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To provide terrain data for the development of physics-based vehicle mobility models, such as the Next Generation NATO Reference Mobility Model, there is a desire to make use of the vast amount of cone index (CI) data available. The challenge is whether the terrain parameters for physics-based vehicle mobility models can be predicted from CI data. An improved model for cone-terrain interaction has been developed that takes into account both normal pressure and shear stress distributions on the cone-terrain interface. A methodology based on Derivative-Free Optimization Algorithms (DFOA) has been developed in combination with the improved model to make use of continuously measured CI vs. sinkage data for predicting the three Bekker pressure-sinkage parameters, kc, kϕ and n, and two cone-terrain shear strength parameters, cc and ϕc. The methodology has been demonstrated on two types of soil, LETE sand and Keweenaw Research Center (KRC) soils, where continuous CI vs. sinkage measurements and continuous plate pressure vs. sinkage measurements are available. The correlations between the predicted pressure-sinkage relationships based on the parameters derived from continuous CI vs. sinkage measurements using the DFOA-based methodology and that measured were generally encouraging.

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 (kc), frictional modulus of soil deformation (kφ), 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) ( Bekker, 1969 ). 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 kc, kφ, and n.

The driving performance of an off-road vehicle is closely related to soil strength. A bevameter is used to measure the soil strength, and it usually consists of two independent devices: a pressure–sinkage test device and a shear test device. However, its development and measurement processes have not been standardized, thus, researchers apply it in various fields according to their own discretion. In this study, a new bevameter was developed, and experiments were conducted to clarify the factors that affect the measurement performance of the bevameter. The pressure–sinkage test device was tested with circular plates of different sizes, and the results confirmed that the pressure–sinkage parameters decreased with the plate size. For the shear-test device, normal pressure was applied using a dead load to prevent normal-pressure variation due to displacement and speed. In addition, a spline was installed on top of the shaft connected to the shear ring to measure slip sinkage during the shear test. The results showed that the slip sinkage increased in proportion to the normal pressure and slip displacement, but the increase gradually decreased and converged to a certain point.

This paper examines pressure-sinkage and shearing behavior via bevameter testing of a light-weight, granular simulant called Fillite in support of laboratory modeling of rover mobility in high-sinkage, high-slip environments typically found on Mars, the Moon, and other planetary bodies. Normal bevameter test results helped to determine parameters for the Bekker model, the New Model of Mobility (N2M) sinkage model, and the Bekker-Wong model. A case study used the Bekker-Wong model parameters to predict the possible sinkage of 84% into Fillite of a wheel on the Mars Spirit rover, a value within the observed sinkage of 50–90% of the wheel diameter of the Spirit rover on Mars. Shear bevameter testing of Fillite provided a second set of parameters to assess shear behavior, this time simulating the stresses and shear deformations imparted by rotating wheels. The results compared well to the estimated shear stresses and deformations of Martian soil caused by the wheels of the Spirit rover. When compared to other simulants (e.g. GRC-1), the results confirm that Fillite is possibly more suitable for high-sinkage and high-slip rover studies than other typical simulants derived from natural terrestrial soils and rocks.

India has been developing technology for deep-sea mining in the Central Indian Ocean Basin from 6000 m water depth. The Central Indian Ocean Basin (CIOB) is abundant in nodules which are rich sources of minerals like manganese, copper, cobalt, and nickel. The intended mining machine has to collect the nodules from the seabed, crush them, and pump it to an interim station before transfer to the mother ship at the sea surface. The mining machine has to be supported on very soft seabed of shear strength less than 5 kPa. The maneuverability of mining machine becomes very critical while operating in such soft soils. One of the major challenges involved in deep-sea mining is the mobility of the mining machine on the soft seabed with predictable and controlled sinkage. Prediction of traction force for a tracked vehicle on very soft clays has been difficult. The existing studies in this area are mainly for soft clay of shear strength about 5 kPa. Conventional terramechanics approach for the prediction of traction forces for tracked vehicle is based on Bekker’s Theory. Bekker’s Theory uses bevameter shear tests to understand the shear behavior of soil. The shear tests help to establish the shear stress–shear displacement relationship of soil which helps to predict the traction forces. The present study aims to identify the shear parameters for very soft clays of less than 3 kPa shear strength, which can in turn be used to predict the traction developed in vehicles. Experimental studies were performed using a bevameter setup to determine the shear parameters of very soft clays. The influence of the variables like ring size, height of blades, number of blades, and normal stress on the shear behavior of the soil was examined experimentally.

