Publication news

Rapid automated soil preparation for testing planetary rover-soil interactions aboard reduced-gravity aircraft

Krzysztof Skonieczny, Parna Niksirat, Amir Ali Forough Nassiraei

Journal of Terramechanics, Volume 83, 2019, Pages 35-44, ISSN 0022-4898

Abstract: Mitigating potential hazards for planetary rovers posed by soft soils requires testing in representative environments such as with Martian soil simulants in reduced gravity. However, constraints imposed by testing aboard an aircraft performing parabolic flights make critical elements of the test procedure, such as soil preparation, challenging. This work describes the design, development, and operation of a novel rover-soil testing system that includes rapid automated soil preparation. The repeatability of the prepared soil condition is demonstrated by cone penetrometer tests in the laboratory as well as in a Falcon 20 aircraft during a parabolic flight campaign.

Keywords: Automatic test equipment; Space exploration; Planetary rovers; Robot motion; Reduced-gravity flights

Experimental verification on analytical models of lunar excavation

Banglu Xi, Mingjing Jiang, Liang Cui, Jun Liu, Huayang Lei

Volume 83, 2019, Pages 1-13, ISSN 0022-4898,

Abstract: In this paper, a series of excavation tests were conducted with a carefully designed apparatus and testbed based on soil mechanics theories to obtain reliable excavation forces in Tongji-1 lunar soil simulant at first. Then the measured data were compared with the forces predicted by six typical analytical models to verify their capability of accurately capturing the effects of cutting depth, rake angle, blade width and cutting speed. The results show that for the horizontal excavation forces, the Zeng model, the Kobayashi model, the Mckyes model and the Swick and Perumpral model can capture the effects of cutting depth, and the Lockheed-Martin/Viking model could capture the effects of the cutting depth, blade width and rake angle. For the vertical excavation forces, the Swick and Perumpral model and the Mckyes model can capture the effects of the cutting depth, blade width and rake angle. The overall assessment of excavation force predictions shows that the Lockheed-Martin/Viking model, the Zeng model, the Swick and Perumpral model and the Mckyes model are recommended for predicting the horizontal excavation force, and the Swick and Perumpral model and the Mckyes model are recommended for predicting the vertical excavation force.

Keywords: Testbed; Boundary effect; Soil-tool interaction; Lunar excavation

Study on applicability of RFT to traveling analysis of wheel with grousers: Comparison with DEM analysis as a virtual test

Hirotaka Suzuki, Kota Katsushima, Shingo Ozaki

Journal of Terramechanics, Volume 83, 2019, Pages 15-24, ISSN 0022-4898,


Abstract: We studied a method to calculate the traveling characteristics of small and lightweight rovers at low cost. Specifically, discrete element method (DEM) was considered as a high-cost and high-accuracy virtual test, and plate tests and traveling analyses of the wheel with grousers were performed. Meanwhile, we adopted resistive force theory (RFT) as a low-cost analysis method and confirmed its applicability to the traveling of wheels with grousers by comparing it with the results obtained by DEM analysis of a loose frictional soil. First, we determined the scale factor necessary for RFT calculation by DEM analysis of the plate penetration test. Then, DEM wheel models with three types of grouser were prepared, and we compared the drawbar-pull under several levels of slippage with the results obtained by RFT. Although RFT cannot sufficiently consider the influences of the shearing of the soil and of distance between grousers, it found that the effects of grousers can be examined at low cost by RFT.

Keywords: RFT; Wheel-soil interaction; Grouser; Trafficability; Slippage

Design optimization of deep-seabed pilot miner system with coupled relations between constraints

Su-gil Cho, Sanghyun Park, Jaewon Oh, Cheonhong Min, Hyungwoo Kim, Sup Hong, Junyoung Jang, Tae Hee Lee

Journal of Terramechanics, Volume 83, 2019, Pages 25-34, ISSN 0022-4898,


Abstract: In the pilot miner system, the hydraulic type collector is sensitive to the traffic ability of moving on cohesive soil. Therefore, the traffic ability needs to be simultaneously considered with collector performances in the design process. This means that the system has coupled disciplines and constraints, which can reduce the size of the feasible region, rendering it difficult to use the current optimization techniques to search the optimum satisfying all of the constraints. In this study, a new technique which stochastically explores the optimum point with the highest probability, improving the objective and satisfying the constraints, is applied to the design of a deep-seabed pilot miner system.

Keywords: Coanda effect; Cohesive soil; Constraint global optimization; Coupled discipline; Deep-seabed pilot miner system; Kriging surrogate model; Ocean mining system

Real time rut profile measurement in varying terrain types using digital image correlation

Theunis Botha, Devin Johnson, Schalk Els, Sally Shoop,

Journal of Terramechanics, Volume 82, 2019, Pages 53-61, ISSN 0022-4898,

Abstract: An important parameter in terramechanics is the rut depth produced when a vehicle traverses deformable soil. The rut depth provides a measure of vehicle tractability as well as the impact on the environment. Rut depth is not uniform on natural terrain and typically only a few manual points are measured. Synchronizing rut depth with other measurements is also problematic. This paper investigates the feasibility of using cameras to measure 3D terrain profiles from which a single rut depth measurement is obtained. Tests were performed on different vehicles, for various dynamic vehicle manoeuvres, over varying terrains including sand, mud, grassland, snow and ice. Results were validated using the traditional stick ruler method. Measurement frequencies of 58 Hz were obtained using affordable commercially off the shelf computational hardware and dedicated software. Determining whether a vehicle can traverse a terrain can significantly improve the vehicle mobility. Therefore, real time measurements of rut depth can be used to determine the mobility of vehicles in off-road conditions that can change rapidly due to environmental conditions e.g. rain or snow. The techniques described can assist in gathering terrain and vehicle mobility data that can be used directly to assist the driver in making safety related decisions.

