@article {2020e-MicCenZacFra,
	title = {Hierarchical nonlinear control for multi-rotor asymptotic stabilization based on zero-moment direction},
	journal = {Automatica},
	year = {2020},
	abstract = {
We consider the hovering control problem for a class of multi-rotor aerial platforms with generically oriented propellers, characterized by intrinsically coupled translational and rotational dynamics. In doing this, we first discuss some assumptions guaranteeing the rejection of generic disturbance torques while compensating for the gravity force. These assumptions are translated into a geometric condition usually satisfied by both standard models and more general configurations. Then, we propose a control strategy based on the identification of a zero-moment direction for the exerted force and a dynamic state feedback linearization based on this preferential direction, which locally asymptotically stabilizes the platform to a static hovering condition. Stability properties of the control law are rigorously proved through Lyapunov-based methods and reduction theorems for the stability of nested sets. Asymptotic zeroing of the error dynamics and convergence to the static hovering condition are then confirmed by simulation results on a star-shaped hexarotor model with tilted propellers.},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2020e-MicCenZacFra.pdf},
	author = {Giulia Michieletto and Angelo Cenedese and Luca Zaccarian and Antonio Franchi}
}
@conference {2019j-MicCenFra,
	title = {Force-Moment Decoupling and Rotor-Failure Robustness for Star-Shaped Generically-Tilted Multi-Rotors},
	booktitle = {In 58th IEEE Conference on Decision and Control},
	year = {2019},
	month = {12/2019},
	address = {Nice, France},
	abstract = {Aerial robotics is increasingly becoming an at- tractive field of research thanks to the peculiar mixture of theoretical issues to be solved and technological challenges to be faced. In particular, recent developments have seen the multiplication of multi-rotor platforms that aim at improving the maneuverability of classical quadrotors in standard and harsh flying conditions, thus opening the field to compre- hensive studies over the structural multi-rotor properties of actuation, decoupling, and robustness, which strongly depend on the mechanical configuration of the systems. This work collocates along this line of research by considering star-shaped generically-tilted multi-rotors (SGTMs), namely platforms with more than four possibly tilted propellers (along two tilting orthogonal axes). For these platforms, we investigate how the structural choices over the number of propellers and the tilting angles affect the force-moment decoupling features and, by recalling the robustness definition that refers to the hovering capabilities of the platform, we provide a robustness analysis and an hoverability assessment for SGTMs having five to eight actuators against the loss of one and two propellers.},
	author = {Giulia Michieletto and Angelo Cenedese and Antonio Franchi}
}
@article {2019a-FraRobMic,
	title = {Online Leader Selection for Improved Collective Tracking and Formation Control: the Second Order Case},
	journal = {IEEE Transactions on Control of Network Systems},
	volume = {6},
	year = {2019},
	month = {12/2019},
	pages = {1415-1425},
	abstract = {In this work, we deal with a double control task for a group of interacting agents having a second-order dynamics. Adopting the leader-follower paradigm, the given multi-agent system is required to maintain a desired formation and to collectively track a velocity reference provided by an external source only to a single agent at time, called the {\textquoteleft}leader{\textquoteright}. We prove that it is possible to optimize the group performance by persistently selecting online the leader among the agents. To do this, we first define a suitable error metric able to capture the tracking performance of the multi-agent group while maintaining a desired formation through a (even time-varying) communication-graph topology. Then we show that this depends on the algebraic connectivity and on the maximum eigenvalue of the Laplacian matrix of a special directed graph depending on the selected leader. By exploiting these theoretical results, we finally design a fully-distributed adaptive procedure able to periodically select online the optimum leader among the neighbors of the current one. The effectiveness of the proposed solution against other possible strategies is confirmed by numerical simulations.},
	doi = {10.1109/TCNS.2019.2891011},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2019a-FraRobMic-preprint.pdf},
	author = {Antonio Franchi and Paolo Robuffo Giordano and Giulia Michieletto}
}
@article {2018a-MicRylFra,
	title = {Fundamental Actuation Properties of Multi-rotors: Force-Moment Decoupling and Fail-safe Robustness},
	journal = {IEEE Trans. on Robotics},
	volume = {34},
