Planetary rovers are different from conventional terrestrial vehicles in many respects, making it necessary to investigate the terramechanics with a particular focus on them, which is a hot research topic at the budding stage. Predicting the wheel–soil interaction performance from the knowledge of terramechanics is of great importance to the mechanical design/evaluation/optimization, dynamics simulation, soil parameter identification, and control of planetary rovers. In this study, experiments were performed using a single-wheel testbed for wheels with different radii (135 and 157.35 mm), widths (110 and 165 mm), lug heights (0, 5, 10, and 15 mm), numbers of lugs (30, 24, 15, and 8), and lug inclination angles (0°, 5°, 10°, and 20°) under different slip ratios (0, 0.1, 0.2, 0.3, 0.4, 0.6, etc.). The influences of the vertical load (30 N, 80 N, and 150 N), moving velocity (10, 25, 40, and 55 mm/s), and repetitive passing (four times) were also studied. Experimental results shown with figures and tables and are analyzed to evaluate the wheels’ driving performance in deformable soil and to draw conclusions. The driving performance of wheels is analyzed using absolute performance indices such as drawbar pull, driving torque, and wheel sinkage and also using relative indices such as the drawbar pull coefficient, tractive efficiency, and entrance angle. The experimental results and conclusions are useful for optimal wheel design and improvement/verification of wheel–soil interaction mechanics model. The analysis methods used in this paper, such as those considering the relationships among the relative indices, can be referred to for analyzing the performance of wheels of other vehicles.
Accurate and efficient tire models for deformable terrain operations are essential for performing vehicle simulations. A direct application of an on-road tire model to simulate tire behavior on a deformable terrain such as soft soil is not possible. The methods for modeling and evaluation of performance of the wheeled vehicles on deformable terrains are influenced by different terrain properties in addition to design and operational parameters. These methods are ranged from very simple empirical methods to highly complex finite element methods. This survey covers the most used models that have been developed for wheeled vehicles in off-road applications. The emphasize is on the models that have made a significant contribution in advancement of techniques for characterizing soil, tire, soil–tire interaction, experimental analysis, model parameterization and model validation. A description is given for selected studies to familiarize the reader with the general terminologies, formulations and modeling approaches. More importantly, two summary tables are given for three groups of models in which the overall features of each model are reviewed and compared to other models. These tables can be used to understand the general picture of the available techniques, and facilitate selecting the appropriate model for future applications.
With the predicted increase in world population to over 10 billion, by the year 2050, growth in agricultural output needs to be continued. Considering this, autonomous vehicles application in precision agriculture is one of the main issues to be regarded noteworthy to improve the efficiency. In this research many papers on autonomous farm vehicles are reviewed from navigation systems viewpoint. All navigation systems are categorized in six classes: dead reckoning, image processing, statistical based developed algorithms, fuzzy logic control, neural network and genetic algorithm, and Kalman filter based. Researches in many agricultural operations from water monitoring to aerial crop scouting revealed that the centimeter level accuracy in all techniques is available and the velocity range for evaluated autonomous vehicles almost is smaller than 1 m/s. Finally it would be concluded although many developments in agricultural automation using different techniques and algorithms are obtained especially in recent years, more works are required to acquire farmer’s consensus about autonomous vehicles. Additionally some issues such as safety, economy, implement standardization and technical service support in the entire world are merit to consideration.
Mars Exploration Rovers (MERs) experienced mobility problems during traverses. Three-dimensional discrete element method (DEM) simulations of MER wheel mobility tests for wheel slips of = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 0.99 were done to examine high wheel slip mobility to improve the ARTEMIS MER traverse planning tool. Simulations of wheel drawbar pull and sinkage MIT data for ⩽ 0.5 were used to determine DEM particle packing density (0.62) and contact friction (0.8) to represent the simulant used in mobility tests. The DEM simulations are in good agreement with MIT data for = 0.5 and 0.7, with reasonable but less agreement at lower wheel slip. Three mobility stages include low slip ( 0.6) controlled by residual soil strength and wheel sinkage depth. Equilibrium sinkage occurred for < 0.9, but continuously increased for = 0.99. Improved DEM simulation accuracy of low-slip mobility can be achieved using polyhedral particles, rather than tri-sphere particles, to represent soil. The DEM simulations of MER wheel mobility can improve ARTEMIS accuracy.
