coordinated transport of a slung load by a team of autonomous rotorcraft

Open Access
Author:
Li, Zuqun
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
January 15, 2014
Committee Members:
  • Jacob Willem Langelaan, Thesis Advisor
Keywords:
  • multilift
  • OBTLC
  • coordinated transport
  • autonomous rotorcraft
  • slung load
Abstract:
This research is motivated by the significant economical efficiency of multilift system for carrying a single heavy payload, which includes both military and commercial cargo. This thesis seeks to develop a solution for the more general problem of multilft that uses two or more autonomous rotorcraft to transport a single payload. This is accomplished with Object Based Task Level Control (OBTLC), where a complex control system of multilift is separated into three control layers. Top-level is the payload trajectory following controller, which is a closed-loop controller computes net force and moment on the load's center of gravity so a desired trajectory is followed. Mid-level is the cable force control, which computes cable force at each attachment point so that the net force and moment on the CG equal to the desired value from the trajectory following controller. Finally, low-level is the flight controller onboard each helicopter that ensures the desired cable force and direction are satisfied. Mid-level control is the main focus of this thesis. A two-step cable force computation is developed: first, solve the least-norm solution to satisfy the desired net force and moment required for payload to follow its trajectory; second, compute null space of cable force to ensure other constraints (such as vehicle separation and cable force constraint) are met. Condition number is used to select the location of attachment points so that any error in the cable force will have minimum effect on the payload. Additionally, cable force angle constraint is developed to improve stability of the payload. A multilift simulation, where each helicopter, cable, and the payload have their own equation of motion, is used to test and validate the aforementioned approach. Result of simulations showing four degree of freedom transport of a load (North, East, Down position and yaw angle) are used to show the utility.