Wheeled Rover Research Articles

Parameter Identification of a Planetary Rover Wheel–Soil Contact Model via a Bayesian Approach

Soft soil contact models developed for planetary exploration rovers play an important role in the study of rover mobility. Nowadays, most of the existing contact models are based on Bekker theory, which requires the evaluation of several soil parameters usually measured via bevameter tests. However, substantial differences existing between the plate–soil contact scenario and the wheel–soil contact scenario, along with large variability associated with the bevameter experiments, give rise to large uncertainty in the choice of the model parameter values. In this paper, a Bayesian procedure is proposed to deal effectively with the presence of uncertainty. In the proposed approach, model parameters are random variables with prior distributions derived from bevameter measurements. The prior distributions are then enhanced to posterior distributions through single wheel test data. At the end, the procedure identifies a set of possible model parameter configurations that result in high experimental‐numerical matching.

Reconfigurable Integrated Multirobot Exploration System (RIMRES): Heterogeneous Modular Reconfigurable Robots for Space Exploration

This paper presents the multirobot team RIMRES (Reconfigurable Integrated Multirobot Exploration System), which is comprised of a wheeled rover, a legged scout, and several immobile payload items. The heterogeneous systems are employed to demonstrate the feasibility of reconfigurable and modular systems for lunar polar crater exploration missions. All systems have been designed with a common electromechanical interface, allowing to tightly interconnect all these systems to a single system and also to form new electromechanical units. With the different strengths of the respective subsystems, a robust and flexible overall multirobot system is built up to tackle the, to some extent, contradictory requirements for an exploration mission in a crater environment. In RIMRES, the capability for reconfiguration is explicitly taken into account in the design phase of the system, leading to a high degree of flexibility for restructuring the overall multirobot system. To enable the systems' capabilities, the same distributed control software architecture is applied to rover, scout, and payload items, allowing for semiautonomous cooperative actions as well as full manual control by a mission operator. For validation purposes, the authors present the results of two critical parts of the aspired mission, the deployment of a payload and the autonomous docking procedure between the legged scout robot and the wheeled rover. This allows us to illustrate the feasibility of complex, cooperative, and autonomous reconfiguration maneuvers with the developed reconfigurable team of robots.

Design of wheels with grousers for planetary rovers traveling over loose soil

The wheels of planetary rovers typically have grousers (i.e., lugs, cleats) on their surface to provide grip for climbing in loose soil. However, from the viewpoint of designing wheels, there exist few theoretical methods or models for determining the grouser interval for a wheel. The goal of this study is to provide a fundamental guideline for determining the grouser interval on a wheel. To this end, the linear traveling speed model of a wheeled rover with grousers is first proposed. Subsequently, to verify the model, traveling tests were performed using a two-wheeled rover with wheels equipped with different grouser intervals and different heights. In the experiment, the angles between grousers were adjusted to 120°, 60°, 30°, and 15°, and the grouser height was set to 5 or 15mm. Finally, the maximum allowed grouser interval for a given wheel is discussed on the basis of the linear speed model. From the experimental results, the proposed model was validated; and on the basis of the model, for a wheel to have a high traveling performance, it was found that there should be more than two grousers between the vertical and the surface of the soil on a wheel.

Analysis on the Movement Effect of Lunar Rover Wheel

It is important to analyze mechanical relationship between lunar wheel and lunar soil for studying passing ability of regolith in lunar soil. Mechanical relationship between lunar wheel and regolith could be reflected by these parameters such as sinkage, drawbar pull, driving torque, motion resistance and slip when the lunar wheel moves. Thus, it is necessary to analyze these parameters of lunar wheel by soil bin test. The test results show that, the four parameters increase with slip and loading, except motion resistance of the test wheel which is under 70N at the speed of 25mm/s. The variations of the four parameters are not significantly influenced by velocity. The variations of the four parameters are significantly influenced by loading.

