Abstract
Limited flight duration is a considerable obstacle to the widespread application of micro aerial vehicles (MAVs)1,2,3, especially for ultralightweight MAVs weighing less than 10 g, which, in general, have a flight endurance of no more than 10 min (refs. 1,4). Sunlight power5,6,7 is a potential alternative to improve the endurance of ultralight MAVs, but owing to the restricted payload capacity of the vehicle and low lift-to-power efficiency of traditional propulsion systems, previous studies have not achieved untethered sustained flight of MAVs fully powered by natural sunlight8,9. Here, to address these challenges, we introduce the CoulombFly, an electrostatic flyer consisting of an electrostatic-driven propulsion system with a high lift-to-power efficiency of 30.7 g W−1 and an ultralight kilovolt power system with a low power consumption of 0.568 W, to realize solar-powered sustained flight of an MAV under natural sunlight conditions (920 W m−2). The vehicle’s total mass is only 4.21 g, within 1/600 of the existing lightest sunlight-powered aerial vehicle6.
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Data availability
All data generated or analysed for this paper are included in the published article, Methods and Supplementary Information. Original videos and sensor data are available from the corresponding authors on reasonable request.
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Acknowledgements
This work is supported by the National Natural Science Foundation of China (grant number 52272384). Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Natural Science Foundation of China.
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Contributions
M.Q. and X.Y. proposed and designed the research. W.S. and J.P. designed and built the ultralight MAV. W.S., R.M. and J.W. conducted the experimental work on the electrostatic-driven propulsion system. J.P. and J. Li conducted the experimental work on the ultralight kilovolt power system. Z.L. and J. Leng contributed to the modelling and data analysis. W.S., J.P. and M.Q. drafted the paper. All authors provided feedback.
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Extended data figures and tables
Extended Data Fig. 1 The structural composition and assembly diagram of the miniaturized prototype.
It can be seen that the vehicle has a very simple structure, making it suitable for further miniaturization.
Extended Data Fig. 2 Characteristics of the electrostatic-driven propulsion system.
a, System photo (an electrostatic motor and a propeller, 1.96 g in mass). b, Power consumption concerning applied high DC voltages, with error bars defined in s.d. c-d, The lift-to-power efficiency characteristics of the propulsion system with four different propellers. e-f, The lift and current curves of propulsion systems from different production batches (A, B, C, D) under different applied voltages.
Extended Data Fig. 3 Experiment and simulation for the electrostatic motor.
a, Voltage-speed curves of electrostatic motors with 0.2 mm width and 3.8 mm width electrode plates. It can be seen that the wide electrode configuration outperforms the narrow electrode configuration. Meanwhile, the rotational speed of the narrow electrode configuration has reached its peak at 6 kV, and the electrostatic motor shows a slight discharge at this voltage, which indicates that the electric field strength to break through the air has been reached. b, Two-dimensional simulation for the electrostatic field of the two electrode configurations. It can be seen that the electrostatic field strength of the wide electrode configuration is consistently higher throughout the entire rotation area (as indicated by the darker color). In contrast, although obtaining a higher electrostatic field strength near the electrodes, the narrow electrode configuration suffers a rapid decline as the distance from the electrodes increases, leading to an overall driving effect that is inferior to that of the wide electrode configuration.
Extended Data Fig. 4 Processing and assembly of electrostatic motors.
The electrostatic motor is mainly assembled into a three-dimensional structure with two-dimensional components.
Extended Data Fig. 5 Detailed characteristics of the high-voltage power converter. The relationship between circuit characteristics and switching frequency, duty cycle, and load resistance when the input voltage is 3.7 V.
A 3.7 V Li-ion battery powers the HVPC and supplies high output voltage for different resistances (100 MΩ, 200 MΩ, 500 MΩ and 1 GΩ). The current through the load resistance is measured, the output voltage is calculated by the equation U = IR, the output power is calculated by Pout = I2R. With a suitable range of frequency and duty cycle, we can ensure that the power conversion efficiency of the HVPC remains constant, allowing for a wide range of output voltage adjustments.
Extended Data Fig. 6 Fabrication process of flexible PCB for the ultra-light kilovolt power system.
a, Attach copper foil to the polyimide film. b, Use laser cutting to create the desired circuit traces without damaging the underlying polyimide film. c, Remove excess copper foil. d, Place adhesive patches. e, Cover the top layer with polyimide containing holes in the shape of solder pads. f, Apply external pressure to compress the layers and heat them at high temperature for 2 h.
Supplementary information
Supplementary Video 1
The integrated vehicle and its sunlight-powered untethered flight. When the sunlight hits the vehicle, the integrated vehicle successfully takes off and performs a sustained flight. When the shading board blocks the sunlight, the vehicle loses power and descends. The sunlight hits the solar cells at an inclination of 48° with a light intensity of about 920 W m−2 (1 sun = 1,000 W m−2).
Supplementary Video 2
Working principle and process of the electrostatic motor. The video shows the process of charge transfer in the electrostatic motor, demonstrating its working principle from a microscopic perspective. During the rotation of the rotor, the rotor blades pass through the electrode plates and come into contact with the electric brushes, while the rotor blades acquire an electric charge through the brushes.
Supplementary Video 3
Stalling test of the electrostatic motor. The current characteristics of the electrostatic motor are opposite to those of traditional electromagnetic motors, which produce maximum current when starting or in a stalled state. The video shows that the electrostatic motor has almost zero current in a stalled state and the current recovers after releasing the rotor.
Supplementary Video 4
Operating temperature comparison of the electromagnetic motor and the electrostatic motor. Benefiting from the characteristic of low current of the electrostatic motor, the power consumption of the electrostatic motor is 0.181 W on average and no heat is generated during the rotation. The video shows that when driving the same propeller at the same rotating speed, the temperature of the electrostatic motor remained at its initial temperature after extended operation, while the traditional electromagnetic motor’s temperature rose rapidly under the same load.
Supplementary Video 5
Long-term test for flight operation. In the video, we conducted a durability test on the vehicle for one hour, and the vehicle remained in flight throughout the experiment. The subsequent experimental results show that the electrostatic motor is still able to work normally and the performance remains stable after one hour of continuous operation.
Supplementary Video 6
An 8-mm ultralight prototype. In the video, we create an 8-mm prototype (mass 9 mg) with low power consumption (0.97 mW) and achieve tethered flight with the lift-to-power efficiency of 9.2 g W−1. To our knowledge, it is the smallest micro-aircraft currently and can fly along vertical guide rails, with a maximum lift-to-weight ratio of 2.3.
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Shen, W., Peng, J., Ma, R. et al. Sunlight-powered sustained flight of an ultralight micro aerial vehicle. Nature 631, 537–543 (2024). https://doi.org/10.1038/s41586-024-07609-4
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DOI: https://doi.org/10.1038/s41586-024-07609-4
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