CAD render of coaxial variable-tilt multicopter
Multirotor helicopters (often colloquially referred to as drones) are exciting and versatile robotic platforms that have found use in tasks that, among others, require aerial navigation/inspection and human less intervention. The standard mechanical configuration makes use of four motor-propeller units, and actuation is achieved by differentially setting the four motor speeds – resulting in differential thrust and torques on the robot body. The weakness of this approach is that the motor time constants (speed up/slow down time) and motor saturation directly affects the rate and amount of thrust that can be produced, and hence limits the overall agility of the quadcopter. The standard configuration also results in under-actuation where the control inputs are less than the number of degrees of freedom, resulting in an inability to follow arbitrary trajectories and poses in space. This limits the manoeuvrability and dexterity of the UAV, and often results in inefficient flight characteristics.
An alternative means of producing differential thrust is to independently adjust the rotation axis of each the propeller blades (in other words the motor and propeller units) around a single axis perpendicular to each rotor arm in one degree of freedom (similar to a Bell Boeing V-22 Osprey, and an illustrative set up previously done in research can be seen here, and here to give further clarity (Oosedo et al, 2015, pp. 2326-2331) (Oliver et al, 2016, pp. 1849-1852). While more mechanically complex, this has the potential to increase the rate at which thrust is produced in specific directions (thrust vectoring), allowing for greatly improved manoeuvrability. The increased control degrees of freedom results in an overactuated system, greatly improving the dexterity of the UAV, and allowing for the possibility of arbitrary trajectories and poses to be followed.
An additional means of producing further thrust, while maintaining the same vehicle footprint and fundamental morphology, is to implement the motor and propeller unit in coaxial configuration (An illustrative example of a coaxial set up previously done in research can be seen here, albeit in a hexacopter configuration with an end-effector manipulator, but a multirotor nonetheless (Bodie et al, 2021, pp.8165-8172)). While more mechanically complex, this has the potential to greatly increase the thrust that is produced with relatively minimal weight gain, again allowing for increased manoeuvrability.
The coaxial variable-tilt configuration has the potential to greatly improve the manoeuvrability and dexterity of the UAV, while also providing fault tolerance and failure redundancy. This combination vastly improves the aerial navigation/inspection and humanless intervention capabilities and provides future research avenues for aerial manipulation in the real-world, among others.
Additionally, the master's project is investigating methods to perform system identification on the UAV's propulsion system. To that end, a Propulsion Rig is being developed. This is a propulsion system test platform used to measure the principal performance characteristics of multirotor propulsion systems. The Propulsion Rig is designed to be low-cost, applicable for small to medium-scale multirotor propulsion systems, and open-source. Data from the Propulsion Rig is used to generate static and dynamic models of the propulsion system. These models can be used to validate conceptual multirotor designs and be incorporated into control schemes. By accounting for propulsion system dynamics, the performance of the control schemes can potentially be improved.
CAD render of propulsion rig
Bodie, K., Tognon, M. and Siegwart, R., 2021. Dynamic end effector tracking with an omnidirectional parallel aerial manipulator. IEEE Robotics and Automation Letters, 6(4), pp.8165-8172.
Oliver, R., Khoo, S.Y., Norton, M., Adams, S. and Kouzani, A., 2016, November. Development of a single axis tilting quadcopter. In 2016 IEEE Region 10 Conference (TENCON) (pp. 1849-1852). IEEE.
Oosedo, A., Abiko, S., Narasaki, S., Kuno, A., Konno, A. and Uchiyama, M., 2015, May. Flight control systems of a quad tilt rotor unmanned aerial vehicle for a large attitude change. In 2015 IEEE International Conference on Robotics and Automation (ICRA) (pp. 2326-2331). IEEE.
Mathematical modelling, mechanical modelling, system identification, MATLAB and Simulink.
1x MSc (Eng), 1x Journal/Conference paper in a leading publication, 1x multi-rotor test platform.