Small unmanned aerial vehicles (drones) are flying robots that can fly freely in three-dimensional space, so various advanced technologies are implemented. These can be roughly classified into five components. These are (1) airframe system, (2) propulsion system, (3) measurement and control system, (4) communication system, and (5) ground control station system. Among these technologies, this paper focuses (3) on the brain that determines the flight control performance of drones, and describes the current state of technology and future prospects.

This article discusses the aerodynamic technology trends of drone propellers, focusing on three topics: technology for improvement of efficiency, technology that contributes to flight stability, and technology for propeller noise reduction. For the improvement of efficiency, basic aerodynamics of propeller blades, design theory, and efficiency improvement using ducted propellers are introduced. As a method to improve flight stability, the improvement of aircraft maneuverability using variable pitch propellers is discussed. For propeller noise reduction, recently proposed “Looprop”and noise evaluation method based on psychoacoustics are introduced.

Technical development of general industrial motors is required to contribute to SDGs. The goal of technology development for drone motors is to increase the output density (output/weight) and achieve higher efficiency. In addition to the motor itself, it is important to have high efficiency as a total system that combines all elements such as the frame, battery, propeller, motor driver device, and controller that make up the drone. In motors for drones, for which the structure and drive method seem to have already been established, we are considering applying a drive method using vector control to a synchronous motor composed of a Halbach array field magnet and a coreless coil.

Aiming for the practical application of 6G (the 6th generation mobile communication network), which is expected to be available in the 2030s, some research and development projects around the world are being planned to build communication networks that integrate ground, maritime, and satellite communications by using drones and satellites. A solar plane is driven by electric-based propulsion systems with power supplied continuously by the endless solar energy. The purpose of this paper is to describe the current state of the art in the research and development of unmanned aerial vehicles using solar energy as the high-altitude platform station (HAPS) of communication service, and to provide an overview of the feasibility, size, and elemental technologies.

As aging infrastructure increases, the demand for close-range inspections rises. To address factors like labor shortage, safety risks, and scaffolding costs, the use of robots for inspections in construction and civil engineering is being explored. Suction drones show promise for these inspections, including hammering testing. This paper focuses on the fundamental technology of suction, enabling drones to adhere and counteract reaction forces. It discusses technical challenges, introduces the universal vacuum gripper, and presents research findings on shape optimization, friction increase, and tactile capabilities. Case studies highlight drone applications in tasks like hammering testing, suction position adjustment, and drilling operations. The paper concludes with future prospects.

The condition monitoring of bearings by integrating a triboelectric sensor into rolling bearings is described. First, the root-causes of drone accidents and the size of rolling bearings used in drone motors are discussed. Next, the possibility of monitoring rotation speed, orbital velocity of rolling elements, and radial load estimation by integrating a triboelectric sensor into the bearing is presented.

Rolling element bearings in a particular application experience premature failure accompanied with white structure in steel. A possible cause of the failure is diffused hydrogen in steel which is generated by the decomposition of lubricant. This paper studied hydrogen generation from lubricant under rolling-sliding contact. A two-roller test was conducted in a sealed chamber, where the sliding speed and the lubricant temperature were controlled. The material of the roller was bearing steel and ceramic. Hydrogen gas concentration in the chamber was measured with a gas chromatograph. It was found that the hydrogen generation due to rolling-sliding contact depended on the lubricating conditions when the bearing steel specimens were used. The hydrogen generation increased by increasing the sliding speed and the oil temperature and decreasing the oil film parameter. Moreover, hydrogen generation was hardly observed under pure rolling condition. Another finding was that when ceramic specimens were used, the hydrogen generation was much smaller than when bearing steel specimens were used. These results suggest that nascent steel surface caused by the combination of metal-to-metal contact and slip accelerates the lubricant decomposition to generate hydrogen.