Learning multiobjective rough terrain traversability

Erik Wallin, Viktor Wiberg, Folke Vesterlund, Johan Holmgren, Henrik J. Persson, Martin Servin

Journal of Terramechanics, Volume 102, 2022, Pages 17-26, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.04.002.(https://www.sciencedirect.com/science/article/pii/S0022489822000313)

Abstract: We present a method that uses high-resolution topography data of rough terrain, and ground vehicle simulation, to predict traversability. Traversability is expressed as three independent measures: the ability to traverse the terrain at a target speed, energy consumption, and acceleration. The measures are continuous and reflect different objectives for planning that go beyond binary classification. A deep neural network is trained to predict the traversability measures from the local heightmap and target speed. To produce training data, we use an articulated vehicle with wheeled bogie suspensions and procedurally generated terrains. We evaluate the model on laser-scanned forest terrains, previously unseen by the model. The model predicts traversability with an accuracy of 90%. Predictions rely on features from the high-dimensional terrain data that surpass local roughness and slope relative to the heading. Correlations show that the three traversability measures are complementary to each other. With an inference speed 3000 times faster than the ground truth simulation and trivially parallelizable, the model is well suited for traversability analysis and optimal path planning over large areas.

Keywords: Traversability; Rough terrain vehicle; Multibody simulation; Laser scan; Deep learning

Agricultural tyre stiffness change as a function of tyre wear

Carl Becker, Schalk Els

Journal of Terramechanics, Volume 102, 2022, Pages 1-15, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.04.001.(https://www.sciencedirect.com/science/article/pii/S0022489822000295)

Abstract: Vehicle designers use tyre characteristic parameters to parameterize tyre models during the design phase of a vehicle to determine the ride comfort, handling and performance. Tyre data is mostly presented only for new tyres with 100% tread on them. Soft terrain traction and minimal compaction have always been major requirements for agricultural tyres, however agricultural vehicles are increasingly being used on asphalt/non-deformable terrain as commercial farms are ever increasing in size. As operational costs are always forced to a minimum, agricultural vehicles operate with tyres ranging from new to fully used condition ranging from 100% down to almost 0% tread on them. During the operational life of a tyre the tyre characteristics change as the tyre tread wears down. This study investigates the change in tyre characteristics on hard terrain with tyre wear at a single load condition, two different inflation pressures and three tread wear conditions. Significant trends are noted with dramatic changes in traction and tyre stiffnesses as the tyre wear changes.

Keywords: Agricultural tyre; Tyre wear; P80 sandpaper; Longitudinal stiffness; Lateral stiffness; Vertical stiffness; Cleat; Inflation pressure; Tyre characteristics

Tread rubber compound effect in winter tires: Benchmarking ATIIM 2.0 with classical models

Mohit Nitin Shenvi, Hoda Mousavi, Corina Sandu

Journal of Terramechanics, Volume 101, 2022, Pages 43-58, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.02.002.(https://www.sciencedirect.com/science/article/pii/S0022489822000167)

Abstract: Tire-terrain interaction is complex and affects the performance of the vehicle; more so when the terrain is ice which affects the handling of the vehicle. Analysis of the contact between the tire and ice, especially in the countries like United States, Canada, etc. is imperative but a trial-and-error approach consisting of the design and manufacture of novel tires for testing and analysis seems a foregone conclusion. Thus, it is important to have accurate methods of simulation of tire performance on ice in order to design better tires without inputting much cost in the manufacturing process. This study chose to simulate the performance of sixteen tires which were identical in all aspects of design and construction except for the tread rubber compound which varied resulting in two tires having the same tread rubber compound. These simulations were performed using the in-house developed ATIIM, ATIIM 2.0, and modified versions of three simplified classical models namely the model by Hayhoe and Shapley and two models by Peng et al. A qualitative comparison of the performance of the models was performed in order to highlight their advantages and disadvantages.

