Performance Of Rover Research Articles

Study on hard rock particle size division based on Mars rover traction performance

To simplify the dynamic solution of the contact between the rigid wheel of Mars rover and the spherical hard stone on the mixed terrain, a model for hard stone particle size division based on the traction performance of Mars rover is proposed. On the mixed terrain of hard rock and soft soil, the movement of hard rock will affect the traction performance of the rigid wheels of Mars rover. According to the different effects of the hard stones on the traction performance of rigid wheels, stones are divided into three types. The static sinkage of rigid wheels is calculated according to the Bekker bearing model, and the calculation formula of sliding sinkage of rigid wheels and hard stone sinkage is proposed. The type of hard stones is determined by comparing the sinkage of hard stones and rigid wheels. Finally, three kinds of hard stones with slip ratios of 0.2, 0.5, and 0.7 were substituted into the single wheel simulation platform and the soil trough experiment platform for simulation and experiment. The results show that on mixed terrain, the error of simulation and experimental results of fixed hard stones under three slip rates is below 5.4%, the error of drawbar pull in simulation and experimental results of movable hard stones is above 126%, and the error of simulation and experimental results of scattered small hard stones is below 2%, which verifies the effectiveness of the hard stone particle size division model.

Design and analysis of a high-speed planetary rover with an adaptive suspension and spring damper

The development of deep space exploration has led to new exploration demands that cannot be met by traditional planetary rovers. This paper proposes a new wheeled rover that combines the advantages of passive all-wheel attachment and vibration reduction at high speeds. This rover can achieve vibration reduction in the vertical direction from ground excitation, preventing the instability of pitch and roll. Flexible wheels were used to reduce the high-frequency excitation of the ground on the rover. The design concept and mechanical principle of the proposed rover were comprehensively analyzed. A quasi-static kinematic model was developed to analyze the overstepping performance of the rover with this new design. Further, the response characteristics of the system to the ground excitation were investigated by vibration equations established using the Lagrangian method. The optimal parameters were obtained using a genetic algorithm to optimize the system with multiple objectives. Furthermore, the overstepping performance, all-wheel attachment, and vibration reduction of the planetary rover were verified through multi-body simulation. The proposed rover has considerable potential for missions such as the Mars sample return and planetary station construction.

Slip ratio of rigid wheels on TRI-1Lunar Simulant

Research work is conducted on performance evaluation of rover/rover wheel mobility in terms of slip ratio and motion resistance, which helps in solving and to overcome the present existing problems on a deformable soil terrain (flat/sloppy). The aim of this paper is to analyze the slip ratio and motion resistance of rigid wheels with various diameters, widths, lug height and different number of lugs, travelling on TRI-1 or Tiruchirappalli – 1 Lunar Soil Simulant. Slip ratio has more impact on the traveling performance of planetary rover which is a trafficability parameter. Hence, trafficability studies are required to understand –its affects, variation, and improvement of mobility from its parameter’s behavior. This paper brings out a best suitable combination of wheel that travels on TRI-1 Simulant, i.e., lugged wheels (small and large) with lug height 15 mm with 16 number of lugs and both wheels (plain small and plain large) are most suitable on Tiruchirappalli – 1 Lunar Soil Simulant with its maximum travelling performance and better mobility within the cases examined.

Science and exploration of the moon enabled by surface telerobotics

Tele-operated rovers have been a feature of space exploration for decades. Ground control teams that operate these rovers generally comprise a robot operations team supported by science and robot engineering groups. But, in the future, astronauts will also remotely operate rovers. Several studies have proposed that astronauts should be able to control rovers from orbiting spacecraft such as the Deep Space Gateway (DSG). This concept of operations offers several benefits to human exploration. Firstly, it will enable astronauts to expand their sphere of influence beyond the confines of a spacecraft. Secondly, it will enable astronauts to safely perform surface work via an avatar. Thirdly, it will reduce the expenditure of life support consumables, and fourthly, it will spare astronauts from spending time on radiation-ravaged planetary surfaces. But integrating tele-operated rovers into human space exploration raises important questions. What system configurations are effective? Which modes of operation and control are most appropriate? When is it appropriate to rely (or not) on tele-operated rovers? The proposed research sought to answer the first two of these questions. It was designed to simulate three mission phases: pre-mission planning, site survey, and surface asset deployment. The study employed a derived terrain model located in the Lunares hab facility (located in Pila, Poland). Operators drove a Turtle rover through task sequences to survey sites while avoiding hazards/obstacles. This study simulated remote rover operations that assessed crew workload, crew situation awareness, robot asset acquisition, task sequence success, system issues, and rover performance. This study demonstrated basic competence in teleoperated rover driving, but more work must be conducted to produce a system that can behave reliably over many weeks and/or kilometers. Results indicated interactive monitoring is an effective strategy for crew-centric surface telerobotics. Safeguarded driving using this mode of operation enabled participants to perform each task successfully – success being measured by the metric of completing assigned tasks and completing the course. Participants maintained good situational awareness (SA) with low effort using interactive visualization of the rover state. From post-test debriefs it was determined participants maintained a high level of SA during operations and that the activity employed via the operator interface was a contributing factor to achieving these high levels. Since the test sessions were designed to be increasingly difficult in terms of task complexity it was expected that SA would decrease and task loading would increase across tasks and the data confirms this was the case.

