Top materials used in drones:
- Carbon fiber-reinforced composites (CRFCs)
- Thermoplastics such as polyester, nylon, polystyrene, etc.
- Lithium ion batteries
It seems like yesterday that drones were novelties, prototypes built by companies and enterprising hobbyists. Now it seems like drones have taken over the world. They are everywhere, serving roles in industry, art, and even as children’s toys. People often overlook the fact that these little flying machines only became common recently. Drones are still in their infancy, and as material and microcontroller technologies improve, the drones of the future will evolve in ways that may seem almost like science fiction.
By examining the way drones are designed and the materials that they are made of, we can understand how this important technology developed and get a sense of how it could advance in the near future.
So, what are drones? How are they designed? And what is driving their surge into becoming a widespread technology?
Let’s find out.
What are drones?
To most people, a “drone” is a specific type of unmanned aerial vehicle (UAV): the multirotor or multicopter. Just as the name implies, these machines fly by directing thrust downwards from two or more motor-driven propellers.
The most popular consumer models are quadcopters (4 rotors), but commercial variants include hexacopters (6 rotors) and octocopters (8 rotors) to provide greater lift. While there are a wide variety of military and civilian drones out there, we will focus on common multirotor drones and the materials they are made of.
In order to fly, drones must be able to generate enough upward thrust to overcome their own weight, so the selection of materials in a drone is dominated by minimising the drone’s mass.
Every gram of material used to make a drone costs energy to lift, and every gram that can be saved improves performance:
- Increased cargo capacity
- Extended flying time
- Reduced inertia and improved manoeuvrability
This process of selecting materials and designing components to minimise mass is called “lightweighting”. This gives us the most important material property selection criteria: minimizing mass by selecting low-density materials.
Drones are complex devices composed of different components working together. Each component fulfils a different function, so different considerations come into play when selecting materials for each part. However, for each piece of a drone, the material density must be taken into account to minimise the weight and maximise performance.
The frame: holding it all together
The frame gives a drone its shape and holds all of the subsystems in place. Because it serves a mechanical function, the most important material property for the frame is strength. For commercial drones, thermoplastics such as variants of nylon, polyester, and polystyrene, are popular choices because they are inexpensive to make into complex parts using injection molding processes.
Thermoplastics also offer good strength and low density, with several varieties having tensile strengths in excess of 100 MPa and densities below 2 g/cm3. Many thermoplastics are also available in filaments which can be used to 3D print custom parts, making thermoplastics a popular component of experimental drones.
While commercial drones can sacrifice some added weight in order to be more affordable, industrial drones prioritise performance. A material which is high in strength can be used in smaller quantities, making for an even lighter, higher-performance drone.
If we use a Matmatch search to find the lowest-density and highest-strength materials, we find the top choice for high-performance drone frames: carbon fiber-reinforced composites. These composites offer high strength, low density, and high stiffness to make light, rigid drone frames.
Motors & propellers: lifting off
Without a source of thrust, a drone would never get off the ground. The motors that drive drones are conventional electric motors with copper windings and permanent magnets. The housing of the motors can be chosen to minimise weight, and either thermoplastics or aluminium alloys present good strength-to-weight ratios.
However, motors can generate significant heat. So, materials with high thermal conductivity, like aluminium, can be used for the housing to help cool the motor.
The rotor blades of drones turn at high speeds, so they tend to absorb the most wear-and-tear when a drone flies (or crashes). Just like the frame materials, choosing an optimal rotor blade material is a matter of maximising strength while minimising weight.
Some rotor blades are made from carbon fiber-reinforced composites. However, rotor blades are frequently damaged and replaced, so many are made of thermoplastics to reduce the cost of replacing them when they break.
Because rotor blades are usually damaged in high-speed impacts while spinning, an engineer seeking to design a durable rotor blade could filter materials by impact strength and density to select a suitable material.
