ABSTRACT. Soft lunar regolith hampers rover mobility through slippage, sinkage, and poor maneuverability. Wheel grousers shear the regolith to generate thrust, so their geometry is crucial on complex terrain for self-extrication, obstacle negotiation, and stable travel. However, under manned-rover loads and realistic regolith properties, systematic comparisons of how different grouser shapes affect coupled traction–vibration behavior remain limited.Here, we design a 350 mm-radius metal elastic wheel with four grouser configurations—straight, interrupted straight, V-shaped, and interrupted V-shaped—build a soil-bin testbed, and apply a time–frequency analysis workflow with traction benchmarking. Experiments at 450 N and 750 N evaluate slip–traction responses and vibration characteristics.Straight grousers deliver the largest slip–traction integral and the lowest low-frequency vibrations at both loads, followed by the interrupted straight design; V-shaped variants perform worse. Relative to other geometries, straight grousers improve stability by 9.45%–37.29%. Increasing load amplifies configuration-dependent differences, with V-shaped RMS vibrations exceeding those of straight grousers by 30.96%–87.46%. Discrepancies between predicted and measured traction and sinkage remain within acceptable bounds. These results inform grouser selection across load cases and surface conditions, supporting optimization of tractive efficiency, energy consumption, and stability.

ABSTRACT. In the context of an emerging space economy, resource extraction on the Moon is expected to play a significant role. Due to the Moon’s low gravitational field and the availability of accessible resources, supplying future manufacturing in space with resources from the Moon’s surface might be more efficient than from Earth. In this work, research data on multi-objective optimised bucket drums are used to develop a novel bucket drum. The novel drum and an existing design are being tested experimentally in various setups in our testbed and in particle simulations using the discrete element method (DEM). The tests are run under conditions similar to those in the initial simulation setup used in the paper on the multi-objective optimised drum. As for the experiment, three tests are conducted to measure mass and establish the correlation between motor current and drum mass, aiming to investigate the difference in performance between the two drums and examine parameters that influence performance. Results indicate the novel bucket drum outperforms the former design across all measured performance metrics in both simulation and laboratory testing. Further investigation revealed a close correlation among all performance parameters and between the drum's horizontal speed and rotational speed. The discussion and comparison between simulation and laboratory testing, as well as between novel and former designs, highlight the problem of defining performance parameters, pointing towards a general problem of non-universal performance parameters in bucket drum design.

ABSTRACT. Bucket drum excavators have emerged as advantageous regolith collection technologies for extraterrestrial in-situ resource utilization, and discrete element modeling has increasingly been used to optimize these excavators. Frequently, these models rely on parameter calibration techniques focused on a granular material’s static angle of repose, an experimentally derived quasistatic bulk behavior. Consensus has not been reached on the comparative applicability of static angle of repose calibration relative to dynamic static angle of repose calibration when modeling dynamic systems, nor how their influencesmight diverge under space environmental conditions.

This study compares a discrete element model developed for terrain-wheel interactions calibrated using the static angle of repose to experimental observations of the dynamic angle of repose in a constantly rotating cylinder at a dynamic steady state, using well-established image processing methodologies.

The dynamic angles of repose between the two models were found to be significantly different (α = 0.01), potentially indicating an inability to accurately simulate a dynamic process with a static angle of repose calibrated model. However, further analysis is necessary to fully quantify this incongruity, with future work planned to develop a discrete element model calibrated with the dynamic angle of repose for specific comparisons between particle parameters calibrated using the static angle of repose.

Consistencies in the angle of repose’s relationship with the drum’s rotational velocity and fill ratio confirm previous literature findings, and both the static angle of repose calibrated simulation and the experimental dynamic angle of repose demonstrated similar slumping and rolling transverse motion modes.

