robotic construction reference: Swarm robotics

Swarm robotics is an approach to the coordination of multirobot systems which consist of large numbers of mostly simple physical robots. It is supposed that a desired collective behavior emerges from the interactions between the robots and interactions of robots with the environment.

The research of swarm robotics is to study the design of robots, their physical body and their controlling behaviours. It is inspired but not limited by the emergent behaviour observed in social insects, called swarm intelligence. Relatively simple individual rules can produce a large set of complex swarm behaviours. A key-component is the communication between the members of the group that build a system of constant feedback. The swarm behaviour involves constant change of individuals in cooperation with others, as well as the behaviour of the whole group. The two other similar fields of study which more or less have the same team structure and almost the same goals are multi-robot exploration and multi-robot coverage.

Unlike distributed robotic systems in general, swarm robotics emphasizes a large number of robots, and promotes scalability, for instance by using only local communication. That local communication for example can be achieved by wireless transmission systems, like radio frequency or infrared (more on Wikipedia link)

Following simple programmed rules, autonomous robots arrange themselves into vast, complex shapes (Harvard, 2014, link)

The Kilobot is a 3.3 cm tall low-cost swarm robot developed by Radhika Nagpal and Michael Rubenstein at Harvard University. They can act in groups, up to a thousand, to execute commands programmed by users that could not be executed by individual robots.
The power source is a rechargeable lithium-ion battery that can power the robot for up to 3–12 hours based on how active the robot is. They are equipped with a three color (red, green, and blue) LED which is used to display information to the user. While wheels are very effective at movement, they are also expensive which substantially increases the cost of each unit. One way the cost was lowered was due to the method of movement being two vibrators. When either is activated, the Kilobot turns at about 45° per second; when both are activated, the robot moves forward at about 1 cm/s. The robot stands on 3 rigid legs, which elevates the robot 2 cm off the surface. The individual robots are each equipped with an infrared transmitter and receiver so that the robots can communicate with each other. The transmitter of a robot sends a light towards the surface which reflects up to the receiver of another nearby robot, which then executes a command based on the program. Some drawbacks of these methods of communication and movement are: the area on which the Kilobot works is limited to flat surfaces and the inability to move precisely over long distances or over an extended period of time

In theory, the Kilobot is meant to simulate swarms of insects, in that each Kilobot works with the whole to perform tasks that would not work on an individual level. The Kilobots are capable of collective transport, which is the movement of a large object by working together. Kilobot collectives can also form different shapes using S-DASH and repair them should it be distorted. Depending on the shape, they may also be able to change its scale. With one program, they simulated insects by starting from a "home" location, which was a certain stationary Kilobot, and scatter around the area in search of "food", which was another stationary Kilobot. When a searching Kilobot found the "food", it traveled back to the "home" location to drop it off. Another program caused a group of robots to travel in a line while following a leader robot. The robots made sure that they wouldn't travel too far ahead so that the following robots would not fall behind. Using their sensors, they also have the ability to synchronize their behavior, such as blinking their lights. By using an overhead infrared controller and the infrared receivers, a user can do scalable operations. This means they don't have to go to each individual robot to do simple tasks such as charging, programming, and start-up. (more on Wiki link)

This Kilobot Robot Swarm was being shown on the Sheffield University stand at the Gadget Show Live 2013. They were being used to demonstrate possible swarm behaviours.
Here the Kilobot drones want to play follow-the-leader - however, there are three different leaders and each drone only wants to have one leader... They have been programmed to randomly move until they have only a single leader signal.
The guy demo'ing the little fellows was very helpful.
The Natural Robotics Lab was founded in 2010. It is led by Dr. Roderich Gross from the Department of Automatic Control and Systems Engineering, The University of Sheffield.
It investigates robotic systems inspired by nature and robotic models of natural systems. Particular emphasis is on the study of self-assembling robotic systems and swarm robotic systems.
The Kilobot was developed by the prestigious Harvard University and it is now produced and distributed by K-Team.
Specifications:
• Processor :
Each Kilobot has an onboard microcontroller (atmega 328)
32K program memory (used for both user program and bootloader)
1K EEPROM for storing calibration values and other non-volatile data.
• Communication :
Kilobots can communicate with neighbours up to 7 cm away by reflecting infrared (IR)
light off the ground surface.
• Sensing :
When receiving a message, distance to the transmitting Kilobot can be determined
using received signal strength.
The brightness of the ambient light shining on a Kilobot can be detected.
• Movement :
Each Kilobot has 2 vibration motors, which are independently controllable, allowing for
differential drive of the robot.
Each motor can be set to 255 different power levels
• Light :
Each Kilobot has a red/green/blue (RGB) LED pointed upward, and each colour has 3
levels of brightness control.
• Battery management :
A Kilobot can sense its own battery voltage.
Each Kilobot has a built-in charger, which charges the onboard battery when +6 volts is
applied to any of the legs, and GND is applied to the charging tab.
• Debug :
A serial output header is available on each robot for debugging via computer terminal.
• Dimension :
The diameter is 33 mm and the height is 34mm (including the legs)

ALSO source: KILOBOTICS with all the resources needed to get started with the kilobots.

article: Evolving Self-Organizing Behaviors
for a Swarm-bot
and article:
article 2 self organizing swarm robots
Evolving Self-Organizing Behaviors for a Swarm-Bot
When Can We Call a System Self-Organizing?