Study on geomechanical properties of lunar soil simulant (LSS-ISAC-1) for chandrayaan mission

Under Chandrayaan - II mission, simulation studies on lunar terrain were required for evaluation of the performance of rover and lander. In order to carry out mobility tests of a rover, it was required to prepare a lunar terrain testbed, which required a large quantity of lunar soil to represent the terrain conditions of the Moon. Under such compelling circumstances, U R Rao Satellite Centre (URSC), Indian Space Research Organization (ISRO), Bangalore, India has decided to manufacture indigenously lunar highland soil simulant, which can represent bulk chemistry, mineralogy and geomechanical properties of actual lunar highland soils brought by Apollo-16 mission of USA. This paper presents the process of manufacturing new lunar highland soil simulant (LSS-ISAC-1) and its various geomechanical properties such as cohesive modulus of deformation, frictional modulus of deformation, sinkage exponent, cohesion stress, angle of internal friction, shear deformation modulus and bulk density. The same were compared with the properties of actual lunar highland soil brought to the Earth by the Apollo-16. This new lunar highland soil simulant is being used for all qualifying tests required to be performed for the indigenously developed rover and the lander of the Chandrayaan mission.

Study on connection between shape of wheel and resistance force from ground for small wheel typed rovers

In recent years, the small wheel typed rovers are focused on as an exploring rover. However, running performance of the small wheel typed rovers is not good. It is difficult to compact the ground by wheels because weight of these rovers is small. Therefore, drawbar pull is low. In previous research, the movement method which improves the running performance of these rovers using effects which are given by vibration to the ground was proposed. Some experiments were carried out in order to confirm effective of proposed method. From theses experimental results, we could get knowledge that how to use vibration to improve running performance for the small wheel typed rovers. Moreover, it was confirmed that sinkage of the wheels to the ground is increased when vibration is given to the ground from the wheel. Sinkage of the wheels to the ground decrease running performance of rover. In this research, the relationship between the shape of wheel and resistance force from the ground was confirmed in order to propose the wheel which reduce subsidence amount to the ground when vibration is given to the ground. In experimental results, the wheel which has flange on side reduced subsidence amount to the ground.

Mathematical modeling and parametric study of a planar Tumbleweed rover demonstrator

Spherical wind-blown Tumbleweed rovers have the potential to significantly expand the type of interplanetary terrain that can be explored on planets such as Mars. Multiple tumbleweed designs have been studied by NASA’s Langley Research Center and Jet Propulsion Laboratory, and one promising design, the box-kite model, relies on internal sails to maneuver over rough terrains with the help of mass actuation within the rover chassis for directional control. This paper sets out to parametrically study the effect of actuating masses on Tumbleweed rover performance. As a first step towards evaluating the performance of a spherical Tumbleweed rover, we study a planar model in this paper. To accomplish our parametric study, a dynamic model and control scheme for a planar tumbleweed rover has been developed with four moving masses within the structure, and a prototype was built based on the model and proposed control scheme. The prototype was used to establish the validity of the dynamic model, and the dynamic model was then used to study the effect of rover diameter, mass actuation speed, and chassis-mass-to-actuating-mass ratios on the performance of the tumbleweed rover. From these studies it was found that the final angular speed of the rover decreases with increasing rover diameter, while the rover linear speed increases with diameter. The time taken to reach a desired angular speed was found to increase with increasing rover diameter for all cases. Additionally, final rover angular speed and linear speed were shown to increase with actuating-mass-to-chassis-mass ratio, and the time taken for reaching a desired angular speed and linear speed, i.e. settling time, was found to decrease with increasing actuating-mass-to-chassis-mass ratio.