A Four-Wheel-Rhombus-Arranged Mobility System for a New Lunar Robotic Rover

Different from traditional ground vehicles, planetary robotic rovers with limited weight and power need to travel in unfamiliar and extremely arduous environments. In this paper, a newly developed four-wheel-rhombus-arranged (FWRA) mobility system is presented as a lunar robotic rover with high mobility and a low-weight structure. The mobility system integrates independent active suspensions with a passive rotary link structure. The active suspension with swing arms improves the rover's capacity to escape from a trapped environment whereas the passive rotary link structure guarantees continuous contact between the four wheels and the terrain. The four-wheel-three-axis rhombus configuration of the mobility system gives a high degree of lightweight structure because it has a simple mechanism with the minimum number of wheels among wheeled rovers with three-axis off-road mobility. The performance evaluation of the lightweight nature of the structure, manoeuvrability and the mobility required in a planetary exploring environment are illustrated by theoretical analysis and partly shown by experiments on the developed rover prototype.

Further study of the method of approach to testing the performance of extraterrestrial rovers/rover wheels on earth

The current practice for experimentally evaluating the performance of extraterrestrial rovers/rover wheels is to conduct tests on earth on a soil simulant, appropriate to the regolith on the extraterrestrial body of interest. In the tests, the normal load (force) applied by the rover/rover wheel to the soil simulant is set identical to that expected on the extraterrestrial surface, taking into account its acceleration due to gravity. It should be pointed out, however, that the soil simulant used in the tests is subject to earth gravity, while the regolith on the extraterrestrial surface is subject to a different gravity. Thus, it is uncertain whether the performance of the rover/rover wheel obtained from tests on earth represents that on the extraterrestrial surface. This issue has been explored previously. A method has been proposed for conducting tests of the rover/rover wheel on earth with identical mass to that on the extraterrestrial surface, instead of with identical normal load used in the current practice [1]. This paper provides further evidence to substantiate the merits of the proposed method, based on a detailed analysis of the test data obtained under various gravity conditions, produced in an aircraft undergoing parabolic flight manoeuvres [8]. In the study, the effect of slip on wheel sinkage has been evaluated. It is found that gravity has little effect on the slip and sinkage relationship of the rover wheel under self-propelled conditions.

Study on the Tractive Ability of Lunar Rover Wheel by Discrete Element Method

It is important to research the relationship between the lunar wheel and lunar soil in the circumstances of lunar surface in order that the lunar rover can work efficiently. Distinct Element Method (DEM) is an ideal method to analyze the relationship between lunar wheel and lunar soil. In this work, a prediction model for rigid-wheel and lunar soil is proposed, and the DEM model for lunar soil is found by the biax-test. The results show that the values of the simulation parameters in lunar soil are close to that of the real lunar soil after adjusting the micro simulation parameters. The Bekker’s model is used to calculate the pressure-sinkage, and the Janosi model is used to describe the shear characteristics. The plate-sinkage-test as well as the shear-test was simulated by PFC2D. The parameters of terra-mechanics were calculated based on the least square method. In the simulation, the value of K is 1635 kN/mn+2, n is 1.22 and k is 1.35 cm. After that, the soil bin system is simulated by the software PFC2D. Further, the tractive test which is checked out by the soil bin test and model calculation was simulated in PFC2D. Finally, by comparing the traffic ability of the nonrug-wheel with the rug-wheel, the results show that the slip radio is 0.52 of the rug-wheel and 3.21% of the nonrug-wheel under the traction load. The draw-bar pull is 121.67 N in the rug-wheel compared that of 7.71 N in nonrug-wheel under the slip is 10%.This indicates the rug-wheel can generate greater draw-bar pull and show better traffic ability than the nonrug-wheel under enough torque condition.

