Researchers at Beihang University in Beijing have developed an ultralightweight solar-powered drone, named ColumbFly, capable of unlimited flight during daylight hours. Weighing only 4 grams, ColumbFly utilizes a solar cell to generate electricity, creating an electric field between oppositely charged plates arranged in a circle. These opposing charges act like repelling magnets, producing enough force to turn the rotor blades and generate the torque needed to lift the robot off the ground.
The drone boasts a high lift efficiency of 30.7 grams per watt and a power system that requires just 0.568 watts. This allows it to fly continuously using solar power under natural sunlight, which provides 920 watts per square meter. The Beihang University team claims that each component of ColumbFly has been meticulously designed to balance efficiency and lightweight, enabling remote monitoring tasks for extended periods.
A significant challenge for the widespread use of micro aerial vehicles (MAVs), particularly those weighing less than 10 grams, is their limited flight duration, typically no more than 10 minutes. While solar power presents a potential solution to improve the endurance of these ultralight MAVs, their limited payload capacity and the low lift-to-power efficiency of traditional propulsion systems have previously hindered untethered, sustained flight. These constraints have impeded the practical application of solar-powered MAVs for extended operational tasks.
To overcome these challenges, the researchers devised a drone with a sizable motor featuring an inner ring of stationary charged plates (stator) made from thin carbon-fiber plates coated with aluminum foil. Adjacent stator plates carry opposing charges, surrounded by a ring of 64 rotating plates. Activation occurs when the 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 the solar cells, achieving 30 percent efficiency but requiring a high-voltage converter due to low voltage. They sacrificed some 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.
During a test flight, ColumbFly launched within 1 second of its solar cell exposure to sunlight. The researchers report 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 over half a watt to stay in the air. Despite significant power loss due to voltage conversion, the motor alone only needs 0.14 watts to operate, achieving an efficiency of more than 30 grams per watt.
Researchers have proposed several enhancements, including raising motor torque, boosting propeller lift, incorporating solar cells into structural elements, and improving voltage converter efficiency. Remarkably, the vehicle’s size has already been refined, with a reduced version weighing only 9 milligrams and standing just 8 millimeters tall, capable of rotating its propeller at over 15,000 rpm using a milliwatt of power.
The ColumbFly represents a significant advancement in the field of solar-powered MAVs, offering promising solutions for sustainable, long-duration flight and remote monitoring applications.
By Impact Lab
