Hardware Architecture Review of Swarm Robotics System: Self-Reconfigurability, Self-Reassembly, and Self-Replication

Table 2

Advantages and disadvantages of various swarm robot platforms.

Sr. no.	System	References	Advantages and Disadvantages
1	PolyBot	Yim et al. [3, 3, 12, 13, 23, 24]	Advantages: 1st system to demonstrate the ability of self-reconfiguration with most active modules in a connected system. Each module fits within the 5 cm cube. They are versatile in nature. Each module contains a Motorola PowerPC 555 processor with 1 MByte of external RAM and DC brushless motor with built in hall effect sensors.; Limitation: insufficient sensory unit for mapping of environment. PolyBot cannot work in unknown environment with rough surface or when obstacle avoidance is not possible.
2	M-TRAN	Tomita et al. [14]	Advantages: very small actuated modules, highly robust, miniature, and reliable. Quick self-reconfiguration and versatile robotic motion.; Limitations: connection mechanism works on an internally balanced magnetic field that is not strong enough to hold the other modules. Single M-TRAN module does not have enough DOFs for switching from one posture to another form. Lack of sensors leads to mapping and control problems. Power consumption is more as it uses servo motor and electromechanical force for connectivity.
3	ATRON	Støy et al. [7, 15]	Advantages: each module is equipped with its own power supply, sensors, and actuators, allowing each module to connect and communicate with a neighbor module. Each module is able to sense the state of its connectivity and relative motion.; Limitation: since each module includes two-axis accelerometers only, a module cannot tell if it is turned upside down or not. When two modules are connected, it is very difficult for them to move themselves, which requires cooperation from its neighbor. They are not mechanically stable and due to this mechanical instability, their electronic performance is poor.
4	SamBot	Wei et al. [33]	Advantages: SamBot is a combination of mobile and chain-based modules capable of self-assembly and self-reconfiguration. SamBot uses 4 docking mechanisms for connecting with other SamBots. Detects other SamBots using infrared sensors.; Limitation: infrared sensors limit the search range and require line of sight between SamBots. SamBot architecture lacks extra actuators, grippers, and sensors for gathering information about the working environment.
5	Swarm Bot (S-Bot)	Mondada et al. [35, 44, 57]	Advantages: robot swarms consisting of 2 to 40 S-bots have been successfully demonstrated. S-Bots are fully autonomous mobile robots capable of self-navigation, perception of the environment and object. Capable of communicating other S-Bots and transporting of heavy objects over very rough terrain.; Limitations: initial cost is high. Images and sound are the only way of communicating with other S-Bots. The large number of sensors and actuators consumes power, reducing functionality and operating time.
6	CONRO	Støy et al. [7, 15]	Advantages: small, rectangular, self-reconfigurable swarm robot with a low price. Versatile.; limitation: uses onboard low-capacity batteries that limit the usefulness of modules. Limited sensors limit ability to sense surroundings. Only two controllable degrees of freedom.
7	MiLyBots	Vega et al. [51]	Advantages: low cost, reliable, robust, reusable, movable, size-efficient, power sparing, wireless, dynamically programmable swarm robots.; Limitation: MiLyBots are not self-reconfigurable, self-assembled swarm robots. Lack actuators and connection mechanisms for physically attaching to other modules.
8	I-Cube	Ünsal et al. [22]	Advantages: I-Cubes are low cost, small lattice based swarm robot with 3 DOF.; Limitation: unable to provide heavy object transport. Limited sensors. Lacks actuator mechanism.