Keywords: Real time; Rut depth; Stereo; Terrain measurement

An in-wheel sensor for monitoring tire-terrain interaction: Development and laboratory testing

Raul G. Longoria, Robert Brushaber, Andrew Simms

Journal of Terramechanics, Volume 82, 2019, Pages 43-52, ISSN 0022-4898,

Abstract: An in-wheel sensor system was developed to monitor the deflection and shape of a tire that it is operating on and interacting with terrain. Three ultrasonic sensors were mounted to rotate with the wheel rim to measure radial distance to the inner tire surface at the mid-plane and at two equidistant lateral planes of the tire. This study describes evaluation of the sensor system using a laboratory drum-test machine which drives the tire over a wide range of speeds at different normal tire loads and inflation pressures. Signal processing methods are described for extracting characteristic measures of the tire contact and shape geometry which can be determined from measurements of inner tire surface deflection. The measurement of contact length compared well with results measured using other methods and reported in the literature. Additional tire shape metrics are defined that may be useful for informing how automated adjustments can be made to inflation pressure by central tire inflation pressure systems. In most of the test cases, the three sensors showed no significant lateral variation in measured deflections, as expected for testing on a rigid drum.

Keywords: Tire-terrain contact measurement; Tire contact area sensor; Contact length

Discrete element modeling of cultivator sweep-to-soil interaction: Worn and hardened edges effects on soil-tool forces and soil flow

Mehari Z. Tekeste, Loran R. Balvanz, Jerry L. Hatfield, Sadaf Ghorbani

Journal of Terramechanics, Volume 82, 2019, Pages 1-11, ISSN 0022-4898,

Abstract: Simulation of tool-to-soil interaction provides opportunities to accelerate new equipment design and evaluate performance of tillage tools. Simulation based evaluation of worn tillage tools performance on soil flow has not been done. Discrete Element Modelling (DEM) has a potential to simulate worn tool to soil interaction problems, where worn tools CAD can be generated using 3D scanning. The DEM parameters of Hertz-Mindlin with Parallel Bond model were calibrated to match draft force and soil failure zone measured from a tool bar moving at 0.22 m/s and 38 mm cutting depth. The draft force and soil forward failure zone were predicted at 7% and 24% relative errors compared to measured values, respectively. Using the optimized DEM soil model, the interaction of three 3D reconstructed sweeps (new sweep, carbide treated-worn, untreated-worn) with soil were simulated to compare their geometric wear dimensional loss, performance on soil forces and soil flow. Results showed that the carbide treated-worn sweep had similar soil draft force and soil forward failure distance as the new sweep. The untreated-worn sweep showed lower vertical force (less suction) and its wing induced soil failure zone (front and lateral) showed poor soil tilth quality compared with the carbide treated-worn sweep and the new sweep.

Keywords: Discrete Element Modeling; 3D scanning; Soil model; Tillage; Carbide treated hardened edge; Wear

Rolling radii and moment arm of the wheel load for pneumatic tyres

Heinz Dieter Kutzbach, Alexander Bürger, Stefan Böttinger,

Journal of Terramechanics, Volume 82, 2019, Pages 13-21, ISSN 0022-4898,

Abstract: Tractors and self-propelled harvesters are equipped with high volume pneumatic tyres with a low tyre inflation pressure. The contact patch can shift forwards or backwards in reference to the wheel centre as reaction on traction or brake forces because of the elastic tyre wall. Theoretical investigations – as necessary for modelling and simulation of dynamic vehicle behaviour – are complicated, since important tyre metrics cannot directly be measured based on the large deformations. Additionally, different definitions are often used. This is especially valid for the conversion of a drive torque into a traction force. In this context, the moment arm of the wheel load and the rolling radius of the tyre at zero slip condition are especially important. In contrast to the hitherto existing perception, the magnitude and position of the moment arm of the wheel load in reference to the wheel centre is dependent on traction and brake forces in addition to the motion resistance. The rolling radius of an elastic pneumatic tyre can be interpreted as radius of a fictitious rigid substitute wheel. This contribution emphasizes the outstanding importance of the rolling radius rdyn for all calculations on pneumatic tyres and the important roll of the variable moment arm of the wheel load for the moment compensation on the wheel.

Keywords: Pneumatic tyres; Rolling radius; Moment arm of the wheel load; Kinetic radius; Kinematic radius; Torque radius; Inner tyre ratio

Characterization of machine learning algorithms for slippage estimation in planetary exploration rovers

Ramon Gonzalez, Samuel Chandler, Dimi Apostolopoulos,

Journal of Terramechanics, Volume 82, 2019, Pages 23-34, ISSN 0022-4898,

Abstract: This paper presents a comprehensive comparison of well-known machine learning algorithms for estimating discrete slip events associated with individual wheels in planetary exploration rovers. This analysis is performed with various tuning configurations for each algorithm (55 setups). This research also shows the key role that environment plays in the performance of the learning algorithms: rover speed (0.05–0.25 [m/s]), type of terrain (gravel vs. sand), and tire type (off-road tires vs. smooth tires). These contributions are validated by using a broad data set collected using a planetary rover equipped with proprioceptive sensing. This work not only identifies the best algorithm to be deployed for discrete slip estimation, but it also helps with the selection and the mounting position of the sensing systems to be employed in future robotic planetary missions.

Keywords: Discrete slip estimation; Feature selection; Field validation; Ground vehicles; LATUV rover; Model selection