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the particularities of the modular systems and thus their scalability is limited.
Basically, most authors focus their attention in the genotypical representation
of the modular system, which is a complex problem, but without paying much
attention to the algorithm itself.
In this paper we propose a constructive evolutionary algorithm with oper-
ators that are designed to control and adapt their exploration capabilities to
this particular type of search spaces and that produce quite good results within
this domain. The algorithm is applied over a heterogeneous modular architec-
ture developed by our group in order to solve the typical benchmark prob-
lem of obtaining a modular robot that maximizes its motion in a straight line
for a given amount of time. The rest of the paper is structured as follows: in
section 2 we provide an overview of the heterogeneous modular system we are
considering. Section 3 is devoted to the presentation of the constructive evolu-
tionary algorithm developed in order to obtain robot morphologies and control
mechanisms. An example of the application of the evolutionary algorithm to the
set of selected modules in a simple task is discussed in section 4. Finally, in
section 5 we will present the main conclusions of this work.
2 Heterogeneous Modular System
Most existing modular systems are made up of homogeneous sets of modules,
which facilitates control and reconfiguration but limits the range of possible
configurations. However, for the sake of completeness, flexibility and simplicity,
the system considered here is heterogeneous and is made up of 4 types of modules:
-
Actuators: those that generate robot motion, through pneumatic or electrical
motors.
-
Effectors: coupled to the actuator module they provide new functionalities,
like legs, wheels or tools.
-
Sensors: they provide external or internal information, like cameras, battery
meters, etc.
-
Linkers: they join other modules.
Fig. 1 displays the final design and implementation of some of the modules in
this architecture. From top to bottom: slider, telescopic and rotational (axis)
modules. The modules can be joined together through coupling connections in
all the faces of the cubes at their extremes except one as well as through the slider
in the slider module. This makes, for example, a total of 14 possible attachment
positions for a slider module.
Communications are mandatory in modular robotics to assure the adequate
coordination between modules. In this system, there are two types of communi-
cations paths: a CAN bus for global coordination and asynchronous local com-
munications to allow intermodule identification (morphological propioception),
and ZIGBEE wireless communications for global coordination in the case we
have isolated robotic units or when the CAN bus is saturated. Each module has
its own embedded microcontroller (pic32mx575f512) and both, centralized and
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