Mid-Air Drone Battery Charging and Swapping

Unmanned Aerial Vehicles (UAVs), colloquially called drones, represent a transformative technological advancement in aviation. UAVs are used in multiple applications across various industries. Due to prolonged operations in different sectors, such as agriculture, logistics, surveillance, military, etc., they require longer battery life. Drone battery charging is the way forward.

To achieve this, UAV or drone manufacturers have started installing costly high-capacity batteries. Due to their high weight, these batteries reduce the overall efficiency of UAVs. Even these high-capacity batteries need regular charging to keep working for extended periods.

Current Challenge in Drone Battery Charging

Moving drones back and forth to the base station for regular recharging is laborious and time-consuming. Since recharging takes much longer than conventional refueling, a charged battery is swapped instead of a drained one. However, one limitation of ground-based swapping stations is an interruption to the mission. For example, if a drone monitors a target, then going to a base station for battery replacement results in a mission delay or failure.

Wouldn’t it be great if batteries were replaced or charged mid-air to overcome the above challenges?

Current Scenario of Drones’ Batteries

Initially, Lithium Polymer (LiPo) batteries were the main source of power for UAVs or drones because they were lightweight and had a high energy density. However, it did have a few disadvantages, including a short lifespan, low discharge rate, and low flight times, often not exceeding 20 minutes. Li-ion batteries were developed as a solution to the issues with LiPo batteries. They offered several advantages, such as high durability and energy density, enabling longer flying times.

Another such development is high-voltage LiPo batteries. They have a high energy storage capacity and prolong their flying time. This technology also enables UAVs to perform more demanding tasks, such as heavy lifting and high-speed maneuvers.

The evolution of drone battery technology has been a journey to remember, marked by continuous innovation and improvement. Each development has played a crucial role in shaping the UAV industry, from the early days of LiPo batteries to solid-state batteries.

Various Applications of UAVs and Operation Time

Over the last decade, UAVs have been used across the world for civilian and military applications.

Applications of UAVs and Operation Time

Figure: Applications of UAVs and Operation Time

Drone Battery Recharging or Replacing

The battery must be constantly recharged or replaced to meet various applications requiring high-performance and long-range operations.

  • Recharging: Recharging a UAV’s battery is tedious and time-consuming. It directly affects the operational time
  • Replacing: Replacing a UAV’s battery can be another option. This process could save some time relative to recharging

UAV battery swapping is a technical advancement in battery recharging that has the potential to significantly improve the profitability of new UAV industries that depend heavily on the usage of tiny unmanned platforms, such as logistics. The fast replacement of modular batteries would allow for the speedy turnaround of UAVs with exhausted batteries and maximize the work duration. Battery swapping is now done on the ground, but this technique might be improved if it could be done while the UAVs are in mid-air.

Mid-Air Battery Swapping

The proposed technology of mid-air battery swapping is similar to mid-air refueling, also referred to as aerial refueling. Aerial refueling is the process of pumping fuel from one aircraft to another in mid-air. This technology enhancement of UAV battery swapping in mid-air can be better than ground-based battery recharging or swapping. With the aid of this technology, UAVs will be able to finish their mission without interruption. This is a niche concept, and a handful of researchers have explored it.

UC Berkeley:

They have developed a technology that allows a main quadcopter to fly using a primary battery and has a docking platform attached to it. A “flying battery” is a mini quadcopter with a backup battery. It mates with the main quadcopter’s platform using its docking legs. During docking, connectors between the legs and the platform allow power transfer from the auxiliary battery to the primary quadcopter. Abrupt switching between the primary and secondary batteries is made possible by a specially designed circuit. The main quadcopter switches back to the primary battery once the secondary battery is fully discharged, and then the flying battery is commanded to undock and return to the ground. Simultaneously, another flying battery docks on the main quadcopter. The process of docking and undocking keeps on repeating until the primary battery of the main quadcopter is completely drained, which is used only between docking and undocking of the mini quadcopter. This increases the flight time of a multi-rotor from 12 minutes to 57 minutes.

Ben-Gurion University of the Negev:

They have introduced a new concept and mechanism, i.e., The Flying Hot-Swap Battery (FHSB), for an in-flight battery replacement system. It involves two different types of UAVs: a leading drone that carries the auxiliary FHSB system and a refueler UAV. The procedure of changing the battery starts when the refueler UAV positions itself over the flight path of the FHSB drone. The battery replacement process begins when the FHSB system detects a charged battery cartridge inside the receiving compartment. The “refueler” UAV then positions itself below the FHSB drone. The drained battery cartridge is scrolled toward the refueler UAV to recharge after the battery cartridge has been replaced. This innovation facilitates battery swapping in mid-air with an average time of 15.2 seconds with only 0.81% energy loss. This allowed the drone to fly continuously without changing its flight direction.

The University of Akron:

They have created computer software that controls two UAVs at a time. One “worker UAV” has an assigned task, and another battery supply UAV carries a charged battery. The software will control the operations and lining up of both UAVs in mid-air. After the two UAVs have been attached, the instructed mechanical parts will swap out the exhausted battery with the newly charged battery. Following the exchange, the UAV will separate, with the worker UAV continuing with its task and the battery supply UAV returning to the ground control station.

Aero Team Eindhoven:

A Netherlands-based company is planning to build expressways from one center to another center, i.e., Distribution centers. If a UAV’s battery is empty midway, charging stations are located on those expressways. Tiny drones fly to the cargo drone from there with a new, full battery. They clip onto the larger drone and swap the battery in mid-air.

Video Credit: TUeCursor

Advantages of Mid-air Drone Battery Swapping

Mid-air battery swapping has several advantages over recent technology, such as,

  • Eliminate interruption in assigned missions
  • Infinite range for operations
  • Eliminate unnecessary traveling of UAVs for battery replacement
  • Enhances safety, reliability, and overall efficiency

Latest Development: Use of Gas Turbine in UAV

Hien Aero Technologies has successfully conducted a levitation test for a large, unmanned eVTOL (electric vertical take-off and landing) using gas turbine power generation for the first time in Asia for approximately one minute. Using a turbine as a power source, the UAV can achieve flight distance and time that are impossible with a pure electric UAV. The Gas turbine-powered UAV was able to achieve a 100 kg maximum take-off weight, with a 180 km maximum cruising distance for a 20kg maximum cargo weight. This enables the further use of UAVs for long-haul and long-payload logistics for various applications.
Deploying mid-air refueling technology can further complement these UAVs. The combination of gas turbines, vertical take-off, and mid-air recharging/refueling can further boost the applicability and functionality of UAVs in multiple industries.

Drone Battery Charging: Conclusion

Mid-air drone battery charging and swapping present a transformative frontier in aerial vehicle technology. The concept holds tremendous promise for extending the operational capabilities of drones and other UAVs. By facilitating on-the-fly energy restoration, these systems can significantly enhance aerial missions’ range, endurance, and overall efficiency. However, the successful implementation of mid-air charging and swapping faces multifaceted challenges.

Safety considerations, technology standardization, and robust infrastructure development are critical aspects that demand careful attention. Overcoming these hurdles is essential for realizing the full potential of this innovation. Despite the complexities, the prospect of seamlessly sustaining flight without the need for extended recharging time offers an exciting glimpse into the future of aerial operations, marking a paradigm shift in how we approach unmanned aerial vehicle capabilities. As technological advancements continue, mid-air drone battery charging and swapping stand poised to revolutionize the landscape of aerial mobility, opening up new possibilities for diverse applications across various industries.

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