A single wheel test rig for ocean world rovers

Athul Pradeepkumar Girija, Rachana Agrawal, Ye Lu, Archit Arora, Maxim de Jong, Sarag J. Saikia, James M. Longuski

Journal of Terramechanics, Volume 109, 2023, Pages 101-119, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.07.001.(https://www.sciencedirect.com/science/article/pii/S002248982300054X)

Abstract: Ocean Worlds such as Europa and Enceladus are known to harbor subsurface liquid water oceans under their icy crust and are high-priority targets for in situ exploration. Compared to the Moon and Mars, Ocean Worlds likely present a significantly more challenging environment for surface mobility systems due to the extremely cold temperature, high radiation dosage, and poorly constrained material properties under these conditions. Small-diameter wheels such as those used by Mars rovers are prone to slip-sinkage in loose soil and damage from sharp rock and ice formations. A 4-wheel rover with a simple drive system and large deployable compliant tires is proposed as a solution for extreme terrain mobility on Ocean World surfaces. The present work describes the design and construction of a single wheel test rig and a prototype large-diameter deployable wheel for Ocean World rovers and initial test results. The test rig allows independent control of the vertical load, slip ratio, slip angle, and camber angle, and accommodates large-diameter deployable wheels. The test rig features a modular test bed that can simulate varied surface features such as fine-grained ice, smooth hard ice, sharp ice formations, and large ice boulder fields.

Keywords: Planetary rover; Wheel; Test rig; Mobility system; Ocean worlds

Justification of the soil dem-model parameters for predicting the plow body resistance forces during plowing

Salavat Mudarisov, Yakov Lobachevsky, Ildar Farkhutdinov, Eduard Khasanov, Ildar Rakhimov

Journal of Terramechanics, Volume 109, 2023, Pages 37-44, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.06.001.(https://www.sciencedirect.com/science/article/pii/S0022489823000502)

Abstract: The discrete element method has recently become a popular tool for developing soil models to be used for modelling the tillage process, which involves using working tools. The research aims to evaluate the parameters of the contact model particles when modelling tillage with large–sized working tools using the discrete element method. The paper presents the results of calibration of the physico-mechanical parameters of the particles of the soil environment model described using the discrete element method. The model is used for modelling the tillage process using moldboard plow. The parameters of the simulated particles to be studied are the Poisson's ratio, coefficients of static and dynamic friction of particles, Young's modulus, surface energy, particles' diameter, coefficients of static and dynamic metal friction of particles. Calibration was carried out according to the horizontal, vertical and transverse components of the traction resistance of the plow body. The obtained dependences of the components of the plow body traction resistance on soil moisture and surface energy help select parameters for the Hertz-Mindlin contact model while modelling the behavior of the soil environment when interacting with the working tools of tillage and sowing machines.

Keywords: Discrete element method; Modelling; Plow body; Tillage; Tractive resistance

On the power characteristics of an unmanned tracked vehicle for autonomous transportation of agricultural payloads

S.M. Shafaei, H. Mousazadeh

Journal of Terramechanics, Volume 109, 2023, Pages 21-36, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.05.006.(https://www.sciencedirect.com/science/article/pii/S002248982300040X)

Abstract: Elucidation of power characteristics of an unmanned tracked vehicle for autonomous transportation of agricultural payloads in greenhouse constructions leads to appearance of an applied research in this study. This novel aim has been chosen based on operational requirement of the vehicle. Hence, it can be highlighted that this paper is initiative study described results of power efficiencies (motion, slip, and tractive power efficiencies) of the vehicle. To this aim, various payloads mounted on a trailer (1–5 kN) were towed by the vehicle through diverse drive speeds (0.17–0.5 m/s). Results illuminate that vehicle drive speed and payload weight had consequential contribution to vehicle motion and tractive power efficiencies. While, vehicle slip power efficiency mainly depended on payload weight. Linear regression approximations demonstrate that dual cumulative contributory effect of the drive speed and payload weight on the motion power efficiency (84.98–97.69 %) and tractive power efficiency (78.62–92.92 %) was antagonist and synergetic, respectively. Meanwhile, the slip power efficiency (81.71–98.36 %) linearly dropped with augmentation of payload weight. Resultant slip and motion power inefficiency were associate with vehicle motion power loss in amplitude of 0.39–67.98 and 2.65–14.03 W, respectively. Consequently, tractive power inefficiency was associate with vehicle motion power loss in amplitude of 3.15–82.01 W. This amplitude spotlights that 3.35–43.62 % of vehicle motion power inevitably wasted inside track-surface interface in agricultural towing tasks. Overall, numerical and analytical descriptions of the results as well as practical suggestions provide appropriate guidelines for vehicle supervisor in order to optimize power characteristics.

