The Application of Sensors and IMUs in Drones

In this chapter, we will learn and understand the major sensors that are used in drones to lift into the air and help their systems fly and navigate to waypoints. With the help of these sensors, the drone can fly in various modes and various patterns in manual and autonomous modes. We will learn about the working of these sensors in this chapter, how they interface, and what output they give. We will also learn about the impact they have on the drone’s system. At the end of this chapter, we will be diving deep into the anatomy of a drone, which helps us to understand how it works.

We will cover the major sensors required in the drone system under the following topics:

• The inertial measurement unit and its role
• The barometer and its role
• GPS and magnetometer and their roles
• Voltage and current sensors and their roles
• Sensor fusion and state estimation

By going through the above topics, we will briefly...

The inertial measurement unit and its role

The inertial measurement unit (IMU) is the most important part of the drone as it helps the drone calculate its linear and angular acceleration; it also helps to measure the attitude angles across roll, pitch, and yaw maneuver, helping the autopilot make decisions and guide its motors and actuators to produce the desired output for level flight.

Composition of an IMU

The IMU is a critical component in multicopter flight control systems. It integrates multiple sensors to provide comprehensive information about the vehicle’s motion and orientation. The IMU typically includes accelerometers, gyroscopes, and sometimes magnetometers. The integration of these sensors is essential for accurate flight control, stability, and navigation.

Components of the IMU:

• Accelerometers: These measure linear acceleration along different axes (X, Y, and Z)
• Gyroscopes: These measure the angular velocity or the rate of rotation around...

The barometer and its role

Barometers provide height information that helps in the accurate control and navigation of a drone. Basically, atmospheric pressure is measured by barometers since air pressure decreases as the altitude increases, and this informs the flight controller of how high it has ascended.

With regard to altitude control, the drone flight controller uses barometer data to estimate the present altitude above sea level. This allows the flight controller to calculate the vertical position of a drone precisely.

The barometer data are fused with other sensors, such as accelerometers and gyroscopes. Thus, it is possible to observe the sensor values in the IMU part of the flight controller. The following two barometers—Bosch Sensortec BMP280 and BMP388—are mostly used in drone flight controllers; they are known to establish co-operation with the IMU that enables a more thorough measurement of data concerning the control of altitude, navigation, and stability...

GPS and magnetometer and their roles

The GPS and magnetometer are the two main and interrelated components of the drone. Both of the components work as the eyes and ears of the drone to help the drone locate itself in the 3D environment with respect to the Earth and also to navigate in the 3D space. The presence of a GPS and compass helps the drone navigate through different waypoints in space completely autonomously and also while returning to the launch position:

Figure 5.4 – An image depicting how a GPS works

How does GPS work?

The GPS module is used to interface with the flight controller by any means of a hardware protocol, i.e., SPI, I2C, or CAN, depending on the manufacturer and model (see product user manual). A GPS module consists of different positioning systems, such as GPS, Glonass, Beidou, and so on, which receive the signals from the satellite network via radio receivers. These signals have the velocity, time, and location co-ordinate...

Voltage and current sensors and their roles

Current and voltage measurements in drones are essential for monitoring the electrical system’s health and power management of the drone, particularly the consumption and battery status. Let’s see how voltage and currents are measured using different onboard sensors:

• Current measurement:
  • Sensors: Generally, a Hall-effect current sensor (for example, ACS712) is used to measure the voltage and current flow.
  • Working: Hall-effect sensors detect the amount of magnetic field generated by the flow of current through a conductor. The sensor outputs an analog voltage proportional to the current strength, which is then read by the flight controller to make respective decisions.
  • Interface: Analog voltage is usually fed into an analog-to-digital converter (ADC) on the flight controller, providing a digital representation of the current.
• Voltage measurement:
  • Sensor: Voltage divider or voltage measurement IC (for example, INA219,...

Sensor fusion and state estimation

Sensor fusion and state estimation represent an important part of flight controller algorithms, as this is the function that helps the drone combine all the data coming into it via the IMU, compass, and GPS; the system then makes a decision on the exact value to velocity, speed, altitude, direction, and angular acceleration. This data is important, as it helps the flight controller to make calculated decisions in terms of maneuverability:

Figure 5.5 – The concept of sensor fusion

The state estimation algorithms take data from the accelerometer and GPS co-ordinates, fuse them together, conduct a sanity check, and pass them to the flight controller, who observes the current acceleration and speed of the drone. Sensor fusion also takes care of errors in the reading of some sensors and ignores them in the decision-making process.

Summary

In this chapter, we have gone through the different sensors that are present in a drone and how each sensor is useful for stable and safe flight. Knowledge of these sensors helps the system engineer design new applications, and this also helps firmware engineers design new algorithms to play with them.

In the next chapter, we will learn more about how these sensors help in flying in different flight modes and how these data are interpreted by the flight Controller.