Researchers have created an ultralight drone with unlimited autonomy — where does it get its energy?

The ultralight research drone can operate autonomously as long as the sun shines. Its shape differs from all previously created drones.

Researchers have developed the CoulombFly drone, which is capable of hovering autonomously in sunlight. The drone’s design combines solar panelsThe solar panel consists of a voltage converter and an electrostatic motor that turns a helicopter-like propeller. All components are customized to balance efficiency, weight, and sunlight gain.

This is a prototype that has many limitations. There is currently no control hardware on board, so the drone can only drift in the wind. Its components are very thin and fragile. The CoulombFly is one of the lightest drones, weighing only 4.21 grams. The study is described in the journal Nature.

. https://youtu.be/-sQR0lG4OLA

Most drones use electromagnetic motors that include many rather heavy metal coils. The developers of CoulombFly decided to focus on developing a lightweight electrostatic motor. They rely on the attraction and repulsion of charge to power the motor. It consists of an inner ring of fixed charged plates called a stator. These plates are created from thin carbon fiber coated with aluminum foil. During operation, adjacent plates have opposite charges. Around the stator is a ring of 64 rotating plates.

The motor starts running when the plates in the outer ring are charged. Since one of the nearest plates on the stator is guaranteed to have an opposite charge, rotation will begin. When the stator and rotor plates reach maximum convergence, thin wires make contact, allowing charge to be transferred between them. This ensures that the stator and rotor plates receive the same charge, turning attraction into repulsion. This system requires very little current to operate, but it also requires a high voltage between the plates.

With a 10 cm diameter propeller with 8 blades, the system produces a lifting force of 5.8 g. This determines the design conditions for all other components.

The solar cells were made of a thin film of gallium arsenide. It is much more expensive than other photovoltaic materials, but provides the highest efficiency of —30% energy conversion, compared to over 20% for others. Batteries provide relatively high current but low voltage — the opposite of what is needed. So it needs a transformer.

With this one, the researchers sacrificed efficiency for light weight. They have created a series of voltage converters that weighs only 1.13 g, but increases the voltage from 4.5 V to 9.0 kV. But the efficiency of power conversion is only 24%. As a result, the CoulombFly’s design is dominated by a cylindrical engine topped with a propeller. Below is a platform with solar cells on one side, balanced by an energy converter on the other.

To test the drone, the researchers simply opened a window on a sunny day. The drone took off and hovered for over an hour, and all indications are that it would continue to do so as long as sunlight provided enough energy.

The system required 0.568 watts of power to stay airborne. Given the total mass of 4.21 g, this means an efficiency of 7.6 g/W. But much of this power is lost during voltage conversion. The motor requires only 0.14 W, giving it an efficiency of over 30 g/W. Some margin allows for the addition of other components — for example, the control system.