How Do Drones Work? A Detailed Guide
One of the factors that drove the surge in popularity of drones in recent years is the fact that they are now simpler and easier to use than ever. Even a first-time drone pilot can fly it around like a pro with just a few hours of practice. This apparent simplicity belies what lies under the hood of these consumer-friendly drones: a system of components that interact with each other in various, complex ways.
So, how exactly does a drone work? The best way to answer that question is to look at each part of the drone and look at its core function, how it works, and how it interacts with the other parts of the drone as part of a well-oiled system. This could be a long read, but a better understanding of your drone can make you an infinitely better drone pilot.
An overview of multicopters
Although there are several types of drones in use today, we’ll focus on the multicopter variants as they are the most popular. While fixed-wing drones still play an important role in various industrial drone applications, they have been overshadowed by multicopters in the past several years. Practically everyone is familiar with multicopters: drones that have lightweight frames that house their various electronics and are supported by multiple (usually four) propellers.
Quadcopters have rapidly become the preferred model consumer-level drones as they are easier to use and don’t require a runway to take off and land. They also can hover in place, which makes them excellent for aerial photography and remote sensing.
The propellers are one of the most visible features of a quadcopter drone. They function in much the same way as the propellers of a helicopter do: they provide both lift and propulsion. This means that the propellers essentially do double duty. Aside from carrying the weight of the drone as well as its payload, the propellers also allow a drone to move forward or sideward according to the commands received from the pilot.
How exactly do the propellers work? There are a few key details that might clue you in on the answer: the fact that there are multiple propellers, and that they rotate in different directions. If any one of the propellers fails, the drone will almost certainly rotate uncontrollably and crash.
Basic physics states that for every action, there exists a corresponding and equal reaction. In the case of drones, the rotational motion that motors exert in the propellers also results in a rotational force on the drone itself. To counteract this, the other drone propellers rotate in an opposite direction. This means that, at any point, the rate and direction of rotation of a drone’s propellers is a delicately coordinated dance designed to maintain the drone’s stability.
Propellers also allow a drone to thrust in whatever direction the drone pilot wants it to. This happens by pitching the drone or making the rotors at one side rotate faster than those at the opposite side. This inequality in thrust is what propels the drone in any direction. In terms of aircraft terminology, a pitch and a roll differ only in the direction (one is forward-backward while the other is side-to-side), but the aerodynamic mechanisms behind them are identical.
Not all propellers are made equal. You may have heard of quieter propellers, or ones that can generate more lift and propulsion. The choice of which propeller to use is often a compromise between price, durability, stability, and power consumption.
Recently, carbon fiber propellers have started to become a thing in both consumer and professional-grade drones. These are more expensive than the old-fashioned plastic propellers but also produce less vibration and are capable of quieter operations. However, they are also more rigid. This lack of flexibility makes them a little less aerodynamic, which means that the motors will have to work more to create the same level of performance.
A tradeoff between lift and motor power consumption is also made when choosing the length of your propeller. Longer propellers are capable of generating more lift but are also heavier, which means that the motors need more power to rotate. Due to their added length and weight, they also carry higher rotational momentum. This makes drones with large propellers a bit sluggish when making sudden changes in direction or even when coming to a stop.
Whichever type of propeller you decide to go for, what’s important is that you always buy and install them in complete sets. Propellers are designed to work together. Mixing and matching propellers from different sets will result in a very unstable flight.
For each propeller in a drone, there has to be a dedicated motor to make it rotate. As we’ve discussed, each propeller has to rotate in a different direction and speed. This means that each drone motor runs independently but has to be coordinated with all other drone motors. This task of coordination is the job of the electronic speed controller (ESC), which we’ll get to in a while.
Outside of toy drones, most consumer and professional-grade drones use brushless motors. The alternative, brushed motors, is still used nowadays but to a much lesser degree. What’s the difference between brushed and brushless motors, and why is this important?
Of the two forms of motor technology, brushed motors were developed earlier. The rotation of the rotor of a brushed motor is induced by the contact of the rotor’s brushed with a direct current supply. This flow of current creates a magnetic field which then interacts with permanent magnets in the motor’s stator, which drives the rotation of the rotor. Speeding up the rotation of the rotor is simply done by increasing the currently supplied to the motor and thus creating a stronger magnetic field.
Brushless motors essentially reverse the process by having permanent magnets installed in the motor’s rotor. The current supply is instead fed to the stator, which features a series of coils along its perimeter. When a current is supplied to these coils, each coil generates its own magnetic field which then interacts with the magnets on the rotor, making it turn. The current supply is shifted from one coil to another to make the rotational motion continuous.
