Bayesian calibration of Vehicle-Terrain Interface algorithms for wheeled vehicles on loose sands

Ian Dettwiller, Masoud Rais-Rohani, Farshid Vahedifard, George L. Mason, Jody D. Priddy

Journal of Terramechanics, Volume 71, June 2017, Pages 45-56, ISSN 0022-4898,   http://doi.org/10.1016/j.jterra.2017.02.003.
http://www.sciencedirect.com/science/article/pii/S0022489817300381

Abstract:   The Vehicle-Terrain Interface (VTI) model is commonly used to predict off-road mobility to support virtual prototyping. The Database Records for Off-road Vehicle Environments (DROVE), a recently developed database of tests conducted with wheeled vehicles operating on loose, dry sand, is used to calibrate three equations used within the VTI model: drawbar pull, traction, and motion resistance. A two-stage Bayesian calibration process using the Metropolis algorithm is implemented to improve the performance of the three equations through updating of their coefficients. Convergence of the Bayesian calibration process to a calibrated model is established through evaluation of two indicators of convergence. Improvements in root-mean square error (RMSE) are shown for all three equations: 17.7% for drawbar pull, 5.5% for traction, and 23.1% for motion resistance. Improvements are also seen in the coefficient of determination (R2) performance of the equations for drawbar pull, 2.8%, and motion resistance, 2.5%. Improvements are also demonstrated in the coefficient of determination for drawbar pull, 2.8%, and motion resistance, 2.5%, equations, while the calibrated traction equation performs similar to the VTI equation. A randomly selected test dataset of about 10% of the relevant observations from DROVE is used to validate the performance of each calibrated equation.  
Keywords: Off-road mobility; Vehicle Terrain Interface (VTI) model; Bayesian calibration; Metropolis algorithm; Sand; Drawbar pull (DP); Traction; Motion resistance; Database Records for Off-road Vehicle Environments (DROVE)

A device to measure wheel slip to improve the fuel efficiency of off road vehicles

A. Ashok Kumar, V.K. Tewari, Chanchal Gupta, C.M. Pareek   
Journal of Terramechanics, Volume 70, April 2017, Pages 1-11, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.11.002.
http://www.sciencedirect.com/science/article/pii/S002248981630088X  

Abstract:  
A hall sensor based simple technique was introduced to measure wheel slip and a microcontroller based embedded digital system was developed to display wheel slip data and warn the operator with audible and visible warnings if the optimum range is exceeds. Hall sensor slip measurement system was validated in controlled soil bin condition, tar macadam surface and actual field condition and compared with the commercial radar sensor. The developed system is simple in construction and can be mounted to any make and model of agricultural tractors by entering the appropriate rolling radius via the computer interface. Field trials were conducted to measure wheel slip and fuel consumption on farm use with and without activation of slip indicator; it was observed that, the amount of fuel saving during various agricultural operation was up 1.3 l/h.  
Keywords: Hall effect sensor; Actual speed measurement; Radar sensor; Display unit; Soil bin; Wheel slip

Bevameter testing on simulant Fillite for planetary rover mobility applications

Michael B. Edwards, Mandar M. Dewoolkar, Dryver R. Huston, Colin Creager
Journal of Terramechanics, Volume 70, April 2017, Pages 13-26, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.10.004.
http://www.sciencedirect.com/science/article/pii/S0022489816300635  
Abstract:  
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.  
Keywords: Bevameter testing; Martian simulant; Fillite; Pressure-sinkage model

Generation of stochastic mobility maps for large-scale route planning of ground vehicles: A case study

