Servo Integrated Nonlinear Model Predictive Control for Overactuated Tiltable-Quadrotors

Quadrotors are widely employed across various domains, yet the conventional type faces limitations due to underactuation, where attitude control is closely tied to positional adjustments. In contrast, quadrotors equipped with tiltable rotors offer overactuation, empowering them to track both position and attitude trajectories. However, the nonlinear dynamics of the drone body and the sluggish response of tilting servos pose challenges for conventional cascade controllers. In this study, we propose a control methodology for tilting-rotor quadrotors based on nonlinear model predictive control (NMPC). Unlike conventional approaches, our method preserves the full dynamics without simplification and utilizes actuator commands directly as control inputs. Notably, we incorporate a first-order servo model within the NMPC framework. Through simulation, we observe that integrating the servo dynamics not only enhances control performance but also accelerates convergence. To assess the efficacy of our approach, we fabricate a tiltable-quadrotor and deploy the algorithm onboard at a frequency of 100Hz. Extensive real-world experiments demonstrate rapid, robust, and smooth pose tracking performance.

BEATLE -- Self-Reconfigurable Aerial Robot: Design, Control and Experimental Validation

Modular self-reconfigurable robots (MSRRs) offer enhanced task flexibility by constructing various structures suitable for each task. However, conventional terrestrial MSRRs equipped with wheels face critical challenges, including limitations in the size of constructible structures and system robustness due to elevated wrench loads applied to each module. In this work, we introduce an Aerial MSRR (A-MSRR) system named BEATLE, capable of merging and separating in-flight. BEATLE can merge without applying wrench loads to adjacent modules, thereby expanding the scalability and robustness of conventional terrestrial MSRRs. In this article, we propose a system configuration for BEATLE, including mechanical design, a control framework for multi-connected flight, and a motion planner for reconfiguration motion. The design of a docking mechanism and housing structure aims to balance the durability of the constructed structure with ease of separation. Furthermore, the proposed flight control framework achieves stable multi-connected flight based on contact wrench control. Moreover, the proposed motion planner based on a finite state machine (FSM) achieves precise and robust reconfiguration motion. We also introduce the actual implementation of the prototype and validate the robustness and scalability of the proposed system design through experiments and simulation studies.

Design and Control of Delta: Deformable Multilinked Multirotor with Rolling Locomotion Ability in Terrestrial Domain

In recent years, multiple types of locomotion methods for robots have been developed and enabled to adapt to multiple domains. In particular, aerial robots are useful for exploration in several situations, taking advantage of its three-dimensional mobility. Moreover, some aerial robots have achieved manipulation tasks in the air. However, energy consumption for flight is large and thus locomotion ability on the ground is also necessary for aerial robots to do tasks for long time. Therefore, in this work, we aim to develop deformable multirotor robot capable of rolling movement with its entire body and achieve motions on the ground and in the air. In this paper, we first describe the design methodology of a deformable multilinked air-ground hybrid multirotor. We also introduce its mechanical design and rotor configuration based on control stability. Then, thrust control method for locomotion in air and ground domains is described. Finally, we show the implemented prototype of the proposed robot and evaluate through experiments in air and terrestrial domains. To the best of our knowledge, this is the first time to achieve the rolling locomotion by multilink structured mutltrotor.

Design and Control of a Humanoid Equipped with Flight Unit and Wheels for Multimodal Locomotion

Humanoids are versatile robotic platforms because of their limbs with multiple degrees of freedom. Although humanoids can walk like humans, the speed is relatively slow, and they cannot run over large barriers. To address these problems, we aim to achieve rapid terrestrial locomotion ability and simultaneously expand the domain of locomotion to the air by utilizing thrust for propulsion. In this paper, we first describe an optimized construction method of a humanoid robot equipped with wheels and a flight unit to achieve these abilities. Then, we describe the integrated control framework of the proposed flying humanoid for each mode of locomotion: aerial locomotion, leg locomotion, and wheel locomotion. Finally, we achieved multimodal locomotion and aerial manipulation experiments using the robot platform proposed in this work. To the best of our knowledge, it is the first time to achieve three different types of locomotion, including flight, by a single humanoid.

Design, Control, and Motion Strategy of TRADY: Tilted-Rotor-Equipped Aerial Robot With Autonomous In-flight Assembly and Disassembly Ability

In previous research, various types of aerial robots were developed to improve maneuverability or manipulation abilities. However, there was a challenge in achieving both mobility and manipulation capabilities simultaneously. This is because aerial robots with high mobility lack the necessary rotors to perform manipulation tasks, while those with manipulation ability are too large to achieve high mobility. To address this issue, a new aerial robot called TRADY was introduced in this article. TRADY is a tilted-rotor-equipped aerial robot that can autonomously assemble and disassemble in-flight, allowing for a switch in control model between under-actuated and fully-actuated models. The system features a novel docking mechanism and optimized rotor configuration, as well as a control system that can transition between under-actuated and fully-actuated modes and compensate for discrete changes. Additionally, a new motion strategy for assembly/disassembly motion that includes recovery behavior from hazardous conditions was introduced. Experimental results showed that TRADY can successfully execute aerial assembly/disassembly motions with a 90% success rate and generate more than nine times the torque of a single unit in the assembly state. This is the first robot system capable of performing both assembly and disassembly while seamlessly transitioning between fully-actuated and under-actuated models.