India has been involved in developing the technology for deep-sea mining in the Central Indian Ocean Basin (CIOB) from approximately 6000 m water depth. The Central Indian Ocean Basin is abundant in nodules which are rich sources of minerals like manganese, copper, cobalt, and nickel. The mining machine has to collect the nodules from the seabed, crush them, and pump to the mother ship at the sea surface. The mining machine has to be supported on very soft sediments of shear strength less than 2 kPa. The maneuverability of mining machine becomes very critical while operating in such soft soils. One of the major challenges involved in deep-sea mining is the mobility of the mining machine on the soft seabed. Predicting the traction of the mining machine is very important for determining the mobility of the mining machine in such soft soils. To analyze the influence of geometrical parameters of the grouser on soft soil for traction performance, the conventional terramechanics approach of Mohr–Coulomb failure criteria method was used to obtain the traction parameters. The shear strength–shear displacement model of deep-sea soft sediments were obtained experimentally using a customized bevameter in bentonite soil to simulate soft soil deep-sea conditions. The traction force model for the various geometrical configurations of the grouser was numerically studied in ABAQUS software using coupled Eulerian–Lagrangian (CEL) technique. The influence of the grouser parameters, viz. shape and size, on the traction performance and the soil displacement was examined. To validate the analysis, experimental studies were undertaken with a scaled-down locomotion vehicle in simulated soft soil tank. The proposed paper brings out the studies undertaken and further analysis planned in the field.

Mechanical properties of snow related to snowmobiles or similar lightweight tracked vehicles aren't widely researched today and it is difficult to find data. One challenge is that snow properties constantly are changing due to aging, climate conditions and location. Also the measuring procedure is difficult since aged snow often contains layers with various densities and hardness. Soil is to some extent similar to snow, in the context that both are granular materials. The bevameter is a popular device for measuring soil properties, however this device needs to be scaled in order to meet criteria of target for research, i.e. in this case snowmobiles. In this paper a new type of portable bevameter is presented, which is designed and built for measuring snow properties in the field. Results from initial tests are also presented. The aim with the bevameter is to measure snow properties which can be used to simulate the interaction between a snowmobile and soft snow. The designed bevameter can be towed with one snowmobile to the field to execute measurements. One full set of test results is introduced and parameters for simulations are extracted from the result data. The parameters from the data were usable but the quality of the measurements can be improved. One problem with the data collected was noise, which was caused by the interaction between the mechanical parts and the low mass of the bevameter. Furthermore, the usability can be improved by reducing cables which can be hard and fragile during cold weather and by replacing the laser distance-sensor with a string wire potentiometer which isn't sensitive to snow dropping in the measurement area. With some improvements the constructed bevameter is a very useful tool which can be used for field measurements to determine snow properties for snowmobile-size vehicle simulations.

This paper studies the energy dissipated during experimental and simulated procedures for the pressure-sinkage and shear-strength test. These tests are performed using a clayey-loam soil and modelled as smoothed-particle hydrodynamics (SPH) technique in Visual Environment's Pam-Crash software. The hydrodynamic elastic plastic material is used to define the equation of state for the clayey-loam soil. The soil is modelled at five different levels of compaction to represent multi-pass of a tyre over soil. The soil calibration is performed using the pressure-sinkage and direct shear-strength test and validated using experimental data from a soil bin facility. The energy dissipation is calculated using the soil sinkage values at every pass of wheel. Finally, the results of experimental and simulation dissipation energy are discussed and the effect of the tyre multi-pass on dissipated energy is investigated and presented. This research will further continue to model an agricultural FEA tyre over the clayey-loam soil to compute tyre performance and interaction characteristics.

