Citation: Melchiorre, M.; Colamartino, T.; Ferrauto, M.; Troise, M.; Salamina, L.; Mauro, S. Design of a Spherical Rover Driven by Pendulum and Control Moment Gyroscope for Planetary Exploration. Robotics 2024, 13, 87. https://doi.org/10.3390/ robotics13060087 Academic Editor: Roberto Sabatini Received: 17 April 2024 Revised: 18 May 2024 Accepted: 26 May 2024 Published: 28 May 2024 Copyright: © 2024 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/). robotics Article Design of a Spherical Rover Driven by Pendulum and Control Moment Gyroscope for Planetary Exploration Matteo Melchiorre * , Tommaso Colamartino, Martina Ferrauto, Mario Troise , Laura Salamina and Stefano Mauro Department of Mechanical and Aerospace Engineering, Politecnico di Torino, 10129 Torino, Italy; tommaso.colamartino@studenti.polito.it (T.C.); martina.ferrauto@polito.it (M.F.); mario.troise@polito.it (M.T.); laura.salamina@polito.it (L.S.); stefano.mauro@polito.it (S.M.) * Correspondence: matteo.melchiorre@polito.it Abstract: The spherical shape is an interesting approach to develop exploration robots, or rovers, thanks to its capability of ensuring omnidirectional motion and of being basically unsensitive to possible rollovers. This works intends to propose a novel detailed design for such a kind of robot and to discuss the performance that can be reached by adopting this solution. The work hence introduces the requirements assumed for the design of the robot and discloses the general layout that was selected, which includes a pendulum for motion transmission and two coupled gyroscopes to overcome high, steep obstacles, such as steps. The paper then summarizes the functional design computation carried out to size and selects the components of the system. Eventually, a control algorithm is described and tested on a complete multibody model of the robot. The results in the execution of standard maneuvers such as motion on a horizontal plane, as well as in the overcome of a step, are shown. The energetic balance of the rover is described, and some preliminary consideration about mission planning are reported in the final discussion. Keywords: rover; spherical robot; control moment gyroscope; planetary exploration; path control 1. Introduction Spherical robots (SRs) are highly advantageous in mobile robotics due to their protec- tive spherical shell, preventing contamination and collisions. Their symmetrical design prevents overturning, allowing for falls and obstacle traversal without damage. The spher- ical shape facilitates energy-efficient rolling on slopes. Additionally, depending on the driving mechanism, SRs can achieve omnidirectional movements. These characteristics make SRs suitable for diverse applications, including exploration of unstructured envi- ronments, disaster area assessment, search and rescue operations, underwater inspection, surveillance, and more. In the literature, many examples of SRs can be found. However, performances depend on the motion principle and on the mechanism employed to achieve it. One of the most common motion principles is the Barycenter Offset (BO). In such systems, the sphere hosts an internal mechanism that moves the barycenter from the equilibrium point so to create a driving torque. The advantage is that the locomotion system can be entirely embedded in the spherical shell, so to create a sealed environment. However, this results in a limited driving torque, as the amount of the offset that can be reached is constrained within the sphere radius. This also affect the capability to climb inclines and overcome obstacles, such as steps. One way to exploit the advantages of BO and to overcome the limitations against obstacles is to combine it with auxiliary systems based on a different physical principle that increases the driving torque. For example, Control Moment Gyroscope (CMG) systems use the gyroscopic torque that is generated by tilting the axis of a flywheel rotating with high speed, which depends on the angular momentum. Robotics 2024, 13, 87. https://doi.org/10.3390/robotics13060087 https://www.mdpi.com/journal/robotics