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In the past decade, there has been much interest in operating quadrotors in uncertain and cluttered environments due to their simplicity. Executing precise agile quadrotor flight maneuvers is an important open research problem for navigating in such environment. Collisions can occur if actuator constraints are not considered in the trajectory tracker design. This paper presents a cascade nonlinear constrained control approach (CNCCA) for trajectory tracking with explicit consideration of actuator constraints, where the output signal of the position controller is converted into the desired command of the attitude controller. The proposed position control loop is shown to be stable and bounded, satisfying the total thrust limits. The proposed attitude tracking control loop is designed as a saturated control law based on a modified geometric controller in SO(3) space. A proof of its stability is provided. The simulation results also show good tracking performance of the proposed approach. [ABSTRACT FROM AUTHOR]

Multi-UAV systems are becoming a true reality. They have wide applications in surveillance, search, hazardous rescue and other civil services. Currently, an important challenge is the robust control against UAV failures. In this paper, the distributed UAV loss detection and auto-replacement scheme is discussed. The basic idea is to use the cooperative method to control the multi-UAV system to accomplish the missions. This is achieved by exchanging heartbeats (HBs) and information fusion. We first use the obtained information to detect if one UAV is lost. Subsequently, an auto-replacement logic is used to send a UAV with low priority to occupy the target position or task which was assigned to the lost UAV. Next, a recovery algorithm is proposed when a newly inserted UAV or a lost UAV is recovered from failures. Finally, the proposed scheme is tested by computer simulations and real experiments. [ABSTRACT FROM AUTHOR]

This paper is focused on designing a distributed adaptive control scheme for a vehicular platoon with unknown bounded velocity/acceleration disturbances and unknown nonlinear dead-zone inputs. Our aim is to design distributed adaptive controllers based on integral sliding mode control techniques that guarantee practical exponential convergence (i.e., exponential stability of an arbitrarily small neighborhood of zero) of the spacing errors and the string stability of the whole vehicular platoon. The contributions of this paper are that: (i) based on a modified constant time headway policy, the whole vehicular platoon is guaranteed to have string stability despite dead zone inputs; (ii) adaptive compensation terms are constructed to compensate for the time-variant effects caused by unknown bounded velocity/acceleration disturbances, and unknown dead zone inputs; (iii) an efficient numerical method for avoiding the singularity problem of the control law is also proposed. Numerical simulation results show the validity and advantages of the proposed method are significantly higher traffic density and string stability. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]