Theoretical analysis of soil reaction on a lug of the movable lug cage wheel

The measurement of soil reaction forces on a lug of a movable lug cage wheel was carried out in a soil bin. To elucidate the experimental results, a theoretical analysis of soil reaction forces on the lug of the movable lug cage wheel was made by using an analysis of the lug trajectory and a modified theory in soil–vehicle mechanics. The existing theory was modified and adjusted by considering the actual lug trajectory and the soil trench made by the preceding lug. The results showed that the theoretical analysis gave a good representation of the reaction forces measured experimentally. The higher pull and lift forces of the movable lug cage wheel compared with those of the fixed lug wheel was supported by the theoretical analysis. Although the theoretical representation of soil reaction forces should be improved by further works, it is sufficiently accurate to estimate the performance of the movable lug cage wheels by the proposed theory.     

Technology showcase applications of enamel coating in agriculture

Recently various experiments were conducted at the Asian Institute of Technology, Bangkok, to study the effect of enamel coating on the performance of some agricultural equipment. In order to reduce soil adhesion on cage wheel lugs, nine different coating materials were tried and enamel coating was found to be the best among these materials. It reduced soil adhesion on cage wheel lugs considerably to avoid cage wheel blocking. To investigate effect of coating on lug forces detailed lab studies were undertaken to measure the lug forces. The effects of lug slip, soil moisture content and sinkage were investigated. It was observed that enamel coating did not affect the lug forces. The pull and lift forces generated by the enamel coated and uncoated lugs were almost the same. When enamel coated bolt-on plates were mounted on the power tiller cage wheel lugs and trials were conducted in actual field conditions, it was observed that in actual field conditions enamel coated bolt-on plates on cage wheel lugs improved the performance of a power tiller. Studies about coating effects on the drag force required to pull floats on soil surface were also conducted. It was observed that enamel coating on floats reduced the drag force significantly. It also greatly improved the scouring of a mouldboard plough used in a wet, sticky clay soil.     

Improvement of a power tiller cage wheel for use in swampy peat soils

This study was aimed at investigating traction performance of a cage wheel for use in swampy peat soils in Indonesia. The tests were conducted in a soil bin filled with peat soil taken from the swampy areas. A set up was developed to measure tractive performance of a single cage wheel. Deep sinkage and high wheel slip were identified as the major problems of using the existing cage wheel design in swampy peat soils. The results revealed that increasing the lug angle from 15 to 35° and the length of lug improved the tractive performance of the cage wheel significantly, while increasing the number of lugs from 14 to 18 and width of lug did not improve the tractive performance significantly. A cage wheel with lug size 325×80 mm, 35° lug angle, 14 lugs (26° lug spacing), with 2 circumferential flat rings installed on the inner side of the lugs, out performed the other settings for use with power tillers in swampy peat soils.     

Effect of circumferential angle, lug spacing and slip on lug wheel forces

This study was conducted to investigate the effect of circumferential angle, lug spacing and wheel slip on forces produced by a cage wheel. Experiments were conducted in a laboratory soil bin having Bangkok Clay soil with 51% (d.b.) soil moisture content. Six ring-type loadcells were used to measure the soil horizontal, vertical and transverse reactions on the cage wheel lugs. The circumferential angle was varied from 0, 15, 30 to 45°. The lug spacing and wheel slip were varied from 20, 30 to 40° and 20, 35 to 50% respectively. All the force measurements were done at a constant 7 cm sinkage. The results showed that increasing circumferntial angle up to 45° can reduce variation in lug wheel forces, at the same time it had little effect on the mean pull and lift values. The side force was affected by the changes of circumferential angle. The 20° lug spacing not only gave the minimum variations but also maximum mean lug forces. The highest lug wheel forces occurred at 35% wheel slip.     

Modes of wet clay soil behaviour under a single cage wheel lug

This paper presents the results of studies on the effect of sinkage and slip of a single cage wheel lug on the deformation of wet clay soil. It was observed that the deformation pattern was strongly influenced by lug sinkage and slip. Soil wedge formation on the lug was also found to be a function of sinkage and slip. Four different deformation patterns were identified during this investigation. It seems unlikely that these can be predicted without a more exact knowledge of stress-strain relationships in soils.     

Design and traction performance of the movable lug wheel

A movable lug wheel using a rollers-sliding groove mechanism was designed, constructed and tested. Two types of lug moving patterns of the movable lug wheel were proposed and evaluated. Tests were conducted in a soil bin test apparatus to determine the traction performance of the wheel as affected by lug moving pattern, lug spacing, horizontal load and vertical load. Similar tests were also conducted using a fixed lug wheel. Generally, under the same level of vertical load, the fixed lug wheel sank more than the movable lug wheels did. However in general, under various horizontal loads, there was no significant difference of slip between the movable lug wheel and the fixed lug wheel. Among the test lug wheels, the movable lug wheel with lug moving pattern-2 required the smallest driving torque and developed the highest traction efficiency.     