Keywords: Unmanned ground vehicle; Agricultural tracked vehicle; Tractor vehicle; Tractive power efficiency; Slip power efficiency; Motion power efficiency

Numerical analysis of wheel locomotion on soft soil using the extended terramechanics model based on cellular automata

Yutaro Watanabe, Shingo Nakano, Hirotaka Suzuki, Shingo Ozaki

Journal of Terramechanics, Volume 109, 2023, Pages 9-20, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.05.005.(https://www.sciencedirect.com/science/article/pii/S0022489823000393)

Abstract: The evaluation of the traveling performance of moon/planetary exploration rovers is the primary aspect of scientific missions and human exploration in space. However, conventional models lack the detailed description of mechanical interaction between the wheels and soft soil. Therefore, in this study, the effectiveness of an extended terramechanics (xTerramechanics) model was investigated by considering the soil deformation actions based on cellular automata for the evaluation of rover traveling performance. First, the results of single-wheel traveling analysis were compared with the experimental results under the forced-slip condition, and it was shown that drawbar-pull and sinkage were represented with good accuracy (mean absolute errors less than 5.5 N and 3.2 mm). Next, we applied the xTerramechanics model under the self-propelled traveling condition at a constant towing load and slope climbing. The model successfully reproduced the well-known “difference in traveling performance depending on traveling conditions.” Furthermore, we used the model for the multibody dynamics analysis of a simple rover, and its applicability to the examination of the overall vehicle performance and multipath effects was demonstrated.

Keywords: Wheel–soil interaction; Trafficability; Multibody dynamics; Multipass effect; Cellular automata

Obstacle detection in snow covered terrain

S.N. Vecherin, J.M. Shaker, M.W. Parker

Journal of Terramechanics, Volume 109, 2023, Pages 1-8, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.05.004.(https://www.sciencedirect.com/science/article/pii/S0022489823000381)

Abstract: This work describes an automatic detection method of obstacles covered by snow. The method is based on the detection of statistical anomalies relative to an estimated background image which contains no obstacles. The sensitivity of the detection can be adjusted by a specified probability of false alarms, and the obstacle detection confidence is characterized by a probability of detection. Statistical properties of the background image are estimated from the given image without additional information on the background. The visible height of obstacles above the snow is related to the actual height of the obstacles above the ground, so that an operator can estimate the actual height of the snow covered obstacle. The developed method requires no training, is self-calibrating to the cluttered images, operates with a single given image, and aligns with a detection quantification adopted in the receiver operating characteristic framework.

Keywords: Obstacle detection; Off-road route planning; Autonomous navigation; Snow covered terrain

Literature review on Archimedean screw propulsion for off-road vehicles

Jorge Villacrés, Martin Barczyk, Michael Lipsett

Journal of Terramechanics, Volume 108, 2023, Pages 47-57, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.05.001.(https://www.sciencedirect.com/science/article/pii/S0022489823000356)

Abstract: This paper provides a comprehensive review of the published literature on screw propulsion for off-road vehicles and amphibious transportation, from its origins in the 18th century to the present day. Additionally, this work describes the basis and elements of an archimedean scroll propulsion mechanism and discusses the most developed dynamic models available in the literature and their limitations. The paper also examines the need for a tested terramechanics dynamic model and explores potential future applications of screw propulsion technology for uncrewed ground vehicles and robotic planetary exploration.

