Design and Implementation of an Innovative Micro-Rover

Mobile robots are of high interest for unmaned planetary exploration. The very successful Pathfinder mission to Mars has impressively demonstrated the potential of mobile platforms for planetary exploration [1]. The European Space Agency (ESA) also started to develop concepts for micro-rovers for Mars missions. Within an interdisciplinary group of companies specialized in space applications and research labs new designs of micro-rovers have been investigated. Two concepts, a simple and robust one and an innovative one, have been selected and functional breadboard models of them are currently built. After a discussion of the key issues for robust locomotion the present paper will focus on the design and control of the more innovative solution. It consists of 6 independently driven wheels arranged in two triangles. It therefore allows not only for efficient rolling on flat surfaces but also to step on obstacles. Additionally the center of mass and the instrumentation carrousel is adjustable, allowing to optimally balance the micro-rover in almost every situation. Even after flipping over the robot will always be able to get back on its wheels

Design and Implementation of an Innovative Micro-Rover

Mobile robots are of high interest for unmaned planetary exploration. The very successful Pathfinder mission to Mars has impressively demonstrated the potential of mobile platforms for planetary exploration [1]. The European Space Agency (ESA) also started to develop concepts for micro-rovers for Mars missions. Within an interdisciplinary group of companies specialized in space applications and research labs new designs of micro-rovers have been investigated. Two concepts, a simple and robust one and an innovative one, have been selected and functional breadboard models of them are currently built. After a discussion of the key issues for robust locomotion the present paper will focus on the design and control of the more innovative solution. It consists of 6 independently driven wheels arranged in two triangles. It therefore allows not only for efficient rolling on flat surfaces but also to step on obstacles. Additionally the center of mass and the instrumentation carrousel is adjustable, allowing to optimally balance the micro-rover in almost every situation. Even after flipping over the robot will always be able to get back on its wheels

SOLERO : Solar Powered Exploration Rover

This abstract presents a perform study on SOLERO, a new and innovative rover concept for regional mobility on planetary surfaces. A rover is the most suited element to bring scientific instrument to a specific site in order to examine geology, mineralogy or exobiology on extraterrestrial planets. In contrast with the Mars Pathfinder mission, the actual need increases in terms of range and duration. These aspects lead to redesign many aspect of the past rovers, in particular the development of most suitable all terrain performances, autonomous navigation and a new power management concept. In this paper we ll focus on the locomotion and the energy utilization without contribution of batteries. To validate the SOLERO possibilities in these domains and its use for future planetary exploration missions, modelization, testing and Mars like mission simulation have been done. Due to extreme temperatures the use of batteries is a critical point and becomes too expensive in term of size and mass for long-time missions. In this case, a locomotion concept reducing power consumption with exclusive use of on board power generation has to be investigated. The SOLERO mechanical structure is an optimization of the Shrimp rover developed at EPFL. It has one wheel mounted on a fork in the front, one wheel in the rear and two bogies on each side. The parallel architecture of the bogies and the spring suspended fork provides a high ground clearance while keeping all its 6 motorized wheels in ground contact. This ensures excellent climbing capabilities over obstacles higher that the wheel diameter. Moreover, this original combination of wheeled locomotion and passive adaptation to help to reduce power consumption compared to active design such as legged rovers, without sensible reduction of climbing abilities. To remove the problems linked with energy storage, not only power reduction is important, but also the power management. SOLERO uses exclusively solar cells to generate the electrical power, because it s currently the most adapted solution for local energy generation on a rover. However the use of solar power only, have several constraints linked with the incoming solar radiation (insolation). To determine SOLERO s power budget and performances, a Mars insolation and environment model has been chosen as reference. The integrated solar power generation restricts the operation time and power to specific daytime. The electrical power provided by a solar panel of 0.3m2 is over 14W during the four hours around noon, this is sufficient for locomotion. The 1kg scientific payload needs less that 8W power and can be used during a maximal time of height hours during daylight. However, the limited power storage capacities and the reduction of power consumption for locomotion allowed this rover to be small, light and operational during more that 100 sols (Martian days). The total mass is only 10kg and its locomotion performance, in comparison with actual rovers, leads SOLERO to become the perfect candidate for long range mission on near-sun planetsLS

Walking planetary rovers-Experimental analysis and modelling of leg thrust in loose granular soils