Sensing and Navigation of Aerial Robot for Measuring Tree Location and Size in Forest Environment

This paper shows the achievement of a sensing and navigation system of aerial robot for measuring location and size of trees in a forest environment autonomously. Although forestry is an important industry in Japan, the working population of forestry is decreasing. Then, as an application of mechanization of forestry, we propose tree data collection system by aerial robots which have high mobility in three-dimensional space. First, we develop tree recognition and measurement method, along with algorithm to generate tree database. Second, we describe aerial robot navigation system based on tree recognition. Finally, we present an experimental result in which an aerial robot flies in a forest and collects tree data.

Design, Modeling and Control of a Quadruped Robot SPIDAR: Spherically Vectorable and Distributed Rotors Assisted Air-Ground Amphibious Quadruped Robot

Multimodal locomotion capability is an emerging topic in robotics field, and various novel mobile robots have been developed to enable the maneuvering in both terrestrial and aerial domains. Among these hybrid robots, several state-of-the-art bipedal \robots enable the complex walking motion which is interlaced with flying. These robots are also desired to have the manipulation ability; however, it is difficult for the current forms to keep stability with the joint motion in midair due to the central\ized rotor arrangement. Therefore, in this work, we develop a novel air-ground amphibious quadruped robot called SPIDAR which is assisted by spherically vectorable rotors distributed in each link to enable both walking motion and transformable flight. F\irst, we present a unique mechanical design for quadruped robot that enables terrestrial and aerial locomotion. We then reveal the modeling method for this hybrid robot platform, and further develop an integrated control strategy for both walking and fl\ying with joint motion. Finally, we demonstrate the feasibility of the proposed hybrid quadruped robot by performing a seamless motion that involves static walking and subsequent flight. To the best of our knowledge, this work is the first to achieve a \quadruped robot with multimodal locomotion capability, which also shows the potential of manipulation in multiple domains.

TrTr: Visual Tracking with Transformer

Template-based discriminative trackers are currently the dominant tracking methods due to their robustness and accuracy, and the Siamese-network-based methods that depend on cross-correlation operation between features extracted from template and search images show the state-of-the-art tracking performance. However, general cross-correlation operation can only obtain relationship between local patches in two feature maps. In this paper, we propose a novel tracker network based on a powerful attention mechanism called Transformer encoder-decoder architecture to gain global and rich contextual interdependencies. In this new architecture, features of the template image is processed by a self-attention module in the encoder part to learn strong context information, which is then sent to the decoder part to compute cross-attention with the search image features processed by another self-attention module. In addition, we design the classification and regression heads using the output of Transformer to localize target based on shape-agnostic anchor. We extensively evaluate our tracker TrTr, on VOT2018, VOT2019, OTB-100, UAV, NfS, TrackingNet, and LaSOT benchmarks and our method performs favorably against state-of-the-art algorithms. Training code and pretrained models are available at https://github.com/tongtybj/TrTr.

Singularity-free Aerial Deformation by Two-dimensional Multilinked Aerial Robot with 1-DoF Vectorable Propeller

Two-dimensional multilinked structures can benefit aerial robots in both maneuvering and manipulation because of their deformation ability. However, certain types of singular forms must be avoided during deformation. Hence, an additional 1 Degrees-of-Freedom (DoF) vectorable propeller is employed in this work to overcome singular forms by properly changing the thrust direction. In this paper, we first extend modeling and control methods from our previous works for an under-actuated model whose thrust forces are not unidirectional. We then propose a planning method for the vectoring angles to solve the singularity by maximizing the controllability under arbitrary robot forms. Finally, we demonstrate the feasibility of the proposed methods by experiments where a quad-type model is used to perform trajectory tracking under challenging forms, such as a line-shape form, and the deformation passing these challenging forms.

Circus ANYmal: A Quadruped Learning Dexterous Manipulation with Its Limbs

Quadrupedal robots are skillful at locomotion tasks while lacking manipulation skills, not to mention dexterous manipulation abilities. Inspired by the animal behavior and the duality between multi-legged locomotion and multi-fingered manipulation, we showcase a circus ball challenge on a quadrupedal robot, ANYmal. We employ a model-free reinforcement learning approach to train a deep policy that enables the robot to balance and manipulate a light-weight ball robustly using its limbs without any contact measurement sensor. The policy is trained in the simulation, in which we randomize many physical properties with additive noise and inject random disturbance force during manipulation, and achieves zero-shot deployment on the real robot without any adjustment. In the hardware experiments, dynamic performance is achieved with a maximum rotation speed of 15 deg/s, and robust recovery is showcased under external poking. To our best knowledge, it is the first work that demonstrates the dexterous dynamic manipulation on a real quadrupedal robot.