This paper analyzes the ground effect in multirotors, that is, the change in the thrust generated by the rotors when flying close to the ground due to the interaction of the rotor airflow with the ground surface. This effect is well known in single-rotor helicopters but has been assumed erroneously to be similar for multirotors in many cases in the literature. In this paper, the ground effect for multirotors is characterized with experimental tests in several cases and the partial ground effect, a situation in which one or some of the rotors of the multirotor (but not all) are under the ground effect, is also characterized. The influence of the different cases of ground effect in multirotor control is then studied with several control approaches in simulation and validated with experiments in a test bench and with outdoor flights.

This letter presents the design, modeling, and control of a multirotor for inspection of bridges with full contact. The letter analyzes the aerodynamic ceiling effect when the aerial robot approaches the bridge surface from below, including its aerodynamic characterization using computational fluid dynamics. The proposed multirotor design takes the modeled aerodynamic effects into account, improving the performance of the aerial platform terms of the stability and position accuracy during the inspection. Nonlinear attitude and position controllers to manage the aerodynamic effects are derived and tested. Finally, outdoor experiments in a real bridge inspection task have been used to validate the system, as well as, the controller and the aerodynamic characterization. The experiments carried out also include a complete autonomous mission of the aerial platform during a structural assessment application.

A wide range of applications for which Unmanned Aerial Vehicles (UAVs) are ideally suited rely on the development of manipulators capable of exchanging forces with the environment. One such application is the installation and retrieval of intelligent sensors for monitoring wide-spread areas and locations that are difficult to access by any other means. Within this paper we report on both indoor and outdoor flights tests of a novel force controlled lightweight compliant manipulator which allows a UAV to carry out this type of task. Installation and retrieval are both demonstrated with different scenarios, indoors and outdoors. Key results include interaction forces up to 22 N exerted by a small-sized multirotor; placement and retrieval operations carried out on flat as well as cylindrical surfaces; and an analysis of the overall system. The results of multiple flight experiments clearly demonstrate the potential of this approach for the deployment of sensors and other force-related tasks.

This paper presents a robotic system using Unmanned Aerial Vehicles (UAVs) for bridge-inspection tasks that require physical contact between the aerial platform and the bridge surfaces, such as beam-deflection analysis or measuring crack depth with an ultrasonic sensor. The proposed system takes advantage of the aerodynamic ceiling effect that arises when the multirotor gets close to the bridge surface. Moreover, this paper describes how a UAV can be used as a sensor that is able to fly and touch the bridge to take measurements during an inspection by contact. A practical application of the system involving the measurement of a bridge’s beam deflection using a laser tracking station is also presented. In order to validate our system, experiments on two different bridges involving the measurement of the deflection of their beams are shown.

This paper presents the design, modeling and control of a fully actuated aerial robot for infrastructure contact inspection as well as its localization system. Health assessment of transport infrastructure involves measurements with sensors in contact with the bridge and tunnel surfaces and the installation of monitoring sensing devices at specific points. The design of the aerial robot presented in the paper includes a 3DoF lightweight arm with a sensorized passive joint which can measure the contact force to regulate the force applied with the sensor on the structure. The aerial platform has been designed with tilted propellers to be fully actuated, achieving independent attitude and position control. It also mounts a “docking gear” to establish full contact with the infrastructure during the inspection, minimizing the measurement errors derived from the motion of the aerial platform and allowing full contact with the surface regardless of its condition (smooth, rough, ...). The localization system of the aerial robot uses multi-sensor fusion of the measurements of a topographic laser sensor on the ground and a tracking camera and inertial sensors on-board the aerial robot, to be able to fly under the bridge deck or close to the bridge pillars where GNSS satellite signals are not available. The paper also presents the modeling and control of the aerial robot. Validation experiments of the localization system and the control system, and with the aerial robot inspecting a real bridge are also included.

The inspection of bridges and other infrastructure with UAVs when the sensors need to be in contact with the surface (i.e. ultrasound for crack inspection or reflector prism for beam deflection) is a great challenge due to the coupling which occurs between the aerial and the inspection problems. This paper presents a new design of a multirotor UAV that can be used in some of these applications to eliminate the coupling and to be able to carry out the inspection by contact in a more effective way. The proposed solution uses the so-called ceiling effect to maintain in contact a specially designed aerial platform to the ceiling. So, the coupling disappears because the multirotor is still in contact with the ceiling in a fixed position while performing inspection. Moreover, the presented results show that making use of the ceiling effect also improved the maximum flight time of the platform. The solution is presented with experimental results in a test stand and flight tests representing a bridge inspection application (Fig. 1). A video of the experiments is also included.