Ramon Gonzalez, Paramsothy Jayakumar, Karl Iagnemma   
Journal of Terramechanics, Volume 69, February 2017, Pages 1-11, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.10.001.
http://www.sciencedirect.com/science/article/pii/S0022489816300519  
Abstract:
This paper describes a simple and efficient methodology to generate a mobility map accounting for two sources of uncertainty, namely measurement errors (RMSE of a Digital Elevation Model) and interpolation error (kriging method). The proposed methodology means a general-purpose solution since it works with standard and publicly-available Digital Elevation Models (DEMs). The different regions in the map are classified according to the geometry of the surface (i.e. slope) and the soil type. A real USGS DEM demonstrates the suitability of the proposed methodology: (1) interpolation of a 26 × 40 -km2 DEM to a finer resolution (30-m to 20-m); (2) analysis of the number of random realizations to account for the variability of the data; (3) efficient computation time (4-million-point DEM requires less than 30 min to complete the whole process); (4) route planning using the stochastic mobility map (constraints in slope and soil properties). UNCLASSIFIED: Distribution Statement A. Approved for public release; distribution is unlimited. #27681    
Keywords: Stochastic conditional simulation; Geographical Information System (GIS); Next-Generation NATO Reference Mobility Model (NG-NRMM); Digital Elevation Model (DEM); Soil moisture

3D contact patch measurement inside rolling tyres

A. Glenn Guthrie, Theunis R. Botha, P. Schalk Els    
Journal of Terramechanics, Volume 69, February 2017, Pages 13-21, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.09.004.
http://www.sciencedirect.com/science/article/pii/S0022489816300507  
Abstract:  
This paper presents a novel method for capturing the 3D profile of the inside of a rolling off-road vehicle tyre at the tyre-road contact region. This method captures the contact region at all times as the vehicle negotiates obstacles. The system uses a pair of inexpensive digital cameras (capable of capturing up to 300 frames per second) and features a purely mechanical stabilisation system to ensure that the cameras capture the contact region at any wheel speed or vehicle acceleration.

The captured images are processed using 3D computer vision techniques using an open source computer vision library called OpenCV. Stereo image pairs are used to create clouds of 3D points showing the profile of the inside surface with good accuracy. Various obstacles were traversed with the deformed tyre profile being compared to the undeformed profile. The system improves on current measurement techniques used to measure the contact patch by capturing a large region of the contact patch, providing full 3D surface geometry, as well as remaining centred on the contact patch irrespective of wheel rotation. The system also enables other imaging techniques to be used such as digital image correlation to determine velocity profiles as well as strain measurements.    
Keywords: Computer vision; Stereography; Tyre deformation; Contact patch; Tyre footprint; Image correlation

Effectiveness evaluation of hydro-pneumatic and semi-active cab suspension for the improvement of ride comfort of agricultural tractors

Kyuhyun Sim, Hwayoung Lee, Ji Won Yoon, Chanho Choi, Sung-Ho Hwang  
Journal of Terramechanics, Volume 69, February 2017, Pages 23-32, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.10.003.
http://www.sciencedirect.com/science/article/pii/S0022489816300623  
Abstract:  
Advances have been made to agricultural tractors to improve their ride comfort. However, the ride comfort of tractors is relatively low compared to that of passenger vehicles. Many researchers have developed various types of suspension for tractors. While most studies have focused on the geometry of the suspension, few studies have been carried out on the development of a control algorithm for tractor suspension.

In this paper, to improve the ride comfort of an agricultural tractor, a hydro-pneumatic suspension model with a semi-active suspension control is developed with computer simulation, and the effectiveness of the suspension is evaluated before the vehicle is equipped with the suspension and placed into production.

An optimal control algorithm for the semi-active suspension of the tractor is developed using a linear quadratic Gaussian. In the simulation, a hydro-pneumatic suspension system model is developed using SimulationX and is applied to a full vehicle model using MATLAB/Simulink. The suspension is assessed by experiments and simulations. The ride comfort using the ride comfort index according to ISO 2631 is evaluated by comparing a vehicle with a passive cab suspension to that with a hydro-pneumatic suspension applied with the semi-active control.  
Keywords: Agricultural tractor; Hydro-pneumatic suspension; Semi-active cab suspension; Ride comfort; Evaluation

Improvement of traction performance and off-road mobility for a vehicle with four individual electric motors: Driving over icy road