This research focuses on prediction of the rolling resistance coefficient of an agriculture tyre using finite element analysis (FEA) technique, and Bekker and Wismer-Luth models. The tyre-soil interaction is modelled using FEA and smoothed-particle hydrodynamics (SPH) techniques in Visual Environment's PAM-Crash software and validated based on experimental results. A single-wheel tester along with a controlled soil bin at Urmia University, Iran is used to investigate the effect of a tyre's multi-pass and vertical load on the rolling resistance coefficient of an off-road tyre. In order to calculate the rolling resistance of Bekker model, a bevameter device is installed on a carriage moving on clayey-loam soil and a digital penetrometer is used for obtaining the output of Wismer-Luth model. Analysis of experimental data shows that rolling resistance coefficient increases as the vertical load increases and decreases with each pass of tyre. These results are used to compare and evaluate the above-mentioned methods. The results of this study will be used in further research on the interaction between a tyre and soil.

This paper is an introduction of terramechanics and its application in off-road vehicle mobility prediction. Firstly the concept of terramechanics is introduced. Terramechanics is an important branch of applied mechanics in which the interaction between the vehicle and its operating terrain is studied. Secondly, many well-known techniques in terramechanics, such as Cone Penetrometer technique, Bevameter technique are introduced. By comparing the RCI of soil with VCI of vehicle, trafficability of Off-road vehicle can be determined which predicts the “go/no go” property of vehicle. Furthermore, to predict the speed behavior of off-road vehicle over trafficable terrain, three types of analyzing methods, empirical, semi-empirical, computer-aided, are presented in detail. It is evident that computeraided method is much more efficient in simulating terrain-vehicle interaction and produces more realistic prediction in vehicle mobility. Therefore, it is meaningful to develop computer-aided method to provide engineers with powerful parametric analysis in vehicle performance and design.

This paper presents the mechanical properties of soil. In order to determine the properties of soil under laboratory conditions, we made use of a special measuring device, viz. a bevameter. Two types of soil with different levels of moisture were examined and their mechanical properties determined. Measurements were taken of non pressed and compressed soil. A measuring network was set up, consisting of measuring and recording devices. In the course of measuring, the force and penetration depth of the pressing plate were recorded simultaneously. Four different diameters of pressing plate were used, resp. 25, 38, 50 and 70 mm. The pressure on the contact area was calculated after completion of the measurements, and the relationships between pressure and penetration depth were presented graphically.

This paper presents the mechanical properties of soil. In order to determine the properties of soil under laboratory conditions, a special measuring device was constructed, viz. a bevameter. Two types of soil with different levels of moisture were examined and their mechanical properties were determined. Measurements were taken of non-compressed soil. A measuring network was set up, consisting of measuring and recording devices. In the course of measuring, the force and penetration depth of the pressing plate were recorded simultaneously. Three different diameters of pressing plate were used, namely 38, 50 and 70 mm. The pressure on the contact area was calculated after completion of the measurements, and the relationships between pressure and penetration depth were presented graphically.