As its name implies, a brushless motor does not need a brush to provide current supply and create a magnetic field. By doing away with any contact between the power terminals and the motor, a brushless motor becomes more reliable and does not require as much maintenance. In terms of longevity, a brushless motor beats a brushed motor by miles. Brushless motors are also inherently quieter and more efficient.
With so many benefits falling under the brushless motor column, you may be wondering how brushed motors have managed to stay relevant until today. There is only a single, major reason that explains this: brushed motors are much cheaper. For low-cost applications, such as for cheap toy drones, the use of brushed motors helps keep the price way down. Issues with wear and tear and overheating are not as apparent with these toy drones since their small batteries prevent them from flying for a long time anyway.
Brushless motors may be the new standard when it comes to drone motors, but there are still a few variants and models available that drone pilots can choose from. Much like propellers, the choice of which motor to use is often a compromise between cost, power consumption, and various performance needs.
Bigger drones or those with heavier payloads will obviously require more powerful motors with a higher thrust-to-weight ratio. Motors with a higher kV rating are capable of spinning at higher RPM but are typically less efficient. Most drone motors come with throttle curves that show how their efficiency responds to various degrees of throttle – some motors are inherently designed for high RPM operations while others reach peak efficiency at lower RPM.
Electronic speed controllers (ESCs)
Since drone motors and propellers have to work together to keep the drone stable and move it according to the commands received by a drone pilot, there has to be a central “brain” which coordinates these separate components. This is the function of an electronic speed controller (ESC), an electronic circuit that translates the pilot’s commands into directives for each individual drone motor.
Both brushed and brushless motors require an ESC, although the ESCs for brushed motors work a bit simpler. An ESC for a brushless motor can be distinguished by three soldering pads which correspond to the three motor phases of the brushless motor.
If you’re attempting to assemble your own drone and are in the process of picking an ESC, then you need to consider ESC voltage and amperage requirements of your drone. Drone motors designed for high RPM operations have a higher current draw, which means you’ll need to get an ESC with a higher amperage rating. The voltage rating of an ESC is solely a function of the type of battery the drone has. Most ESCs are rated for 3 or 4-cell batteries, which should cover most consumer-grade drones.
Through the years, the technology for drone ESCs has become a realm of competition for drone manufacturers. 32-bit ESCs have now become the norm for most drones as they are capable of transmitting data such as RPM, temperature, and current draw. ESCs that utilize a sine-wave signal for current switching result in quieter and more efficient motors compared to the traditional square-wave ESCs.
A fairly new innovation in the field of drone motors and ESCs is the concept of dynamic braking. This works by utilizing the residual momentum of drone propellers to induce a back-voltage which recharges the drone’s battery by a small amount. ESCs play a role in this process by allowing a switch to Generator mode, where the current flow from the rotor to the battery is reversed.
Flight time has been a perennial issue with quadcopter drones. Upgrading a battery to extend the flight time isn’t always a viable option since the added weight of a bigger battery effectively cancels out the benefits of the additional battery capacity. ESC upgrades and improvements are one of the more creative and innovative ways for drone manufacturers to extend their drones’ flight times without having to resort to upgrading batteries.
ESCs certainly are one of the more complicated parts of a drone. Luckily, if you tend to buy and use as-built drones from famous brands such as Yuneec and DJI, you might never have to worry about ESCs at all. Popular drones come with built-in ESCs that are specifically tailored to their motors, propellers, and batteries. Most of them even use System-on-a-Chip solutions that integrate various components, such as the ESC and flight controller, on a single chip. This has made modern drones smaller, lighter, and easier to repair.
All of the components of a drone work together to achieve a single ultimate goal: to make the drone do what the drone pilot commands it to do. A transmission system acts as a link between the drone and the remote controller that is in the hands of the drone pilot. This is done through either WiFi or by radio frequency signals.
Wi-Fi, despite sounding like it’s the more modern of the two types of transmission signals, is actually only an option for beginner or budget drones. Wi-Fi transmission is cheap and simple to implement, but also has a very limited range. However, Wi-Fi controls allow Wi-Fi enabled devices such as phones and tablets to interface with your drone. Either 2.4 and 5.8 GHz frequency bands are available through Wi-Fi, and drone transmission systems normally switch between them based on which one has a stronger signal.
2. Radio waves
For a wider control range, most drones use radio frequency signals. With such a wide frequency range (from 3 Hz to 3000 GHz), radio waves allow a drone to fly much further away before suffering from signal dropout or attenuation. To ensure that your controller is uniquely paired to your drone, receivers and transmitters are identified using radio frequency identification (RFID). Of course, they also need to be tuned to the same frequency.