Dzmitry Savitski, Dmitrij Schleinin, Valentin Ivanov, Klaus Augsburg, Emilio Jimenez, Rui He, Corina Sandu, Phil Barber   
Journal of Terramechanics, Volume 69, February 2017, Pages 33-43, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.10.005.
http://www.sciencedirect.com/science/article/pii/S0022489816300647  
Abstract: 
To control speed and wheel slip for severe conditions of tire-surface interaction is a challenging task in the design of traction control system for electric vehicles with off-road capability. In this regard, the present paper focuses on a specific traction control for an electric vehicle with four individual in-wheel motors over icy road. The study demonstrates that a proper integration of the speed controller and wheel slip controller can essentially improve the mobility of the vehicle in the cases of acceleration and slope climbing. The paper discusses relevant case studies with particular attention given to the system architecture (sliding mode and PID control methods), extremum-seeking algorithm for maximum tire-road friction and corresponding slip value, and experimental validation of the tire model used in the controller with the help of the Terramechanics Rig in the Advanced Vehicle Dynamics Laboratory (AVDL) at Virginia Polytechnic Institute and State University.  
Keywords: Traction control; Speed control; Wheel slip control; Electric vehicle; Tire-ice interaction

Design and development of a new transformable wheel used in amphibious all-terrain vehicles (A-ATV)

Xiaolin Xie, Feng Gao, Chuan Huang, Wen Zeng   
Journal of Terramechanics, Volume 69, February 2017, Pages 45-61, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.11.001.
http://www.sciencedirect.com/science/article/pii/S0022489816300829  
Abstract:  
Conventional ground-wheeled vehicles usually have poor trafficability, low efficiency, a large amount of energy consumption and possible failure when driving on soft terrain. To solve this problem, this paper presents a new design of transformable wheels for use in an amphibious all-terrain vehicle. The wheel has two extreme working statuses: unfolded walking-wheel and folded rigid wheel. Furthermore, the kinematic characteristics of the transformable wheel were studied using a kinematic method. When the wheel is unfolded at walking-wheel status, the displacement, velocity and acceleration of the wheel with different slip rates were analyzed. The stress condition is studied by using a classic soil mechanics method when the transformable wheel is driven on soft terrain. The relationship among wheel traction, wheel parameters and soil deformation under the stress were obtained. The results show that both the wheel traction and trafficability can be improved by using the proposed transformable wheel. Finally, a finite element model is established based on the vehicle terramechanics, and the interaction result between the transformable wheel and elastic–plastic soil is simulated when the transformable wheel is driven at different unfold angles. The simulation results are consistent with the theoretical analysis, which verifies the applicability and effectiveness of the transformable wheel developed in this paper.  
Keywords: Transformable wheel; Soft terrain; Wheel-terrain interaction; Tractive performance

Predictability of boreal forest soil bearing capacity by machine learning

J. Pohjankukka, H. Riihimäki, P. Nevalainen, T. Pahikkala, J. Ala-Ilomäki, E. Hyvönen, J. Varjo, J. Heikkonen   
Journal of Terramechanics, Volume 68, December 2016, Pages 1-8, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.09.001.
http://www.sciencedirect.com/science/article/pii/S0022489816300453  
Abstract:  
In forest harvesting, terrain trafficability is the key parameter needed for route planning. Advance knowledge of the soil bearing capacity is crucial for heavy machinery operations. Especially peatland areas can cause severe problems for harvesting operations and can result in increased costs. In addition to avoiding potential damage to the soil, route planning must also take into consideration the root damage to the remaining trees. In this paper we study the predictability of boreal soil load bearing capacity by using remote sensing data and field measurement data. We conduct our research by using both linear and nonlinear methods of machine learning. With the best prediction method, ridge regression, the results are promising with a C-index value higher than 0.68 up to 200 m prediction range from the closest point with known bearing capacity, the baseline value being 0.5. The load bearing classification of the soil resulted in 76% accuracy up to 60 m by using a multilayer perceptron method. The results indicate that there is a potential for production applications and that there is a great need for automatic real-time sensoring in order to produce applicable predictions.  
Keywords: Terrain trafficability; Soil bearing capacity prediction; Forest harvesting; Machine learning; Open data