Multirotor Platforms Research Articles

A Truly-Redundant Aerial Manipulator System With Application to Push-and-Slide Inspection in Industrial Plants

We present the design, motion planning, and control of an aerial manipulator for non-trivial physical interaction tasks, such as pushing while sliding on curved surfaces-a task which is motivated by the increasing interest in autonomous non-destructive tests for industrial plants. The proposed aerial manipulator consists of a multidirectional-thrust aerial vehicle-to enhance physical interaction capabilities-endowed with a 2-DoFs lightweight arm-to enlarge its workspace. This combination makes it a trulyredundant manipulator going beyond standard aerial manipulators based on collinear multirotor platforms. The controller is based on a PID method with a “displaced” positional part that ensures asymptotic stability despite the arm elasticity. A kinodynamic task-constrained and control-aware global motion planner is used. Experiments show that the proposed aerial manipulator system, equipped with an Eddy current probe, is able to scan a metallic pipe sliding the sensor over its surface and preserving the contact. From the measures, a weld on the pipe is successfully detected and mapped.

Design of an Anthropomorphic, Compliant, and Lightweight Dual Arm for Aerial Manipulation

This paper presents an anthropomorphic, compliant and lightweight dual arm manipulator designed and developed for aerial manipulation applications with multi-rotor platforms. Each arm provides four degrees of freedom in a human-like kinematic configuration for end effector positioning: shoulder pitch, roll and yaw, and elbow pitch. The dual arm, weighting 1.3 kg in total, employs smart servo actuators and a customized and carefully designed aluminum frame structure manufactured by laser cut. The proposed design reduces the manufacturing cost as no computer numerical control machined part is used. Mechanical joint compliance is provided in all the joints, introducing a compact spring-lever transmission mechanism between the servo shaft and the links, integrating a potentiometer for measuring the deflection of the joints. The servo actuators are partially or fully isolated against impacts and overloads thanks to the flange bearings attached to the frame structure that support the rotation of the links and the deflection of the joints. This simple mechanism increases the robustness of the arms and safety in the physical interactions between the aerial robot and the environment. The developed manipulator has been validated through different experiments in fixed base test-bench and in outdoor flight tests.

Optimal Sizing of Electric Multirotor Configurations

A sizing tool for the definition of the configuration of electrically powered multirotor platforms is developed, which accounts for a realistic battery discharge model. The tool is developed to provide the community with the possibility of deriving the best configuration for performing a given task, while accounting for specific constraints and performance requirements. An evolutionary algorithm is used for searching the design space and to identify feasible designs with optimal performance in terms of maximum hovering time on the target and payload weight fraction.

Small unmanned airborne systems to support oil and gas pipeline monitoring and mapping

Oil and gas transmission pipelines require monitoring for maintenance and safety, to prevent equipment failure and accidents. Unmanned aerial vehicles (UAVs) technology is emerging as an opportunity to supplement current monitoring systems. Small UAV technological solutions are flexible and adaptable and with a demonstrated capacity to obtain valuable data at small to medium spatial scales. Systematic surveys of extensive areas are better completed with fixed-wing platforms and automatic flight design, whilst multirotor platforms provide flexibility in shorter and localized inspection missions. The type of sensor carried by an aerial platform determines the sort of data acquired and the obtainable information; sensors also determine the need for specific mechanical designs and the provision of energy on-board required from the system. UAV systems prototyped to monitor pipelines are reviewed in this paper, and a number of monitoring scenarios are proposed and illustrated. Notwithstanding difficulties encountered in the generalization of use for civilian applications, small UAVs have demonstrated, through research and operational cases, the capacity to support the inspection and monitoring of oil and gas pipelines.

A Low-Cost Technique for Radio-Tracking Wildlife Using a Small Standard Unmanned Aerial Vehicle

Recent advances in using unmanned aerial vehicles (UAVs) to study wildlife offer promise and may improve data collection efficiency, and small UAVs, such as multirotor platforms, are suitable for t...

EVALUATING UNMANNED AERIAL PLATFORMS FOR CULTURAL HERITAGE LARGE SCALE MAPPING

When it comes to large scale mapping of limited areas especially for cultural heritage sites, things become critical. Optical and non-optical sensors are developed to such sizes and weights that can be lifted by such platforms, like e.g. LiDAR units. At the same time there is an increase in emphasis on solutions that enable users to get access to 3D information faster and cheaper. Considering the multitude of platforms, cameras and the advancement of algorithms in conjunction with the increase of available computing power this challenge should and indeed is further investigated. In this paper a short review of the UAS technologies today is attempted. A discussion follows as to their applicability and advantages, depending on their specifications, which vary immensely. The on-board cameras available are also compared and evaluated for large scale mapping. Furthermore a thorough analysis, review and experimentation with different software implementations of Structure from Motion and Multiple View Stereo algorithms, able to process such dense and mostly unordered sequence of digital images is also conducted and presented. As test data set, we use a rich optical and thermal data set from both fixed wing and multi-rotor platforms over an archaeological excavation with adverse height variations and using different cameras. Dense 3D point clouds, digital terrain models and orthophotos have been produced and evaluated for their radiometric as well as metric qualities.

