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 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.     

Performance of coated floats in different soils

Experiments were conducted in a laboratory soil bin to evaluate the performance of coated floats in different soils. Two coating materials were studied, namely enamel and Teflon, and three soil types, namely clay, loam and sandy soil were used for testing. The forces required to overcome the drag of the floats and pull them over the soil surface were measured. The normal loads were varied to 25, 44 and 64 N. The effect of moisture content (db) was evaluated by varying the soil moisture from 21.2 to 62.4% for clay soil, 16.6 to 36.1% for loam soil and 0.7 to 13.8% for sandy soil. All tests were conducted at a constant speed of 0.20 m/s. The performance of the enamel coated float was superior to Teflon and uncoated floats in all soil conditions. In clay and loam soils, the drag force increased initially until the soil moisture content reached the plastic limit. The drag forces showed a decreasing trend once soil moisture exceeded the plastic limit. In sandy soil, the drag force increased with increase in moisture content. The overall reductions for the enamel coated float compared to uncoated float were from 4 to 64% in clay soil, 16 to 46% in loam soil and 26 to 45% in sandy soil. Besides this superior performance, the enamel coated float compared to the other floats showed excellent resistance to wear due to abrasion and superior scouring.     

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.     

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.     

Effects of low-to-medium slip, lug spacing and moisture content on lug forces

The effects of low-to-medium slip, lug spacing and moisture content on lug forces in clay soil were investigated in a laboratory soil bin with the help of two model lugs. Perpendicular and radial soil reactions on the lug were measured and they were converted to lug pull and lift forces. The lug slip was varied from 5 to 10, 15, 20 and 25%. The measurements were conducted in clay soils with 6.3, 27.4 and 51% soil moisture contents. The lug spacing was varied from 20° to 30° and 40°. The perpendicular, pull and lift forces increased after lug entry into the soil and, after attaining a certain peak value, they decreased and reached a zero value at lug exit. The increase in lug slip from 5 to 25% caused an increase in lug forces on both lugs. The increase in the soil moisture content from 6.3 to 27.6% caused increase in lug forces on both lugs, but further increase in moisture content to 51% decreased the lug forces. Lug spacing showed a significant effect on lug forces produced by the succeeding lug. The increase in lug slip increased the lug forces at any given lug spacing and moisture content.     

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.     

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.     

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.     

Limitations of passive earth pressure theory for cage wheel lug and tine force predictions

Experiments in wet clay soil with cage wheel lug showed that the failure pattern in front of a lug was totally different from that assumed in passive soil pressure theory. Based on the failure pattern, the area of deformation zone and surcharge buildup in front of the lug, it was observed that the existing passive soil pressure theory could not be used to describe the soil movement caused by the action of the cage wheel lug. While working with a tine, four types of soil failure patterns were observed. It was found that these types of soil failures in front of a rigid tine were a strong function of soil moisture content. Passive pressure theory does not accurately predict the forces measured.     

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.     

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.     

Characteristics of normal and tangential forces acting on a single lug during translational motion in sandy soil

Lugs (i.e., grousers) are routinely attached to the surfaces of wheels/tracks of mobile robots to enhance their ability to traverse loose sandy terrain. Much previous work has focused on how lug shape, e.g., height, affects performance; however, the goal of this study is to experimentally confirm the effects of lug motion on lug–soil forces. We measured normal and tangential forces acting on a single lug as functions of inclination angle, moving direction angle, sinkage length, horizontal displacement, and traveling speed. The experimental results were mathematically fitted by using least square method to facilitate quantitative analyses on effects of changes in these motion parameters. Moreover, we compared the measured tangential forces to values calculated from a conventional tangential force model to evaluate the effects of the lug-tip surface, which is generally ignored in existing terramechanics models. The conclusions from this study would be useful for estimating the traveling performance of locomotive mechanisms equipped with lugs, modeling interaction mechanics between lugged wheels and soil, etc.     

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.     