ABSTRACT. Analyzing planetary soil samples can provide insights into planetary formation and the origin of life on Earth. However, the surfaces of celestial bodies are affected by space weathering and other environmental factors, making it difficult to obtain high-quality samples. In addition, extreme temperature variations impose large mechanical and thermal loads on exploration robots. Therefore, subsurface exploration robots have attracted increasing attention. Previous studies developed a robot that moves through soil by altering ground conditions using vibration. The robot uses vibration motors and linear actuators to change soil resistance and generate propulsive force. However, the shape of the vibrating unit used for subsurface locomotion has not been sufficiently investigated. This study proposes a vibrating unit with barbs on its lateral surfaces. Each barb has a gentle slope in the forward direction and a steep face in the backward direction, forming an asymmetric structure that reduces forward resistance while increasing backward resistance. Towing experiments were conducted using units with and without barbs to measure soil reaction forces. The results showed that forward resistance decreased when vibration was applied. Subsurface locomotion experiments using a testbed also demonstrated that the proposed unit increased displacement compared with a conventional unit. These results indicate that the proposed vibrating unit improves subsurface mobility.

ABSTRACT. In deep-space exploration, the physical and mechanical properties of regolith and their spatial variability strongly affect rover mobility and exploration efficiency. Because real extraterrestrial samples are extremely limited, simulated regolith has become an essential basis for experimental investigation and model development. In this study, simulated regolith materials with adjustable compositional and structural parameters were prepared based on constraints from in-situ exploration and remote-sensing observations, enabling the representation of typical planetary surface characteristics in particle gradation, packing state, and mechanical response. Wheel–regolith interaction tests were then conducted to analyze sinkage, shear deformation, and traction behavior under wheel loading, and key mechanical parameters of regolith were inversely identified. By further integrating terramechanics theory with deep learning, a trafficability assessment model was developed for quantitative prediction of rover mobility under different regolith conditions and operating scenarios. The simulated regolith was also applied in ground tests of rover mobility systems, providing support for trafficability evaluation and locomotion strategy analysis.

ABSTRACT. Hydropneumatic suspensions are often used on heavy mining, construction, military and agricultural vehicles. In these suspensions, the mass of gas determines the non-linear spring characteristic of the struts. To simulate a vehicle with such a suspension, the spring characteristics can be modelled non-linearly using ideal or real gas laws (e.g. Benedict-Webb-Rubin), ranging from simpler models making use of adiabatic or isothermal assumptions to more complex models solving the energy equation for a gas in a closed container and incorporating heat transfer effects. All these models require accurate mass of gas parameterisation for accurate performance. However, the mass of gas loaded into such a suspension system cannot be easily measured. In this study, a gas mass calculation method is developed and implemented on a test vehicle equipped with a bespoke hydropneumatic suspension system. The gas mass calculation uses existing measurement instrumentation on the test vehicle. Values determined through this calculation method are used to better characterise the suspension during validation of various vehicle models of the test vehicle.

ABSTRACT. To ensure safe road travel and enable long operating times for drivers through vibration isolation, tractor suspension systems have been continuously developed. Suspended front axles, cab suspension, and seat suspension are state of the art. The potential of standard tractor chassis for optimizing driving safety and comfort was investigated using a standard lower-middle-class tractor (Fendt 313 Vario, 93 kW). A MBS model of this tractor was combined with the Hohenheim tire model, a spoke-based approach with physical modelling of tire-soil interaction. This enables the simulation of complex road surfaces. To validate the simulation model, test runs were conducted on an ISO 5008 smoother track with various parameter combinations. For the potential assessment, various chassis variants of the test tractor were developed and designed. In addition to different front axle suspension designs in the first step, the chassis was extended in the second step by integrating various rear axle/rear wheel suspensions into the simulation model of the test tractor. The evaluation was carried out in relation to the state of the art of the test tractor using a conflict diagram. This diagram presents various measures for the driver's vibration isolation as a function of the mean wheel load factor, which serves as a measure of driving safety. Integration of front axle/front wheel suspension into the chassis primarily results in improved driving safety by reducing the front wheel load factor. By adding rear axle/rear wheel suspension improves both driving safety and driver vibration isolation. The chassis of the standard tractor has significant potential to further improve both driving safety and the vibration isolation of the driver.

