Hikaru Otsuka

Volcanic ash observation in active volcano areas using teleoperated mobile robots - Introduction to our robotic-volcano-observation project and field experiments

Observation of an active volcano is very important to determine a strategy for estimating its eruptive activity and providing residents with an evacuation warning. However, it is too dangerous for humans to install cameras during eruptive activity to determine the status of a volcano. Furthermore, permanently installed cameras might be damaged by eruptions, and craters can emerge in unanticipated positions. To handle this situation, we proposed robotic observations in a volcanic area after an eruption using a multi-rotor UAV (unmanned aerial vehicle) and a small ground robot. Field experiments are effective at promoting this type of research and development. Therefore, we performed several field experiments at Mt. Asama. In this paper, we introduce our robotic observation project, and report on the field experiments conducted with teleoperated mobile robots in October 2012 at Mt. Asama.

Thrust loss saving design of overlapping rotor arrangement on small multirotor unmanned aerial vehicles

Small multirotor unmanned aerial vehicles (UAVs) are suitable for surveillance or inspection operations, such as disaster site observations or building inspections, as they can hover. Therefore, engineers and associations plan to use them for civilian applications. However, the payload capacity of current UAVs is too small to carry heavy sensors or batteries. Thus, improving payload capacity by increasing the number of rotors has been considered to achieve an increase in the thrust for a limited body size. Although, most rotor arrangements cause rotor flow interaction, which degrade the total thrust. To design a rotor arrangement on small multirotor UAVs, it is necessary to first evaluate the thrust from an aerodynamic perspective. In this study, we evaluated the effect of rotor flow interactions on thrust for three two-rotor configurations. The investigation showed that the thrust of rotors in wake flow is degraded. Thus, we proposed a new octorotor UAV configuration based on the results of our evaluation of the rotor flow interaction and verified the thrust improvement compared to a coaxial octorotor UAV configuration. This investigation demonstrated a thrust improvement of 24% over the total thrust of the coaxial octorotor UAV.

Evaluation of Hovering Thrust Performance of Shrouded Rotors for Multi-rotor UAVs to Reduce Weight

In this study, we experimentally evaluated the hovering performance of shrouded rotors for small multi-rotor unmanned aerial vehicles (UAVs). In a shrouded rotor, the rotor is surrounded by a round duct. This rotor is superior to normal open rotors because it protects the rotary wing, reduces noise, and improves hovering performance. However, shrouded rotors have not been used much in small UAVs because they increase the weight of the UAV body. To design a shroud that maintains the hovering performance at a reduced weight, we evaluated the effects of different shroud shapes on the hovering performance. We examined three components of a shroud that affect the aerodynamic performance: (1) the shroud position to the rotor, (2) the diffuser length, and (3) the length of the inlet curve. The experimental results confirmed that the hovering performance was improved with a compact shrouded rotor compared to an open rotor. We were able to reduce the shroud weight and maintain the improved hovering performance of the shrouded rotor for small UAV flight.

Reduction of the head-up pitching moment of small quad-rotor unmanned aerial vehicles in uniform flow:

Multi-rotor unmanned aerial vehicles are unstable in headwind because of nose-up pitching moment generation and thrust degradation. Reducing the pitching moment generation could enhance the tolerance of the unmanned aerial vehicles to wind and improve cruise flight speed. In this study, a canted rotor configuration was proposed to reduce the moment in uniform flow and examined. The objective of the study is to evaluate the effect of moment reduction by canted rotors. First, flow interactions between rotors of the quad-rotor were visualized using a smoke wire method. Second, the moment reduction by canted rotors was estimated based on isolated rotor performance. Third, the moment of the quad-rotor varying the body pitching angle was examined using a wind tunnel. At an 8 m/s wind, when the body pitching angle is horizontal, slanting the rotor by 20° to outside the body degraded the moment by 26% compared with the parallel rotor configuration.

Investigation on Relationship between Rotors Axis Length and Ground Effect on a Small Quadrotor UAV Performance

無人航空機の中でも複数の回転翼を持つ小型マルチロータ機 は, 垂直離着陸やホバリング飛行が可能であるという特徴を持つ. 小型マルチロータ機は小型で安価であることから, 期待される用 途は多岐にわたる. 近年では, 被災屋内探査において, 小型マル チロータ機の利用が試みられてきた [1]. マルチロータ機の運用 において, マルチロータ機が着陸する際に, ロータ後流と地面の 間で地面効果が発生し, 機体姿勢が不安定になることが知られて いる. 地面効果が生じる際には, ロータ推力が不規則に変化する ため, 推力制御に意図しない入力が与えられることから, 機体が 不安定となると考えられる. このように着陸挙動が不安定になる ことで, 目標位置への正確な着陸が困難となるだけでなく, 着陸 時に機体が転倒し, マルチロータ機が破損することも予想される. これらの問題点を解決するためには, 地面効果の着陸への影響を 検証し, 着陸挙動を安定化させる対策が求められる. 地面効果がロータに与える影響については, これまで, 有人ヘ リコプタを対象とした研究が行われてきたが [2], 小型マルチロー タ機のように複数の小型ロータが近接して存在する状態が地面 効果に与える影響に関しては, これまで十分に検証されていない. そこで本研究では, 4つのロータをもつクアッドロータ機につい て, 地面効果を受けた際にロータ軸間距離が推力とホバリング効 率に及ぼす影響を解明することを目的とした空気力計測実験を 行った. 本稿では, 地面効果を受けている単独ロータの推力とト ルクの計測ならびに, ロータ軸間距離を変化させた際のクアッド ロータ機の推力変化とホバリング効率の変化について報告する.