Characteristics of adhesion between soil and solid surfaces

The capillary attraction and viscous resistance caused by a water film between two solid surfaces were evaluated theoretically. The surface morphology of soil at the soil-solid adhesion interface was examined by scanning electron microscopy. The contact models of the soil adhesion interface are given and mechanism of the normal adhesion is discussed. The wettability and normal soil adhesion of polytetrafluoroethylene (PTFE) sheet, polyethersulforne (PES)-PTFE coating, enamel coating, iron base alloy-epoxy composite coating and the conventional material were determined. The draft force of ploughs with mouldboards coated with PES-PTFE, enamel and iron base alloy-epoxy and the conventional mouldboard plough were measured. The soil surface at the soil-solid interface displays rough structure at various sizes. The adhesion force between soil and solid is mainly composed of Laplace pressure, meniscus tension and viscous resistance caused by water film and loops. Polymers can reduce both normal adhesion and sliding resistance, whereas, enamel coating or iron base alloy-epoxy composite coating can reduce the sliding resistance to some extent.     

Experimental study and analysis on driving wheels’ performance for planetary exploration rovers moving in deformable soil

Planetary rovers are different from conventional terrestrial vehicles in many respects, making it necessary to investigate the terramechanics with a particular focus on them, which is a hot research topic at the budding stage. Predicting the wheel-soil interaction performance from the knowledge of terramechanics is of great importance to the mechanical design/evaluation/optimization, dynamics simulation, soil parameter identification, and control of planetary rovers. In this study, experiments were performed using a single-wheel testbed for wheels with different radii (135 and 157.35 mm), widths (110 and 165 mm), lug heights (0, 5, 10, and 15 mm), numbers of lugs (30, 24, 15, and 8), and lug inclination angles (0°, 5°, 10°, and 20°) under different slip ratios (0, 0.1, 0.2, 0.3, 0.4, 0.6, etc.). The influences of the vertical load (30 N, 80 N, and 150 N), moving velocity (10, 25, 40, and 55 mm/s), and repetitive passing (four times) were also studied. Experimental results shown with figures and tables and are analyzed to evaluate the wheels’ driving performance in deformable soil and to draw conclusions. The driving performance of wheels is analyzed using absolute performance indices such as drawbar pull, driving torque, and wheel sinkage and also using relative indices such as the drawbar pull coefficient, tractive efficiency, and entrance angle. The experimental results and conclusions are useful for optimal wheel design and improvement/verification of wheel-soil interaction mechanics model. The analysis methods used in this paper, such as those considering the relationships among the relative indices, can be referred to for analyzing the performance of wheels of other vehicles.     

Why does soil not stick to enamel coating?

Recently, a number of investigations into the use of enamel coating for agricultural applications have been carried out. These investigations have revealed that an enamel coating reduces friction, adhesion and draft requirements of agricultural equipment in the soil. It is not known which characteristics of the enamel coating help in the improved performance. Therefore, this study was conducted to look into some physical, chemical and mechanical properties of enamel coating. The investigation included measurement of surface roughness, soil-metal adhesion and friction, hardness, and electrical conductivity, as well as electron scanning microscopy. The properties of the enamel coating studied were compared with the properties of a mild steel surface. These investigations revealed that an enamel coating does possess some special characteristics, different from the mild steel surface, which improve its performance in agricultural applications.     

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.     

The characteristics of soil reaction forces on a single movable lug

In order to understand clearly the characteristics of the soil reaction forces on a single movable lug, the resultant of measured soil reaction forces was determined and presented along with its position on the lug plate. The resultant of soil reaction forces acting on the movable lug increased gradually and reached the maximum value when the lug was on about its lowest position in the soil, then it decreased without offering any downward resistance to the lug till the lug left the soil. The maximum resultant force of the movable lug was higher than that of a fixed lug. The point of action of the resultant force on the movable lug shifted in a similar way in all test cases, that is, it moves to the center of the lug from the outer tip until it reaches the position where it becomes the maximum, then it moves to the outer tip till the lug leaves the soil. The inclination angle of the resultant force increased with the decrease of lug inclination angle. The bigger lug sinkage of the movable lug produced bigger soil reaction forces and shifted the point of action of the resultant force from the tip part to the central part of the lug. However, there was no significant effect of the lug sinkage on the direction of the resultant force. The increase in lug slippage from 25% to 50% brought bigger soil reaction forces on the movable lug, but did not influence the direction and point of action of the resultant force.     

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.