This study aimed to investigate the influence of the mechanical behaviour of the soil surface on the traction performance and the fuel consumption of an agricultural tractor, both in qualitative and in quantitative terms, in order to increase the consciousness about the major role of the soil mechanical response in the optimisation of the energy aspects involved in the traction developed by a tractor and promote the development of new strategies to reduce costs of tillage management and improve agricultural sustainability. The traction performance of a 65kW MFWD tractor at tyre pressures of 60 and 160 kPa was compared on four Swiss agricultural soils: a clay with corn stubbles, a clay loam with wheat stubbles, a silty loam and a loamy sand both with corn stubbles. Tests performed with a bevameter pointed out noticeable differences in the mechanical behaviour of the soils. According to such differences, the drawbar pull on the four soils was significantly disparate with differences in maximal values of about 16% at a tyre pressure of 60 kPa and up to 37% at a tyre pressure of 160 kPa. Simulations with a semi-empirical tractor-soil interaction model also showed dissimilarities in traction coefficient, motion resistance, and traction efficiency. Measurements of the fuel consumption pointed out the presence of a narrow slip range where the specific fuel consumption SFC is minimised. This range doesn’t vary significantly among the considered soils as well as with the tyre pressure and doesn’t differ very much from the range where the power delivery efficiency is maximised. The SFC differed for almost 20% among the considered soils at a tyre pressure of 60 kPa and for ca. 10% at a tyre pressure of 160 kPa. The increase in tyre pressure from 60 to 160 kPa produced an increment in SFC up to 16%. The results of this study clearly pointed out how the traction performance is a characteristic of the tractor-soil system and not of the tractor only, therefore, a proper knowledge of the soil mechanical behaviour should aid in developing strategies oriented towards reducing fossil fuel consumption.

Soft soil contact models developed for planetary exploration rovers play an important role in the study of rover mobility. Nowadays, most of the existing contact models are based on Bekker theory, which requires the evaluation of several soil parameters usually measured via bevameter tests. However, substantial differences existing between the plate-soil contact scenario and the wheel-soil contact scenario, along with large variability associated with the bevameter experiments, give rise to large uncertainty in the choice of the model parameter values. In this paper, a Bayesian procedure is proposed to deal effectively with the presence of uncertainty. In the proposed approach, model parameters are random variables with prior distributions derived from bevameter measurements. The prior distributions are then enhanced to posterior distributions through single wheel test data. At the end, the procedure identifies a set of possible model parameter configurations that result in high experimental-numerical matching. (C) 2013 Wiley Periodicals, Inc.

The tractor-mounted bevameter consists of a main frame, an instrument box which contains the hydraulic and electrical components, a leveling system that applies a safe load vertically onto the soil, sinkage plates with three different shapes to characterize the soil pressure–sinkage relationships, and a carrier supporting the bevameter unit and sinkage plates. The accuracy of the displacement and force measurements were ±0.01 mm and ±2 N, respectively. A laptop data acquisition and a software tool were used to assist in real-time measuring, recording the applied loads, and the resulting sinkage of the plate during the field sampling operation. The experiments were carried out at a penetration rate 3 cm/s for sinkage plates. Field tests of the tractor-mounted bevameter unit were conducted with three different types of the sinkage plates. Statistical analysis and graphs produced from collected data showed that the shapes of the sinkage plates had considerable influence on the soil parameters. Soil sinkage is affected by the shape of sinkage plates. The values of k c and k φ are affected by the values of p , z and b.

In field experiments conducted over a period of 6 years, seedbed preparation was carried out on four different sites with clay contents of 45, 27, 24 and 15%. Over the years soil conditions varied considerably. Seedbed preparation was conducted in the spring with implements of different designs such as drags and harrows, twin rotor, gyro- and rotaspikes. In analysing the fragmentation due to tillage, the soils could be grouped according to moisture contents and soil compaction. Soil with a moisture content greater than 0.20 kg kg −1 was classified as wet soil irrespective of the state of compactness. Soil with a lower moisture content was classified as moist soil and divided into the following compactness states: loosened, workable and compacted. Loosened soil was ploughed or chiselled just before seedbed preparation, workable soil was autumn ploughed and compacted soil was unploughed. A normalisation procedure transforming the fragmentation effect and the specific energy supply to dimensionless quantities eliminated the difference between all the unloosened soil states, i.e. states where the soil was a continuous compact material. This normalisation procedure related the increase in aggregate surface area to the initial surface area. The specific energy supply was related to the specific energy needed to fracture a clod or to fracture the soil in the ground with a bevameter. With this normalisation procedure the fragmentation effect of the three compact states—workable, compacted and wet soils—was described by the same function. Loosened soil was, however, still different and had a much lower effective fragmentation than the other states. In general, the strength of the clods determined the fragmentation in this soil state. The normalisation procedure provided a basis for an investigation of the energy efficiency of fragmentation of various tillage implements and tools. For the compact soil states, drags were superior in fragmentation compared to harrows and rotary implements ( ∗∗ P . There was no difference in fragmentation between harrows and rotary fragmentation implements. For the loosened soil state, there was no significant difference between the three implement groups. Rotary implements seemed, however, to be more effective in the conversion of energy to fragmentation.