More sophisticated transmission systems have provisions for dual-band transmissions, automatically switching between 2.4 and 5.8 GHz to optimize communication. This isn’t always the case, and drones that only use a single frequency band or more prone to signal loss.
Aside from transmitting the commands from the remote controller to the drone, radio waves are also used to transmit real-time video data from the drone’s camera to the controller’s integrated screen or to a tethered device. There is some inherent latency to this problem, although drone manufacturers continue to strive to keep the delay as low as possible.
Some enterprise drones even provide an option for master and slave controls, where the gimbal and the camera can be controlled independently. This can be a particularly great feature for professional drone photography teams, as it allows for worry-free framing and composition of shots.
Neither Wi-Fi nor radio communications is exclusive to drone use. This means that signal interference is something that drone pilots need to anticipate and avoid. Electrical wires and radio communication towers can be particularly problematic. Large obstacles, such as buildings and mountains, also greatly attenuate radio signals and can drastically reduce the effective range of control of a drone.
Radar location system
Most drones nowadays are equipped with some form of Global Navigational Satellite System (GNSS). Many have GPS modules, while a few have a redundant dual system of GPS and GLONASS. These systems employ different satellite constellations but function using the same concept. By receiving signals from several satellites in the Earth’s orbit, the onboard GNSS module determines the drone’s location by a system of triangulation.
A radar positional system serves a lot of functions in drones and has become the basis for many commercial drone applications.
1. Autonomous flight modes
GNSS technology allows a drone to carry out autonomous flight which can be triggered by simple commands from the pilot, such as the setting of flight paths or a single point destination. GNSS guidance also allows a drone to have a Return-to-Home (RTH) function.
2. Survey capabilities
Drones used for surveys – whether for mapping, precision agriculture, inspection, or thermal imaging – will need some sort of radar positioning system to geotag the data that they collect. Even a professional drone photographer can benefit from a geotagging function, as it makes organization and documentation of photos much easier.
3. Flight stabilization
Drones also use GNSS positioning to help maintain a stable hover. When a drone receives a command to hover in place, it uses all the sensors and resources at its disposable to maintain that hover. If the drone detects any deviation from its intended location, this deviation is reported to the drone’s PID controller (which we’ll discuss later on), and the drone makes the moves needed to correct it.
The most basic of drone sensors, gyroscopes have been integrated into even the cheapest drones since they are very affordable and rudimentary. Despite their simplicity, gyroscopes play such an essential that they are still important navigational tools in high-end aircraft and space shuttles.
Based on the concept of conservation of angular momentum, a gyroscope simply consists of a spinning disk mounted on a movable frame. Since the disk continuously spins, its axis of rotation remains permanent, even when the frame it’s mounted on tilts and rotates. The inertial reference frame established by the spinning disk serves as the reference for the tilt, rotation, or angular velocity of its frame, or in our case, the drone itself.
A gyroscope serves both as a tool for measurement and correction. When integrated with accelerometers, a gyroscope measures the degree of pitch, yaw, and roll of a drone as it moves. This data can either be collected for mapping applications or fed back to the drone’s PID controller for course correction.
Gyroscopes play a big role in flight stabilization in practically all drones. When a drone is commanded to hover in place, it can still drift off its intended position due to gusts of wind. When these unintended movements occur, the gyroscope records the data and feeds it back to the drone’s PID controller. The PID controller then directs the drone to counteract the movements and fly the drone back into position.
Gyroscopes only make up a portion of the sensors that detect and record data on the drone’s movements. While gyroscopes specialize in detecting rotational movements, accelerometers detect linear movements in either the x, y, or z-axis. In tandem with GPS technology, accelerometers allow for accurate route tracking of drones, or even your phone or fitness devices.
There are a couple of different types of accelerometers, but the most common is the piezoelectric variant. A piezoelectric accelerometer uses microscopic crystals that produce a current whenever they undergo stress. The force produced by the movement of a drone is enough to induce this current, with the strength of the current directly proportional to the strength of the accelerative force.
Aside from providing feedback on the movement speed of the drone, the accelerometers also play a big role in drone stabilization. When a drone has been instructed to hover, any unintended lateral or longitudinal movement of the drone is detected by the accelerometers and corrected.
The combination of a 3-axis gyroscope and a 3-axis accelerometer is what is commonly known as 6-axis gyro stabilization. This basic system is an essential component of drones – even the cheap toy drones – that allow a drone to maintain a stable hover even in the absence of a GNSS signal.