Insulation For Earth And Space

While the Curiosity rover wheels around Mars examining the chemical composition of the soil there, materials scientists here on Earth are already preparing for more advanced missions to the Red Planet. According to National Aeronautics & Space Administration scientist Mary Ann B. Meador, before sending people or larger vehicles to Mars, scientists must develop insulating materials to counter the planet’s exotic environment. Unlike the moon, Mars has a low-pressure atmosphere, said Meador when speaking last month at the American Chemical Society national meeting in Philadelphia. For this reason, space suits worn by astro­nauts for the past 40 years, with their simple, heat-reflecting metallized layers of insulation, just won’t cut it on the Red Planet: The layers would collapse on each other and permit heat transfer. To insulate the space suits, NASA is eyeing aerogels, high-surface-area porous solids prized for their light weight and low heat conduction. The materials could also ...

Parameter identification and contact modeling for planetary wheeled rovers in soft soil

A challenging topic in the field of planetary rover simulations is the modeling of the contact between the rover and its environment. Multibody simulation models are used to represent the kinematic structure of a wheeled rover, but its interface with the environment relies on sand-wheel contact dynamics. A new advanced contact model is presented and tuned according to single wheel experiments by comparison between experimental data and predicted values. Finally, stochastic model updating is performed to assess parameter uncertainty level due to soil properties. As a result, the mean percentage error of the tuned model is inside the acceptable range, but additional improvements in the rover sinkage computation model are still desired.

Measurement on the Shear Property Parameters of the Eruption Powder

The powder with size distribution was made from eruption to be used for the simulant of lunar soil. One of the most important factors is shear property, to simulate lunar soil behavior under the rover wheels. Therefore, it is necessary to measure the shear parameters of the simulant. The direct shear detector with controlled sample weight was used for selecting suitable method to obtain the shear parameters of the simulant, and finding effect actors for the measurement. Results found that the parameters changed greatly with the powder bulk density (or unit weight), and the calibration was vitally important for measuring cohesion of the powder.

1A2-K08 駆動型サスペンションを有する車輪型惑星探査ローバの不整地走破性能に関する考察(【宇宙工学部門】宇宙工学とロボティクス・メカトロニクス(1))

In planetary missions, rovers that can traverse over rough terrain are required in order to explore craters and slopes which have high scientic value. Rovers with wheeled locomotive system are used broadly in planetary missions, because the wheeled locomotive system has low energy consumption and its configuration is simpler than other types of locomotive system, such as the tracked locomotive system. However, wheeled rovers have low traversability. Recently, several rovers with articulated suspension have been studied. In this paper, the authors propose a new mobility system with articulated suspension, which has high eficiency and high traversability. The simulation results show the effectiveness of the proposed mobility system in its ability to climb a step using articulated suspension.

Fault-Tolerant Control Strategy for Steering Failures in Wheeled Planetary Rovers

Fault-tolerant control design of wheeled planetary rovers is described. This paper covers all steps of the design process, from modeling/simulation to experimentation. A simplified contact model is used with a multibody simulation model and tuned to fit the experimental data. The nominal mode controller is designed to be stable and has its parameters optimized to improve tracking performance and cope with physical boundaries and actuator saturations. This controller was implemented in the real rover and validated experimentally. An impact analysis defines the repertory of faults to be handled. Failures in steering joints are chosen as fault modes; they combined six fault modes and a total of 63 possible configurations of these faults. The fault-tolerant controller is designed as a two-step procedure to provide alternative steering and reuse the nominal controller in a way that resembles a crab-like driving mode. Three fault modes are injected (one, two, and three failed steering joints) in the real rover to evaluate the response of the nonreconfigured and reconfigured control systems in face of these faults. The experimental results justify our proposed fault-tolerant controller very satisfactorily. Additional concluding comments and an outlook summarize the lessons learned during the whole design process and foresee the next steps of the research.

