In this article, a novel quadcopter capable of changing shape midflight is presented, allowing for operation in four configurations with the capability of sustained hover in three. This is accomplished without requiring actuators beyond the four motors typical of a quadcopter. Morphing is achieved through freely rotating hinges that allow the vehicle arms to fold downwards by either reducing or reversing thrust forces. Constraints placed on the control inputs of the vehicle prevent the arms from folding or unfolding unexpectedly. This allows for the use of existing quadcopter controllers and trajectory generation algorithms with only minimal added complexity. For our experimental vehicle at hover, we find that these constraints result in a 36% reduction of the maximum yaw torque the vehicle can produce, but do not result in a reduction of the maximum thrust or roll and pitch torques. Experimental results show that, for a typical maneuver, the added limits have a negligible effect on the trajectory tracking performance. Finally, the ability to change configurations is shown to enable the vehicle to traverse small passages, perch on hanging wires, and perform limited grasping tasks.

This paper presents a novel quadcopter design that uses passive rotary joints to enable rapid aerial morphing without the use of additional actuators. The normally rigid connections between the arms of the quadcopter and the central body are replaced by sprung hinges that allow for the arms of the quadcopter to fold downward when low thrusts are produced by the propellers, resulting in a reduction of the largest dimension of the vehicle by approximately 50%. The ability of the vehicle to reduce its size during flight allows, e.g., for the traversal of gaps through which a non-morphing quadcopter could not pass. The vehicle is designed such that existing quadcopter controllers and trajectory generation algorithms can be used, provided that some additional constraints on the control inputs are met. The nonlinear dynamics of the system are presented, and design rules are given that minimize transition time between configurations and maximize the available range of control inputs. A method for performing gap traversal maneuvers is proposed and validated experimentally.

We present a continuous-time collision detection algorithm for quickly detecting whether certain polynomial trajectories in time intersect with convex obstacles. The algorithm is used in conjunction with an existing multicopter trajectory generation method to achieve rapid, obstacle-aware motion planning in environments with both static convex obstacles and dynamic convex obstacles whose boundaries do not rotate. In general, this problem is difficult because the presence of convex obstacles makes the feasible space of trajectories nonconvex. The performance of the algorithm is benchmarked using Monte Carlo simulations, and experimental results are presented that demonstrate the use of the method to plan collision-free multicopter trajectories in milliseconds in environments with both static and dynamic obstacles.

This paper presents a novel quadcopter design with an added momentum wheel for enhanced stability. The novel vehicle has improved torque disturbance rejection capabilities compared to a standard quadcopter. An analysis of the vehicle dynamics shows that the effect of torque disturbances decreases monotonically with increasing angular momentum of the momentum wheel. A framework for choosing the mass moment of inertia and speed of the momentum wheel is given based on an upper bound on the allowable energy stored in the wheel. Theoretical results are experimentally validated by comparing responses to torque impulses applied to the vehicle with and without the momentum wheel spinning.