Generic slung load transportation system using small size helicopters

Abstract

In this paper we present an overview of techniques and approaches used for a load transportation system based on small size unmanned helicopters. The focus is on the control approach and on the movement of the rope connecting helicopters and load. The proposed approach is based on two control loops: an outer loop to control the translation of each helicopter in compound and an inner loop to control the orientation of helicopters. The challenge here is that in both loops the dynamics of the whole system -all helicopters and load -should be accounted for. It is shown, that for designing the outer loop controller a complex model of the helicopters and load can be replaced by a simplified model based on interconnected mass points. For designing the inner loop controller, the complete dynamics of the whole system are considered. The usage of force sensors in the ropes is proposed in order to simplify the inner loop controller and to make it robust against variations of system parameters. The presented inner loop controller is independent of the number of coupled helicopters. The outer loop controller depends on the number of helicopters. The problem of oscillations in the flexible ropes due to external disturbancies (e.g. wind gusts) is discussed and a solution based on load state observer is presented. The performance of the presented system was verified in simulations and in real flight experiments with one and three helicopters transporting the load. The worldwide first demonstration of a slung load transportation using three helicopters was performed in December 2007.

Dynamic collaboration without communication: Vision-based cable-suspended load transport with two quadrotors

“…autonomous [4] rotorcraft. Apart from increasing the payload range of a multi-quadrotor system, carrying an object with multiple quadrotors makes it possible to control the orientation of the object without applying any torque to individual quadrotors [5].…”

Suspended load motion control using multicopters

“…Further, Figure 7(b) shows that the load is transported to the desired location [1,5,0] T . From Figure 8, it is seen that the velocitycontroller for hexacopter 1 follows the desired velocities.…”

“…Instead, the hexacopters will be equipped with other sensors to measure their relative position to the load. Notable results for multi-lift systems with small-size helicopters have been reported by [4], [5] and [6]. In the latter, three helicopters autonomously transported a sensor-node equipped with a camera to the top of a building for aiding in a simulated search and rescue mission.…”

Autonomous transportation and deployment with aerial robots for search and rescue missions

“…The details of the presented control algorithms can be found in (Kondak et al, 2006;Kondak et al, 2007;Bernard and Kondak, 2009;Bernard and Kondak, 2010).…”