Christian Brommer | Foto: aau/Müller

Enabling drones to fly long-durations autonomously

In practical settings, ten minutes of flight time are generally not enough for most applications. A team comprised of researchers from the University of Klagenfurt (AAU) and NASA-JPL/California is working on ways to enable the autonomous flight of drones in several stages with intermittent charging phases. Christian Brommer, AAU doctoral student, has recently published the results of his research.

When Christian Brommer came to Klagenfurt from California, he brought a subtle, barely noticeable American accent with him. We met him to discuss his recent publication on the autonomous and long-duration flight of helicopter-drones, also known as rotorcraft UAS. It quickly became clear that the mission time of such small drones, roughly the size of a shoebox is even shorter than one might generally assume.

The origins of Brommer’s work can be traced back to the time he spent at NASA’s Jet Propulsion Laboratory (JPL) at the California Institute of Technology in Pasadena. The department of agricultural sciences and the Robotic Aerial Mobility Group located there are collaborating on a particular study case: Rotorcraft UAS equipped with multispectral cameras are deployed to patrol agricultural land by air. It is hoped that data collected in this way will allow biologists to determine the condition of the plants. To date, this task has been performed by stationary instruments, which have a limited reach, and light aircraft, which lead to significantly higher costs.

Helicopter-drones can offer an agile and cost-efficient alternative, though they have a disadvantage due to their size. Equipped with a battery the size of a typical smartphone, these helicopters can only fly for a few minutes at a time.

The goal the research team initially set itself was to allow this process to run autonomously. During the flight, the helicopter-drone should recognize when the battery is running low and return to a charging station in a timely manner. Having arrived there, the on-board computer transmits the recorded data to a basestation while the helicopter battery is automatically charged. Once recharged, the drone should be able to take off again. Using this mission plan, a plot of arable land can be accurately surveyed in several stages.

For this sequence to work smoothly, several challenges must be faced, as Christian Brommer explains: “We need sophisticated state-estimation algorithms that provide an accurate location of the helicopter to navigate and touch down precisely on the one square metre charging platform. Markings applied to the charging platform help us to achieve this. These are recognized by a camera and allow greater precision for the navigation required during the landing phase. Our algorithms for the state estimation combine data from several sensors to determine the best possible position of the helicopter. While the navigation of drones in laboratory environments and the aid of motion capture systems are already very accurate, once we are outdoors, numerous factors such as wind, changes in air pressure or lighting conditions that affect the sensors make it more difficult to estimate an accurate location. Especially because the usual GPS positioning only allows an accuracy of about five meters.

The results of the study were recently presented at the internationally renowned IROS conference (IEEE/RSJ International Conference on Intelligent Robots and Systems) and in the Journal of Field Robotics (JFR), in a special issue focusing on agricultural robotics. Having first met Stephan Weiss at NASA’s research centre in California several years ago, Christian Brommer has recently joined him in Klagenfurt, to pursue his doctoral degree here. Brommer grew up in Werne, a small town in the northwest of Germany and is the first one in his family who pursues his PhD. “But life in the countryside also laid strong foundations for my subsequent move into technology and I could always count on the support of my family”, he told us during the interview. He studied at the University of Applied Sciences in Dortmund and then went to JPL to complete his Master’s degree. The initial 6-month contract turned into three and a half years, which had a lasting effect on him: “At JPL you have the opportunity to work with the very best in each discipline. The intensive concentration of knowledge in one place gives you the feeling of having many more opportunities to choose from.” Stephan Weiss, professor at the Department of Smart Systems Technologies at the University of Klagenfurt is widely regarded as the driving force in the area of state estimation for unmanned aerial vehicles (UAV). As a member of Weiss’s research group, Christian Brommer is ideally placed to take his next steps in the world of science.

Christian Brommer, Danylo Malyuta, Daniel R. Hentzen, and Roland Brockers. Long-duration autonomy for small rotorcraft UAS including recharging. In Proc. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2018. https://ieeexplore.ieee.org/document/8594111

Danylo Malyuta, Christian Brommer, Daniel Hentzen, Thomas Stastny, Roland Siegwart and Roland Brockers. Long-Duration Fully Autonomous Operation of Rotorcraft UAS for Remote-Sensing Data Acquisition. Journal of Field Robotics (JFR) Special Issue on Agricultural Robotics. DOI:10.1002/rob.21898

A few words with … Christian Brommer

What would you be doing now, if you had not become a scientist?

I think I would still be working in the field of electrical engineering, in an R&D department, as this fascinated me even at a very young age. Prior to taking up my studies I worked as a DJ, but I gave that up when I entered university.

Do your parents understand what it is you are working on?

My family is very technically minded. When I describe my research topic schematically, my family can easily follow what I am working on.

What is the first thing you do when you arrive at the office in the morning?

I start up my laptop, get myself a coffee, scan my e-mails for important messages and then work through my to-do list.

Do you have proper holidays? Without thinking about your work?

That’s actually quite tricky. I’d like to say yes, but I do think about my work during my time off. When I go on vacation, I make a real effort to devote that time to my family and my girlfriend, who are excellent at distracting me from my work.

What makes you furious?

Not much, I generally stay calm.

What calms you down?

Living in California for three and a half years, I rarely ever saw rain. As a result, I find rainy weather very relaxing at the moment. Cooking and sports are also great.

Who do you regard as the greatest scientist in history, and why?

I would not single out one particular person who made all the difference or made everything possible. In my field, many scientists contribute to the progress, “standing on the shoulders of giants”, as Isaac Newton once said. We all benefit from the small steps that someone else took before us. I can tell you, however, that the first book on robotics that gave me more profound introduction to the theory was by Peter Cork.

What are you looking forward to?

Receiving confirmation that a scientific article I have laboured over for a long time has finally been accepted or has been published is always a joyful moment, as it represents the completion of one of the stages along my path.

Studying technology at the Universität Klagenfurt

Research and teaching excellence is what sets Alpen-Adria-Universität Klagenfurt’s technology programmes apart. Established in 2007, the Faculty of Technical Sciences prides itself on its exceptional student-supervisor relationships, which facilitate continuous, profitable exchange between tutors and students at all levels. Our technology programmes, which have a large practical component and focus on our key strengths (e.g. Informatics, Information Technology and Technical Mathematics), open up a world of opportunities for our students. And if you decide to take a Joint or Double Degree, you can also gain new experience overseas by taking a semester abroad or attending a summer school. More