Three-Dimensional Vibration-Based Terrain Classification for Mobile Robots

Extraterrestrial celestial patrol missions have introduced very strict requirements for the performance of rovers, due to their high cost. Vision-based or Lidar-based environment sensing technology has matured. However, due to its perceptual characteristics, it is impossible to predict the traversability of the terrain completely, and it lacks the judgment of the physical properties of the terrain, such as the degree of hardness and softness. Due to the spectrum of risks that the rover is facing, a wide range of detection processes is required. This research paper proposes a terrain classification approach based on 3-D vibrations induced in the rover structure by the wheel-terrain interaction. Initially, the acceleration information of the three directions is obtained by using the Inertial measurement unit of the rover. Then, the characteristics of the vibrations of the known terrain are learned. The Fast Fourier Transformation (FFT) is used to transform the labeled three-axis vibration vectors into a frequency domain. Then the training feature vectors are obtained through normalization. Taking into account the characteristics of the environment, an improved back propagation (BP) neural network is used to get the mapping relationships between the vibrations and the terrain types. Finally, classification testing has been conducted on five kinds of environments, including concrete, grassland, sand, gravel, and mixed. After 20 times random testing experiments, the classification accuracy has proven to be in the range 88.99%-100%, which verified the validity and the robustness of the algorithm and laid a foundation for the subsequent identification of terrain characteristic.

Experimental and DEM analyses on wheel-soil interaction

In this paper, the wheel-soil interaction for a future lunar exploration mission is investigated by physical model tests and numerical simulations. Firstly, a series of physical model tests was conducted using the TJ-1 lunar soil simulant with various driving conditions, wheel configurations and ground void ratios. Then the corresponding numerical simulations were performed in a terrestrial environment using the Distinct Element Method (DEM) with a new contact model for lunar soil, where the rolling resistance and van der Waals force were implemented. In addition, DEM simulations in an extraterrestrial (lunar) environment were performed. The results indicate that tractive efficiency does not depend on wheel rotational velocity, but decreases with increasing extra vertical load on the wheel and ground void ratio. Rover performance improves when wheels are equipped with lugs. The DEM simulations in terrestrial environment can qualitatively reproduce the soil deformation pattern as observed in the physical model tests. The variations of traction efficiency against the driving condition, wheel configuration and ground void ratio attained in the DEM simulations match the experimental observations qualitatively. Moreover, the wheel track is found to be less evident and the tractive efficiency is higher in the extraterrestrial environment compared to the performance on Earth.

The Effect of Assistive Anchor-Like Grousers on Wheeled Rover Performance over Unconsolidated Sandy Dune Inclines.

Typical rovers with wheels equipped with conventional grousers are prone to getting stuck in unconsolidated sandy dune inclines as the wheels tend to sink into the sand. This phenomenon is caused by the motion of the grouser through the sand during the latter half of the rotation, in which the grouser pushes the sand from underneath the wheel upwards and towards the backside of the wheel. This creates a space that the wheel can sink into. To minimize sand movement and subsequent sinkage, we propose the concept of using an “assistive grouser”, which is attached to the side of a conventional rover wheel. The assistive grouser is designed to be able to autonomously maintain a uniform angle relative to the rover body independent of the rotation of the wheels. Rotating the wheel causes the assistive grousers to automatically penetrate into the sand slope surface at a constant angle of attack, thereby acting as an anchor and providing traction for the wheel. Maintaining a uniform grouser angle as opposed to a rotating motion also assists in extracting the grouser out of the sand without moving the sand towards the back of the wheel. Moreover, the angle of the assistive grousers is held constantly by a single dedicated motor, meaning that the angle of the assistive grousers can be optimized to provide the least amount of sinkage for each slope angle. The experimental results showed that for slope angles of 0–30 degrees, the rover equipped with the proposed assistive grousers experienced significantly less sinkage and consumed less current compared to the rover equipped with conventional grousers.

