Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers learn why robots get stuck in the sand -- and how to keep them going

10.02.2009
Today's advanced mobile robots explore complex terrains across the globe and even on Mars, but have difficulty traversing sand and other granular media like dirt, rubble or slippery piles of leaves.

A new study published February 10 in the journal Proceedings of the National Academy of Sciences takes what may be the first detailed look at the problem of robot locomotion on granular surfaces. Among the study's recommendations: robots attempting to move across sandy terrain should move their legs more slowly, especially if the sand is loosely packed.

"We have discovered that when a robot rotates its legs too fast or the sand is packed loosely enough, the robot transitions from a rapid walking motion to a much slower swimming motion," said Daniel Goldman, an assistant professor in the School of Physics at the Georgia Institute of Technology. This project was funded by the Burroughs Wellcome Fund and the U.S. Army Research Laboratory.

The physics of movement on granular media has been largely unexplored systematically, so Goldman and his team set out to systematically investigate the performance of a small six-legged device called SandBot. The robot was designed by Haldun Komsuoglu and Daniel Koditschek at the University of Pennsylvania.

"This is new territory because researchers have not examined the interaction between an animal's foot and sand like they have a whale or duck's flipper and water," said Goldman. "Sand is a uniquely challenging terrain because it can shift quite easily from solid to fluid to solid and requires different locomotion strategies."

To conduct controlled experiments, Georgia Tech physics graduate student Chen Li built a trackway for SandBot to run along. The trackway consists of an eight-foot-long poppy seed-filled container with tiny holes in the bottom through which air can be blown. The air pulses elevate the granules and cause them to settle into a loosely packed solid state, allowing the researchers to closely control the density of the material.

"We used poppy seeds as the granular material because they were large enough not to get into the SandBot motors but light enough to be manipulated with our air blowers," explained Goldman. "We have done experiments with small glass beads, which more closely approximate desert sand, and found no qualitative change in the results."

In the desert, typical volume fractions for granular media range from 55 to 64 percent. For the study's initial experiments, the researchers packed the poppy seeds to a volume fraction of 63 percent, placed SandBot onto the surface and set its c-shaped legs to rotate five times per second. The little robot, which could bounce quickly across hard ground, became completely stuck in the granular material after just a few steps.

The researchers discovered that the problem was the rotational motion of the robot's limbs. The SandBot moves its limbs in an alternating tripod gait and during a rotation, each limb moves fast while it is in the air and slow while it is in the ground. The researchers found that the robot could walk across the sand quickly – at a speed of one body length per second – if the rotation frequency was fixed and three parameters were adjusted: the durations of the slow and fast phases and the angle at which the limb changed from slow to fast.

"A systematic study of the motion then revealed that changes in volume fraction of less than one percent resulted in either rapid motion or slower swimming," added Goldman. "We saw similar sensitivity when we changed the limb rotation frequency."

To study this phenomenon further, Goldman and Paul Umbanhowar of Northwestern University developed a simple kinematic model of penetration and slip of a curved limb on granular media. The model results showed that the relationship of the speed to the volume fraction and frequency of leg rotation was largely controlled by the degree to which the robot limbs penetrated into the sand with each step.

The higher the limb frequency and the looser the granular material, the deeper the robot sank into the granular material. Thus the length of the step the robot could take was shortened and when the step size became too short, the robot took its next step into ground disturbed by the previous step. This triggered a catastrophic loss of speed and a shift from walking to continuous paddling through the poppy seeds.

Goldman believes that this study's experiments and model describing the basic behavior of motion on granular media will help biologists understand how animals appear to move effortlessly across a diversity of complex substrates.

He also plans to use the information to help roboticists design devices with the appropriate feet and limb motion to move well in complex terrain – including sand. Future robots may have the ability to sense the type of material they are walking across, allowing them to adjust their limb motion accordingly. Such smart robots would advance the exploration of other planets, as well as search-and-rescue missions in disaster settings.

John Toon | EurekAlert!
Further information:
http://www.gatech.edu

More articles from Studies and Analyses:

nachricht Europe’s Demographic Future. Where the Regions Are Heading after a Decade of Crises
10.08.2017 | Berlin-Institut für Bevölkerung und Entwicklung

nachricht Scientists reveal source of human heartbeat in 3-D
07.08.2017 | University of Manchester

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

Im Focus: Scientists improve forecast of increasing hazard on Ecuadorian volcano

Researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, the Italian Space Agency (ASI), and the Instituto Geofisico--Escuela Politecnica Nacional (IGEPN) of Ecuador, showed an increasing volcanic danger on Cotopaxi in Ecuador using a powerful technique known as Interferometric Synthetic Aperture Radar (InSAR).

The Andes region in which Cotopaxi volcano is located is known to contain some of the world's most serious volcanic hazard. A mid- to large-size eruption has...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

New thruster design increases efficiency for future spaceflight

16.08.2017 | Physics and Astronomy

Transporting spin: A graphene and boron nitride heterostructure creates large spin signals

16.08.2017 | Materials Sciences

A new method for the 3-D printing of living tissues

16.08.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>