Keywords: Terramechanics; Propulsion systems; Archimedean screws; Amphibious vehicles; Literature review

Three-dimensional DEM tillage simulation: Validation of a suitable contact model for a sweep tool operating in cohesion and adhesion soil

Chunling Zhang, Jin Xu, Zihao Zheng, Weiwei Wang, Lichao Liu, Liqing Chen

Journal of Terramechanics, Volume 108, 2023, Pages 59-67, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.05.003.(https://www.sciencedirect.com/science/article/pii/S002248982300037X)

Abstract: Discrete element modelling (DEM) is widely used to estimate soil-tool interaction and tillage forces. To run an accurate simulation, it is essential to determine the appropriate DEM contact model and parameters. Although previous work has been introduced to determine the DEM contact model and parameters, the accuracy of numerical simulation is not high because of the soil differences when tillage tools operate in cohesion and adhesion soil in the middle and lower reaches of the Yangtze River in China. In this paper a Hertz-Mindlin with JKR Cohesion contact model and Linear Cohesion contact model were used to predict soil disturbance area and draft forces. The DEM parameters were determined using cone penetration, and uniaxial unconfined compression as an assisted test. The field experiment using sweep tool was used to validate the simulation results. A good agreement has been showed between simulation results and experiment results. Using verified model, the relative error for the predicted soil disturbance area at speeds of 0.50, 0.75 and 1.00 m/s were 5.3, 3.6 and 7.1 %, respectively. The maximum and average relative errors between simulated and measured draft forces were 6.98 and 3.91%, respectively. The effect of tillage depth and speed at soil disturbance area and draft forces were found which can provide some guidance for the selection of parameters during actual operation.

Keywords: Discrete element modelling; Sweep tool; Cohesion and adhesion; Soil disturbance; Draft forces

Terrain classification using mars raw images based on deep learning algorithms with application to wheeled planetary rovers

Junlong Guo, Xingyang Zhang, Yunpeng Dong, Zhao Xue, Bo Huang

Journal of Terramechanics, Volume 108, 2023, Pages 33-38, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.04.002.(https://www.sciencedirect.com/science/article/pii/S0022489823000344)

Abstract: Scene information plays a crucial role in motion control, attitude perception, and path planning for wheeled planetary rovers (WPRs). Terrain recognition is the fundamental component of scene recognition. Due to the rich information, visual sensors are usually used in terrain classification. However, teleoperation delay prevents WPRs from using visual information efficiently. End-to-end learning method of deep learning (DL) that does not need complex image preprocessing was proposed to deal with this issue. This paper first built a terrain dataset (consists of loose sand, bedrock, small rock, large rock, and outcrop) using real Mars images to directly support You Only Look Once (YOLOv5) to test its performance on terrain classification. Because the capability of end-to-end training scheme is positively correlated with dataset, the performance of YOLOv5 can be significantly improved by exploiting orders of magnitude more data. The best combination of hyperparameters and models was achieved by slightly tuning YOLOv5, and data augmentation was also applied to optimize its accuracy. Furthermore, its performance was compared with two other end-to-end network architectures. Deep learning algorithms can be used in the future planetary exploration missions, such as WPRs autonomy improvement, traversability analysis, and avoiding getting trapped.

Keywords: Terrain classification; Deep convolutional neural network; Mars raw images; Wheeled planetary rover

Correlations between moisture content and color spectrum of sandy soils

György Pillinger, Ahmed Elawad Eltayeb Ahmed, Kornél Bessenyei, Péter Kiss

Journal of Terramechanics, Volume 108, 2023, Pages 39-45, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.05.002.(https://www.sciencedirect.com/science/article/pii/S0022489823000368)

Abstract: It is a well-known phenomenon that the color of sand changes due to moisture. As the moisture content increases, the sand will typically become darker. In our research, we are looking for the answer to the exact function according to which this darkening process changes and what relationship there may be between the different, initial (dry) soil colors and how this relationship can influence the evolution of the darkening process. Using the suitably chosen range of the color spectrum, we created a color parameter to characterize the color of the measured sandy soil, and then, in addition to determining the moisture content, we also looked for other uses of the color spectrum for sandy soil. Thus, based on the color spectrum and other input parameters, not only the moisture content can be calculated, but in the case of two components, the grain composition can also be determined.

Keywords: Spectroscopy; Particle composition; Moisture content; Spectral signature; Sandy soil; Soil color; Reflectance