In this blog post, we’ll explore the background, core technology, and social significance of “ANGELSWING,” a disaster relief drone developed in response to the Nepal earthquake.
At approximately 11:56 a.m. (local time) on April 25, 2015, a massive magnitude 7.8 earthquake struck Nepal. The quake caused extensive loss of life and property damage, and the devastation was further exacerbated by a strong magnitude 7.3 aftershock in May of the same year. The disaster was widely reported around the world through various media outlets, and students at Seoul National University in South Korea also learned of the news. Some of them joined forces to provide even a small amount of assistance in this severe disaster situation, deciding to develop a drone for disaster relief and donate it to Nepal free of charge. I also participated in this effort as an engineer, and the project that emerged from this collaboration is “ANGELSWING.”
“ANGELSWING” is a drone designed to acquire spatial information and create crowdsourced maps necessary for locating survivors and delivering relief supplies. It was also developed to be suitable for use at disaster sites, as it is less expensive to manufacture than existing commercial drones and relatively simple to operate. To effectively carry out these missions, it required features that set it apart from ordinary drones, with the core capabilities being “long-endurance flight” and “long-range communication.” Of course, these technologies had already been applied to existing drones, but implementing them within a low production cost budget was the most important goal for “ANGELSWING.”
First, let’s examine the technology that enables “ANGELSWING’s” long flight duration. For an unmanned aerial vehicle to fly in the air for an extended period, it must have a stable power supply within the airframe. This is because it is difficult to utilize a separate power source while in the air. Accordingly, rather than using commercially available batteries as-is, we developed our own battery system capable of providing power for extended periods.
It is easy to assume that connecting more batteries generally allows for longer flight times, but experimental results showed that simply increasing the number of batteries could actually reduce efficiency in some cases. This is because more energy is consumed to support the increased weight of the batteries. Therefore, determining the optimal battery capacity was of the utmost importance, and we conducted numerous flight tests on various combinations of propellers, motors, and batteries to optimize the aircraft.
This allowed us to calculate the thrust required for mission execution, and the UAV’s cruising speed was determined to be approximately 12–13 m/s. Based on this, we conducted additional tests to identify a powertrain capable of generating the necessary thrust with minimal power consumption. Various BLDC motors—including 650 kV, 680 kV, and 830 kV models—were used in the experiments, and the motor that produced the required thrust with the least power was selected for the prototype. The battery was also selected through comparative testing using the same method.
The 5,200 mAh lithium polymer (Li-Po) 4S1P battery enabled flight times of over 40 minutes, while the 10,000 mAh battery allowed for flights of up to approximately 90 minutes, securing a range of over 60 km. Ultimately, “ANGELSWING” adopted a 4-cell-4-pack or 4-cell-5-pack configuration. The 4-cell configuration connects four batteries in series to achieve high output, while the 4-pack or 5-pack configuration connects these battery packs in parallel to extend flight time. This enabled the creation of a drone capable of flying for about 1 hour and 30 minutes without a separate power source.
However, this flight time alone was not sufficient. Therefore, solar energy was utilized as an additional power source. Mounting solar panels on both wings of the drone allows for a further extension of flight time. Of course, since the panels also add weight, an optimal design that considers the overall balance and efficiency of the aircraft was necessary. Solar panels are a highly effective technology for extended flight, as they offer the advantage of providing a continuous power supply during flight, rather than relying solely on batteries stored inside the drone. Ultimately, by appropriately combining high-capacity batteries with solar panels, we were able to significantly increase the drone’s flight time.
Next, we’ll examine long-range communication technology. Most drones developed and used at the time relied on radio communication. While this method posed no problem for users controlling drones within direct line of sight, it was not suitable for disaster response drones like “ANGELSWING” that needed to be operated from a distance.
To address this, “ANGELSWING” utilized the LTE (Long Term Evolution) mobile communication network instead of conventional radio communication. The method was relatively simple. A microcomputer connected to an LTE modem was installed on the drone; before flight, a program was loaded to automatically set up a server, and data was then transmitted and received through that server.
By connecting to nearby cell towers using a USB dongle capable of 3G and 4G communication, the drone could be operated over long distances wherever an internet connection was available. The USB dongle transmitted information generated by the autopilot in real time and, conversely, relayed commands from the ground control system to the autopilot.
It was also possible to transmit real-time video from a camera connected to the drone’s onboard microcomputer to the ground control system. However, video delays occurred in some situations due to a temporary loss of communication caused by insufficient power to the microcomputer, which was powered by a 5V 2A power supply. To resolve this, a 5V 5A BEC was connected to ensure a stable power supply.
The biggest advantage of this method is that it utilizes mobile communication networks, allowing the drone to be operated even from remote locations. Of course, slight errors may occur depending on the communication environment, but these were at a level that field managers could easily compensate for, so there were no major issues in actual operation.
In this way, “ANGELSWING” implemented two core technologies—long-duration flight and long-range communication—at a relatively low cost. It offered performance that set it apart from existing commercial drones, and the prototype developed at the time achieved extended flight time and LTE communication capabilities at a production cost of approximately 2 million won. It was also significant in that it was developed at a much lower cost compared to the eBee, a commercial product with similar performance at the time.
Subsequently, the “ANGELSWING” project confirmed the potential of disaster response technology by delivering a test drone to a disaster site in Nepal. Furthermore, “ANGELSWING,” which has since grown into a startup, continues to utilize drone technology for mapping disaster-stricken areas and conducting humanitarian activities. As drone technology continues to spread into various industries and everyday life, the “ANGELSWING” case serves as a prime example of how cutting-edge technology can be harnessed to save lives and contribute to society.
