Recent innovations in autonomous drones have facilitated time-optimal flight in single-drone configurations, and enhanced maneuverability in multi-drone systems by applying optimal control and learning-based methods. However, few studies have achieved time-optimal motion planning for multi-drone systems, particularly during highly agile maneuvers or in dynamic scenarios. This paper presents a decentralized policy network using multi-agent reinforcement learning for time-optimal multi-drone flight. To strike a balance between flight efficiency and collision avoidance, we introduce a soft collision-free mechanism inspired by optimization-based methods. By customizing PPO in a centralized training, decentralized execution (CTDE) fashion, we unlock higher efficiency and stability in training while ensuring lightweight implementation. Extensive simulations show that, despite slight performance tradeoffs compared to single-drone systems, our multi-drone approach maintains near-time-optimal performance with a low collision rate. Real-world experiments validate our method, with two quadrotors using the same network as in simulation achieving a maximum speed of 13.65 m/s and a maximum body rate of 13.4 rad/s in a 5.5 m × 5.5 m × 2.0 m space across various tracks, relying entirely on onboard computation [video33https://youtu.be/KACuFMtGGpo][code44https://github.com/KafuuChikai/Dashing-for-the-Golden-Snitch-Multi-Drone-RL].

Autonomous high-speed flight in unknown, clut-tered environments is essential for a variety of quadrotor applications, such as inspection, search, and rescue. In this study, we propose a novel trajectory planner designed to achieve efficient, high-speed, collision-free flights in such environments. The proposed approach begins by generating a safe flight corridor based on the path found by Lazy Theta*, representing the safe regions with polytopic sets. These sets are then used to define discrete-time control barrier function (DCBF), ensuring the quadrotor stays within safe bounds during flight. By selecting a single waypoint ahead of the quadrotor on the path as the next waypoint, the trajectory is optimized by considering both the total flight time and safety constraints. Extensive simulations and real-world experiments have confirmed our method's feasibility, demonstrating its capability for high-speed performance and reliable obstacle avoidance. [video44https://www.youtube.com/playlist?list=PLJFduoH7QICOhcIX3JFsZwB4IgS4_-sPt]

The flying speed of autonomous quadrotors has increased significantly in the field of autonomous drone racing. However, most research primarily focuses on the aggressive flight of a single quadrotor, simplifying the racing gate traversal problem to a waypoint passing problem that neglects the orientations of the racing gates or implicitly considers the waypoint direction during path planning. In this paper, we propose a systematic method called Pairwise Model Predictive Control (PMPC) that can guide two quadrotors online to navigate racing gates with minimal time and without collisions. The flight task is initially simplified as a point-mass model waypoint passing problem to provide time optimal reference through an efficient two-step velocity search method. Subsequently, we utilize the spatial configuration of the racing track to compute the optimal heading at each gate, maximizing the visibility of subsequent gates for the quadrotors. To address varying gate orientations, we introduce a novel Magnetic Induction Line-based spatial curve to guide the quadrotors through racing gates of different orientations. Furthermore, we formulate a nonlinear optimization problem that uses the point-mass trajectory as initial values and references to enhance solving efficiency. The feasibility of the proposed method is validated through both simulation and real-world experiments. In real-world tests, the two quadrotors achieved a top speed of$6.1m/s$on a 7-waypoint racing track within a compact flying arena of$5m\times 4m\times 2m$.

Over the past decade, there has been a remarkable surge in utilizing quadrotors for various purposes due to their simple structure and aggressive maneuverability. One of the key challenges is online time-optimal trajectory generation and control technique. This paper proposes an imitation learning-based online solution to efficiently navigate the quadrotor through multiple waypoints with near-time-optimal performance. The neural networks (WN&CNets) are trained to learn the control law from the dataset generated by the time-consuming CPC algorithm and then deployed to generate the optimal control commands online to guide the quadrotors. To address the challenge of limited training data and the hover maneuver at the final waypoint, we propose a transition phase strategy that utilizes MINCO trajectories to help the quadrotor ‘jump over’ the stop-and-go maneuver when switching waypoints. Our method is demonstrated in both simulation and real-world experiments, achieving a maximum speed of 5.6m/s while navigating through 7 waypoints in a confined space of 5.5m × 5.5m × 2.0m [video3]. The results show that with a slight loss in optimality, the WN&CNets significantly reduce the processing time and enable online control for multi-point flight tasks.

Recent advancements in large language models (LLMs) have significantly enhanced text generation capabilities, yet evaluating their performance in generative writing remains a challenge. Existing benchmarks primarily focus on generic text generation or limited in writing tasks, failing to capture the diverse requirements of high-quality written contents across various domains. To bridge this gap, we present WritingBench, a comprehensive benchmark designed to evaluate LLMs across 6 core writing domains and 100 subdomains. We further propose a query-dependent evaluation framework that empowers LLMs to dynamically generate instance-specific assessment criteria. This framework is complemented by a fine-tuned critic model for criteria-aware scoring, enabling evaluations in style, format and length. The framework's validity is further demonstrated by its data curation capability, which enables a 7B-parameter model to outperform the performance of GPT-4o in writing. We open-source the benchmark, along with evaluation tools and modular framework components, to advance the development of LLMs in writing.

Although current text-guided music generation technology can cope with simple creative scenarios, achieving finegrained control over individual text-modality conditions remains challenging as user demands become more intricate. Accordingly, we introduce the TEAcher Adapter (TEAdapter), a compact plugin designed to guide the generation process with diverse control information provided by users. In addition, we explore the controllable generation of extended music by leveraging TEAdapter control groups trained on data of distinct structural functionalities. In general, we consider controls over global, elemental, and structural levels. Experimental results demonstrate that the proposed TEAdapter enables multiple precise controls and ensures high-quality music generation. Our module is also lightweight and transferable to any diffusion model architecture. Available code and demos will be found soon at https://github.com/Ashley1101/TEAdapter.

Visual-Inertial Odometry (VIO) has been widely used by autonomous drones as an onboard navigation method. However, it suffers from drifts especially in scenarios where the environments have few texture features such as an empty room with solid color walls. Optical flow sensors are another type of onboard sensor used by drones that face downward and measure the velocity by detecting changes in pixels between consecutive images, which don’t introduce accumulative error. In this work, we present an efficient tight-coupled estimator to improve the accuracy of VIO by fusing the measurements of a downward-facing optical flow sensor into the VIO framework consistently. We further analyze the observability of the estimators and prove that there are four unobservable directions in the ideal case and then we utilize OC-EKF to maintain the consistency of the estimator. Furthermore, we extend an adaptive weighting algorithm to the proposed method, which can better adapt to the scenes where feature tracking is less accurate. Finally, both simulation and real-world experiments demonstrate the feasibility of the proposed method.