In consequence of growing interests of science exploration on our solar system’s planets and moons, increased mobility demands are arising for planetary exploration vehicles. The locomotion capabilities of these systems strongly depend on the interaction with soft granular soils. Thus a major design challenge is to develop suitable solutions for locomotion equipment and strategies. The mastering of these challenges depends on detailed soil interaction models to predict the system behaviour and get a better understanding of the underlying effects. To meet these demands a new soil interaction model based on the three-dimensional Discrete Element Method (DEM) is developed. The strength of granular materials is highly dependent on the grain’s shape and friction. Since non-spherical particles are less computational efficient than spheres, a new interparticle contact model has been developed to mathematically cover the rotational behaviour of anisotropically elongated and angular grains, while using computationally efficient spheres for contact detection. To show the applicability of the model, bevameter as well as single wheel simulations for planetary rovers were carried out.

The multi-sleeve friction penetration system is an in-situ testing device that is derived from the well established cone penetration test. It incorporates a series of friction sleeves with varying surface texture in addition to the standard smooth friction sleeve located directly beneath the tip. The multiple measurements made with this device allow it to provide new insight into soil type and stratigraphic variations as well as insitu shear strengths as a function of sleeve texture height. This paper describes a next generation version of this device that incorporates torsional load sensing capabilities in addition to the standard axial load sensing capabilities. In this manner, the effects of different vertical and horizontal stress states on measured sleeve stresses can be explored. This device offers significant benefits as an alternative to the portable bevameter, which was used in the past to measure the mechanical response of lunar soils under normal and shear loading conditions that were likely to be imposed by various wheel and track systems.

Although a lot of information about soil parameter identification exists in literature, there is currently no algorithm who makes use both of state of the art identification methodologies and incorporating statistical analysis. In this paper a state of the art soil parameter identification method is presented including the calculation of its standard deviations and a proper weighting of the objective function. With this algorithm and a Bevameter with advanced sensor and actuator technology a test campaign is started to find a reliable soil preparation, which is applicable to a large planetary rover performance testbed. Furthermore, the preparation method has to be valid and stable for various types of dry, granular and frictional soils, typically used for planetary rover testing in space robotics, since the result of pre-tests show that the soil parameters are highly depending on the preparation. Besides preparation, the soil parameters are also influenced by different Bevameter test setup variables. Thus, the effect of the penetration velocity as well as the penetration tool geometry for pressure–sinkage tests on soil parameters is investigated. For shear tests the influence of the dimension of the shear ring is analysed as well as the variation of the grouser height, the number of the grousers and the increase of the rotational shear velocity. The results of the extensive test campaign are evaluated by the proposed identification algorithms.

This chapter describes the results of the measurement and characterization of the shearing behavior of a variety of terrains, including mineral terrain, muskeg, and snow-covered terrain. The measurements are made using a vehicle-mounted bevameter with the associated computerized data acquisition and processing system. When a multiaxle wheeled vehicle (or a tracked vehicle) is in straight-line motion over an unprepared terrain, an element of the terrain is subject to the repetitive shearing of the consecutive wheels (or roadwheels). In order to predict the shear stress distribution on the vehicle–terrain interface, the response to repetitive shear loading of the terrain should be known. The response of a frictional terrain (a dry sand) to repetitive shear loading under a constant normal load indicates that when the shear loading is reduced to zero and is then reapplied, the shear stress–displacement relationship during reshearing is similar to that when the terrain is being sheared in its virgin state. The variation of the shearing force beneath a rectangular shear plate on dry sand subject to a vertical harmonic load with a frequency of 10.3 Hz indicates that during the loading portion of each cycle, the shearing force S does not reach its maximum value instantaneously.