Batteries: the power to fly
Of all the components in a drone, improvements to battery technology might be the most important breakthrough that made modern multirotor drones possible. In the same way that strength-to-weight ratios are considered when designing mechanical components, battery performance can be measured in terms of the battery’s weight.
Measurements like specific energy (J/kg) and specific power (W/kg) describe a battery’s ability to store and release energy in terms of the battery’s mass.
Older lead-acid and Ni-Cd batteries weighed too much for a drone they powered to fly for long, if it could lift itself off the ground at all. However, modern lithium ion batteries offer enough energy and power in a lightweight package to make today’s multirotor drones possible. Future advancements in battery and capacitor technology will enable even lighter, higher-performance drones.
Sensors: the drone’s nervous system
Multirotor drones are engaged in a delicate balancing act every time they fly. If one motor provides too much thrust, the drone will tilt or even flip. Just like how the human body uses a complex network of senses and nerves to balance itself when walking, multirotor drones use an impressive set of sensors and feedback mechanisms to stay in the air.
The most vital parts of a drone’s “nervous system” are its tilt sensors. Combining a mix of gyroscopic sensors and accelerometers, tilt sensors are tied into feedback loops with the drone’s motors.
A drone in flight constantly makes tiny adjustments to motor thrust to remain level, allowing it to recover from air currents and extreme manoeuvres. Some advanced drones can also independently tilt each rotor, allowing the drone to control both the direction and strength of the thrust it gets from each rotor.
Drones can also employ a variety of other sensors to monitor their internal systems and the world around them. Current and voltage sensors help the drone track the energy drawn from its power reserves, helping its pilot know when it is time to land and recharge.
GPS and magnetic sensors aid in navigation by measuring the drone’s location and orientation. Airflow sensors allow drones to detect their airspeed or wind currents, and that information can be fed back into its balancing circuits to make the drone’s flight even more stable.
Microcontrollers and cameras: smarter drones
The same advancements in microchip technology that created the modern smartphone make it possible for drones to be flying computers. Many of the same chips that can be found in smartphones (Intel, Nvidia, Qualcomm, Arm, etc.) also appear in drones.
As drones get smarter, they are becoming capable of taking on more sophisticated tasks with less human control. At present, this means drones can follow predetermined paths without a human pilot or record measurements from an even larger array of sensors. But researchers are learning how to program drones to perform increasingly complex tasks without human help.
To most people, the entire purpose of drones is to carry a camera to heights a human could not otherwise reach. Even basic consumer-level drones carry a camera that either broadcasts video back to a smartphone or records images to memory.
Movie studios use high-end drones to shoot their big-budget films. However, advancements in the field of “computer vision” are turning cameras into more than just a payload or aid for human pilots. The drones of the future will use cameras to see the world around them and use that information to pilot themselves.
Drones are becoming increasingly capable of flying without help from either a human pilot or even GPS to navigate, and this is giving rise to a powerful new capability: drones working together. Drone swarms have previously been comprised of teams of drones using GPS and communicating with a central controller to determine where each individual fits into the group.
However, cutting-edge research has produced drones that use their own onboard sensors, and even their cameras, to recognise other drones and fly in formation. Soon, it may become common to see teams of autonomous drones acting as lifeguards, caring for crops, or flying in search formations to aid disaster relief efforts.
Technology with global impact
Drones seem to be everywhere now. They are shooting movies, starring in movies, helping sell real estate, broadcasting sports, creating new sports, working at farms and factories, hunting other drones, and soon they may be delivering packages. As materials, AI, and microcontrollers improve, drones will continue to revolutionise a broad range of industries.
The future of drones
Drones are growing more popular by the day and revolutionising the way the world works and plays. The materials used in drones are selected to enhance performance with high-strength frames and high battery capacities while minimising weight.
Minimising the drones’ weight maximises their performance, whether it is a matter of making a cinema drone able to perform longer shoots or making a racing drone even more manoeuvrable. Drones are constantly getting smarter, too, and it may not be long before autonomous drones have become an inherent part of everyday life.