World’s tiniest, 4-gram solar drone can fly forever with high lift efficiency

The drone has a high lift efficiency of 30.7 grams per watt and a very light power system that uses only 0.568 watts. This allows it to fly continuously using solar power under natural sunlight (920 watts per square meter).

The team at Beihang University in Beijing claims that each component has been designed to balance efficiency and lightweight, and such a design can enable remote monitoring tasks for long periods of time.

Innovative drone design

Limited flight duration is a major challenge for the widespread use of micro aerial vehicles (MAVs), especially those weighing less than 10 grams. These vehicles typically have a flight time of no more than 10 minutes.

Sunlight power is a potential solution to improve the endurance of these ultralight MAVs. However, due to their limited payload capacity and the low lift-to-power efficiency of traditional propulsion systems, previous studies have not achieved untethered, sustained flight for MAVs fully powered by natural sunlight.

According to researchers, these constraints have hindered the practical application of solar-powered MAVs for extended operational tasks.

To tackle these challenges, the team devised a drone with a sizable motor featuring an inner ring of stationary charged plates (stator) crafted from thin carbon-fiber plates with an aluminum foil coating. Adjacent stator plates carry opposing charges, surrounded by a ring of 64 rotating plates, as reported by Ars Technica.

Activation occurs when outer ring plates are charged, initiating attraction between opposite stator plates and setting the rotation in motion. As stator and rotor plates align closely, contact via thin wires facilitates charge transfer and equalization, converting attraction to repulsion. This mechanism sustains rotor movement, ensuring successive rotor plates hold opposite charges to the following stator plate.

Researchers used a thin film of gallium arsenide for solar cells, achieving 30 percent efficiency but requiring a high-voltage converter due to low voltage. They sacrificed efficiency for low weight, arranging multiple converters in series. The system weighs 1.13 grams and steps up the voltage from 4.5 V to 9 kV at 24 percent efficiency.

Optimizing solar flight

During a test flight, ColumbFly launched within 1 second of its solar cell exposure to sunlight. Researchers claim that it can currently fly untethered for 1 hour at a height of 15 centimeters, carrying up to 2 grams of small sensors or controls.

While this may seem modest, the team is optimistic that design improvements will enhance its endurance and payload capacity over time.

With a 4-gram mass, the device achieves a lift-to-power efficiency of 7.6 grams per watt, requiring just more than half a watt to stay in the air. Nevertheless, voltage conversion results in significant power loss. With an efficiency of more than 30 grams per watt, the motor alone only needs 0.14 watts to operate.

Researchers have already proposed several enhancements, including raising motor torque, boosting propeller lift, incorporating solar cells into structural elements, and raising voltage converter efficiency, reports Ars Technica.

Remarkably, the vehicle’s size has already been refined, with a reduced version that weighs only 9 milligrams and stands just 8 millimeters tall. It can rotate its propeller at a speed of over 15,000 rpm using a milliwatt of power.

The details of the team’s research were published in the journal Nature.