# Where is the gyroscope located in aircraft

## What is a gyroscope? Easily explained

Gyroscopes, or gyros, are devices that measure or maintain rotational motion. MEMS gyros (microelectromechanical systems) are small, inexpensive sensors that measure angular velocity. The units of angular velocity are measured in degrees per second (° / s) or revolutions per second (RPS). Angular velocity is simply a measurement of the speed of rotation.

Gyroscopes, similar to the one above, can be used to determine orientation and are found in most autonomous navigation systems. For example, if you want to balance a robot, a gyroscope can be used to measure the rotation from the balanced position and send corrections to a motor.

### How does a gyroscope work?

When things rotate around an axis, they have what is known as an angular velocity. A rotary knob can be measured in revolutions per second (RPS) or degrees per second (° / s).

Note that the z-axis of the gyro below is aligned with the axis of rotation of the wheel.

If you connect the sensor to the wheel pictured above, you can measure the angular velocity of the z-axis of the gyro. The other two axes would not measure rotation.

Imagine the wheel turns once every second. It would have an angular velocity of 360 degrees per second. The direction of rotation of the wheel is also important. Is it clockwise around the axis or is it counterclockwise?

A three-axis MEMS gyroscope similar to the one pictured above (ITG-3200) can measure rotation about three axes: x, y, and z. Some gyros come in single-axis and two-axis variants, but the three-axis gyro in a single chip is smaller, cheaper, and more popular.

Gyroscopes are often used on objects that do not rotate very quickly. Airplanes (hopefully) don't turn. Instead, they rotate a few degrees around each axis. By detecting these small changes, gyros help stabilize the aircraft's flight. Also note that the aircraft's acceleration or linear velocity does not affect the gyro's measurement. Gyros only measure angular velocity.

How does the MEMS gyro record the angular velocity?

The gyroscope sensor in the MEMS is tiny (between 1 and 100 micrometers, the size of a human hair). As the gyro is rotated, a small resonant mass is displaced as the angular velocity changes. This movement is converted into very weak electrical signals that can be amplified and read by a host microcontroller.

### How to choose the right gyroscope

There are many specifications to consider when choosing which sensor to use. Here are some of the most important:

• The Measuring range or the full scale range is the maximum angular velocity the gyro can read. Think about what you are measuring. Do you need to measure the spin of a turntable that is very slow or a spinning wheel that could be very fast?
• The sensitivity is measured in mV per degree per second (mV / ° / s). Don't let the comical dimension of this value scare you. It determines how much the voltage changes for a given angular velocity. For example, if you specify a gyro with a sensitivity of 30 mV / ° / s and the output is changed by 300 mV, you have rotated the gyro 10 ° / s. A good rule to keep in mind: as sensitivity increases, the area decreases. For example, take a look at the datasheet of the LPY503 gyro.
• Bias:As with any sensor, the values ​​you measure will contain some errors or deviations. You can see the tilt of the gyro by measuring the output while the gyro is still stationary. Although you'd think you'd see 0 ° if the gyro was still stationary, the output always shows a small non-zero error. These errors are sometimes referred to as bias drift or bias instability. The temperature of the sensor has a strong influence on the bias. To minimize the source of error, most gyros have a built-in temperature sensor. In this way you can read the temperature of the sensor and correct temperature-dependent changes. To correct these errors, the gyro must be calibrated. This is usually done by holding the sensor steady and zeroing all readings in your code.

### What is the difference between a gyroscope and an accelerometer?

The main difference between the two devices is simple: one can sense rotation, the other can't. In a sense, the accelerometer can measure the orientation of a stationary object with respect to the earth's surface. When accelerating in a certain direction, the accelerometer cannot distinguish between acceleration and acceleration due to gravity. If you consider this handicap when using it on an airplane, the accelerometer quickly loses its appeal.

The gyro maintains its effectiveness by being able to measure the speed of rotation around a specific axis. When measuring the rate of rotation around the roll axis of an aircraft, it determines an actual value until the object stabilizes. According to the basic principles of angular momentum, the gyroscope helps to determine the orientation. In comparison, the accelerometer measures linear acceleration based on vibrations.

The typical two-axis accelerometer tells users the direction of gravity on an airplane, smartphone, car, or other device. In comparison, a gyroscope should determine an angular position according to the principle of spatial rigidity. The applications of the individual devices vary greatly despite their similar purpose. A gyroscope is used, for example, for navigation on unmanned aerial vehicles, compasses and large boats, which ultimately contributes to the stability of the navigation. Accelerometers are also widely used and can be found in the fields of mechanical engineering, mechanical engineering, hardware monitoring, building and structure monitoring, navigation, transportation and even in consumer electronics.

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