Moving away from the complex functions of the gyroscopes and accelerometers, barometers have a very simple job: to measure the altitude of the drone. Many people know that barometers measure air pressure, so the method with which it determines the drone’s altitude is quite indirect. First, a barometer needs to be calibrated at sea level. This is done so that the barometer records a baseline sea level air pressure to which all succeeding air pressure readings will be compared to.
With the calibration data on record, the barometer can determine the drone’s cruising altitude by merely comparing the current air pressure with the sea level air pressure. Although this measurement method can be disrupted by strong winds or other unusual air patterns, it is still a more reliable and faster altitude measurement method than GNSS technology. Barometers need to be calibrated every now and then, but they are one of the simpler sensors that drones have.
While not all drones are outfitted with rangefinders, it’s still a common enough feature for the drones available today that it’s worth even a short discussion. A rangefinder is typically a sonar or laser emitter-sensor located at the bottom of the drone that acts as an alternative method to determine the drone’s altitude.
You might ask: why the need for an alternative to the barometer? The difference between the two methods lies in accuracy. Rangefinders are much more accurate, sensitive to minor variations in topography, and are unaffected by meteorological conditions. However, a rangefinder has a very limited range, which is why some drone models have chosen to forego this feature.
The drone’s proportional-integral-derivative (PID) controller, which we have mentioned several times now, is the brain that makes sense of all the data that the drone receives from its sensors. Basically, the PID controller uses that data from the sensors to compare the drone’s current status to its intended or ‘desired’ status. The PID controller then issues the command to the drone motors so that the drone can move closer to its desired position.
In the context of the PID controller, the desired status isn’t just about maintaining a stable hover. It also includes pilot commands, such as moving to a position on the map, flying up to the desired altitude, or following a pre-determined flight path. Such a command will be the basis for the drone’s next set of movements, and the PID controller is responsible for receiving all the data and commanding the individual components of the drone to satisfy the desired conditions.
As its name implies, a PID controller relies on three different algorithms so it can satisfy the desired conditions. These algorithms are aptly called proportional, derivative, and integral methods. None of these algorithms is perfect, and it is through the results of all of them that a drone can achieve the desired conditions as accurately and as quickly as possible.
Each of the three algorithms is different enough to warrant its own discussion, but we’ll keep it short for this article.
- The proportional term allows for rapid correction, especially when there is a huge gap between current and desired values. As this gap diminishes, the overall effect of the proportional term also continues to get reduced. Since the effect of the proportional term becomes infinitely small as the current value approaches the desired value, it becomes impossible for the proportional term alone to make the necessary correction to actually reach the desired value.
- The integral term takes a slightly different approach by considering the accumulated error over time as it approaches the desired value. This accumulated error can either be negative or positive. This means that the integral term will most likely overshoot the desired state on the first approach, and then oscillate back and forth as the accumulated error approaches zero. While it’s theoretically possible for the integral term to eventually reach the desired state, it can take a really long time as it bounces around from positive to negative error margins.
- The differential term considers the rate of change of the error over time as it approaches the desired state. This means that as the actual value approaches the desired value, the differential term works to slow down the rate of approach. This minimizes the overshoot effect of the integral term so that the desired state can be attained more quickly.
Fine-tuning of PID controllers is a hobby that’s pretty huge among the community of DIY drone pilots, and there’s a lot that you can learn by doing it. For those into drone racing, PID fine-tuning is also a way to customize the handling of a drone to better fit their flight style. However, it’s not something you’ll need to bother with if you own an out-of-the-box drone, as these come with perfectly tuned PID controllers.
There isn’t much that needs to be said about the function of a drone’s battery. It provides power to all the essential functions of the drone – the motors, camera, gimbal, sensors, GPS module, and ESCs. LiPo battery technology has pretty much become the standard for all drones due to its compact and lightweight nature. LiPo batteries are quite fragile though, and extra care must be taken when charging or transporting them.
Camera and gimbal
Any drone worth its salt, including some mini-drones and toy drones, are equipped with a camera. The quality of cameras varies greatly across different drone models. Cheap toy drones can have 420p cameras that have really bad latency, while higher-end models can shoot videos at 5.2K resolution, have optical and digital zoom capabilities, and come with a suite of creative camera modes.
Cameras have greatly expanded the horizon of what drones can do. Aside from allowing drone photography and filmmaking, providing drone pilots with real-time video from the perspective of the drone has made drone flight so much more fun and exciting. FPV flight has given drone pilots a level of control and maneuverability over their drones that just cannot be achieved by just relying on visual line-of-sight.