Experimental analysis of soil reaction on a lug of a movable lug wheel

A movable lug wheel was tested in a soil bin test apparatus to determine its traction performance and to measure the soil reaction forces on its lugs. Similar tests were also conducted using a fixed lug wheel. The effects of the lug motion pattern, lug spacing and horizontal load on pull and lift forces were studied. From the experiments it is confirmed that the movable action of the lug plate could generate superior pull and lift forces in comparison with the fixed lug wheel. Among the test wheels, lug motion pattern-2 generated the highest pull and lift forces. Within the range of the test conditions, there was no significant difference in pull and lift forces of the lug plate between the test lug wheels with 12 lugs and 15 lugs at the same level of horizontal and vertical loads. The increase of horizontal load up to 200 N generally increased the pull force and generated smaller rolling resistance before the lug left the soil, but did not increase the lift force significantly. The patterns of pull force, lift force and drawbar pull generated under a constant slip were slightly different from those under a constant horizontal load. Finally, the results were also elucidated by their actual lug trajectories in soil.     

Effect of tine rake angle and aspect ratio on soil failure patterns in dry loam soil

Studies were conducted in a laboratory glass-sided soil bin with dry compact loam soil (c = 0.02 kPa, Φ = 20° and cone index 210 kPa) with the specific objective of observing the effect of flat tine rake angle and aspect ratio on soil failure patterns. The tine was moved in the soil in a quasi-static condition and soil failure patterns were observed through a glass window. Tine rake angles of 50°, 90° and 130° were used while aspect ratio effects were studied by varying both width and depth of the tine. Individual effects of width and depth were investigated by maintaining a constant aspect ratio of 2.0 but varying width and depth. Results obtained indicated that soil failure patterns are affected by tine design parameters. Soil failure patterns were observed to be of progressive shear type in all cases. For 50° rake angle tines, the patterns consisted of inclined shear lines starting from the tine tip and gradually moving upwards towards the horizontal soil surface, intersecting it at an average failure angle of 32°. In the case of 90° rake angle tines, the inclined shear surface was at a distance from the tine tip whereas, for 130° rake angle tines, prismatic-shaped stationary soil wedges were formed adjacent to the tine. Failure angles for the 90° and 130° rake angle tines were almost the same as those for 50° rake angle tines. The results of this study also indicated that aspect ratio alone cannot account for changes in soil failure patterns, their corresponding soil reactions, forward rupture or surcharge profiles. The effects are mainly due to the individual changes in width and depth. There were no distinct zones as described in the passive soil pressure theory. Soil failures were in regular cycles resulting in corresponding variations in the soil reactions on the tines.     

Development of a data acquisition system for measuring the characteristics of real time forces by cage wheels

A new data acquisition system was introduced that could be used to monitor the real time wheel forces to solve the limitations of obtaining precise performance characteristics of actual cage wheels. Contrary to previous methods, in which the cage wheel forces were obtained by summing up the individual lug forces. The new method enables measurement of the components of lug force in three orthogonal directions simultaneously. A single unit dynamometer system, with two extended octagonal rings was designed and fabricated using a solid mild steel block, was able to measure force up to 5 kN in each direction. It was used in a soil-bin test rig to determine the characteristics of the forces produced by a cage wheel with opposing circumferential lugs. The characteristics of the pull and lift forces agreed with measured drawbar pull and calculated wheel forces respectively. The force signals fluctuated periodically with rotation angle and the corresponding period approximately equal to the interval of angular lug spacing. The side force fluctuated between positive and negative values and the average was closer to zero due to the balancing effect of opposing lugs. The new system showed better output compared to the previous attempts, confirming its applicability for accurate measurement of real time wheel forces.     

An indoor traction measurement system for agricultural tires

To reliably study soil–wheel interactions, an indoor traction measurement system that allows creation of controlled soil conditions was developed. This system consisted of: (i) single wheel tester (SWT); (ii) mixing-and-compaction device (MCD) for soil preparation; (iii) soil bin; (iv) traction load device (TLD). The tire driving torque, drawbar pull, tire sinkage, position of tire lug, travel distance of the SWT and tire revolution angle were measured. It was observed that these measurements were highly reproducible under all experimental conditions. Also relationships of slip vs. sinkage and drawbar pull vs. slip showed high correlation. The tire driving torque was found to be directly influenced by the tire lug spacing. The effect of tire lug was also discussed in terms of tire slip.     

