Load transportation with an elastic cable: modeling and control

Finished: 2023-07-07

BSc assignment

Multi-rotor UAVs have been applied for load transportation, such as package delivery, and even flying taxis in the future. However, attaching load, especially those with large sizes, directly underneath the UAV can disturb the airflow detrimentally and consequently reduce the aerodynamic efficiency.

The sling load operation is a solution to tackle this issue, in which the load is connected to the UAV through a tether. Existing controllers typically neglect the elasticity of the cable, treating it as a rigid link, hence lacking accuracy.

In order to know more about how the elasticity of the cable affects the system behaviour, we consider the system consists of a single quadrotor UAV, a point-mass load, and an elastic cable.

1. Given the control input of the system is the thrust of four propellers, define the full nonlinear dynamic model of the system, including the states and parameters needed.
2. Find the equilibrium for hovering. Express the equilibrium with parameters included as variables.
3. Define a linearized model around the hovering flight, which is defined as flying at zero translational velocity.
4. Design a linear controller to control the position of the load for stable hovering at a set point.
5. Design a linear controller (e.g., gain scheduling LQR) to control the position of the load to track a circular trajectory in the horizontal plane.
6. Validate the controller in a nonlinear simulation.