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Control >> Cooperative transport >> Different shapes and sizes

Transport of objects of different shapes and sizes

Aiming at a cooperative transport behaviour which is less sensitive to the characteristics of the prey than the ones described previously, we conducted a new experiment with the following focus: the objective is to let the s-bots self-assemble into structures which are capable of pulling or pushing prey of different shape and size towards a target location.

In this study, the simulated s-bots are provided with the ability to rotate their turret with respect to the chassis, In addition, the s-bots can sense each other with the camera.

Experimental setup

Four s-bots are put at random positions in the neighbourhood of the prey. The s-bot controllers are supposed to let the s-bots localise and approach the prey, and self-assemble into structures physically linked to the prey, in order to pull or push it towards a beacon.

The prey is modelled as a cylinder or as a cuboid of height 12 or 20 cm. Depending on its weight, the cooperative behaviour of at least 2 or 3 s-bots is necessary to move the prey.

The s-bot can control its left and right wheels, the rigid gripper, and the orientation of the chassis with respect to the turret. In addition, the s-bot can control the heading of the (simulated) directional camera.

Using its directional camera, the s-bot perceives its teammates and the prey. It can also determine the direction to a beacon (the target location), unless it is shadowed by an object. In addition, the s-bot can determine whether it is grasped to another object or not.

The group of s-bots is controlled by a simple recurrent neural network that is synthesised by an evolutionary algorithm. All the s-bots of a group transporting a prey are initially equipped with an identical neural network. To favour the evolution of controllers that make use of the gripper element, the fitness function takes the assembling performance into account.

An evolutionary algorithm is utilised in order to obtain the weights of the s-bots' neural controllers. Starting from a population of 80 random initial candidate solutions, each one is assigned a fitness value reflecting its quality. In each generation, the best 20 individuals are selected to produce the subsequent generation of 80 candidate solutions.

Results

The experimental setup described above has been used in ten independent evolutionary runs of 850 generations each. The evolved controllers perform quite well, independently of the shape and size of the prey, and allow the group to transport the prey towards a moving target. Additionally, the controllers evolved for a relatively small group can be applied to larger groups, making possible the transport of heavier prey.


References



Control >> Cooperative transport >> Different shapes and sizes

Swarm-bots project started
on October 1,2001
The project terminated
on March 31, 2005.
Last modified:
Fri, 27 Jun 2014 11:26:47 +0200
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