One of the principal differences between locomotion in granular soils using legs when compared with wheels is that the drag between the leg assembly and the regolith material provides additional thrust. Experimental work is presented which demonstrates that this additional force is substantial, and can significantly augment legged vehicle Drawbar Pull. The paper also demonstrates that the drag force depends in a highly non-linear manner on sinkage depth, and linearly on leg cross section yet is only weakly dependent on leg cross-sectional shape, leg material frictional properties, or leg velocity. Comparison with modelled forces using established wedge theory techniques demonstrates poor correlation between predicted and actual results; in contrast, a modelling approach based on an analysis of the dynamics of granular materials produces an excellent correlation with experimental results and enables the drag force to be accurately characterised by deriving a constant coefficient which is characteristic of the soil material. Future work will investigate the relationship between this characteristic coefficient and the physical properties of the soil material to develop a robust method of predicting the coefficient for any soil. © 2013 ISTVS. Published by Elsevier Ltd. All rights reserved

Walking planetary rovers-Experimental analysis and modelling of leg thrust in loose granular soils

One of the principal differences between locomotion in granular soils using legs when compared with wheels is that the drag between the leg assembly and the regolith material provides additional thrust. Experimental work is presented which demonstrates that this additional force is substantial, and can significantly augment legged vehicle Drawbar Pull. The paper also demonstrates that the drag force depends in a highly non-linear manner on sinkage depth, and linearly on leg cross section yet is only weakly dependent on leg cross-sectional shape, leg material frictional properties, or leg velocity. Comparison with modelled forces using established wedge theory techniques demonstrates poor correlation between predicted and actual results; in contrast, a modelling approach based on an analysis of the dynamics of granular materials produces an excellent correlation with experimental results and enables the drag force to be accurately characterised by deriving a constant coefficient which is characteristic of the soil material. Future work will investigate the relationship between this characteristic coefficient and the physical properties of the soil material to develop a robust method of predicting the coefficient for any soil

European Tracked Micro-Robot for Planetary Surface Exploration

In the frame of future exploratory missions within the solar system the European Space Agency (ESA) has identified the need to extend therange of scientific measurement from the immediate vicinity of staticlanding stations to a wider radius of a few tens of meters. This paper describes the results of development work on a small mobile robot carried out within the framework of ESA`s Technological Research and Development Program. The purpose of the vehicle is to deploy instruments or sensor heads, acting as an `extended robotic arm` rather than covering large distance on various types of terrain,while maximizing the mass allocation for scientific equipment. Even with this limited mobility is becomes possible to expand the investigated area by several orders of magnitude compared to the capabilities of a purely landermounted payload. Applications of the vehicle could be the projected European mission to Mars, called `Mars Express`, to be launches in 2003, and future European missions to the Moon as well as potential international missions. The requirements call for a simple, robust device with a net vehicle mass of less than 2 kg and with low power consumption, capable to transport and positition a 1.4 kg package of scientific instruments. In this paper the main requirements are listed and the tracked concept called `Nanokhod`, which was chosen in response to them, is described, with emphasis on the control and data handling aspects, including navigation

The Effects of Increasing Velocity on the Tractive Performance of Planetary Rovers

An emerging paradigm is being embraced in the conceptualization of future planetary exploration missions. Ambitious objectives and increasingly demanding mission constraints stress the importance associated with faster surface mobility. Driving speeds approaching or surpassing 1 m/s have been rarely used and their effect on performance is today unclear. This study presents experimental evidence and preliminary observations on the impact that increasing velocity has on the tractive performance of planetary rovers. Single-wheel driving tests were conducted using two different metallic, grousered wheels —one rigid and one flexible— over two different soils, olivine sand and CaCO3-based silty soil. Experiments were conducted at speeds between 0.01–1 m/s throughout an ample range of slip ratios (5–90%). Three performance metrics were evaluated: drawbar pull coefficient, wheel sinkage, and tractive efficiency. Results showed similar data trends among all the cases investigated. Drawbar pull and tractive efficiency considerably decreased for speeds beyond 0.2 m/s. Wheel sinkage, unlike what published evidence suggested, increased with increasing velocities. The flexible wheel performed the best at 1 m/s, exhibiting 2 times higher drawbar pull and efficiency with 18% lower sinkage under low slip conditions. Although similar data trends were obtained, a different wheel-soil interactive behavior was observed when driving over the different soils. Overall, despite the performance reduction experienced at higher velocities, a speed in the range of 0.2–0.3 m/s would enable 5–10 times faster traverses, compared to current rovers driving capability, while only diminishing drawbar pull and efficiency by 7%. The measurements collected and the analysis presented here lay the groundwork for initial stages in the development of new locomotion subsystems for planetary surface exploration. At the same time, these data support the creation of velocity-dependent traction models required in the later stages of the development and subsequent operation of future, fast-moving planetary rovers