Unmanned air vehicles (UAVs) have traditionally been considered as "eyes in the sky", that can move in three dimensions and need to avoid any contact with their environment. On the contrary, contact should not be considered as a problem, but as an opportunity to expand the range of UAVs applications. In this paper, we designed, fabricated, and characterized a whisker sensor unit based on MEMS barometers suitable for tactile localization on UAVs, featuring lightweight, low stiffness, high sensitivity, a broad sensing range, and scalability. Then, for the challenging task of contact point localization, we propose a Recurrent Multi-output Network (RMN) for predicting 3D contact points under continuous contact conditions to address the problems of non-linearity, hysteresis, and non-injective mapping between signals and contact points by considering time series. In addition, we propose an azimuth prediction loss function which reduces the RMSE by 3.24◦compared to L1loss. Finally, we conduct experiments on a linear stage to validate the 3D contact point localization capability of the proposed whisker system and model. The results show that our localization can achieve excellent performance, with an inference time of 1.4 ms and a mean error of only 9.18 mm in Euclidean distance within 3D space, laying a robust foundation for future implementation of tactile localization on UAVs. The design files, dataset, and source code are available on: https://github.com/BioMorphic-Intelligence-Lab/Whisker-3D-Localization.

Aerial robots are well-established technologies in environments characterized by reliable GNSS signals and favorable conditions for navigation based on cameras or LiDARs. However, their robustness is significantly challenged whenever ambient lighting is insufficient, GNSS signals are blocked, and range measurements are corrupted, for example, in underground, dark, or foggy environments. There, conventional navigation methods solely based on computer vision are very limited. This work proposes a completely novel approach to Aerial Tactile Odometry for pose estimation of aerial robots exploiting contact to precisely determine the system’s pose. By employing a compliant end-effector design with onboard tactile information by means of a trackball, we infer the complete UAV’s pose with respect to the environment, and the path traveled during contact. Through a large set of experiments, the proposed method shows centimeter-level accuracy for various relative orientations between the environment and the robot as well as for different trajectories. Akin to conventional dead-reckoning odometry methods in wheeled robotics, this method provides a valuable additional source of pose estimation, increasing the robustness of aerial robots – especially aerial manipulators – in the real world.

In this paper, we present the ADAPT, a novel reconfigurable force-balanced parallel manipulator for spatial motions and interaction capabilities underneath a drone. The reconfigurable aspect allows different motion-based 3-DoF operation modes like translational, rotational, planar, and so on, without the need for disassembly. For the purpose of this study, the manipulator is used in translation mode only. A kinematic model is developed and validated for the manipulator. The design and motion capabilities are also validated both by conducting dynamics simulations of a simplified model on MSC ADAMS, and experiments on the physical setup. The force-balanced nature of this novel design decouples the motion of the manipulator's end-effector from the base, zeroing the reaction forces, making this design ideally suited for aerial manipulation applications, or generic floating-base applications.

The tasks that unmanned aerial vehicles (UAVs) have taken upon have progressively grown in complexity over the years, alongside with the level of autonomy with which they are carried out. In this work, we present an example of aerial screwing operations with a fully-actuated tilt-rotor platform. Key contributions include a new control framework to automate screwing operations through a robust hole search and in-hole detection algorithm. These are achieved without a-priori knowledge of the exact hole location, and without the use of external tools, such as vision based hole detection or force sensors. Wrench coupling is implemented to account for the platform's kinematic constraints during screwing. The application of a constant contact force and a compliant response to induced disturbances are obtained with the use of admittance control. The full framework is validated with extensive flight experiments that demonstrate the effectiveness of each subsystem, as well as the complete architecture. We also validate the robustness of the detection algorithm against false positives. Within the results we demonstrate the ability to perform the automated task with a 86% success rate over 35 flights, and measured hole search time of 9s (median value).

In this paper a force controller via energy tanks is implemented for novel applications in aerial contour follow. This control approach allows the aerial vehicle to trace out a boundary whilst in continuous contact with a surface by means of an actively compliant manipulator. This represents the first step towards tactile-based aerial navigation, which can be used to complement more traditional mapping approaches such as visual SLAM. Key results show that the energy-based approach can be used to apply a continuous shear force through the manipulator while the vehicle remains in contact with the surface of interest. Results also show the robustness and repeatability of this approach for prolonged aerial interaction, and the potential for future use in more complex, un-modeled environments.

As roles for unmanned aerial vehicles (UAVs)continue to diversify, the ability to sense and interact closely with the environment becomes increasingly important. Within this paper we report on the initial flight tests of a novel adaptively compliant actuator which will allow a UAV to carry out such tasks as the “pick and placement” of remote sensors, structural testing and contact-based inspection. Three key results are discussed and presented; the ability to physically apply forces with the UAV through the use of an active compliant manipulator; the ability to tailor these forces through tuning of the manipulator controller gains; and the ability to apply a rapid series of physical pulses in order to excite remotely placed sensors, e.g. vibration sensors. A series of over sixty flight tests have been used to generate initial results which clearly demonstrate the potential of this new type of compliant aerial actuator.