IEEE Robotics & Automation Magazine - December 2013 - 66

use of absolute positioning systems, such as GPS, 3-D tracking cameras (which require preinstallation), illuminationdependent visual processing, or computationally expensive
laser scanning.
The eye-bot uses a quadrotor-like propulsion configuration but with a 4 # 2 coaxial rotor system. Each rotor system
consists of a coaxial counter-rotating brushless motor
(Himax Outrunner HC2805-1430), which provides 500 g
thrust at 9 V (750 g at 12 V). This gives a total platform
thrust of at least 2,000 g, sufficient to lift the payload for the
advanced sensory-motor systems. The main body has a carbon fiber structure and houses the batteries and the main
PCBs, such as the flight computer and the i.MX31 ARM 11
processor. Attached to the bottom of the body structure is
the propulsion system, which consists of four carbon fiber
arms that support the motors, the rotary systems, and the
range and bearing module. On top of the eye-bot resides the
ceiling attachment mechanism. Finally, the eye-bot has four
carbon fiber legs for support. These legs also protect the
rotors and the delicate pan-tilt camera system. In total, the
carbon fiber structure weighs only 270 g. The outer diameter
is 50 cm, and the total height, including the legs and ceiling
attachment, is 54 cm.
As mentioned above, the eye-bot is reliant on the range and
bearing communication device. This communication system
allows an eye-bot to communicate with other eye-bots, to
coordinate movements in 3-D, and to facilitate controlled
flight without platform drift. The system is fully compatible
with the similar devices developed for the foot-bot and the
hand-bot and permits bidirectional communication between
the different robotic platforms. The system mounted on the
eye-bots provides the range and bearing of robots within 12 m
as well as low-bandwidth local communication.
Inter-robot communication can also take place via colorbased visual signals. An array of RGB LEDs around the
perimeter of the eye-bot can be illuminated in different color
patterns. To view the color LED rings of other robots and to
detect target objects of interest, the eye-bots are equipped
with a high-resolution color CMOS camera mounted on a
two-axis pan-tilt mechanism. This allows the eye-bot to have
high-resolution imaging in the volume of space beneath the

Controller
Control Interface
Actuators

Sensors

Entities
Simulated 3-D Space

Physics Engines

Visualizations

Figure 6. The architecture of the ARGoS simulator.

IEEE ROBOTICS & AUTOMATION MAGAZINE

DECEMBER 2013

eye-bot. The same pan-tilt mechanism additionally holds a
5-mW Class IIIA laser pointer. This laser can be pointed in
any direction beneath the eye-bot.
Simulation
ARGoS is a new simulator that we designed and implemented
in-house to simulate the swarmanoid robots and to enable fast
prototyping and testing of robot controllers. ARGoS is unique
in that it offers high scalability without sacrificing flexibility.
In traditional simulator designs, such as those of Webots
[31], USARSim [32], and Gazebo [33], accuracy is the main
driver and is achieved at the cost of limited scalability.
Simulators designed for scalability, such as Stage [34], are
focused on very specific application scenarios, thus lacking
flexibility. To achieve both scalability and flexibility, in the
design of ARGoS we made a number of innovative choices.
ARGoS' architecture is depicted in Figure 6. Its core, the
simulated space, contains all the data about the current state
of the simulation. Such data are organized into sets of entities
of different types. Each entity type stores a certain aspect of
the simulation. For instance, positional entities contain the
position and orientation of each object in the space. Entities
are also organized into hierarchies. For example, the embodied entity is an extension of the positional entity that includes
a bounding box. Robots are represented as composable entities, i.e., entities that can contain other entities. Each individual robot feature is stored into dedicated entity types. For
instance, each robot possesses an embodied entity and a controllable entity that stores a pointer to that robot's sensors,
actuators, and control code.
Our organization of data in the simulated space provides
both scalability and flexibility. Scalability is achieved by organizing entities into type-specific indexes, optimized for speed.
For instance, all positional entities are organized into space
hashes, a simple, state-of-the-art technique to store and
retrieve spatial data. Flexibility is ensured because entities are
implemented as modules. In addition to the entities offered
natively by ARGoS, the user can add custom modules, thus
enriching ARGoS' capabilities with novel features.
Analogously, the code accessing the simulated space is
organized into several modules. Each individual module can
be overridden by the user whenever necessary, thus ensuring
a high level of flexibility. The modules are implemented as
plug-ins that are loaded at runtime.
Controllers are modules that contain control code developed by the user. Controllers interact with a robot's devices
through an application programming interface (API) called
the common interface. The common interface API is an
abstraction layer that can make underlying calls to either a
simulated or a real-world robot. In this way, controllers can be
seamlessly ported from simulation to reality and back, making behavior development and its experimental validation
more efficient.
Sensors and actuators are modules that implement the
common interface API. Sensors read from the simulated space
and actuators write to it. The optimized entity indexes ensure

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2013