This chapter describes the measurement and characterization of the response of a variety of terrains, including mineral terrain, muskeg, and snow-covered terrain. One of the fundamental tasks in the characterization of terrain behavior is to establish functional relationships that can realistically describe the responses of the terrain to various types of loading, such as the stress–strain relationship, pressure–sinkage relationship, and shear stress–shear displacement relationship. The responses of a variety of mineral terrains in Eastern Ontario, Canada, including sand (LETE sand), sandy loam, clayey loam, and loam to normal and repetitive loadings were measured and characterized. The results indicate that there is little difference between the values of the pressure–sinkage parameters obtained using a set of rectangular plates of large aspect ratios and those obtained with a set of circular plates having radii equal to the widths of the rectangular plates. The responses of two muskegs in the Petawawa area, Ontario, Canada, to normal load and to repetitive loading were measured using the bevameter together with the automatic data acquisition and processing system. A well-defined critical pressure at which the surface mat of the muskeg is broken can be identified.

Publisher Summary The cone penetrometer technique and the bevameter technique are widely used in the measurement of the mechanical properties of terrain for the study of vehicle mobility in the field. The selection of the technique for measuring terrain properties is closely related to the method of approach chosen for the study of vehicle–terrain interaction—the cone penetrometer technique is usually employed to identify terrain conditions for the study of vehicle mobility using empirical relations and the bevameter technique is primarily used in methods intended for detailed parametric analyses of vehicle performance and design. With the rapid progress in electronics and computer technology, a variety of cone penetrometers using electrical (or electronic) sensors for monitoring the force, and penetration depth and computer technology for storing and processing data have been developed. The bevameter technique provides the closest simulation of vehicle loading conditions among the various measuring techniques presently in use. Accordingly, the terrain data obtained by the bevameter are used as input for a detailed examination of vehicle–terrain interaction. In a bevameter developed by the Petawawa National Forest Institute (PNFI) of Canada, the devices for pressure–sinkage and shear tests have been integrated into a single mechanism capable of performing both test functions. This is achieved by using a specially developed hydraulic cylinder in combination with a hydraulic motor.

A variety of models predicting and evaluating tracked vehicle performance have been developed over the years. This chapter provides a brief review of some of the empirical methods and methods for parametric analysis and for predicting static pressure distributions beneath tracks. Empirical models are based on the test results of a number of representative tracked vehicles over a range of terrains of interest. The measured vehicle performance is then empirically correlated with terrain conditions, usually identified by observations and simple measurements. This can lead to the establishment of a scale for evaluating vehicle mobility on the one hand and terrain trafficability on the other. One of the better-known methods for parametric analysis of tracked vehicle performance is the one that originally developed by Bekker. In this method, the track in contact with the terrain is assumed to be similar to a rigid footing. If the center of gravity of the vehicle is located at the midpoint of the track contact area, the normal pressure distribution may be assumed as uniform. On the other hand, if the center of gravity of the vehicle is located ahead of or behind the midpoint of the contact area, a sinkage distribution of trapezoidal form will be assumed. Based on the assumed contact pressure, and making use of the pressure–sinkage relationship obtained from the bevameter, the sinkage of the track can be predicted.

A study of the correlation between the measured and predicted vehicle performance over undistributed and preconditioned snow using the Nepean Tracked Vehicle Performance Model, NTVPM, has been carried out. It is shown that on undisturbed snow in Fernie, British Columbia, the performance of a BV 206 predicted by NTVPM correlates very well with measured performance obtained in the field. On preconditioned snow, there is also a reasonable correlation between the measured vehicle performance and predicted one using NTVPM. It is found that predictions of vehicle performance made by NTVPM using pressure-sinkage data obtained with the Swiss Rammsonde and with the bevameter are comparable. This indicates that the pressure-sinkage data obtained using the Rammsonde can be used as input to the NTVPM for predicting tracked vehicle performance over snow. It is shown that in comparison with an earlier version, NTVPM-85, the latest version of the Nepean Tracked Vehicle Performance Model, NTVPM-86, which takes into account fully the characteristics of roadwheel suspension systems, provides improved predictions of vehicle performance over snow where track sinkage is significant. It is suggested that the computer simulation model NTVPM, using pressure-sinkage data obtained by the Rammsonde as input, could form a useful interface with cone based models, such as the NATO Reference Mobility Model, to provide them with an additional capability of predicting tracked vehicle performance over snow.

