How do you successfully pilot a remote-controlled helicopter in the remote expanses of the Arctic Ocean when the compass can’t provide reliable positioning data? Engineers on board the Alfred Wegener Institute’s research icebreaker Polarstern specially programmed a multicopter, allowing it to navigate despite the deviations produced by the Earth’s magnetic field near the North Pole. The researchers recently celebrated the copter’s first successful autonomous flight and landing on an ice floe.
According to Sascha Lehmenhecker, an engineer at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), “At high latitudes, autonomous navigation is a major challenge.” “Navigation systems normally use magnetic sensors. But near the poles, the lines of the Earth’s magnetic field are nearly perpendicular to the ground, making precise navigation extremely difficult. That’s why commercial multicopter control systems aren’t well suited for use in polar regions.”
Together with the PhD candidates Michael Strohmeier and Tobias Mikschl from the University of Würzburg, Lehmenhecker refined the control systems for multicopters –these roughly half-metre-long devices, powered by multiple propellers, are intended to land on ice floes and fly back to their “mother ship” autonomously several hours later. The particular task: both the ice floe and the ship are in motion. The ship has to continue on its scheduled course to conduct other research, while wind, waves and currents cause the ice floe to drift. And it’s precisely the direction and speed with which it drifts that the multicopter needs to determine.
The development team pursued two approaches to allow the multicopter’s control system to compensate for the distortions in the positioning. “In the first approach, the multicopter remains in constant contact with a receiving station, which uses the copter’s GPS data to calculate the discrepancies. In other words, the multicopter transmits its GPS position to the station, which in turn transmits back the corresponding, adjusted coordinates,” explains Lehmenhecker. “The second option: we use two onboard GPS receivers to calculate the actual change in the copter’s position. Though this is the better method, it’s also much more complex, and we’re still just starting to develop it,” clarifies the AWI engineer.
The system passed its first test, conducted on an ice floe in the arctic Fram Strait (79° N parallel), with flying colours: the team and copter were left on a floe. Now clear of the magnetic interference produced by electric motors on board the Polarstern, the team manually flew the copter roughly three kilometres out, to the edge of visual range. They then activated the autonomous return programme – and the multicopter flew to the pre-set coordinates and safely landed on its own.
Sascha Lehmenhecker and his colleagues in the AWI Deep-Sea Research Group came up with the idea for this development in connection with the use of sensitive devices under the ice. One example is the Group’s torpedo-shaped autonomous underwater vehicle (AUV) “Paul”, which explores the ocean beneath the sea ice. “In order to optimally plan its dives, it’s important to have precise information on the movement of the sea ice,” explains Lehmenhecker. Conventionally, this was achieved by deploying “ice trackers” on floes with the help of a Zodiac boat or a helicopter – a difficult and time-consuming method. Further, the researchers generally try to avoid leaving the safety of the Polarstern wherever possible; after all, water temperatures hovering around the freezing point, jagged ice floes drifting to and fro, not to mention polar bears, represent additional risks and should be kept to a minimum.
The Deep-Sea Research Group first used a multicopter developed by the AWI during a 2012 expedition. Flying by remote control, it landed on the ice and used GPS to determine its position, then transmitted the data back to the research ship, which was monitoring Paul’s dive. In this way, the multicopter took on an important role, offering navigational support for the AUV. Once each dive was complete, the ship had to return fairly close to the multicopter’s position: the pilot had to remotely guide the copter back to the ship, which was only possible in visual range. Extremely pleased by the successful test, which was conducted under the auspices of the Helmholtz Alliance “Robotic Exploration of Extreme Environments” (ROBEX), Sascha Lehmenhecker recaps what it means for researchers: “This new development will expand the service radius of our copters from visual range to as much as ten kilometres.”