Experimental analysis of vertical soil reaction and soil stress distribution under off-road tires

In this study, the vertical soil reaction acting on a driven wheel was measured by strain gages bonded to the left rear axle of a 2WD tractor driven under steady-state condition on different soil surfaces, tractor operations, and combinations of static wheel load and tire inflation pressure. In addition, the measurements of radial and tangential stresses on the soil–tire interface were made simultaneously at lug’s face and leading side near the centerline of the left rear tire using spot pressure sensors. The experimental results indicate that the proposed method of vertical soil reaction measurement is capable of monitoring the real-time vertical wheel load of a moving vehicle and provides a tool for further studies on vehicle dynamics and dynamic wheel–soil interaction. Furthermore, the measured distributions of soil stresses under tractor tire could provide more real insight into the soil–wheel interactions.     

Collapse failure in dry clay soils caused by tine implements

The relation between forces applied to the soil and the resultant soil reaction was studied in dry clay soils under a quasi-static condition. As a tine advanced in dry compact clay soils at 5.2% dry basis moisture content, masses of soil collapsed one by one in front of the tine. The horizontal and vertical components of soil resistance measured were cyclic and in phase, with distinct peak and trough values. The peak values and trough values indicated the soil stress conditions before and immediately after each failure occurred. The frequency of failure depended on the size of the tine. The magnitude of the peak values depended on level of compaction and trough values on density of collapsed mass. The paper presents the details of observations.     

Dynamic behaviour of an open lugged wheel under paddy soil conditions

Many experimental studies of open lugged wheel-soil interaction have been conducted, mainly based on the condition of constant slip and sinkage. As a result the reaction force to lugs seemed to be equal to the soil cutting resistance to a metal surface. However, analyses based on such methods do not appear to represent the actual behaviour of lugged wheel-soil interaction, especially when the lugs are spaced widely. The actual motion the wheel axle. In this study, an experimental device for a model lugged wheel was constructed to investigate the characteristics of the interaction between a lugged wheel and soil. Experiments were conducted under several test conditions of soil including paddy soil with a hard pan. The result of both theoretical and experimental data indicated that slip and sinkage of a lugged wheel showed a fluctuation with rotation angle of which the period is equal to the angular lug spacing. In each test soil condition used, the motion of the lugged wheel and the reaction forces acting on each lug from the soil for a free sinking wheel were different from that of the condition of constant slip and sinkage. It was found that the results obtained from this study could clarify the actual behaviour of lugged wheel-soil interaction.     

Discrete element method analysis of single wheel performance for a small lunar rover on sloped terrain

The purpose of this study is to analyze the performance of a lugged wheel for a lunar micro rover on sloped terrain by a 2D discrete element method (DEM), which was initially developed for horizontal terrain. To confirm the applicability of DEM for sloped terrain locomotion, the relationships of slope angle with slip, wheel sinkage and wheel torque obtained by DEM, were compared with experimental results measured using a slope test bed consisting of a soil bin filled with lunar regolith simulant. Among the lug parameters investigated, a lugged wheel with rim diameter of 250 mm, width of 100 mm, lug height of 10 mm, lug thickness of 5 mm, and total lug number of 18 was found, on average, to perform excellently in terms of metrics, such as slope angle for 20% slip, power number for self-propelled point, power number for 15-degree slope and power number for 20% slip. The estimation of wheel performance over sloped lunar terrain showed an increase in wheel slip, and the possibility exists that the selected lugged wheel will not be able to move up a slope steeper than 20°.     

Effects of tine rake angle and aspect ratio on soil reactions in dry loam soil

Study was conducted in a laboratory glass-sided soil bin with dry compact loam soil with 5.2% (d.b.) moisture content. The specific objective of this study was to determine the effects of flat rigid tine rake angle (forward angle between tine face and horizontal soil surface) and aspect ratio (tine width/tine depth) on soil reactions. The tine was moved in the soil in a quasi-static condition and soil reactions were recorded using L-shaped force transducers. Corresponding soil failure patterns were observed through a glass window. Tine rake angles of 50°, 90° and 130° were used. The effects of aspect ratio were studied by varying both width and depth of the tines. Individual effects of width and depth were investigated by maintaining a constant aspect ratio of 2.0 but varying width and depth. Observations indicated that soil reactions are affected by tine design parameters. For all tine rake angles and aspect ratios, soil reactions were observed to be cyclic in nature and could be matched well with corresponding soil failure patterns. The horizontal and vertical soil reactions were in phase. Investigations into the individual effects of tine width and depth revealed that the aspect ratio alone cannot account for changes in soil reactions. The effects are mainly due to the individual changes in width and depth.     