Assessing the mobility of off-road vehicles is a complex task that most often falls back on semi-empirical approaches to quantifying the vehicle–terrain interaction. Herein, we concentrate on physics-based methodologies for wheeled vehicle mobility that factor in both tire flexibility and terrain deformation within a fully three-dimensional multibody system approach. We represent the tire based on the absolute nodal coordinate formulation (ANCF), a nonlinear finite element approach that captures multi-layered, orthotropic shell elements constrained to the wheel rim. The soil is modeled as a collection of discrete elements that interact through contact, friction, and cohesive forces. The resulting vehicle/tire/terrain interaction problem has several millions of degrees of freedom and is solved in an explicit co-simulation framework, built upon and now available in the open-source multi-physics package . The co-simulation infrastructure is developed using a Message Passing Interface (MPI) layer for inter-system communication and synchronization, with additional parallelism leveraged through a shared-memory paradigm. The formulation and software framework presented in this investigation are proposed for the analysis of the dynamics of off-road wheeled vehicle mobility. Its application is demonstrated by numerical sensitivity studies on available drawbar pull, terrain resistance, and sinkage with respect to parameters such as tire inflation pressure and soil cohesion. The influence of a rigid tire assumption on mobility is also discussed.
A wheeled ground robot was designed and built for better understanding of the challenges involved in utilization of accelerometer-based intelligent tires for mobility improvements. Since robot traction forces depend on the surface type and the friction associated with the tire-road interaction, the measured acceleration signals were used for terrain classification and surface characterization. To accomplish this, the robot was instrumented with appropriate sensors (a tri-axial accelerometer attached to the tire innerliner, a single axis accelerometer attached to the robot chassis and wheel speed sensors) and a data acquisition system. Wheel slip was measured accurately using encoders attached to driven and non-driven wheels. A fuzzy logic algorithm was developed and used for terrain classification. This algorithm uses the power of the acceleration signal and wheel slip ratio as inputs and classifies all different surfaces into four main categories; asphalt, concrete, grass, and sand. The performance of the algorithm was evaluated using experimental data and good agreements were observed between the surface types and estimated ones.
The working performance of agricultural machinery is largely determined by the walking performance of the wheel when driving in complex unstructured soil. However, the driving performance of existing wheels is not satisfactory for paddy field with muddy soil. The purpose of the current study is therefore to propose a novel rigid wheel for agricultural machinery which is applicable to paddy field with muddy soil. Firstly, a novel arc edge shaped wheel was designed based on the principles of mechanics on the ground. Then the driving performance of this arc edge shaped wheel was evaluated using FE modeling of interaction between rigid wheel and soil. Finally, the structure originally designed arc edge shaped wheel was improved according to FE modeling results, and this improved design was further evaluated by both FE simulation and prototype experiments. Both FE modeling and experimental results indicate that the improved arc edge shaped wheel proposed in this study has a good driving performance with regarding to wheel sinkage and soil reaction force. The proposed arc edge shaped wheel could be used as an effective component of rice harvester for paddy field with muddy soil.
In the United States, the NATO Reference Mobility Model (NRMM) has been used for evaluating military ground vehicle mobility and the Vehicle Cone Index ( ) has been selected as a mobility metric. represents the minimum soil strength required for a vehicle to consistently make a specific number of passes, usually one or fifty passes. In the United Kingdom, the Mean Maximum Pressure ( ) has been adopted as a metric for assessing military vehicle cross-country mobility. is the mean value of the maxima occurring under all the wheel stations of a vehicle. Both and are empirically based. This paper presents a review of the basis upon which and were developed, as well as their applications to evaluating vehicle mobility in practice. With the progress in terramechanics and in modelling and simulation techniques in recent years, there is a growing desire to develop physics-based mobility metrics for next generation vehicle mobility models. Based on the review, criteria for selecting physics-based mobility metrics are proposed. Following these criteria, metrics for characterizing military vehicle traction limits and traversability on a given operating area are recommended.