1A2-I11 軟弱砂利フィールドを対象とした車輪型軽量移動ロボットの斜面走行性能に関する研究(車輪型/クローラ型移動ロボット(2))

When a volcano erupts, it is very dangerous to approach. However, if we use a rover, we can approach there. But there are loose sand field and loose gravel field in volcano. So the main challenge when developing a rover is traversability. To avoid slippage and increase the wheel's drawbar pull, the wheels of the rover typically have lugs, i.e., grousers. Experimental verification for traversability of a lugged wheeled rover has been done on loose sand field. But it has not been done on loose gravel field. Therefore, we conducted experiments on the traversability in loose sand field and loose gravel field using a two-wheeled testbed. And we evaluated the results of the experiments.

1A2-L06 斜面における車輪型移動ロボットの走行性能に土壌環境が及ぼす影響の評価(【宇宙工学部門】宇宙工学とロボティクス・メカトロニクス(1))

This paper presents the influence of lugs (i.e., grousers) on the traveling performance of wheeled rover in various loose soils. To evaluate the influence of lugs, slope-climbing tests were performed using a two-wheeled rover with wheels equipped with lugs in sandboxes covered with Toyoura sand/lunar regolith simulant. According to the experimental results, we confirmed that an increase in the number of lugs enhances traveling performance on both soils, and it has a greater impact on lunar regolith simulant, especially for wheels with short lugs. Furthermore, an increase in lug height has a great impact even on the traveling performance of wheels with small numbers of lugs on lunar regolith simulant.

Predicting the performances of rigid rover wheels on extraterrestrial surfaces based on test results obtained on earth

With a growing number of nations interested in planetary exploration, research and development of extraterrestrial rovers have been intensified. The usual practice is to test the performances of rovers on soil simulants on earth, prior to their deployment to extraterrestrial bodies. It is noted that in the tests the soil simulant is subject to the earth gravity, while the terrain on the extraterrestrial surface is subject to a different gravity. Therefore, it is uncertain whether the rover/rover wheel would exhibit the same performance on the extraterrestrial surface as that obtained from tests conducted on earth. This paper describes a practical methodology that can be employed to predict the performances of rover wheels on extraterrestrial surfaces, based on test results obtained on earth. As rigid wheels are used in many extraterrestrial rovers, this study focuses on examining the effects of gravity on the sinkage and compaction resistance of rigid rover wheels. Predictions obtained using the methodology are shown to correlate reasonably well with test data.

Discrete element modeling of a Mars Exploration Rover wheel in granular material

Three-dimensional discrete element method (DEM) simulations were developed for the Mars Exploration Rover (MER) mission to investigate: (1) rover wheel interactions with martian regolith; and (2) regolith deformation in a geotechnical triaxial strength cell (GTSC). These DEM models were developed to improve interpretations of laboratory and in situ rover data, and can simulate complicated regolith conditions. A DEM simulation was created of a laboratory experiment that involved a MER wheel digging into lunar regolith simulant. Sinkage and torques measured in the experiment were compared with those predicted numerically using simulated particles of increasing shape complexity (spheres, ellipsoids, and poly-ellipsoids). GTSC simulations, using the same model regolith used in the MER simulations, indicate a peak friction angle of approximately 37–38° compared to internal friction angles of 36.5–37.7° determined from the wheel digging experiments. Density of the DEM regolith was 1820kg/m3 compared to 1660kg/m3 for the lunar simulant used in the wheel digging experiment indicating that the number of grain contacts and grain contact resistance determined bulk strength in the DEM simulations, not density. An improved correspondence of DEM and actual test regolith densities is needed to simulate the evolution of regolith properties as density changes.

Survival of Bacillus subtilis Endospores on Ultraviolet-Irradiated Rover Wheels and Mars Regolith under Simulated Martian Conditions

