Drones can determine the direction of gravity without accelerometers.

How drones can determine gravity direction without accelerometers
Drones use accelerometers for proper operation to determine gravity direction. A team of scientists from Delft University of Technology and the CNRS, along with Aix-Marseille University, published a study in Nature on the 19th of October 2022 that showed drones could estimate gravity direction by combining visual movement detection with a model of their movements. These results could explain how flying insects decide the direction of gravity. They are also a step towards the creation of small autonomous drones.

Although drones use accelerometers in order to determine the direction of gravity they are unable to sense acceleration. A team of European scientists, led by Delft University of Technology and involving a CNRS scientist, has demonstrated that drones are able to assess gravity using motion modeling and visual motion detection.

Scientists have studied optical flow to develop this new concept. This is how an individual perceives their movement in relation to their environment. When we move, our retina is swept by the visual movement. When we are riding a train for example, the trees near the tracks move faster than distant mountains. An insect cannot tell the direction of gravity by just looking at optical flow.

Source:
https://techxplore.com/news/2022-10-drones-gravity-accelerometers.html