This paper reviews experimental methods for the conversion of cone index measurements to bevameter parameters in support of vehicle soil/tire/track interactions for two general soil types, sand and lean clay. The accurate prediction of traction, motion resistance, and sinkage of tire/tracks off-road requires estimates of soil strength. Equipment used in the measurement of soil strength to support predictions of off-road mobility include the bevameter and the cone penetrometer. The portability of the cone penetrometer and rapid estimates of spatial/temporal variability in all terrain conditions make it an invaluable tool. The bevameter, a less portable tool, is used for the mechanical analysis of soils. The bevameter measures parameters defining soil strength in terms of cohesive modulus of soil deformation (k ), frictional modulus of soil deformation (k ), exponent of soil sinkage (n), cohesion (c), angle of internal friction (φ), and the plate pressure at 1 in. (2.54 cm) of penetration (K) ( ). The field of terramechanics would greatly benefit from having the ability to convert cone penetrometer data in areas where bevameter parameters are difficult to collect. That ability to convert from cone index to bevameter parameters could be used for the large sets of existing cone index data to support determination of traction and motion resistance. This paper examines those methods for converting cone index to bevameter plate penetration parameters k , k , and n.
The interaction between off-road machines and soil is usually a dynamic process of soil shearing. However, in practice, in order to interpret these processes, the empirical modified static Coulomb criterion, which does not take into account the soil strengthening, is commonly used. At Wrocław University of Technology a proposal for a method for predicting dynamic shear strength in soils was developed. This method takes into account primarily the soil shear velocity, the scale effect of the test device and its kinematics, which include the parameters of the process under investigation in terramechanics. The method will be presented in two parts of the following publication. The first part presents the results of the tests on soil shear strength carried out by the author of the article by means of soil ring shear test device. These results are discussed against the background of the results of soil research performed all around the world. On the basis of the tests conducted by the author, a new dynamic criterion of soil shear strength was formulated and the requirements for the innovative method for predicting dynamic shear strength in soils were established. This experimental method will be presented in the second part of the article.
This paper is the first of three papers describing a study focused on developing a lumped-mass discretized tire model using Kelvin-Voigt material elements. The main motivation was to develop a tire model able to capture the dynamic behavior on tire-soft soil interaction, while also being able to run on rigid (flat and rough) surfaces. This paper presents underlying mathematical formulations for characterizing the tire material properties and the kinetics and kinematics of the tire structure; the second paper focuses on the modelling of the tire-terrain interaction. The interface for connecting the tire model developed with the vehicle modeling software CarSim, in order to perform full vehicle simulations is provided. To minimize the computational time of the code, different techniques were used in stiffness matrix partitioning, parameter initialization, and multi-processing. This resulted in significant improvements for efficiency of the code making it suitable for use by commercially-available vehicle simulation packages.
This is the second of three papers on the HSSTM. Part I introduced the tire structure model. Part III presents the tire model parameterization and validation. Part II describes the computational contact models for evaluating the tire/terrain interaction. Its main objective is to characterize the terrain in the normal and tangential directions during tire-terrain interaction. A contact search algorithm examines tire nodal points close to the ground and detects the penetration of the contact surfaces. Next, the contact interface algorithm applies the contact constraints to minimize or eliminate penetration. For deformable terrain, the algorithms are based on semi-empirical formulations and are implemented using a numerical approach in a 3D scheme. The normal and shear stress distribution simulation results for rigid wheel-soil contact are validated against experimental data. The contact interface algorithm for non-deformable terrains is implemented using a distributed 3D brush model enhanced with a transient module for dynamic manoeuvres.
This publication series describes the phenomenon of dynamic strengthening of soils. This part presents a literature review, based on which a new tester was designed. It allows shearing of soils in a wide range of speeds, it is not susceptible to the scale effect, wall effect and the bulldozing effect, as well as it has shear kinematics adequate to the modelled process. Comparison of the test device with direct shear tester showed a substantial decrease of cohesion and increase of internal friction angle of cohesive soils with the new tester. Four different cohesive and non-cohesive soils have been investigated in this study. Dynamic shearing tests have confirmed that cohesive soils may increase shear strength by up to almost 3 times compared to quasi-static shearing. Non-cohesive soil (quartz sand) did not exhibit distinct increase of shear strength. Validation of the new criterion proved it can be used to describe the shear strength – shear speed relationship of agricultural soils. The proposed model correlated with experimental data at R over 0.85 for cohesive soils and over 0.64 for sand.
Tire/terrain interaction has been an important research topic in terramechanics. For off-road vehicle design, good tire mobility and little compaction on terrain are always strongly desired. These two issues were always investigated based on empirical approaches or testing methods. Finite element modeling of tire/terrain interaction seems a good approach, but the capability of the finite element has not well demonstrated. In this paper, the fundamental formulations on modeling soil compaction and tire mobility issues are further introduced. The Drucker–Prager/Cap model implemented in ABAQUS is used to model the soil compaction. A user subroutine for finite strain hyperelasticity model is developed to model nearly incompressible rubber material for tire. In order to predict transient spatial density, large deformation finite element formulation is used to capture the configuration change, which combines with soil elastoplastic model to calculate the transient spatial density due to tire compaction on terrain. Representative simulations are provided to demonstrate how the tire/terrain interaction model can be used to predict soil compaction and tire mobility in the field of terramechanics.
