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Hardware >> The s-bot

Swarm-bots hardware

Concept and design

An important part of the swarm-bots project consists in the physical construction of at least one swarm-bot, that is, a self-assembling and self-organising robot colony made of a number (30-35) of smaller devices, called s-bots. Each s-bot is a fully autonomous mobile robot capable of performing basic tasks such as autonomous navigation, perception of its surrounding environment, and grasping of objects. A s-bot is also able to communicate with other peer units and physically join either rigidly or flexibly to them, thus forming a swarm-bot. A swarm-bot is supposed to be capable of performing exploration, navigation and transportation of heavy objects on very rough terrains, especially when a single s-bot has major problems at achieving the task alone. The hardware structure is combined with a distributed adaptive control architecture inspired upon ant colony behaviours.

The s-bot design is shown in figure 1. The mobility is ensured by a differential treels© drive system, composed by tracks and wheels. Each treel© is controlled by a motor so that a robot can freely move in the environment and rotate on the spot. Treels allow each s-bot to move even on moderately rough terrain, with more complex situations being addressed by swarm-bot configurations.

The motor base with the treels© can rotate with respect to the main body by means of a motorised axis.

S-bots can connect to each other with two types of possible physical interconnections: rigid and semi-flexible.

Rigid connections between two s-bots are implemented by a gripper mounted on a horizontal active axis. This gripper has a very large acceptance area that can securely grasp at any angle and lift (if necessary) another s-bot.

Semi-flexible connections are implemented by flexible arms actuated by three motors positioned at the point of attachment on the main body. The three degrees of freedom allow to move the arm laterally and vertically as well as extend and retract it.

Using rigid and flexible connections, s-bots can form a swarm-bot having 1D or 2D structures. These structures can bend and take 3D shapes.

Rigid and flexible connections have complementary roles in the functioning of the swarm-bot. The rigid connection is mainly used to form rigid chains that have to pass large gaps, as illustrated in Figure 4. The flexible connection is adapted for configurations where each robot can still have its own mobility inside the structure. The swarm-bot can of course also have mixed configurations, including both rigid and flexible connections, as illustrated in figure 2.

Potential application of this type of swarm robotics are, for instance, semi-automatic space exploration, search for rescue or underwater exploration.

 

Figure 1: A graphic visualisation of the first s-bot design. The diameter of the main body is 116 mm.

Figure 2: Most swarm-bot configurations will include both rigid and semi-flexible connections.

Figure 3: Swarm-bot configurations can be used to pass large obstacles.

Figure 4: The rigid connection can be used to form chains and pass very big obstacles and large gaps.

The main features of this design are:

  • Compact size: 116 mm in diameter of the main body, 100 mm in height
  • All-terrain mobility using a treels© drive mechanism
  • Rotation of the main body in respect to the motion base
  • One degree of freedom rigid arm with gripper
  • Three degrees of freedom flexible arm with gripper
  • Optical barriers on grippers
  • 15 IR proximity sensors around the robot
  • 4 IR proximity sensors on the bottom of the robot
  • 8x3 colour LEDs around the robot body
  • 8 light sensors around the robot body
  • Force sensor between treels© base and main body
  • Torque sensor on wheels and body rotation
  • 3 axis accelerometer
  • Humidity sensors
  • Temperature sensors
  • One speaker and four microphones
  • Omnidirectional camera

A QuickTime visualisation of the design is available here (5.3M, you need quicktime to see it)

Figure 5: Detailed mechanical design of the s-bot.

 

Figure 6: Electronic design structure of the s-bot.

Implementation

Figure 8shows a prototype of the full s-bot following the description of figure 5 has been built. It includes full mechanics and electronics (14 PCBs supporting 14 processors and all sensors and actuators control). The main control board is running LINUX, is equipped with wireless LAN and controls camera and sound systems.

One of the very spectacular features of the prototype is its light ring for communication with others s-bots. Figure 7shows several possible colours. Each of the 8 sectors of the light ring can take RGB colours and can blink at different frequencies. This ring can be observed with the omnidirectional camera.

Figure 7: Light ring around the robot for communication purposes.

Figure 8: S-bot prototype.

S-bot and swarm-bot behaviour

Several tests have been performed to verify the functionalities of the s-bot as single robot, its ability to self assemble into a swarm-bot and pass some large obstacles. The three videos presented here on the right show these several aspects.

The first video shows an s-bot behaviour based on two competitive behaviours: follow an humidity source and avoid obstacles (small hills) detecting them using the inclinometer available on the robot.

The second video illustrates two s-bots assembling into a swarm-bot and passing a large gap, exploiting in a passive way the rigidity of the connection.

In the third video the swarm-bot exploits actively the connection to pass a step.

An s-bot following humidity gradient while avoiding obstacles using accelerometer information. MPEG, (3.9 MB).

A swarm-bot (consisting of 2 s-bots) joining to go over a gap. MPEG, (2.3 MB).

A swarm-bot (consisting of 2 s-bots) climbing up a step MPEG, (1.5 MB).

Figure 9: Swarm-bot robot configuration to pass a large gap.



Hardware >> The s-bot

Swarm-bots project started
on October 1,2001
The project terminated
on March 31, 2005.
Last modified:
Fri, 27 Jun 2014 04:26:47 -0500
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swarm-bots@iridia.ulb.ac.be