Adrien Briod

A Collision-resilient Flying Robot

Flying robots that can locomote efficiently in GPS-denied cluttered environments have many applications, such as in search and rescue scenarios. However, dealing with the high amount of obstacles inherent to such environments is a major challenge for flying vehicles. Conventional flying platforms cannot afford to collide with obstacles, as the disturbance from the impact may provoke a crash to the ground, especially when friction forces generate torques affecting the attitude of the platform. We propose a concept of resilient flying robots capable of colliding into obstacles without compromising their flight stability. Such platforms present great advantages over existing robots as they are capable of robust flight in cluttered environments without the need for complex sense and avoid strategies or three-dimensional mapping of the environment. We propose a design comprising an inner frame equipped with conventional propulsion and stabilization systems enclosed in a protective cage that can rotate passively thanks to a three-axis gimbal system, which reduces the impact of friction forces on the attitude of the inner frame. After addressing important design considerations thanks to a collision model and validation experiments, we present a proof-of-concept platform, named GimBall, capable of flying in various cluttered environments. Field experiments demonstrate the robots ability to fly fully autonomously through a forest while experiencing multiple collisions.

A perching mechanism for flying robots using a fibre-based adhesive

Robots capable of hover flight in constrained indoor environments have many applications, however their range is constrained by the high energetic cost of airborne locomotion. Perching allows flying robots to scan their environment without the need to remain aloft. This paper presents the design of a mechanism that allows indoor flying robots to attach to vertical surfaces. To date, solutions that enable flying robot with perching capabilities either require high precision control of the dynamics of the robot, or a mechanism robust to high energy impacts. In this article, we propose a perching mechanism comprising a compliant deployable pad and a passive self-alignment system, that does not require any active control during the attachment procedure. More specifically, a perching mechanism using fibre-based dry adhesives was implemented on a 300 g flying platform. An adhesive pad was first modeled and optimized in shape for maximum attachment force at the low pre-load forces inherent to hovering platforms. It was then mounted on a deployable mechanism that stays within the structure of the robot during flight and can be deployed when a perching manoeuvre is initiated. Finally, the perching mechanism is integrated onto a real flying robot and successful perching manoeuvres are demonstrated as a proof of concept.

Euler spring collision protection for flying robots

This paper addresses the problem of adequately protecting flying robots from damage resulting from collisions that may occur when exploring constrained and cluttered environments. A method for designing protective structures to meet the specific constraints of flying systems is presented and applied to the protection of a small coaxial hovering platform. Protective structures in the form of Euler springs in a tetrahedral configuration are designed and optimised to elastically absorb the energy of an impact while simultaneously minimizing the forces acting on the robots stiff inner frame. These protective structures are integrated into a 282 g hovering platform and shown to consistently withstand dozens of collisions undamaged.

An indoor flying platform with collision robustness and self-recovery

This paper presents a new paradigm in the design of indoor flying robots that replaces collision avoidance with collision robustness. Indoor flying robots must operate within constrained and cluttered environments where even natures most sophisticated flyers such as insects cannot avoid all obstacles and should thus be able to withstand collisions and recover from them autonomously. A prototype platform specifically designed to withstand collisions and recover without human intervention is presented. Its dimensions are optimized to fulfill the varying constraints of aerodynamics, robustness and self-recovery, and new construction techniques focusing on shock absorption are presented. Finally, the platform is tested both in-flight and during collisions to characterize its collision robustness and self-recovery capability.

An Active Uprighting Mechanism for Flying Robots

Flying robots have unique advantages in the exploration of cluttered environments such as caves or collapsed buildings. Current systems, however, have difficulty in dealing with the large amount of obstacles inherent to such environments. Collisions with obstacles generally result in crashes from which the platform can no longer recover. This paper presents a method to design active uprighting mechanisms for protected rotorcraft-type flying robots that allow them to become upright and subsequently take off again after an otherwise mission-ending collision. This method is demonstrated on a tailsitter flying robot, which is capable of consistently uprighting after falling on its side using a spring-based “leg” and returning to the air to continue its mission.

Contact-based navigation for an autonomous flying robot

Autonomous navigation in obstacle-dense indoor environments is very challenging for flying robots due to the high risk of collisions, which may lead to mechanical damage of the platform and eventual failure of the mission. While conventional approaches in autonomous navigation favor obstacle avoidance strategies, recent work showed that collision-robust flying robots could hit obstacles without breaking and even self-recover after a crash to the ground. This approach is particularly interesting for autonomous navigation in complex environments where collisions are unavoidable, or for reducing the sensing and control complexity involved in obstacle avoidance. This paper aims at showing that collision-robust platforms can go a step further and exploit contacts with the environment to achieve useful navigation tasks based on the sense of touch. This approach is typically useful when weight restrictions prevent the use of heavier sensors, or as a low-level detection mechanism supplementing other sensing modalities. In this paper, a solution based on force and inertial sensors used to detect obstacles all around the robot is presented. Eight miniature force sensors, weighting 0.9g each, are integrated in the structure of a collision-robust flying platform without affecting its robustness. A proof-of-concept experiment demonstrates the use of contact sensing for exploring autonomously a room in 3D, showing significant advantages compared to a previous strategy. To our knowledge this is the first fully autonomous flying robot using touch sensors as only exteroceptive sensors.

Automatically calibrating the viewing direction of optic-flow sensors

Because of their low weight, cost and energy consumption, optic-flow sensors attract growing interest in robotics for tasks such as self-motion estimation or depth measurement. Most applications require a large number of these sensors, which involves a fair amount of calibration work for each setup. In particular, the viewing direction of each sensor has to be measured for proper operation. This task is often cumbersome and prone to errors, and has to be carried out every time the setup is slightly modified. This paper proposes an algorithm for viewing direction calibration relying on rate gyroscope readings and a recursive weighted linear least square estimation of the rotation matrix elements. The method only requires the user to realize random rotational motions of its setup by hand. The algorithm provides hints about the current precision of the estimation and what motions should be performed to improve it. To assess the validity of the method, tests were performed on an experimental setup and the results compared to a precise manual calibration. The repeatability of the gyroscope-based calibration process reached ±1.7° per axis.