Endospores of Bacillus subtilis HA101 were applied to a simulated Mars Exploration Rover (MER) wheel and exposed to Mars-normal UV irradiation for 1, 3, or 6 h. The experiment was designed to simulate a contaminated rover wheel sitting on its landing platform before rolling off onto the martian terrain, as was encountered during the Spirit and Opportunity missions. When exposed to 1 h of Mars UV, a reduction of 81% of viable endospores was observed compared to the non-UV irradiated controls. When exposed for 3 or 6 h, reductions of 94.6% and 96.6%, respectively, were observed compared to controls. In a second experiment, the contaminated rover wheel was rolled over a bed of heat-sterilized Mars analog soil; then the analog soil was exposed to full martian conditions of UV irradiation, low pressure (6.9 mbar), low temperature (-10°C), and an anaerobic CO(2) martian atmosphere for 24 h to determine whether endospores of B. subtilis on the contaminated rover wheel could be transferred to the surface of the analog soil and survive martian conditions. The experiment simulated conditions in which a rover wheel might come into contact with martian regolith immediately after landing, such as is designed for the upcoming Mars Science Laboratory (MSL) rover. The contaminated rover wheel transferred viable endospores of B. subtilis to the Mars analog soil, as demonstrated by 31.7% of samples showing positive growth. However, when contaminated soil samples were exposed to full martian conditions for 24 h, only 16.7% of samples exhibited positive growth-a 50% reduction in the number of soil samples positive for the transferred viable endospores.

Cohesions, friction angles, and other physical properties of Martian regolith from Mars Exploration Rover wheel trenches and wheel scuffs

[1] The Mars Exploration Rovers Spirit and Opportunity investigated the physical properties of Martian regolith in 7 wheel trenches and 20 wheel scuffs distributed along traverses at Gusev crater and Meridiani Planum. Specialized wheel-trenching sequences allowed analysis of wheel motor and suspension telemetry to determine regolith friction angle ϕ and cohesion c at trench sites. Friction angles were 30°–37°, and cohesions were 0–2 kPa. Simpler wheel-scuff maneuvers were analyzed for cohesion by assuming the range of ϕ determined from trenches; cohesions in wheel-scuffed regoliths were from 0 to 11 kPa. Regolith ϕ and c can be related to regolith origins. Grain sorting, compaction, shape, size, and angularity influence ϕ. Impact cratering and aeolian processes have affected grain angularity and sorting of Martian regolith at both Mars Exploration Rover (MER) landing sites and contend in opposing ways to determine grain characteristics in the regolith. Friction angles are consistent with dry, rigid, nonplaty grains with particle size frequencies dominated by very fine sand (as seen by the Microscopic Imager or MI) with at least some grain rounding (unresolved by MI), reflecting physical weathering from aeolian saltation. Friction angle results from MER trenches therefore indicate that regolith states are between fully mature aeolian materials and impact debris. MI and color Pancam views show trench tailings and trench floors are redder, brighter, and have more intermixed extremely fine (unresolved) grains than regolith closer to the surface disturbed and exposed only by rolling tracks.

1P1-J12 軟弱地盤走行に有効な月面探査ローバ用弾性車輪の走行性の検証(車輪型/クローラ型移動ロボット)

Lunar rovers are required to move on rough terrains such as in craters and rear cliffs where it is scientifically very important to explore. Recently, wheel typed rovers are popular for planetary exploration missions. However, there is a problem that the wheel typed rovers have possibility of stack. Therefore, this paper investigates a mechanism of kinetic behavior between the wheels of the exploration rovers and loose soil. This paper proposes the flexible wheel. The flexible wheel has the surface which can be changed flexibly toward rough terrain. Therefore, we measure the contact angle between flexible wheel and loose soil using sensor. Moreover, this result are compared with the result of rigid circular wheel.

Slip Ratio Based Traction Coordinating Control of Wheeled Lunar Rover with Rocker Bogie

This paper investigates the traction coordinating control issue of the wheeled lunar rover with Rocker Bogie in rough terrain. Based on the improved exponential approach law, the algorithm of coordinating control is designed to optimize the traction force and minimize the slip ratio, including the velocity and normal force control and sliding mode control. Then the co-simulations between ADAMS and MATLAB/Simulink are carried out in order to validate the proposed algorithm. Simulation results for a wheeled rover traversing moon-like terrain slopes and ditches demonstrate the effectiveness of the proposed control algorithm and the mobility improvement.