This work highlights the significance of the rotor dynamics in control design for small-scale aerobatic helicopters, and proposes two singularity free robust attitude tracking controllers. The first uses backstepping technique and uses full state feedback. The second uses only angle feedback and preserves the inherent damping structure present in the helicopter dynamics. Further, it has been shown to be almost globally asymptotically stable. Its performance is evaluated experimentally by performing aggressive flip maneuvers.
A preliminary version of this work was presented at the 56th IEEE CDC conference.
The Biplane Quadrotor Tailsitter UAV was designed for the purpose of emergency medical delivery in remote locations. The vehicle is capable of hovering like a helicopter and fixed-wing type forward flight. The transition between these flight models is made by tilting the entire vehicle about the pitch axis by 90 deg. The smooth transition seen in the video is made possible by the geometric attitude controller and GPS based heading control.
Apologies for the shaky video.
The torque generation capability of the conventional biplane quadrotor shown above is 10 times less about the body frame Z-axis when compared to the X and Y axes. Rotation about the body frame Z-axis represents yaw motion in the quadrotor hover mode and roll motion in the biplane forward flight mode. In order to overcome this torque limitation, a new vehicle, called the swiveling biplane-quadrotor, was developed.
This vehicle has two wings like that of the conventional biplane quadrotor, but they are connected by a single rod through a bearing. The bearing gives it an extra degree of freedom and allows for the relative angle between the wings to be changed during flight. The net thrust vector of each wing, when not aligned would produce a resultant torque about the body fixed Z-axis, which is much more than the one generated by a conventional biplane-quadrotor design. However, this extra degree of freedom also makes the vehicle underactuated in the attitude dynamics. In this work, we develop an attitude tracking controller for this system using dynamic feedback-linearization in a geometric control framework.
A real time on-board algorithm for a biplane-quadrotor to iteratively learn a forward transition maneuver via repeated flight trials is provided. The maneuver is controlled by regulating the pitch angle and propeller thrust according to feedforward control laws that are parameterized by polynomials. Based on a nominal model with simplified aerodynamics, the optimal coefficients of the polynomials are chosen through simulation such that the maneuver is completed with specified terminal conditions on altitude and air speed. In order to compensate for modeling errors, repeated flight trials are performed by updating the feedforward control parameters according to an iterative learning algorithm until the maneuver is perfected. Further, a high-fidelity thrust model of the propeller for varying advance-ratio and orientation angle is obtained from wind tunnel data. Experimental flight trials are performed to demonstrate the robustness and rapid convergence of the proposed learning algorithm.
Gyroscopes have interesting and nonintuitive behavior. If you are not familiar with gyroscopes, you could get a quick introduction from Prof. Walter Lewin's lecture: http://y2u.be/XPUuF_dECVI
In this work we design a reduced attitude controller for reorienting the spin axis of a gyroscope in a geometric control framework. The proposed reduced attitude controller preserves the inherent gyroscopic stability associated with a spinning axi-symmetric rigid body. Due to the time critical nature of the control input, the controller is extended to incorporate the effect of actuator dynamics for practical implementation. The controller is validated on an experimental spinning tricopter.
Automatica: https://doi.org/10.1016/j.automatica.2020.109471