	year = {2018},
	month = {06/2018},
	doi = {10.1109/TRO.2018.2821155},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2018a-MicRylFra-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/video1_explaination.mp4 , https://homepages.laas.fr/afranchi/robotics/sites/default/files/video2_triggered_failures.mp4 , https://homepages.laas.fr/afranchi/robotics/sites/default/files/video3_hitting_failures.mp4},
	author = {Giulia Michieletto and Markus Ryll and Antonio Franchi}
}
@conference {2017f-MicRylFra,
	title = {Control of Statically Hoverable Multi-Rotor Aerial Vehicles and Application to Rotor-Failure Robustness for Hexarotors},
	booktitle = {2017 IEEE Int. Conf. on Robotics and Automation},
	year = {2017},
	month = {05/2017},
	address = {Singapore},
	abstract = {Standard hexarotors are often mistakenly considered {\textquoteleft}by definition{\textquoteright} fail-safe multi-rotor platforms because of the two additional propellers when compared to quadrotors. However this is not true, in fact, a standard hexarotor cannot statically hover with {\textquoteleft}only{\textquoteright} five propellers. In this paper we provide a set of new general algebraic conditions to ensure static hover for any multi-rotor platform with any number of generically oriented rotors. These are elegantly formulated as the full-rankness of the control moment input matrix, and the non-orthogonality between its null-space and the row space of the control force input matrix. Input saturations and safety margins are also taken into account with an additional condition on the null-space of control moment input matrix. A deep analysis on the hoverability properties is then carried out focusing on the propeller loss in a hexarotor platform. Leveraging our general results we explain why a standard hexarotor is not robust and how it can be made robust thanks to a particular tilt of the rotors. We finally propose a novel cascaded controller based on a preferential direction in the null-space of the control moment input matrix for the large class of statically hoverable multi-rotors, which goes far beyond standard platforms, and we apply this controller to the case of failed tilted hexarotor.},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2017f-MicRylFra-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/2017f-MicRylFra.mp4},
	author = {Giulia Michieletto and Markus Ryll and Antonio Franchi}
}
@conference {2017i-MicCenZacFra,
	title = {Nonlinear Control of Multi-Rotor Aerial Vehicles Based on the Zero-Moment Direction},
	booktitle = {20th IFAC World Congress},
	year = {2017},
	month = {07/2017},
	address = {Toulouse, France},
	abstract = {A quaternion-based nonlinear control strategy is here presented to steer and keep a generic multi-rotor platform in a given reference position. Exploiting a state feedback structure, the proposed solution ensures the stabilization of the aerial vehicle so that its linear and angular velocity are zero and its attitude is constant. The main feature of the designed controller is the identification of a zero-moment direction in the feasible force space, i.e., a direction along which the control force intensity can be assigned independently of the control moment. The asymptotic convergence of the error dynamics is confirmed by simulation results on a hexarotor with tilted propellers.
},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2017i-MicCenZacFra-preprint.pdf},
	author = {Giulia Michieletto and Angelo Cenedese and Luca Zaccarian and Antonio Franchi}
}
@conference {2016o-MicCenFra,
	title = {Bearing Rigidity Theory in SE(3)},
	booktitle = {55th IEEE Conference on Decision and Control},
	year = {2016},
	month = {12/2016},
	pages = {5950-5955},
	address = {Las Vegas, NV},
	abstract = {Rigidity theory has recently emerged as an efficient tool in the control field of coordinated multi-agent systems, such as multi-robot formations and UAVs swarms, that are characterized by sensing, communication and movement capabilities. This work aims at describing the rigidity properties for frameworks embedded in the three-dimensional Special Euclidean space SE(3) wherein each agent has 6DoF. In such scenario, it is assumed that the devices are able to gather bearing measurements w.r.t. their neighbors, expressing them into their own body frame. The goal is then to identify the framework transformations that allow to preserve such measurements maintaining it rigid. Rigidity properties are mathematically formalized in this work which differs from the previous ones as it faces the extension in three-dimensional space dealing with the 3D rotations manifold. In particular, the attention is focused on the infinitesimal SE(3)-rigidity for which a necessary and sufficient condition is provided.},
	attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2016o-MicCenFra-preprint.pdf},
	author = {Giulia Michieletto and Angelo Cenedese and Antonio Franchi}
}
