What is the difference between a gyroscope and an accelerometer?

The first thing to point out is the fact there are 6 possible movements usually known as 6 degrees of freedom or 6 axes. They are:

• Up/down
• Left/right
• Forward/backward
• Roll
• Pitch
• Yaw

The first 3 means the object travels in a direction. The last 3 are when the object remains in the same place but is rotated. So imagine standing up, if I then said turn 90 degrees clockwise this would be a yaw movement. But if I said lie on your back on the floor that would be pitch movement. Accelerometers can detect the up/down, left/right, forward/backward movements but they CANNOT detect the roll, pitch and yaw movements.

A good example would be travelling in a lift/elevator; you press the button and wait for the lift to arrive at your floor, the doors open and you walk into the lift. An accelerometer would detect your movement walking into the lift. The buttons in the lift are on your left so you turn to face them, an accelerometer would not detect you turning to face the buttons but a gyroscope could detect that movement. Also when the lift starts to move the accelerometers would detect that movement but gyroscopes would not. This is why gyroscopes and accelerometers are often used together as you can detect every motion.

How accurate are gyroscopes?

The accuracy of gyroscopes is actually a really good question, but it really depends on the type of gyroscope and how it is used. For example, MEMS gyroscopes used in many electronics devices such as phones, tablets and a radio controlled aircraft and drones, will have a drift rate as well as a noise error. These types of gyroscopes have improved over the last couple of decades and now offer a drift rate of under one degree per minute, the noise rate can be as little as a 10th of a degree on the industrial versions (as of 2024).

A ship's gyro compass on the other hand always synchronises to true North and although it may take time to synchronise and there are scenarios where it can be briefly wrong, but over time it does give a true north reading. These types of mechanical ships gyrocompasses in the 1970s had achieved 0.4 ° accuracy.

Another example is the gyroscopes used on ICBMs (intercontinental ballistic missiles). These types of gyroscopes are probably the most accurate in the world and allow the missiles to travel halfway around the world and a hit target roughly within the size of a stadium. The CEP (circular error probable) which is commonly used to define the certainty of the strike, defines the area that it will hit 50% of the time. Although the exact figures are classified for the latest and current systems we know from various sources that the CEP is down to tens of meters.

Note: Some ICBMs use secondly measurements such as a Star alignment check while in space to further enhance the accuracy.

Are there any everyday objects that use gyroscopes?

There are a few items that you are likely to come into contact that have a gyroscope. If you have a modern phone or tablet it is likely to have multiple gyroscopes. These gyroscopes will be able to detect the twists and turning movements of the phone or tablet. This is useful for all sorts of reasons, including taking panoramic photos, making images less blurry (when taking normal photos), and detecting when the screen is turned between landscape and portrait. It is also used in a lot of games.

In fact game controllers are another device that you may come across that has gyroscopes in, which some games use to control the game play in some way.

Another everyday use of gyroscopes that most people are unlikely to know about is the ones used in modern cars. Electronic stability control systems look at the steering position and speed, then compare to the on board gyroscopes and accelerometers. The system will also compare the rotations of some or all of the wheels. If there are discrepancies then the car is slipping in some way and the system will attempt to regain traction, by controlling/limiting power to driving wheels and applying brakes to some of the wheels.