have been used for this purpose since the German V-1 and V-2 missiles of World War 2.
Typically, missiles will carry at least two gyroscopes for this purpose, with each gyro providing a fixed reference line from which any deviations can be calculated. One reference tends to include the spin axis of a vertical gyroscope.
From this axis, deviations in pitch, roll, and yaw can be readily measured. Gyroscopes also found their way into gunsight stabilizers, bombsights, and platforms for carrying guns and radar systems onboard warships.
4. Gyroscopes can also be found in orbital spacecraft
Another interesting application of gyroscopes is for the inertial guidance systems of orbital spacecraft. Such small craft requires a high degree of precision when it comes to stabilization, and gyroscopes are pretty much perfect for the job.
There are some larger and heavier devices, called momentum wheels or reaction wheels, that are also employed for altitude controls of some larger satellites too.
5. Part of Star Wars: Return of the Jedi was filmed using gyroscopes
A device called a "Steadicam" was used to film certain scenes in the film Star Wars: The Return of the Jedi (as well as in many other movies). This device, used in conjunction with several gyroscopes, held the camera stable when filming the background shots for the famous speeder bike chase on Endor.
Invented by Garrett Brown, he operated the rig to walk through a redwood forest running the camera at one frame per second. When the footage was sped up to 24 frames per second, it gave the impression of a high-speed journey through the trees.
Today, Steadicam's descendants are a common feature of many movie productions.
6. Your phone might just have one too
Gyroscopes have also been finding their way into various consumer products over the last few years. By including them within handheld devices, like smartphones, allows for a highly accurate way to determine movement in a 3D space.
Gyroscopes are typically combined with accelerometers in modern smartphones to provide excellent directional and motion-sensing. Notable examples include the Samsung Galaxy Note 4, HTC Titan, iPhone 5s, etc.
Modern game consoles also tend to include some form of gyroscope too. From the Wii Remote to various Playstation 3 and 4 peripherals, gyroscopes have opened up an entirely new way to play computer games.
7. Lest we forget drones
Yet another interesting application of gyroscopes in our everyday lives is in drones. For these devices to fly perfectly they require gyroscopes, among other devices, to be able to hover and fly level.
Modern commercial drones tend to use three and six-axis gyro stabilizers to provide navigational information to the flight controller, which makes drones easier and safer to fly.
And that's all folks.
In all, gyroscopes are pretty incredible, even if you don't realize they are there. Amazing to think that such a simple device can have such interesting and varied applications.
While relatively simple devices, they have fantastic properties that scientists and engineers have exploited to make our world that little bit better.
If this article has sparked your imagination and want your very own gyroscope, there are plenty of online retailers to choose from. How on Earth could you refuse?
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