To examine the feasibility of using the pressure-sinkage data obtained with a Rammsonde as input to a proposed module for the NATO Reference Mobility Model for predicting tracked vehicle performance over snow, a series of measurements of penetration resistance of undisturbed and preconditioned snow was made using a Rammsonde, and compared with those obtained with a bevameter and Rammsonde cones driven by a bevameter. This paper describes the results of the field measurements made using the three types of device, as well as the approaches to the characterization of the pressure-sinkage data obtained. It is found that the data obtained using the Rammsonde, the bevameter and the Rammsonde cone driven by a bevameter are, in general, comparable, considering the possible variations of terrain conditions in the field. It is shown that the pressure-sinkage equations proposed by Bekker could form a common basis for characterizing the data obtained using the three different techniques. It is found that in soft, undisturbed snow (with density less than 0.2 g/cm3), the small (or standard) Rammsonde cone of 4 cm in diameter cannot be used to obtain meaningful pressure-sinkage data within a certain snow depth. Under these circumstances, the use of the large Rammsonde cone of 10 cm in diameter is recommended. Over preconditioned snow, both the small and large Rammsonde cones could provide comparable data. The size effect of the sensing element (such as the diameter of the Rammsonde cone or the bevameter sinkage plate) on the pressure-sinkage relationships was examined. It is found that in many cases, the values of the pressure-sinkage parameters derived from data obtained using a single sensing element of 10 cm in diameter are comparable to those obtained using two sizes of sensing elements of 4 and 10 cm in diameter.

For planetary rovers, demonstration of the overall mobility performance on soft soil is a demand to guarantee for mission success. Since several years, DLR’s Institute of Robotics and Mechatronics is strongly engaged in planetary mobile system developments. For the very important wheel-soil interaction a 3D-MBS tool for modeling and simulation of the overall terramechanics behavior, making use of Bekker’s well-known terramechnical equations, has been developed. Currently, major applications are followed within ESA’s Exomars mission. For the purpose of verification and validation of the 3D-MBS tool intensive hand in hand rover testing in a lab environment is necessary. Therefore, a new facility for planetary locomotion systems including a large testbed and a novel, high-precision bevameter to characterize the soil on which the tests are to be carried out is presented. For precise rover pose estimation inside the testbed a high-level position tracking system is used, and for proper soil surface determination on an in-house developed digital elevation mapping system is relied on. For the Bekker parameter determination, a portable and lightweight bevameter equipped with a state-of-the-art sensor technology is designed. Different design concepts are analysed open minded without any orientation on existing bevameter designs. This leads to a tripod design with electromechanical actuators and sensors integrated in a real-time computing environment to develop own control algorithms. Besides soil testing and soil preparation influence detection, the bevameter is mainly used for identifying soil parameters of the testbed. Finally, for correlation purposes, these parameters are taken as inputs to the 3D-MBS tool for simulating the drive manoeuvres performed inside the testbed. Results obtained from bevameter testing are presented together with the testbed setup design.

The relationship between the soil parameters measured during soil testing using the bevameter system and horizontal forces acting on a simple tillage tool were investigated. Field experiments were conducted on untilled, compacted and recently tilled soil. On both soils, five sites were randomly chosen where bevameter and draft measurements were performed. The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating speed and horizontal draft. A statistical analysis of data indicated that a mathematical model for predicting draft should include operating depth, dry bulk density and modulus of deformation.