A novel concept for analysis and performance evaluation of wheeled rovers

The analysis, design, and operation planning of rovers are often based on predictive dynamic simulation, where the multibody model of the vehicle is combined with terramechanics relations for the representation of the wheel–ground interaction. There are, however, limitations in terramechanics models that prevent their use in parametric analysis and simulation studies.Increasing mobility is generally a primary objective for the design and operation of rovers. The models and assumptions used in the analysis phase should target this objective. In this paper we put forward a new concept for the analysis of wheeled rovers, particularly for applications in off-road environments on soft soil. We propose a novel view of the problem based on the development of models that are primarily intended to represent how parameter changes in the robot design can influence performance. These models allow for the definition of indicators, which gives information about the behavior of the system. We term such models observative.In the reported work, a set of indicators for rover performance is formulated using such models. The ability of these indicators to characterize the behavior of a rover is assessed with a series of simulation tests and experiments. The indicators defined using observative models succeeded to capture the changes in rover performance due to variations in the system parameters. Results show that the proposed models can provide a useful tool for the design and operation of planetary exploration rovers.

Theoretical Analysis of Diversity in an Ensemble of Automatic Speech Recognition Systems

Diversity or complementarity of automatic speech recognition (ASR) systems is crucial for achieving a reduction in word error rate (WER) upon fusion using the ROVER algorithm. We present a theoretical proof explaining this often-observed link between ASR system diversity and ROVER performance. This is in contrast to many previous works that have only presented empirical evidence for this link or have focused on designing diverse ASR systems using intuitive algorithmic modifications. We prove that the WER of the ROVER output approximately decomposes into a difference of the average WER of the individual ASR systems and the average WER of the ASR systems with respect to the ROVER output. We refer to the latter quantity as the diversity of the ASR system ensemble because it measures the spread of the ASR hypotheses about the ROVER hypothesis. This result explains the trade-off between the WER of the individual systems and the diversity of the ensemble. We support this result through ROVER experiments using multiple ASR systems trained on standard data sets with the Kaldi toolkit. We use the proposed theorem to explain the lower WERs obtained by ASR confidence-weighted ROVER as compared to word frequency-based ROVER. We also quantify the reduction in ROVER WER with increasing diversity of the N-best list. We finally present a simple discriminative framework for jointly training multiple diverse acoustic models (AMs) based on the proposed theorem. Our framework generalizes and provides a theoretical basis for some recent intuitive modifications to well-known discriminative training criterion for training diverse AMs.

Terramechanics and its applications to the evaluation of terrestrial and extraterrestrial vehicle mobility: theory into practice

This paper traces the development of terramechanics – the study of the mechanics of vehicle-terrain interaction that provides the foundation for a comprehensive understanding of the behaviour of a vehicle operating on unprepared terrain. It highlights the development of computer-aided methods for performance and design evaluation of tracked and off-road wheeled vehicles, based on the principles of terramechanics. Examples of the applications of these computer-aided methods to guiding the development and design of off-road vehicles on earth, as well as the evaluation of the performance of rovers for exploration of the Moon, Mars and beyond, are presented. These signify that results of research on terramechanics have been put into engineering practice in enhancing the development of terrestrial and extraterrestrial vehicles. Prospects for further development of terramechanics, as well as challenges and opportunities in the field, are reviewed.

Tests on Effect of Gravity and Soil Density on Soil Cone Index

The cone index is one of the important indicators that can describe the comprehensive physical characteristics of lunar regolith. Its closely related to the sink and sideslip of lunar rover and also has widely used in prediction the trafficability, adhesion property, tractive performance of lunar rover. Based on component method, a kind of low gravity simulator, the tiltable test-bed has been built. This study has got the stable low gravity along axial direction and measured the penetration resistance characteristics of JLU-2 in different gravity through tests. The results shows that the gravity environment has an obvious impact on the cone index of lunar soil simulant, CI values reduce with the decreasing of gravity environment. Namely, in the low gravity condition, it shows weaker resistance ability for a foreign object to penetrate into. The result has important application value of prepare, optimize and risk assessment in walking mechanism of lunar rover and the sampling mechanism.

Fast Computation of the Performance of Lunar Rover Drive Motor with Skewed Stator Slots Based on 2D FEM

In order to study the performance of rare earth PM brushless DC motor with skewed stator slots for lunar rover driving wheel at extreme temperatures of lunar surface rapidly and accurately, a computational method based on 2D FEM was proposed. The skewed motor was equivalent to a certain number of straight slot motor units in series and the mathematical expression of calculation accuracy was deduced. In order to make the winding current of motor units in the same slot equal, a circuit with ideal current source was proposed to couple with the geometric model in 2D FEM. No-load back-EMF and electromagnetic torque were calculated for the prototype and the calculation accuracy was estimated according to the spectra of air-gap flux density at different relative positions of the stator and rotor in axial direction of the skewed motor. The proposed method is simpler and much more timesaving than 3D FEM. The calculated results closely match those of 3D FEM with the relative error less than 3.7%. The effectiveness of the method is verified by comparing with experimental results of multiple prototypes and the absolute error is less than 0.014Nm.