Tire models used in vehicle dynamics simulation for CAE durability and ride comfort assessment need to be capable of predicting the non-linear deformation and enveloping characteristics which occur when traversing large road obstacles. Normally, transient dynamic characteristics of a rolling tire are determined from tire rig tests, and the tire parameters are transferred into multi-body system for vehicle dynamic analysis. However rig design limitations mean that tests cannot be carried out in the most severe conditions, particularly for traversing high ramp or large obstacles. However, using detailed FE tire models, such tests can be carried out virtually. A FE tire model was developed specifically for this purpose using explicit integration in ABAQUS™. Tire enveloping tests in traversing obstacles of different sizes were then carried out, virtually, using the validated FE tire model. Satisfactory results of transient responses were obtained by comparison with the experimental tests for the tire traversing obstacles with different heights. Tire transient dynamic behaviour was investigated by analysing the influence of tire rolling velocity and height of road obstacle on transient spindle responses, dynamic stiffness, together with tire deformation for the tire impacting obstacles. Finally, the investigation showed that longitudinal dynamic stiffness decreases when the tire traverses a higher obstacle. In addition, with the increase of height of road obstacle, the resonant amplitude of spindle force response as well as the tire deformation becomes larger in both longitudinal and vertical directions, especially for the tire rolling over 25 mm × 25 mm rectangular obstacle. Also, it is found that higher travelling velocity of the tire leads to higher resonant amplitude of spindle forces in the vertical direction.
Tire performance over soft soil is of interest for automotive and geotechnical engineers; the automotive engineers are mainly interested in tire tractive performance, and geotechnical engineers are concerned with the effects of the traffic brought by the tire to the soil. This two-part paper documents a series of tire and soil tests (Part I) and the application of their test data to the study of tire tractive performance over soft soil (characterized by drawbar pull) and to the model parameterization (Part II). Part I of this paper details the series of tests that are comprised of static tire deflection tests, static tire-soil tests, soil properties tests, and dynamic tire-soil tests, and describes the influence of tire inflation pressure or soil compaction level on the test data. The experimental approach presented herein produces parameterization and validation data that can be used in tire off-road traction dynamics modeling and terramechanics modeling.
This paper addresses the design of rigid wheels for planetary rovers in loose, granular soil. Wheel surface features, such as grousers, are known to improve tractive capability in planetary-relevant soils. However there are no comprehensive design guidelines for these wheel features. In this research, a series of intensive and extensive parametric studies were carried out in full-scale vehicle slope experiments and single-wheel tests that assess the influence of grouser count, height, orientation, and end-cap in various longitudinal and lateral slip conditions. This work also investigates the traction process of grousers based on a soil flow imaging technique. The soil motion analysis reveals that grousers reduce forward soil flow/motion resistance and increase net traction. A grouser design formula is derived from the soil flow observation, and design guidelines of rigid wheels of planetary rovers for loose soil are proposed based on these results. The proposed guidelines are applied to the modification of grouser design of the Mars Science Laboratory rover to improve tractive performance on loose terrain.
We analyze the capabilities of various recently developed techniques, namely granular Resistive Force Theory (RFT) and continuum plasticity implemented with the Material Point Method (MPM), in capturing dynamics of wheel-dry granular media interactions. We compare results to more conventionally accepted methods of modeling wheel locomotion. While RFT is an empirical force model for arbitrarily-shaped bodies moving through granular media, MPM-based continuum modeling allows the simulation of full granular flow and stress fields. RFT allows for rapid evaluation of interaction forces on arbitrary shaped intruders based on a local surface stress formulation depending on depth, orientation, and movement of surface elements. We perform forced-slip experiments for three different wheel types and three different granular materials, and results are compared with RFT, continuum modeling, and a traditional terramechanics semi-empirical method. Results show that for the range of inputs considered, RFT can be reliably used to predict rigid wheel granular media interactions with accuracy exceeding that of traditional terramechanics methodology in several circumstances. Results also indicate that plasticity-based continuum modeling provides an accurate tool for wheel-soil interaction while providing more information to study the physical processes giving rise to resistive stresses in granular media.