Tech Explained: Gyroscopes

Gyroscopes have a huge variety of uses, find out how they work in our latest Tech Explained.

There are a number of different devices used to determine the position and orientation of an object. One of the most common is the gyroscope. You may think of a gyroscope as a children’s toy. However, these devices can be found in everything from the space shuttle to shoes. So how do they work?

Gyroscopes were invented in the 19th century by French physicist Jean-Bernard-Léon Foucault. In 1908, German inventor H. Anschütz-Kaempfe developed the first compass based on a gyroscope. Just one year later, this ‘gyrocompass’ was used to create the world’s first autopilot.

A gyroscope consists of a freely-rotating disk, called a rotor, mounted on a spinning axis in the centre of a larger wheel. As the axis turns, the rotor remains upright and continues to spin in its original orientation. The laws of motion explain how this occurs. Newton’s first law of motion states that an object that is moving tends to keep moving in the same direction and speed unless it is acted upon by an outside force. When this happens, the speed or direction change is in the same direction as the force. For example, if you push a toy car down a ramp, it moves in the direction of the push until something stops it (friction, a brick wall, etc.).

When force is applied to a spinning object, like a gyroscope rotor, something similar happens. The difference is that the change in momentum is not in the direction of the force, but at right angles and in the direction of the momentum. For example, if you push on a spinning top, the top will move off at a right angle to the push, not in the direction of the push. Instead of falling over from the force of gravity, a gyroscope rights itself by moving sideways.

The effect of all this is that, when you spin a gyroscope, its axle wants to keep pointing in the direction of gravitational pull (‘down’). To make practical use of this, a gyroscope can be mounted in a set of gimbals, so that it will continue pointing in the same direction no matter how the vehicle around it is oriented. This is the basis of inertial navigation systems.

In an inertial navigation system, a gyroscope is mounted on a platform and sensors are placed on the gimbals’ axle to detect when the platform rotates. Those signals show how the vehicle is oriented relative to the platform. When paired with an accelerometer – an instrument that measures the rate of acceleration – the inertial navigation system can determine exactly where the vehicle is heading and how its motion is changing. With this information, an airplane’s autopilot can keep the plane on course, and a self-driving vehicle can know exactly where it is and how fast it is moving.

The gyroscope described above is a mechanical gyroscope. There are several other types of gyroscope in use today. A type of gyroscope called a microelectromechanical sensor (MEM) is used to measure changes in the forces acting on identical masses that are moving in opposite directions. These are commonly used in vehicles, drones, and electronic devices. Optical gyroscopes use light to calculate orientation. A beam of light is split into two, and the twin beams travel in opposite directions along a circular pathway, before meeting at a light detector. Because light travels at a constant speed, rotating the device causes one of the two beams to arrive at the detector before the other. This is used to calculate orientation. Optical gyroscopes tend to be quite large, but a newly-devised design allows them to be miniaturised to fit on a chip smaller than a grain of rice.

In gas-bearing gyroscopes the rotor is suspended in pressurised gas. This reduces the amount of friction between moving parts. Gas-bearing gyroscopes are much quieter than other forms of gyroscopes and also have greater accuracy. They were used in the development of the Hubble Telescope.