Strategies for Maintaining Large Robot Communities

English, S., Gough, J., Johnson, A., Spanton, R., Sun, J., Crowder, R. and Zauner, K. P. (2008) Strategies for Maintaining Large Robot Communities. In: Artificial Life XI, 5-8 August, 2008, Winchester. p. 763.

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Abstract

The confluence of progress in micro-actuators, power sources, and
mixed-signal microelectronics have recently moved swarm robotics
and robot communities from simulation to reality. Swarms of 20 to
100 robots are in use already, implementations with several
hundred robots are practicable, and communities exceeding a
thousand robots are certainly conceivable. Such large robotic
communities provide platforms for numerous exciting research
directions including collaborative swarms and self-reconfiguring
structures.

Maintaining hundreds of robots, however, poses significant
practical challenges. The literature on strategies for
maintaining software and hardware in large robot communities is
sparse, even if applicable concepts from wireless sensor-networks
are included. Crucial for the viability of any such strategy is
its impact on cost per robot.

To provide a realistic setting we introduce a robot platform
designed to be fabricated in full on standard printed circuit
board (PCB) assembly lines. In this context we introduce a
framework for on-line testing and calibration based on code
pieces, termed plasmids, that migrate among the micro-controllers
of the robots. The proposed approach allows the robots access to
a larger library of code then what could be stored locally.

The robot consists of a single PCB that doubles as chassis and
contains no custom mechanical components. Inexpensive motors
(mass produced to vibrate mobile phones) are directly soldered to
the circuit board and used in direct drive. Our prototypes use a
200 mAh rechargeable lithium polymer battery giving the robot
over an hour of autonomy while moving at a speedy 1 m/s. An
MSP430F2131 microcontroller controls the robot and communicates
with neighbouring robots via infrared light. The simplicity of
the design allows the entire robot to be assembled with low-cost
PCB manufacturing techniques and is well suited for small-scale
mass production of several hundred robots.

While this design significantly reduces the current cost barrier
to obtaining a robot swarm, it also shifts the attention to the
practical problem of maintaining hundreds of robots. Recharging
batteries, sieving out robots with worn tyres or accidental
damage is one aspect. A second aspect is testing and
calibration. It can not be performed in the PCB assembly process
and cost considerations prevent proprioceptive
sensor. Collaboration among robots to verify performance and
provide feedback (e.g., drift direction during a run and return)
provide a scalable alternative. A third aspect is the
maintenance of software in the robot community.

Our plasmid framework addresses all three aspects with a design
that is lightweight enough to run on the microcontrollers. Pieces
of code and associated attributes (version, target number for
redistribution, lifetime, conditions for transmission) are
propagated among robots that meet. For example, the code may
perform a test on the robot and require to be forwarded to four
other robots that have not encountered this test, before it is
deleted. Such test plasmids traverse the robot community which,
in its collective memory,contains and executes more code than
would fit within the program memory of a single device.