Citation: Bruzzone, L.; Nodehi, S.E.; Fanghella, P. Tracked Locomotion Systems for Ground Mobile Robots: A Review. Machines 2022, 10, 648. https://doi.org/10.3390/ machines10080648 Academic Editors: Dan Zhang and Peng Shi Received: 30 June 2022 Accepted: 28 July 2022 Published: 4 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). machines Review Tracked Locomotion Systems for Ground Mobile Robots: A Review Luca Bruzzone * , Shahab Edin Nodehi and Pietro Fanghella Department of Mechanical, Energy, Management and Transportation Engineering, University of Genoa, 16145 Genoa, Italy * Correspondence: luca.bruzzone@unige.it Abstract: The paper discusses the state-of-the-art of locomotion systems for ground mobile robots comprising tracks. Tracked locomotion, due to the large contact surface with the ground, is par- ticularly suitable for tackling soft, yielding, and irregular terrains, but is characterized by lower speed and energy efficiency than wheeled locomotion, and lower obstacle-climbing capability than legged locomotion. Therefore, in recent years academic and industrial researchers have designed a wide variety of hybrid solutions, combining tracks with legs and wheels. The paper proposes three possible parallel taxonomies, based on body architecture, track profile, and track type, to help designers select the most suitable architecture on the basis of the operative necessities. Moreover, modeling, simulation, and design methodologies for tracked ground mobile robots are recalled. Keywords: mobile robot; tracked locomotion; tracks; crawlers; classification 1. Introduction Service robotics is presently one of the fastest-growing technological fields [1]. Never- theless, while Automated Guided Vehicles (AGV) moving on flat and compact grounds are already commercially available and widely used to move components and products inside industrial buildings, the extensive application of ground mobile robots in environ- ments that are unstructured or structured for humans is a promising challenge for the next years [2]. The important application fields are agriculture [3,4], planetary exploration [5,6], reconnaissance in dangerous situations, such as radioactive or chemical contamination [7], homeland security and military operations [8], demining [9], intervention in case of terrorist attacks [10], and surveillance [11]. The design of a ground mobile robot is highly multidisciplinary since it involves the fields of locomotion, perception, cognition, and navigation [12]. Focusing on the mechanical aspect, ground mobile robots, excluding special-purpose ones for specific environments and surfaces (e.g., slithering, or adhesive robots) can have wheeled (W), legged (L), or tracked (T) locomotion, or hybrid combinations of these principles (LW, LT, WT, LWT). A systematic comparison of these locomotion systems is outlined in [13], in terms of maximum speed, obstacle-crossing capability, step/stair climbing capability, slope climbing capability, walking capability on soft terrains, walking capability on uneven terrains, energetic efficiency, mechanical complexity, control complexity, and technology readiness. Another work dealing with the classification of mobile robots is [14], in which not only locomotion is considered, but also perception, cognition, control, and navigation. A classification based on structural and kinematic properties is presented in [15], although limited to wheeled robots. In [16], specific chapters are focused on locomotion architectures, in particular of wheeled robots, snake-like and continuum robots, and limbed systems (with body, legs, and arms), while other chapters of the same book discuss all aspects of mobile robotics: sensing and estimation, localization and mapping, motion planning, modelling and control of legged and wheeled robots, and of multiple robot systems. A work focused mainly on the mechanics of legged robots is [17], while [18] is more centered Machines 2022, 10, 648. https://doi.org/10.3390/machines10080648 https://www.mdpi.com/journal/machines