EVALUATING UNMANNED AERIAL PLATFORMS FOR CULTURAL HERITAGE LARGE SCALE MAPPING

Abstract. When it comes to large scale mapping of limited areas especially for cultural heritage sites, things become critical. Optical and non-optical sensors are developed to such sizes and weights that can be lifted by such platforms, like e.g. LiDAR units. At the same time there is an increase in emphasis on solutions that enable users to get access to 3D information faster and cheaper. Considering the multitude of platforms, cameras and the advancement of algorithms in conjunction with the increase of available computing power this challenge should and indeed is further investigated. In this paper a short review of the UAS technologies today is attempted. A discussion follows as to their applicability and advantages, depending on their specifications, which vary immensely. The on-board cameras available are also compared and evaluated for large scale mapping. Furthermore a thorough analysis, review and experimentation with different software implementations of Structure from Motion and Multiple View Stereo algorithms, able to process such dense and mostly unordered sequence of digital images is also conducted and presented. As test data set, we use a rich optical and thermal data set from both fixed wing and multi-rotor platforms over an archaeological excavation with adverse height variations and using different cameras. Dense 3D point clouds, digital terrain models and orthophotos have been produced and evaluated for their radiometric as well as metric qualities.

A Comparison of Closed-Loop Performance of Multirotor Configurations Using Non-Linear Dynamic Inversion Control

Multirotor is the umbrella term for the family of unmanned aircraft, which include the quadrotor, hexarotor and other vertical take-off and landing (VTOL) aircraft that employ multiple main rotors for lift and control. Development and testing of novel multirotor designs has been aided by the proliferation of 3D printing and inexpensive flight controllers and components. Different multirotor configurations exhibit specific strengths, while presenting unique challenges with regards to design and control. This article highlights the primary differences between three multirotor platforms: a quadrotor; a fully-actuated hexarotor; and an octorotor. Each platform is modelled and then controlled using non-linear dynamic inversion. The differences in dynamics, control and performance are then discussed.

Maximum endurance for battery-powered rotary-wing aircraft

The paper presents an analytical framework for addressing the hovering time prediction of rotary-wing aircraft, with a particular focus on multi-rotor platforms. By imposing the balance between required and available power, the endurance expression is derived as a function of airframe features, rotor parameters, and battery capacity. The best endurance condition is also obtained in terms of optimum capacity and hovering time, by means of two approximate closed-form solutions. The proposed methodology was validated by means of numerical simulation and flight testing. Results show the effectiveness of the proposed approach.

Modular Multi-Rotor Helicopter Platforms

The results presented in this paper describe a practicable solution to multi-rotor platforms constructed and put together with standardized components to allow flexibility and customizability. The extensive utilization of universal parts supports an easy introduction of changes in case of necessary design alterations and speeds up the whole process when constructional changes are required. The research has been applied to a variety of special use multi-copters and has proven to be very useful. Further development will follow to secure subcomponents with necessary Ingress Protection ratings and even further optimize universal components. The constructional layout of multi-copters is relatively simple and usually consists of the main middle frame that houses control electronics, batteries and payload fastenings. Protruding boom arms have motors mounted in the tips and power cables running inside. The frame, payload and boom arms are generally fastened with hexagonal socket head cap screws, which means that assembling and disassembling takes a notable amount of valuable time when setting the UAV up on the field. For this reason, modularity and rapid assembling are needed.Fig. 1. Multi-rotors performing ice-bank and high-rise inspection

Multielement FSO Transceivers Alignment for Inter-UAV Communications

Given the increased interest in aerial communications, free-space optics (FSO) has gained considerable attention for its ability to deliver wider bandwidth, license-free, and secure communication. FSO was initially developed for fixed platforms. As such, the current push to introduce mobility is one of the greatest challenges for FSO developers. This paper presents the first open-loop alignment/stability analysis of hovering multirotors proven to maintain an FSO link despite inherent instability. Communication distance, wavelength, and platform deviation are among the many parameters evaluated in our model. We characterize fiber-bundle transceivers, as an example of optical arrays and their applicability to aerial FSO communication. Our simulation is based on static lab measurements combined with theoretical analysis and optical geometrical intersection models. Analyses indicated that rotational deviation has a much higher impact on performance than translational deviation. Current commercial multirotor platforms proved adequate for future FSO communication, with 16% to 30% expected throughput when employing suitable optical arrays. We conducted a parametric sweep test to determine optimal and marginal receiver parameters based on platform characteristics and performance metrics. This analysis was conducted and reported as one example of the many applications that our developed mathematical models support.