ABSTRACT. Ground vehicle power transmissions arguably constitute one of the most diverse areas within the field of mechanical engineering, with countless highly specialized implementations for the different final applications. While standard mechanical diagrams accurately represent the actual implementation, they fall short in abstracting the underlying functional concepts, to streamline the high-level functional analysis of a given architecture. SFATT (Smart Functional Abstraction Tool for power Transmissions) has been developed, leveraging the Python ecosystem, to implement said abstraction, in the form of functional block diagrams, with a library of functional components representing planetary gear trains, clutches, variators, etc. SFATT executes multiple steady-state simulations, for the allowed combinations of input commands, with both linear and non-linear models; the former is an idealized (lossless) version of the latter, providing a quick solution, to be then fed as initial guess to the non-linear solver. The non-linear steady-state solutions are an extremely valuable initial result, providing deep insight into the system functionality, to guide the development and execution of subsequent fully-fledged dynamic models. A typical use case is gaining prior knowledge on critical/significant operating points via SFATT before the detailed, computationally demanding dynamic simulations. SFATT has been validated by successfully simulating a wide range of transmission implementations, focusing on power-split continuously variable transmissions (CVTs) for agricultural tractors, in input/output/compound coupled configurations, with multiple arrangements of the output mechanical ranges (gears), with both (traditional) hydromechanical and electric hybrid variable units.

ABSTRACT. In recent years, electrification has advanced rapidly not only in passenger vehicles but also in off-highway trucks. By leveraging the advantages of electrification, electric motors enable improved vehicle motion control due to their fast response and precise measurability. However, the complexity of electric mining dump truck drivetrain systems, which include reduction gears, a differential, and driveshafts, poses a challenge for model-based control design. To address this issue, this study establishes a systematic procedure for accurately obtaining the drivetrain plant model of an electric mining dump truck using a frequency-domain system identification method. By applying a chirp excitation signal together with a model fitting technique, the procedure enables the drivetrain dynamics to be modeled as a two-inertia system, which is then utilized for speed controller design. Notably, the identified model was found to accurately predict the vibration characteristics of the speed control system, as confirmed through theoretical analysis, simulation, and experimental validation. The novelty of this paper lies in demonstrating that system identification using electric motors, commonly applied to passenger vehicles, can also be applied to electric mining dump trucks, and that the performance of the speed controller can be improved based on the identified model. Future work will focus on developing a complete traction control system based on the proposed system identification procedure.

ABSTRACT. Precise in-situ detection of the mechanical properties of lunar regolith is critical for the success of future lunar base construction and resource exploitation. However, existing detection methods predominantly rely on the indirect inversion of rover wheel-soil interactions, which are limited in accuracy, real-time capability, and detection depth. Furthermore, there is a lack of specialized automated equipment capable of adapting to the complex lunar surface environment. To address this, this study designed and developed a novel autonomous in-situ penetrating shear instrument. This device automatically performs penetration and shear operations, recording real-time data with a maximum penetration force of 25 N, a shear torque of 2.5 N·m, a penetration depth of 300 mm, and a rotation angle of 360°. Based on a maximum normal load of 16 N provided by the lunar rover, and to maximize detection efficiency, we systematically tested 24 probe combinations—varying in cone angle, projected area, and number of vanes—using lunar soil simulants with three particle sizes and two density levels. Recognizing that launch mass directly constrains payload conditions, and targeting the lightweight payload limit (16 N) of the lunar rover, we conducted multi-objective optimization to maximize detection efficiency (specifically, penetration depth and shear torque). The results indicate that a probe combination with a 15° cone angle, a 3.24 cm² projected area, and 2 vanes exhibits the best comprehensive performance across all conditions, achieving an average penetration depth of 51.61 mm and an average shear torque of 0.055 N·m.

