For instance, the Quince GMRs ( Figure 3) are characterized by four front and rear tracked rotating legs (double flippers), and have been adopted for unmanned exploration missions inside the buildings of the Fukushima nuclear power plant. Examples are the PackBot, with two tracked swing extensions (flippers) on the front, or other general-purpose tracked platforms with double (front and rear) flippers. The TGMRs-A-A-LT-TOL category includes many commercial realizations for homeland, military, or surveillance applications.

In the first case, the legs can be tracked extensions of the robot main body (TGMRs-A-A-LT-TOL, Tracks On Legs) or non-tracked and connected to the main frame (TGMRs-A-A-LT-TOF, Tracks On Frame). Therefore, some researchers have proposed an internal mechanism to shift the longitudinal position of the robot’s center of gravity, improving the step climbing capabilities (Dyjob robot, Figure 2) the obvious drawback is the weight increase and the reduction of the internal room for hosting the payload. The main limitation of TGMRs-NA is their limited capability of overcoming high obstacles, steps, and stairs: to start the climbing maneuver, the height of the obstacle at the initial contact point must be lower than the track radius, even if this condition is not strictly mandatory, depending on the friction conditions and on the position of the robot’s center of gravity. Moreover, if the robot is symmetric with the tracks thicker than the robot body (as for the Trackbot), and has no payload mounted externally, it can operate even after a capsize. The benefits of this architecture are its extreme mechanical simplicity, and the consequent reliability and ease of control. Many small-scale TGMRs equipped with two tracks performing differential steering are available on the market for surveillance and inspection tasks an example is the Trackbot by Inspectorbots (, the TGMR-NA-T in Figure 1). The category of TGMRs-NA is very widespread.

Tank tracks vs wheels for robots