Traveling performance evaluation of planetary rovers on loose soil

AbstractIn designing a planetary rover, it is important to consider and evaluate the influence of parameters such as the weight and dimensions of the rover on its traveling performance. In this study, the influence of a rover's weight on its performance was evaluated by conduct experiments using a monotrack rover and an inline four‐wheeled rover with different rover weights. Then the influence of the wheel diameter and width was quantitatively determined by performing experiments using a two‐wheeled rover, equipped with wheels, with different diameters and widths. The results of the experiments were compared with those of a numerical simulation based on terramechanics. Finally, the influence of the wheel surface pattern on the traveling performance of planetary rovers was evaluated by conducting experiments using a two‐wheeled rover equipped with wheels with different numbers of lugs (i.e., grousers) on their surfaces. Based on the results of these experiments, we confirmed the following influences of the parameters: in the case of the track mechanism, the traveling performance does not change with the increase in rover weight. On the other hand, in the case of the wheel mechanism, an increase in rover weight decreases the traveling performance. Moreover, the experimental results show that the wheel diameter contributes more to the high traveling performance than the wheel width. In addition, a comparison between the experimental and simulation results shows that it is currently difficult to accurately predict the traveling performance of lightweight vehicles on the basis of terramechanics models. Finally, the experimental results show that having lugs always improves the traveling performance, even at the expense of wheel diameter. © 2012 Wiley Periodicals, Inc.

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.

Mechanical Analysis and Experiment of Wheel-Soil Interaction of Lunar Rover

The mechanics behavior between soil and wheel has important influence on the traction performance of the lunar rover. For analyzing the interaction between soil and wheel, the mechanical model is established and the experiment devices adopting gas bearing and tracking mechanism are set up in this paper. The relation of wheel structure, soil parameters, load, slip rate, traction force of the wheel is analyzed. Some experiments are done to test the mechanical property and the effect of slip angle, slip rate and soil parameters on the traction performance of the rover. The results prove the validity of the theoretical model.

A systematic approach to reliably characterize soils based on Bevameter testing

Although a lot of information about soil parameter identification exists in literature, there is currently no algorithm who makes use both of state of the art identification methodologies and incorporating statistical analysis. In this paper a state of the art soil parameter identification method is presented including the calculation of its standard deviations and a proper weighting of the objective function. With this algorithm and a Bevameter with advanced sensor and actuator technology a test campaign is started to find a reliable soil preparation, which is applicable to a large planetary rover performance testbed. Furthermore, the preparation method has to be valid and stable for various types of dry, granular and frictional soils, typically used for planetary rover testing in space robotics, since the result of pre-tests show that the soil parameters are highly depending on the preparation. Besides preparation, the soil parameters are also influenced by different Bevameter test setup variables. Thus, the effect of the penetration velocity as well as the penetration tool geometry for pressure–sinkage tests on soil parameters is investigated. For shear tests the influence of the dimension of the shear ring is analysed as well as the variation of the grouser height, the number of the grousers and the increase of the rotational shear velocity. The results of the extensive test campaign are evaluated by the proposed identification algorithms.

Terrain modelling in simulation-based performance evaluation of rovers

In this work, we investigate the effect of terrain modelling on the performance of planetary rovers by evaluating various design concepts under typical rover manoeuvres. The analysis is based on implementations in CMLabs’ Vortex, a dynamics simulation environment for complex mechanical systems. Vortex can be used to model the contact of wheels under various terrain conditions. The particular focus is on motion on soft terrain, investigating the physical phenomena exhibited by such terrain, and the possibility of modelling these with the primary purpose of representing the effects of the terrain on rover behaviour. Two semi-empirical terramechanics models are used to represent the effect of soft soil. The implementation of these terramechanics models in Vortex and their adaptation to fit a multibody dynamics simulation environment are explained in detail. The effects of terrain modelling approaches on the performance of rover concepts under typical rover manoeuvres are investigated. These include: (i) stra...