ABSTRACT. This paper presents the development of the “Terrain Testing Instrument (TTI)”, selected as a payload for the planned Chinese Chang’e 8 lunar landing and roving mission in 2028. In the initial phase of lunar surface exploration by the United States and the Soviet Union, dedicated instruments were used to measure in situ physical properties of the regolith (“soil”) column in various locations. This was done by penetrometry and vane-cone instruments. On the lunar landing and roving missions of the modern era however, no instruments have yet been flown to measure terrain physical properties. But it will be particularly important to understand bearing and shear strength in the South polar region where extensive landing, roving, mining, and construction activities are foreseen over the next several decades. To address this gap, the TTI instrument on Chang’e 8 will measure penetration resistance via a cone penetrometer, and shear strength via a shear vane, with both techniques combined in a so-called vane-cone instrument. A permittivity sensor is integrated with the instrument and will allow to infer bulk density and ice content of the regolith, with ice being a valuable resource on the Moon. A linear translation mechanism drives the TTI vane-cone assembly into the regolith, followed by rotation of the front shear vane to indicate shear resistance as a function of shear angle. Depth range of the instrument is ~5 cm as it will be carried on the relatively small JINNAH-1 rover of SUPARCO with limited available reaction force. The TTI will perform multiple measurement runs at various locations. TTI overall mass is ~1.5 kg. The TTI is being developed by a team of entities from Germany, the Netherlands, France, China, and the two Special Administrative Regions Macau and Hong Kong.

ABSTRACT. To generate a realistic digital environment is extremely expensive and both crewed vehicles and AGV’s operate over larger areas necessitating the use of remote scanning technologies. Due to its availability and low cost, the use of small drones with cameras and LiDAR. This paper presents the method applied to do an initial evaluation of the levels of accuracy and the data generated and processing efficiency using commercially ArcGIS Pro® software for drone-based photogrammetry and LiDAR. The captured area included undulating grassed terrain, boulders, roads, trees and various structures. Strict preparation of ground control points and accurate geolocation of both the ground based, and airborne platforms drone and terrestrial LiDAR were processed as was the oblique photogrammetry in ArcGIS Pro® commercial software. LiDAR processing included sensor OEM software preprocessing requiring considerable computing power to display and analyse. From the oblique photogrammetry data, a terrain mesh was extracted within less than a day. The mesh was imported into Unity®, presenting a useable digital operating environment for the AGV modeling and simulation. The data was exported to Gazebo where it was used to assist in the development and verification of an autonomy stack leader-follower capability. The oblique photogrammetry was able to provide obstacle, tree and bush heights as well as a realistic rendered environment. The technique works well in open wooded areas; however, it is limited and misses crucial terrain data in covered or dense bushy and treed terrain. In such cases the LiDAR is able to provide the required terrain data supporting the current thrust to combining sensors data for digital terrain mapping for off-road mobility and AGV modelling and simulation.

ABSTRACT. The Yade DEM-based wheel-soil-box simulator, publicly available on GitHub, is presented as an open-source educational tool enabling student teams to model tractive performance of a rigid wheel in granular soil for the ISTVS 2026 Student Wheel Design Competition. The simulator uses Yade discrete element framework (Šmilauer et al., 2015). Initial version aims to reproduce the wheel-performance results of Nakanishi (2020) using Hertz-Mindlin contact model while allowing to read alternative wheel geometry from an STL-format file. The simulator is then extended to additional contact models and simulation configurations, including box and wheel geometry from a benchmark by Jelinek et al. (2024) where multi-sphere particles are used. The benchmark multi-sphere particle model results are compared to single-sphere results to assess the influence of particle shape on the predicted drawbar pull, gross traction, and sinkage. Post-processing routines for extracting soil surface height and wheel sinkage from DEM particle positions and sizes are introduced. The simulator and documentation are freely available to competition participants and the broader terramechanics community.