Keywords: Tire-ice model; Dry friction; Fluid friction; Water film height; Tread rubber compound; Winter tires

Dynamic behavior of an agricultural power take-off driveline for rattle noise reduction: Part 2. Experimental analysis of rattle noise effect according to spline tolerance level

Chanho Choi, Houngjong Ahn, Jihun Yu, Young-Jun Park, Jinwoong Lee, Jinkam Park, Su-chul Kim

Journal of Terramechanics, Volume 101, 2022, Pages 33-42, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.03.002.(https://www.sciencedirect.com/science/article/pii/S0022489822000180)

Abstract: Agricultural tractors comprise power take-off (PTO) drivelines, which that transmits engine power to the outside for various agricultural work, and various mechanical components are connected by spline couplings with tolerances. Dynamic behavior of the spline couplings causes a jumping phenomenon where the rotation speed fluctuation amplifies and then rapidly decreases. This paper experimentally examined the effects of spline tolerance on the dynamic behavior and PTO gear rattle noise for four different spline tolerance levels. For the fit tolerance (0.1 mm), no jumping was observed. For increasing tolerance levels of 0.5, 0.9, and 1.3 mm, the jumping rotation speed decreased to 920, 890, and 880 rpm, respectively. With increasing tolerance, both the rotation speed fluctuation and noise level immediately before jumping increased gradually. Furthermore, for the specimen with tolerance levels of 1.3 mm(type D), a transient range was observed in which the dynamic behaviors before and after jumping were mixed and rotation speed fluctuation and sound pressure level showed large deviations from their respective average values.

Keywords: Agricultural tractor; PTO driveline; Rattle noise; Spline tolerance

Prediction of tractor drive tire slippage under different inflation pressures

Algirdas Janulevičius, Vidas Damanauskas

Journal of Terramechanics, Volume 101, 2022, Pages 23-31, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.03.001.(https://www.sciencedirect.com/science/article/pii/S0022489822000179)

Abstract: The slippage of various sizes tractors under similar operating conditions can be compared based on the traction coefficient. However, a preliminary prediction of tractor drive tire slippage is problematic because the numerical expression of tire inflation pressure is not directly included in known mathematical models. The purpose of this study is to find a method for predicting the slippage of a tractor's driving tires, which includes a numerical expression of the tire inflation pressure. Based on the results of experimental studies of Case Farmall 115U MFWD tractor equipped with radial-ply tires, on wheat stubble on a loam soil, a method was developed to predict tire slippage based on the traction coefficient by estimating the tire inflation pressure. The obtained empirical equation allows to theoretical prediction of drive tire slippage in 4WD and 2WD modes, estimating the radial-ply tire inflation pressure in the range of 70–195 kPa.

Keywords: Wheel tractor; Drawbar pull; Traction coefficient; Tire inflation pressure; Drive tire slippage

Speed-made-good: Mobility map generation for wheeled vehicles on soft terrain

Eric Karpman, Wei Huang, Jozsef Kövecses, Marek Teichmann

Journal of Terramechanics, Volume 101, 2022, Pages 11-22, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.01.003.(https://www.sciencedirect.com/science/article/pii/S0022489822000039)

Abstract: The Nepean Wheeled Vehicle Performance Model (NWVPM) software has been in use for decades as a tool for engineers in industry and governmental agencies to predict the performance of off-road wheeled vehicles. It is based on the Bekker-Wong wheel-terrain interaction model which takes into account both the normal pressure and shear stress distributions at the wheel-terrain interface and uses the Bekker-Wong terrain parameters to characterize the terrain behavior. Using terrain and vehicle parameters as inputs, NWVPM computes various traction indicators such as drawbar pull, tractive effort, sinkage, and external motion resistance as functions of wheel slip by solving a set of equilibrium equations. This paper describes a novel method for predicting vehicle speed-made-good mobility maps and fuel consumption through an analytical approach using NWVPM. To evaluate the proposed method for predicting speed-made-good, a comparison is made with predictions obtained using Vortex, a commercial multibody dynamic simulation software that performs dynamic simulations of vehicles on soft terrain. In addition, a comparison of the capabilities of NWVPM and Vortex in predicting off-road vehicle performance over a range of terrains is presented and the results of the drawbar pull traction test from both software are compared with experimental data.

