Precision Modeling and Optimallysafe Design of Quadcopters for Controlled Crash Landing in Case of Rotor Failure The seminal work cited in 1,2 showed, for the first time, that flight stability of quadcopters would be possible in case of one or even multiple rotor failures. However, the quadcopter can remain airborne only by going through a spinning maneuver about an axis, fixed w.r.t the vehicle (i.e., resolved yaw). Furthermore, positional control can be achieved by periodically tilting this axis. This paper builds upon this concept with two major improvements: (1) introducing a precise aerodynamic model of propellers that takes the flapping torque due to unbalanced lifting force in the advancing and retreating blades subjected to freestream, into account, and (2) adding to the stability and flight efficiency of the quadcopter by introducing symmetric fixed tilting angles to the trust vectors. In our previous work 3, it was shown how the flight stability and energy efficiency can be improved by introducing fixed tilting angles in the thrust vectors. For controlled crash landing in case of one rotor failure, where a resolved yaw maneuver would be inevitable, introducing a titling angle in rotors can generate a reasonable resolvedrateyaw spinning speed to keep the quadcopter airborne at a lower rotational speed of the blades by taking advantage of the freestream generated by spinning. This tilting angle would also lead to passive stability in yaw motion of the quadcopter before the failure. Our hypothesis was successfully tested via simulations.

Mathematical modeling and control of a quadrotor aerial vehicle with tiltrotors aimed for interaction tasks With a wide spectrum of applications ranging from entertainment to military use, quadrotors, in their conventional construction with four fixed rotors, have proven to be sufficiently capable of robustly performing numerous tasks. However, the capability to generate thrust just in one direction, i.e., normal to its main plane, is very restrictive and drastically reduces the maneuverability and agility of the vehicle. In this paper, an alternative model of the quadrotor is presented. Constructively, the difference lies in the addition of a mechanism that tilts the rotors in the longitudinal direction, which in practice adds maneuverability by enabling the longitudinal translation uncoupled from the pitching movement. In addition to this new thrust component in the longitudinal direction, this configuration also yields a significant increase in the yaw torque. These are highly desired features in a UAV used to execute tasks that require physical interaction with the surrounding environment. The mathematical model of the entire system is obtained by employing the EulerLagrange formalism and a multibody approach. In addition, a basic control scheme is used to verify, through simulation, the obtained model.