The dawn of drone-mounted high-resolution cameras has also opened up a lot of commercial applications for drones. Aside from the usual aerial photography, drones have been used for mapping using photogrammetry, real estate advertising, civil engineering inspection, monitoring of construction projects, surveillance, and search and rescue. These are just some of the things that are possible with standard RGB cameras and does not even include the applications of drones with other, more advanced sensors.
Cameras are great, but a gimbal attachment elevates drone photography to even greater heights. Not all camera drones come with gimbals. Up to this day, gimbals are accessories that are exclusive to high-end models. However, if you want to go into professional drone photography, you will absolutely need a drone with a gimbal. The mechanical stabilization provided by gimbals in camera drones can never be equaled by digital stabilization.
Gimbal technology is not exclusive to drones. It has been used for decades by the filmmaking industry to stabilize videos, even under rough conditions. Gimbals utilize a system of internal gyroscopes to maintain the camera position at a predetermined axis. The motors inside the gimbal continuously work to keep the camera along the desired axis, regardless of movement and rotation of the frame and other vibrations.
Obstacle avoidance systems are far from being a standard feature in drones. They are pretty much exclusive to the newer and more modern models. In recent years, obstacle avoidance technology has improved by leaps and bounds – perhaps more than any other drone component. This feature is highly sought after by professional drone pilots, as it helps keep their drones safe and allows for more autonomous flight modes.
There is no standard method for obstacle detection and avoidance. In fact, this is another field where drone manufacturers have constantly been trying to one-up each other. Right now, these are some of the most common technologies developed for obstacle detection:
- Ultrasonic sensors transmit and receive ultrasonic waves. The time difference between signal transmission and reception is then used to deduce how far away an obstacle is. This technology has a limited range and is quite prone to interference.
- Infrared sensors work much like ultrasonic sensors but instead emit and detect infrared waves. Infrared waves have a wider range and are less vulnerable to interference. They are also more expensive.
- Stereoscopic sensors are far more sophisticated. Using a system of two cameras, stereoscopic technology can recreate a model of the drone’s surroundings with 3D features and accurate measurements. The algorithm behind stereoscopic technology is much more complex, and the system is also quite expensive.
For DJI, the most sophisticated obstacle avoidance system they have so far is the one that is featured on the Mavic 2 drones. Using a combination of infrared sensors and stereoscopic technology, the Mavic 2 drones effectively have obstacle detection in all directions. The Mavic 2 drones are the first drones from DJI to have an omnidirectional obstacle avoidance system.
Yuneec stands shoulder to shoulder with DJI in this field with their Intel RealSense technology. Features in the Typhoon line of drones, this technology uses dedicated cameras to reconstruct a 3D representation of the drone’s surroundings. The drone then uses this model to map out an optimal route through all the potential obstacles. Moreover, Intel RealSense can remember the models that it has reconstructed to that it no longer needs to remodel a location that it has already visited.
The firmware is of a drone is the software that makes it work. It contains all the built-in features of the drone, its flight modes, autonomous camera modes, camera settings, and allows it to interact with the remote controller. Think of it as the blood that courses through the drone’s circulation system, allowing separate components to interact and work together. Firmware isn’t much of an issue with simple toy drones, but more complex drones are greatly dependent on a fully functioning, bug-free firmware.
In more complex drones, it’s not even just the drone that has firmware. Intelligent batteries, such as those used by the DJI Phantom and Mavic lines, have built-in firmware that helps in battery management and feedback of battery level data. Mechanical gimbals also have firmware that allow them to respond to user commands and to transmit data to the remote controller.
Drone manufacturers periodically release updates to the firmware of their drones. These updates are a way to introduce new features or fixes to existing bugs. In the past few years, DJI has used firmware updates to introduce safety-enhancing features such as geofencing or the feature that prevents flying into pre-identified No-Fly Zones.
The necessity of firmware updates has long been a contentious issue among drone pilot communities, especially since drone manufacturers have started to roll out features that restrict drone flight in the interest of airspace safety. This is a serious issue that warrants a thorough discussion – perhaps in another article.
By looking at the individual components of a drone and how they work together, we can truly appreciate all the complexity behind our beloved flying machines. Underneath the hood of these drones is a complicated interplay of software, circuits, motors, sensors, and data, all functioning in perfect harmony to keep our drones in the sky and make them follow our commands. Armed with the knowledge of what goes on behind the scenes, we can become much better drone pilots.
Perhaps this will inspire you to take the DIY route and build your own drone from spare parts. There’s a whole community behind it, and it really is one of the best ways to understand how each drone component functions. In any case, we owe it to ourselves and to our community to become safer and more educated drone pilots.