Just the other day, a noisy helicopter was flying above campus, carrying large batches of solar panels to hard to reach rooftops. You might have also seen people dangling from helicopters in rescue missions or the transportation of materials in military, industrial and construction applications. Pushing the limits of aerial payload transportation this spring, the Alinghi catamaran was “shipped” to sea using a Mil Mi-26 helicopter, the biggest and most powerful in the world (see picture below).
Rather than going for large helicopters with experienced pilots, Michael et al. explore the possibility of using multiple autonomous quadrotors. By working together, the robots can potentially lift heavy objects and can position themselves in such a way that the pose of the object can be controlled. Simply put, in the image above, there is no way to tilt the catamaran sideways by 45 degrees whereas a system with multiple robots could do the trick.
More specifically, the researchers consider the problem of controlling multiple robots manipulating and transporting a payload in three dimensions via cables. To do so they derive a mathematical model that ensures static equilibrium of the payload at a desired pose while respecting constraints on cable tensions.
Experiments shown in the video below were conducted with three AscTec Humming-bird quadrotors from Ascending Technologies GmbH. Localization information was provided by a Vicon motion capture system that consists in a set of cameras in the room that monitor the robots at high speed. The robots are able to lift a triangular payload, change its pose and transport it while avoiding inter-robot collisions.
In the future, Michael et al. hope to find a way to make the robots damp out oscillations that occur when the payload moves.