Robot-Assisted Drone Recovery on a Wavy Surface Using Error-State Kalman Filter and Receding Horizon Model Predictive Control

Recovering a drone on a disturbed water surface remains a significant challenge in maritime robotics. In this paper, we propose a unified framework for Robot-Assisted Drone Recovery on a Wavy Surface that addresses two major tasks: Firstly, accurate prediction of a moving drone's position under wave-induced disturbances using an Error-State Kalman Filter (ESKF), and secondly, effective motion planning for a manipulator via Receding Horizon Control (RHC). Specifically, the ESKF predicts the drone's future position 0.5s ahead, while the manipulator plans a capture trajectory in real time, thus overcoming not only wave-induced base motions but also limited torque constraints. We provide a system design that comprises a manipulator subsystem and a UAV subsystem. On the UAV side, we detail how position control and suspended payload strategies are implemented. On the manipulator side, we show how an RHC scheme outperforms traditional low-level control algorithms. Simulation and real-world experiments - using wave-disturbed motion data - demonstrate that our approach achieves a high success rate - above 95% and outperforms conventional baseline methods by up to 10% in efficiency and 20% in precision. The results underscore the feasibility and robustness of our system, which achieves state-of-the-art (SOTA) performance and offers a practical solution for maritime drone operations.

SCKD: Semi-Supervised Cross-Modality Knowledge Distillation for 4D Radar Object Detection

3D object detection is one of the fundamental perception tasks for autonomous vehicles. Fulfilling such a task with a 4D millimeter-wave radar is very attractive since the sensor is able to acquire 3D point clouds similar to Lidar while maintaining robust measurements under adverse weather. However, due to the high sparsity and noise associated with the radar point clouds, the performance of the existing methods is still much lower than expected. In this paper, we propose a novel Semi-supervised Cross-modality Knowledge Distillation (SCKD) method for 4D radar-based 3D object detection. It characterizes the capability of learning the feature from a Lidar-radar-fused teacher network with semi-supervised distillation. We first propose an adaptive fusion module in the teacher network to boost its performance. Then, two feature distillation modules are designed to facilitate the cross-modality knowledge transfer. Finally, a semi-supervised output distillation is proposed to increase the effectiveness and flexibility of the distillation framework. With the same network structure, our radar-only student trained by SCKD boosts the mAP by 10.38% over the baseline and outperforms the state-of-the-art works on the VoD dataset. The experiment on ZJUODset also shows 5.12% mAP improvements on the moderate difficulty level over the baseline when extra unlabeled data are available. Code is available at https://github.com/Ruoyu-Xu/SCKD.

A Manipulator-Assisted Multiple UAV Landing System for USV Subject to Disturbance

Marine waves significantly disturb the unmanned surface vehicle (USV) motion. An unmanned aerial vehicle (UAV) can hardly land on a USV that undergoes irregular motion. An oversized landing platform is usually necessary to guarantee the landing safety, which limits the number of UAVs that can be carried. We propose a landing system assisted by tether and robot manipulation. The system can land multiple UAVs without increasing the USV's size. An MPC controller stabilizes the end-effector and tracks the UAVs, and an adaptive estimator addresses the disturbance caused by the base motion. The working strategy of the system is designed to plan the motion of each device. We have validated the manipulator controller through simulations and well-controlled indoor experiments. During the field tests, the proposed system caught and placed the UAVs when the disturbed USV roll range was approximately 12 degrees.