Visualization and analysis of wheel camber angle effect for slope traversability using an in-wheel camera

This paper visualizes and analyzes an effect of a wheel camber angle for the slope traversability in sandy terrain. An in-wheel camera developed in this work captures the wheel-soil contact phenomenon generated beneath the wheel through a transparent section of the wheel surface. The images taken by the camera are then analyzed using the particle image velocimetry. The soil flows with various wheel camber angles are analyzed with regard to the soil failure observed on the slope surface. The analysis reveals that the slope failure and soil accumulation in front of the wheel significantly affect the wheel forces and distributions of the wheel sinkage in the wheel width direction. Further, the side force of the wheel in traversing a slope decreases as the slip ratio increases because the shear stress in the slope downward direction decreases owing to the slope failure.     

Tractive performance analysis of a lugged wheel by open-source 3D DEM software

Open-source software (OSS) is free to use and has accessible source codes, thus, it can be modified by various users. By using OSS, it is possible to easily and economically develop a target program for interaction studies in terramechanics. Yet Another Dynamic Engine (YADE) is an OSS for the 3D discrete element method (DEM), but its applicability to various contact interaction problems in terramechanics is not well-known. To investigate the applicability of YADE in terramechanics, the tractive performance of a lugged wheel was analyzed in this study. An idea of a proportional-integral-differential control model was applied to realize the constant rotation of the wheel in YADE. Our previous experiments on the locomotion of a small lugged wheel on a lunar-soil simulant were analyzed by YADE, and the results were found to be qualitatively similar to the obtained experimental results when considering the effects of the lug height, lug thickness, lug number, and wheel diameter. By applying a quasi-2D analysis with the same soil bin width and wheel width, the computational load of 3D DEM by YADE can be reduced up to 36.8% with similar net traction behavior against the wheel slip in a 3D analysis.     

Effect of design parameters on the performance of rigid traction wheels on saturated soils

A dimensional analysis was carried out to study the effect of individual wheel parameters, namely the lug angle, lug height, rim width and lug spacing on the traction performance of rigid wheels in saturated soils. The performance of the test wheels was evaluated on the basis of drawbar pull, slip and torque data obtained at different normal loads ranging between 50 and 100 kg (790–980 N). The data were utilized to compute the performance values such as tractive efficiency and overall performance index. Through the regression analysis, the optimum values of lug angle, rim width and lug spacing were found to be 20°, 200 mm and 110 mm respectively for a wheel of 685 mm dia. However, a definite conclusion regarding the optimum value of lug height could not be drawn, though the analysis for higher loads indicated this value as of 38 mm. The wheel parameter most influencing the traction performance of the wheel was found to be the rim width.     

Measurement of soil reaction forces on a single movable lug

In order to clarify characteristics of a new mechanism called a movable lug, a model of a single movable lug equipped with an L-shaped force transducer has been developed. The soil reaction forces (normal and tangential) on a flat single movable lug, a curved single movable lug and a fixed lug were measured on wet sandy loam soil in the laboratory soil bin test. These measured forces then were converted to lug pull and lift forces. The pull and lift forces obtained by the flat movable lug with 45° lug inclination angle and the curved movable lug were higher than those of the fixed lug. It was observed that the lift force of the fixed lug achieved its peak and dropped earlier than those of the movable lugs. However, the peaks of pull and lift forces of the flat and curved movable lugs were almost the same. The flat movable lug with 45° lug inclination angle generated a slightly higher peak of pull force than those with 30° and 60° lug inclination angles. However, the higher lug inclination angle produced, the lower peak of lift force. It was observed that the pull and lift forces increased as the sinkage increased. In contrast to the flat movable lug with 45° lug inclination angle, the curved movable lug produced greater lift force especially at high sinkage. The increase in lug slip from 5% to 25 and 50% caused an increase in the peaks of pull and lift forces. The soil moisture content affected the lug forces significantly.     

Estimation of a three-dimensional tyre footprint using dynamic soil–tyre contact pressures

A method for estimating the three-dimensional (3D) footprint of a 16.9R38 pneumatic tyre was developed. The method was based on measured values of contact pressure at the soil–tyre interface and wheel contact length determined from the contact pressures and the depths and widths of ruts formed in the soil. The 3D footprint was investigated in an area of the field where the pressure sensors of the tyre passed in a soft clay soil. The tyre was instrumented with six miniature pressure sensors, three on the lug face and the remaining three on the under-tread region between two lugs. The instrumented tyre was run at a constant forward speed of 0.27 m/s and 23% slip on a soft soil, 0.48 MPa cone index, 25.6% d.b. moisture content for four wheel load and tyre pressure combination treatments. The 3D footprint assessment derived from soil–tyre interface stress used in this research is a unique methodology, which could precisely relate the trend profile of the 3D footprint to the measured rut depth. The tyre–soil interface contact pressure distributions results showed that as inflation pressure increased the soil strength increased significantly near the centre of the tyre as a compaction increase sensed with the cone penetrometer.