What are redundant systems in drones?

A major technical breakthrough in modern drones that improves safety and reduces the likelihood of malfunctions during operation.

What on earth is a redundant system in drones?

Drones are driven by an interplay of many technological and engineering breakthroughs. These technological developments enable affordable production and safe, efficient flight. One of these major breakthroughs is that of redundant systems. Above all, these systems make flying a drone safer. Many top drones use them, but the truth is that many people wonder: What on earth is a redundant system in drones?

Here you will find the answer!

What are redundant systems in technology?

Redundancy is an engineering concept where critical components or functions within a system are duplicated to increase reliability. For example, redundant information, motors, complete devices, control lines, power reserves, and so on. Safety systems are designed to run multiple times in parallel so that if one component fails, another backup component can step in. In addition, efforts are made to physically separate redundant systems, which reduces the risk of a common failure. Sometimes components from different vendors are used to prevent systematic failure of all redundant components. In software engineering, redundant systems should be programmed by different teams, different programming languages are used, different compilers, etc.

In aviation, various systems are designed with triple redundancy, which is called triple modular redundancy. In triple redundant systems, such a system consists of three subcomponents, and all three components must fail before the entire system fails. Special care is taken to ensure that each subcomponent is of the highest quality to prevent any single component from ever failing. This minimizes the likelihood of all 3 components or replacement components failing. These include fly-by-wire, hydraulic systems, and parts of the aircraft controls. Human lives depend on it!

Functions of redundancy in a system

Basically, there are 2 types of redundancy in systems, namely active and passive redundancy. Both are designed to prevent degradation of performance or exceeding of specification limits without the need for human intervention. To better understand the functions of redundancy, the different types are briefly discussed here.

Passive redundancy or operational redundancy:

This means that additional resources are made available, but they are only needed in the event of a failure or malfunction. An example from practice would be the additional strength of cables or bracing in bridges. The additional bracing in a bridge makes it possible for the structure to stand even if some structural components are broken.

Another good example of redundant systems is your eyes and ears. Losing vision in one eye does not make you blind, although depth perception is affected. Similarly, loss of hearing in one ear does not cause total deafness, even though the sense of direction is lost.

In short, with passive redundancy, a limited number of failures will not cause the entire system to fail, even if a drop in performance is expected.

Active redundancy:

In active redundancy, a drop in power is prevented by monitoring the power, which works in the form of a tuning logic. This tuning logic works with an electronic circuit. An example of active redundancy is electrical power distribution systems. Here, there are multiple power lines connecting individual power generation facilities to customers. Here, each power line is monitored to detect an overload, which can then be rerouted with circuit breakers. If an overload is detected on a power line, it is shut down and the power is redistributed to the remaining lines.

The logic of active redundancy

Active redundancy systems operate on the principle of coordination logic. The systems monitor the power supply, and in the event of a failure, the components coordinate how to reconfigure individual components to continue operation without violating the specified limits of the overall system. Such systems are commonly used in computers, but can also be used in systems not specifically intended for computers.

Power systems, for example, use active redundancy to adjust the output of power generation equipment when a generator fails. In this way, power outages can be prevented during major events such as earthquakes or other disasters. Computer systems typically use only a simple form of this coordination logic, consisting of two components. A primary system and an alternate system. These two systems run on similar software, with the alternate system doing nothing during smooth operation.

So how does this redundancy logic work for systems?

The primary component of the system monitors itself and periodically sends an activity message to the alternate component that all is well. However, if the primary system detects an error, it immediately stops all output, including the activity message to the secondary system. Once there are no more messages from the primary component, the secondary system takes over the tasks of the primary system.

Another type of voting logic, which is also more reliable, involves an odd number of components, 3 or more. All components perform identical tasks and the outputs of the components are compared. Now the voting logic determines if there are disagreements between the components. The majority now turns off the component with the discrepant output. In this way, normal operation is not interrupted. Such systems are used in aviation or a drone.

