958 research outputs found
Axel: A Minimalist Tethered Rover for Exploration of Extreme Planetary Terrains
Recent scientific findings suggest that some of the most interesting sites for future exploration of planetary surfaces lie in terrains that are currently inaccessible to conventional robotic rovers. To provide robust and flexible access to these terrains, we have been developing Axel, the robotic rover. Axel is a lightweight two-wheeled vehicle that can access steep terrains and negotiate relatively large obstacles because of its actively managed tether and novel wheel design. This article reviews the Axel system and focuses on those system components that affect Axel's steep terrain mobility. Experimental demonstrations of Axel on sloped and rocky terrains are presented
Planetary Cliff Descent Using Cooperative Robots
Future robotic planetary exploration will need to traverse geographically diverse and challenging terrain. Cliffs, ravines, and fissures are of great scientific interest because they may contain important data regarding past water flow and past life. Highly sloped terrain is difficult and often impossible to safely navigate using a single robot. This paper describes a control system for a team of three robots that access cliff walls at inclines up to 70°. Two robot assistants, or anchors, lower a third robot, called the rappeller, down the cliff using tethers. The anchors use actively controlled winches to first assist the rappeller in navigation about the cliff face and then retreat to safe ground. This paper describes the coordination of these three robots so they function as a team to explore the cliff face. Stability requirements for safe operation are identified and a behavior-based control scheme is presented. Behaviors are defined for the system and command fusion methods are described. Controller stability and sensitivity are examined. System performance is evaluated with simulation, a laboratory system, and testing in field environments
Axel rover paddle wheel design, efficiency, and sinkage on deformable terrain
This paper presents the Axel robotic rover which has been designed to provide robust and flexible access to extreme extra-planetary terrains. Axel is a lightweight 2-wheeled vehicle that can access steep slopes and negotiate relatively large obstacles due to its actively managed tether and novel wheel design. This paper reviews the Axel system and focuses on its novel paddle wheel characteristics. We show that the paddle design has superior rock climbing ability. We also adapt basic terramechanics principles to estimate the sinkage of paddle wheels on loose sand. Experimental comparisons between the transport efficiency of mountain bike wheels and paddle wheels are summarized. Finally, we present an unfolding wheel prototype which allows Axel to be compacted for efficient transport
A Framework for Automatic Behavior Generation in Multi-Function Swarms
Multi-function swarms are swarms that solve multiple tasks at once. For
example, a quadcopter swarm could be tasked with exploring an area of interest
while simultaneously functioning as ad-hoc relays. With this type of
multi-function comes the challenge of handling potentially conflicting
requirements simultaneously. Using the Quality-Diversity algorithm MAP-elites
in combination with a suitable controller structure, a framework for automatic
behavior generation in multi-function swarms is proposed. The framework is
tested on a scenario with three simultaneous tasks: exploration, communication
network creation and geolocation of RF emitters. A repertoire is evolved,
consisting of a wide range of controllers, or behavior primitives, with
different characteristics and trade-offs in the different tasks. This
repertoire would enable the swarm to transition between behavior trade-offs
online, according to the situational requirements. Furthermore, the effect of
noise on the behavior characteristics in MAP-elites is investigated. A moderate
number of re-evaluations is found to increase the robustness while keeping the
computational requirements relatively low. A few selected controllers are
examined, and the dynamics of transitioning between these controllers are
explored. Finally, the study develops a methodology for analyzing the makeup of
the resulting controllers. This is done through a parameter variation study
where the importance of individual inputs to the swarm controllers is assessed
and analyzed
Aspects of quality control of wind profiler measurements in complex topography
It is well known in the scientific community that some remote sensing
instruments assume that sample volumes present homogeneous conditions within
a defined meteorological profile. At complex topographic sites and under
extreme meteorological conditions, this assumption may be fallible depending
on the site, and it is more likely to fail in the lower layers of the
atmosphere. This piece of work tests the homogeneity of the wind field over
a boundary layer wind profiler radar located in complex terrain on the coast
under different meteorological conditions. The results reveal the
qualitative importance of being aware of deviations in this homogeneity
assumption and evaluate its effect on the final product. Patterns of
behavior in data have been identified in order to simplify the analysis of
the complex signal registered.
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The quality information obtained from the homogeneity study under different
meteorological conditions provides useful indicators for the best
alternatives the system can offer to build wind profiles. Finally, the
results are also to be considered in order to integrate them in a quality
algorithm implemented at the product level
The new Mars: The discoveries of Mariner 9
The Mariner 9 encounter with Mars is extensively documented with photographs taken by the satellite's onboard cameras, and an attempt is made to explain the observed Martian topography in terms of what is known about the geomorphological evolution of the earth. Early conceptions about the Mars surface are compared with more recent data made available by the Mariner 9 cameras. Other features of the planet Mars which are specifically discussed include the volcanic regions, the surface channels, the polar caps and layered terrain, the Martian atmosphere, and the planet's two moons--Phobos and Deimos
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