Snake Aerial Manipulators: A Review <s> C. TAKE-OFF AND LANDING DESIGN CONSIDERATIONS <s> This paper proposes a method to investigate into helicopter landing on uneven terrain by means of using a scaled articulated robotic landing gear. A mathematical model of an articulated robotic landing gear that adapts to uneven ground conditions is considered. The model consists of a planar landing gear composed of two legs connected by a base and a skid at each end. Each skid has two degrees of freedom with PID joint controllers to provide stability while landing. A combination of Lagrange and Newton-Euler techniques is used to model the system dynamics. This work also includes a model of the ground interaction, a thrust controller and a level controller to maintain stability while landing. Experimental results with a laboratory-build scaled prototype are included and compared with the simulations. <s> BIB001 </s> Snake Aerial Manipulators: A Review <s> C. TAKE-OFF AND LANDING DESIGN CONSIDERATIONS <s> We propose a novel aerial manipulation platform, an omnidirectional aerial robot, that is capable of omnidirectional wrench generation with opportunistically distributed/aligned Sectional rotors. To circumvent the tight thrust margin and weight budget of currently available rotor and battery technologies, we propose a novel design optimization framework, which maximizes the minimum-guaranteed control force/torque for any attitude while incorporating such important and useful aspects as interrotor aerointerference, anisotropic task requirement, gravity compensation, etc. We also provide a closed-form solution of infinity-norm optimal control allocation to avoid rotor saturation with the tight thrust margin. Further, we elaborate the notion of electronic speed controller induced singularity and devise a novel selective mapping algorithm to substantially subdue its destabilizing effect. Experiments are performed to validate the theory, which demonstrate such capabilities not possible with typical aerial manipulation systems, namely, separate translation and attitude control on SE(3), hybrid pose/wrench control with downward force of 60 N much larger than its own weight (2.6 kg), and peg-in-hole teleoperation with a radial tolerance of 0.5 mm. <s> BIB002
The take-off is one of the simplest but dangerous part of the operation of an aerial system, this is because there is a bias in which the propellers turn on but the system does not get elevation. Even each propeller has its own starting value in dependence on the mechanical balance of the whole system or the adequate balance of each propeller. The software implication in this part is to ensure an optimal starting value for all the system without reaching the shutdown level, and also to establish a value where the system changes from one phase to another phase of operation. The landing is another simple but significative operation, consisting on gradually turning off the motors but taking care that they stay in their mode of thrust support (that means,that they have enough force to ensure that the system does not fall). As it has been said, motors do not have a homogeneous bias, so orientational control takes higher priority in both modes of operation (it is the way to compensate the irregular bias of each propeller) and also in consequence is crucial to keep the sensors and actuators working in precise times that ensures a smooth and non-destructive landing or take off. Discussion: It is well known that most aircraft accidents occur in this parts of the flight, and in the case of these snake aerial manipulators this is not the exception. Especially by considering those whose engines are multicopter teams, where this aircraft must not only worry about take off and landing themselves but also of the whole structure that they integrate, this implies a high precision individual and cooperative control of the attitude and altitude, then it is convenient to develop research in scenarios where: The entire aerial manipulator system has an attitude with respect to the surface with angles equal to or tending to zero, but individual aircraft do not (ie slopes or irregular terrain). Here is needed research on active control methods or passive landing (landing gear design for example) BIB001 . Take-off algorithms, as it was said, the propellers in general do not have immediate reversibility, so at the beginning of the snake-type aerial manipulation, the take-off was done with the aerial manipulator pre-held by a human or supported on stilts BIB002 . Like in many previous points, fault tolerance algorithms in the case that one or more propellers are burned or destroyed, are needed Given that one of the problems is related with ''immediate'' or faster reversibility, it is appropriate to design thrust vectoring methods that allow or emulate this reversibility (as in the case of airplane braking by reverse thrust used in the turbines of passenger aircraft).