Keywords: speed-made-good; off-road; wheel-terrain; multibody dynamic simulation

Dynamic impact of wheeled skidders on forest soil in felling areas

Igor Grigorev, Ol'ga Kunickaya, Evgeniy Tikhonov, Edward Hertz, Varvara Druzyanova, Oksana Timokhova, Viktor Ivanov, Igor Kruchinin

Journal of Terramechanics, Volume 101, 2022, Pages 1-9, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.02.001.(https://www.sciencedirect.com/science/article/pii/S0022489822000155)

Abstract: Soil compaction from wheeled vehicles poses a huge challenge for the forest ecosystems. Modeling the impact of skidding machines on the soil could help solve the problem. The present work seeks to construct a mathematical model of soil compaction under the cyclic dynamic loading of wheeled skidding machines using the vibration analysis method for elastic dynamic systems. The study found that 4 × 4, 6 × 6 and 8 × 8 forestry vehicles have similar amplitude-frequency characteristics regardless of driving speed and load. The analysis of soil compaction from dynamic loading revealed that loaded and unloaded skidder passes cause the least damage (21–31%) to forest roads compared to skid trails. As regards skid trails, 4 × 4 and 6 × 6 tractors were found to compact the soil by 23–50% in the first four passes. The subsequent passes will lead to 60–66% of compaction. Finally, 8 × 8 trucks cause 98–99% of soil compaction. The difference between the experimental and theoretical values of soil density does not exceed 12%. The unevenness coefficient of the soil compaction and the confidence interval fall within the acceptable range. The mathematical models are in good agreement with the experimental data and can be used to calculate the operating modes of wheeled forestry equipment.

Keywords: Amplitude-frequency characteristics; Mathematical model; Skidding; Soil compaction; System efficacy; Wheeled tractor

Tensegrital wheel for enhanced planetary surface mobility: Part 2 - Performance assessment of a ruggedized, double-layer tensegrital wheel

Georgia Crowther, Dimitrios (Dimi) Apostolopoulos, Stuart Heys

Journal of Terramechanics, Volume 100, 2022, Pages 87-101, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2021.11.007.(https://www.sciencedirect.com/science/article/pii/S0022489821000902)

Abstract: This paper details ProtoInnovations’ work on a novel wheel design concept for planetary mobility. The tensegrital wheel for enhanced surface mobility exploits the geometric and mechanical attributes of tensegrity to mimic the compliant and load-distributing properties of a pneumatic tire using space-qualified materials. The third iteration of these wheel concepts, dubbed the TW3, was subject to particular scrutiny. In this paper, we explore the development of the TW3 and evaluate its performance in lab tests, performed at ProtoInnovation’s in-house testing facility, and field experiments, performed in conjunction with NASA Ames Research Center at the Atacama Rover Astrobiology Drilling Studies (ARADS). We compare the TW3 performance to baseline wheels and conclude with suggestions for further tensegrital wheel development.

Keywords: Tensegrity; Planetary mobility; Rovers; Wheel design; NASA

Field tests of the experimental installation for soil processing

Yuri Syromyatnikov, Alexandra Orekhovskaya, Dmitriy Klyosov, Nataliia Vodolazskaya, Petr Syromyatnikov, Vitaliy Sementsov

Journal of Terramechanics, Volume 100, 2022, Pages 81-86, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.01.004.(https://www.sciencedirect.com/science/article/pii/S0022489822000040)

Abstract: The subject of the study is the parameters of the soil crumbling, depending on the rotation frequency of the rotor of the soil treatment installation under different initial parameters of moisture and density of the soil structure. Field tests of an experimental soil tillage installation with a loosen-separating device have been carried out. In order to determine the value of the soil crumbling, depending on the rotor rotation frequency of the grinding and separating device of the soil tillage installation, different mathematical models of soil crusting were obtained at different initial humidity and soil density parameters. The object of the study is the influence of the investigated factors on the soil crumbling. The effective grinding of soil with a soil cultivating installation with a wide range of initial parameters of the density of the structure and the moisture content of the surface layer of soil was revealed, increasing the rotor speed increased with adverse parameters of density and soil moisture. In variants with increased parameters of the density of the structure (1,3–1,4 g/cm3) after the passage of guns managed to get a sowing layer with a satisfactory content of agronomic useful lumps. The target group of information consumers in the article - designers, specialists who are engaged in the development of soil working working bodies.

Keywords: Tillage; Cultivation; Soil layer; Rotor; Lumps; Differentiation; Experiment; Tillage installation