Research Showcases Unmanned, Solar-Powered UAVs
If you've ever had a drone deliver a package to your front door or eaten conventional produce, chances are you've participated in one of the many uses of unmanned aerial vehicles (UAVs). These pilotless aircraft function within various industries, including agriculture, military operations, delivery services, and weather monitoring.
Although UAVs have many functions, their reliance on batteries also causes many limitations. Batteries add heavy weight and high costs, shorten flight durations, incur significant downtime due to recharging and (often expensive) battery replacement and maintenance. Additionally, the lithium mining required to produce batteries releases fossil fuels and CO2 into the atmosphere. Extracting lithium also uses a vast amount of water — contributing to water insecurity, often in water-poor regions such as Chile and Argentina.
Recent research from Georgia Tech's Schools of Interactive Computing and Computer Science, led by Georgia Tech professor, director of Ka Moamoa research lab, and TSRB resident Dr. Josiah Hester and PhD student Rishabh Goel, reveals how to eliminate these challenges: implementing solar power.
An article published by the team in February describes the process and outcome of developing a battery-free UAV that can sustain long-term air missions by harvesting solar energy. The aircraft stores harvested energy in capacitors, which store and release electrical energy by distributing charges onto plates. According to the article, unlike batteries, the capacitors are "lightweight, can endure millions of charging cycles, and intelligently regulate the energy for all operations." Thus, the switch from batteries to solar energy stored in capacitors can potentially increase the widespread use of UAVs.
Goel said that while he and Hester had individual interests in battery-free computing, the idea for the UAVs was born out of collaboration. "I'm a robotics person, and I always loved creating… So I was talking with [Hester] and just brainstorming ideas for what my research could potentially be. And we were joking like, 'Oh, it would be fun if we could combine computing with [robotics]," said Goel. Although it began jokingly, when the pair teamed up with collaborators at the University of Massachusetts Amherst, the idea started to solidify into something tangible. They published their first article on battery-free UAVs in 2023 and continue to evolve the idea, with their most recent publication being the February article.
However, the process wasn't without obstacles. Many of these obstacles stemmed from the lack of prior knowledge about batteryless UAVs and the large amount of space required for the design. Furthermore, the removal of batteries presented challenges that do not exist for traditional flight controllers, one being the aircraft's energy awareness. "The big issue with battery-free robotics, or anything battery-free, is you have to be very aware of the energy in your system — not just how much energy is in your system right now, but also how much energy you are harvesting," explained Goel. With traditional flight controllers, energy is expended whenever necessary; however, with solar power, the amount of energy available for use depends on external factors, like weather, time of year, and the angle and direction of the craft.
Goel developed an algorithm to enhance the device's energy awareness to address this issue. It began by logging the amount of energy in the aircraft's system and capacitors. "We use that data to predict if our energy and system are going up or down. And based on that, we can predict if we can be more aggressive with how we're using our energy or [if] we have to be more conservative because we're going to run out," explained Goel.
Along with managing energy awareness, the team also focused on designing a lightweight UAV that could sustain long flights. Ironically, according to Goel, the earliest prototype had wings that were too light. "It could fly, but with a sudden wind gust, it would become unstable and lead to crashing," said Goel. So, creating a system that was simultaneously lightweight and controllable was vital.
Finally, making UAVs more widespread also required making them environmentally conscious. For Goel, this means making sustainability a first step: "If we don't think about sustainability from the start, it's going to lead to the system becoming more of a burden on the environment rather than helping it."
In upcoming research, the team aims to develop more intelligent methods for predicting how much energy they harvest. One idea presented by Goel is to "actually forecast, like a weather forecast, how much energy we'll be getting and use that information for more intelligent controls." The team also aims to add a collaborator specialized in aerodynamics, who can assist with the in-flight stability of the UAV.
However, the primary goal remains to make UAVs more widespread by combating the limitations created by batteries. "As long as we can make a more robust and stable flight in good weather conditions, we can fly indefinitely while the sun is out. That's the dream," said Goel.
Ultimately, Hester and Goel’s findings display how switching from batteries to solar power not only makes for a more sustainable device but also expands the limitless uses for UAVs.