###### Abstract  
This work presents the electro-mechanical design, physical implementation, and experimental testing of an intermediate-sized mobile robotic platform, Hygrobot, which is powered by the hybridization of a PEMFC fuel cell and LiPo batteries. Future mobile robots are anticipated to require sustainable and cost-effective energy solutions to increase their working time and adhere to ecological guidelines. Although substantial advancements have been achieved in creating marketable mobile robot designs, including improvements to their physical composition, sensory systems, navigation algorithms, and operational management, their widespread integration is still hindered. This obstacle is mainly attributable to the lack of robust power systems capable of functioning in varied and often unpredictable settings. Hydrogen, as an energy carrier, offers a promising solution to overcome these obstacles. Experimental tests reveal that the Hygrobot platform can achieve a linear speed of 17 km/h, a continuous operating time of over 8 h, and power consumption below 324 WA. Its mechanical design means that Hygrobot is able to overcome obstacles, facilitating movement in the three XYZ axes, and can perform tasks over rough terrain efficiently. 14 March 202514 March 20  
efficient energy systems suitable for use in hostile environments. For example, battery-based power systems for ground robotic platforms present significant challenges in terms of off-road applications. One of the primary limitations is the relatively low energy density, which restricts the range and operational endurance of these vehicles [4]. In off-road scenarios, where robots often traverse rugged terrain or perform prolonged tasks in remote areas, the energy constraints of battery-powered systems become more pronounced, requiring frequent recharging or battery swapping, which can disrupt operations. Additionally, the weight of batteries, which directly correlates with their energy storage capacity, impacts the overall performance of the robotic platform. Heavier batteries reduce manoeuvrability, making it more difficult for robots to navigate challenging landscapes. This weight penalty also limits the payload capacity [5]. Furthermore, battery performance can degrade rapidly in extreme temperatures [6]. As a result, there is a pressing need for research into higher-density energy storage solutions and innovative designs to optimize the energy-to-weight ratio of robotic systems. In this new scenario, hydrogen-based hybrid power systems are explored as potential solutions to extend operational time and improve the overall robustness of off-road robotics [7; 8]. Hybrid solutions should meet eco-friendly requirements: zero-emission operation, avoiding NO\({}_{\omega}\), CO, HC, SO\({}_{\omega}\), and CO\({}_{2}\) toxic emissions, reduced noise levels, limited thermal signatures, and extended operating time. Additionally, power systems that combine fuel cells and batteries provide the benefits of both energy storage technologies, taking advantage of the bi-directionality of the batteries, their rapid response, and their high power density, while the fuel cell provides a high energy density that helps to reduce the overall weight of the system and significantly increase its range; at the same time, endurance is doubled (\(\geq\)8 h) in comparison with battery-based systems [9]. This paper describes the design, manufacturing, and testing of a ground robotic platform powered by a hybrid power system consisting of LiPo batteries [10] and a proton exchange membrane (PEM) fuel cell [8]. Among its main features is an innovative traction system, with six independent drive wheels that maintain maximum ground contact at all times. The integration of a LiPo battery with a PEM fuel cell allows the system to respond to sudden changes in power demand. The LiPo battery was selected over other battery types due to its high power density (\(\geq\)98% charge-discharge efficiency) and its ability to operate across a wide state-of-charge range (20-100% SOC).