How do drones use redundant systems?

Modern drones today have very fail-safe mechanisms such as the "go-home" function or the ability to perform an emergency landing when the battery is low or with one or, depending on the model, multiple motors.

What actually happens if one of these secure systems fails?

Redundant systems are designed for the scenarios and can reduce the risk to a minimum, avoiding serious accidents. A redundant system makes the drone heavier, but can also increase accuracy and performance and stabilization many times over.

Here are some examples of how such systems work with the DJI M30T

Double inertia measurement

An inertial measurement unit (IMU) measures the triaxial acceleration and angular velocity of a drone in real time. This helps calculate the drone's speed, position and attitude angle. In the event of an inertial measurement unit failure, the main unit is deactivated and the backup unit is activated.

Dual barometer

Barometers are built in to accurately determine the relative altitude of the drone, based on atmospheric pressure, so altitude can be accurately determined. Dual barometer redundancy allows the defective barometer to be turned off and the backup barometer to be used in the event of a barometer failure, which does not affect the safe operation of the drone.

Two RTK antennas + GNSS module

The RTK (Real Time Kinematic) system enables centimeter-precise positioning of the drone. The dual redundancy of the system with 2 RTK antennas and a GNSS module ensures very stable operation of the positioning system. The dual RTK antennas also support the drone's compasses, allowing stable operation even in complex environments with electromagnetic interference.

Double compass

A compass provides heading information to the drone. There are 2 compasses installed in the DJI M30T, so if one compass fails, the backup compass will step in. The compasses are also supported by the RTK modules, so the compasses can support the drone even if the RTK modules fail.

Image sensors

The DJI M30T has 6 pairs of image sensors that provide the drone with binocular image processing system. These detect the position of the drone and help to detect and avoid obstacles. If one or more pairs of sensors fail (less than 6), the infrared sensors can step in.

Infrared sensors

Infrared sensors can determine the distance to an object by measuring the travel time of an infrared light signal. The DJI M30T is equipped with 6 infrared sensors that provide real-time distance information from all 6 sides of the drone. When the drone is used at night or in low light conditions, or when the visual sensors fail, the system can rely on the infrared sensors.

Redundancy of the control signals

The communication link between the flight control system and the motor speed control (ESC) system uses a serial peripheral interface (SPI) and a Universal Asynchronous Receiver Transmitter (UART) to ensure secure and stable communication between the flight control system and the drone ESC system.

Two batteries

The DJI M30 series uses 2 batteries for operation. If one battery fails, the other battery can continue operation independently to ensure a safe landing.

Dual transmission ports

The DJI M30 series drones are equipped with four redundant antennas. Each antenna is capable of providing the drone with transmission data. It also uses different bands such as 2.400 to 2.4835 GHz and 5.725 to 5.850 GHz. This allows the drone to switch to the other band even in noisy environments where one band might be disturbed. Furthermore, it is even possible to additionally connect this drone via the 4G network, which ensures the highest level of flight safety.

Emergency landing with defective propeller or motor

In the event of an in-flight motor failure, the M30 Series can also perform a three-motor emergency landing while maintaining basic controls such as climb, descent and horizontal movement to ensure landing away from people, buildings or other hazards.

ADS-B receiver

Another safety-relevant feature of modern drones is an ADS-B receiver. This increases safety in the airspace, as this receiver can detect aircraft and helicopters within a radius of approximately 20 km. Data such as altitude, course and speed of the manned flying object are recorded. The risk of a close encounter is now communicated to the drone pilot via the remote control so that he can quickly make an informed decision.

Redundant systems for drones are indispensable today

As you can see, modern drones are equipped with a variety of protection mechanisms similar to those found in airplanes to avoid the risk of an accident or collision. Since you are moving in an airspace where airplanes and helicopters also travel, it is essential to consider drones as aircraft and equip them with the highest possible safety standards.

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