ABSTRACT. For modelling and testing off-road vehicle mobility, it is essential to understand how a tyre interacts with soft, deformable terrain. Accurately measuring this interaction, particularly the true contact patch and resulting soil deformation, remains a major challenge. Traditional laboratory methods cannot replicate the complex, dynamic behaviour of a rolling tyre, while existing terrain measurement techniques often fail to capture the simultaneous deformation of both the tyre and soil. This research study will add to recent advances achieved by the Vehicle Dynamics Group (VDG), e.g., the use of the Tyre-Terrain Camera (T2Cam) system and the emerging methods for predicting outer tread geometry from inner tyre deformation. T2Cam uses an RGB-D camera inside a tyre to capture the deformation of the tyre’s inner surface under realistic loading conditions. This inner geometry was used to successfully predict the tyre’s contact area on flat, rigid surfaces. The aim of this research study is to develop an algorithm capable of extracting the contact patch on deformable terrain. Preliminary results demonstrate that contact patch deformation can be reliably identified on flat surfaces and this might be extended to moderately deformable terrains. The development of this algorithm could establish a foundation for future soft-soil experiments and integrated tyre-terrain characterization. Such capability has far-reaching applications: e.g., adaptive tyre pressure and traction control, improved off-road tyre design, precision agriculture with reduced soil degradation, mobility prediction for autonomous vehicles, and terrain-condition assessment for civil and military operations.

ABSTRACT. Accurate modeling of vehicle–terrain interactions is essential for effective mission planning, optimizing off-road vehicle design, and reliable control of semi-autonomous or autonomous off-road systems. Traditional terramechanics models, based on classical pressure-sinkage and shear stress–shear displacement relationships obtained using the bevameter technique, have not taken into account the additional vehicle sinkage due to wheel or track slip, commonly known as the slip-sinkage. This omission of the slip-sinkage effect leads to less reliable predictions of key vehicle performance metrics such as motion resistance, thrust, drawbar pull, and tractive efficiency. Consequently, vehicle mobility assessments and traversability predictions become less reliable, particularly on highly deformable terrains.

While various models for predicting slip-sinkage have been developed over the years, this paper presents a new constitutive modeling approach. The method leverages test data obtained using the bevameter technique to derive a unified relationship linking normal pressure and shear displacement with slip-sinkage. Model parameters are identified using a least-squares optimization procedure applied to experimental datasets obtained using the bevameter on various terrain types, including dry sand, wet sand, and clay. The resulting formulation captures the nonlinear coupling between slip-sinkage and shear displacement under various normal pressures. Thus, the proposed model for slip-sinkage enhances the predictive fidelity of simulation models of vehicle–terrain interactions. This improvement supports the development of better traction control strategies, advancements in off-road vehicle designs, and safer autonomous navigation in complex off-road environments.

ABSTRACT. The impact of vehicles operating in the field on soil structure strongly depends on the actual state of the soil, particularly its moisture content and consistency. The objective of this study is to evaluate the deformation behaviour of clay soils under load using a soil state characterization based on consistency limits. The investigation focused on soil textures commonly occurring in Hungary, primarily loam and clay soils. Soil deformation was determined using a plate loading device under constant surface pressure. Measurements were carried out at different moisture contents in order to examine the effect of soil water content on deformation behaviour. Soil conditions were characterized using the Atterberg consistency limits. The results indicate that the magnitude of soil sinkage shows a strong relationship with the value of the relative consistency index. Based on the obtained results, ranges of the relative consistency index can be identified in which the soil is still capable of supporting the applied load.

ABSTRACT. Sediment accumulation at the bottom of dams causes a significant threat to flood control. While underwater bulldozers offer an efficient solution for sediment removal, optimizing the bulldozer blade design is critical to improving operational efficiency. High-fidelity simulation technique is of particular approach for analyzing the blade-soil interaction; however, Discrete Element Method (DEM) simulations alone fail to simultaneously capture the fluid-like behavior and resistance of oversaturated soils. The primary objective of this study is to establish a high-fidelity simulation environment by calibrating a coupled DEM-SPH (Smoothed Particle Hydrodynamics) framework against experimental bulldozing resistance time-histories. In this study, four different calibration approaches—introducing adhesive force model, applying particle size distribution, considering density scaling, and carefully calibrating SPH parameters—were implemented and evaluated. The calibration results verified that adjusting fluid viscosity and surface tension of SPH provided the most robust solution, yielding results that closely aligned with experimental data. Furthermore, this study investigates the bulldozing characteristics with varied excavation depth and different blade widths. Future work will involve constructing a reduced-order model of blade-soil interaction to enable computationally-efficient calculation of bulldozing resistance, facilitating the optimized design of blade shapes for improving operational efficiency.