  In this paper, we propose a time-efficient approach to generate safe, smooth
and dynamically feasible trajectories for quadrotors in obstacle-cluttered
environment. By using the uniform B-spline to represent trajectories, we
transform the trajectory planning to a graph-search problem of B-spline control
points in discretized space. Highly strict convex hull property of B-spline is
derived to guarantee the dynamical feasibility of the entire trajectory. A
novel non-uniform kinodynamic search strategy is adopted, and the step length
is dynamically adjusted during the search process according to the Euclidean
signed distance field (ESDF), making the trajectory achieve reasonable
time-allocation and be away from obstacles. Non-static initial and goal states
are allowed, therefore it can be used for online local replanning as well as
global planning. Extensive simulation and hardware experiments show that our
method achieves higher performance comparing with the state-of-the-art method.
