Planetary rover wiggles its rear wheels to overcome loose terrain

Scientists at the Georgia Institute of Technology have looked to shore up the mobility and freedom of future planetary rovers with a new design to tackle loose, troublesome terrain. The team’s Mini Rover uses some clever trickery to get itself out of tight spots, which includes a wiggling maneuver that pushes it up and over steep slopes of fine granular material.

When robotic space instruments become stuck on another planet, it can create all sorts of headaches for mission control back home. The Mars InSight lander is a prime example of this, with the drill component becoming lodged in the Martian terrain last year, forcing the team to suspend operations while coming up with ways to get it moving again.

The Georgia Tech research team were investigating how they can prevent rovers from becoming stuck in sand or other fine materials when roaming the hills of Mars or the Moon. To do this, the team developed a scaled down version of a NASA built robot called RP15, which has the ability to lift its wheeled appendages as needed to perform a range of motions.

“By creating a small robot with capabilities similar to the RP15 rover, we could test the principles of locomoting with various gaits in a controlled laboratory environment,” says team member Andras Karsai. “In our tests, we primarily varied the gait, the locomotion medium, and the slope the robot had to climb. We quickly iterated over many gait strategies and terrain conditions to examine the phenomena that emerged.”

The small robot the team experimented with features four wheeled appendages that are driven by 12 different motors, enabling it to carry out a wide variety of maneuvers. One that proved particularly impressive was a combination of paddling, walking and wheel-spinning, through which the robot was able to overcome a steep slope of poppy seeds.

This saw the robot stir up the material with the front wheels, push the seeds back towards the rear wheels which then wiggled from side to side, before lifting and spinning in a motion that resembled paddling through water. This had the effect of altering the slope in front of the rear wheels and made it easier to climb.

“When loose materials flow, that can create problems for robots moving across it,” said Dan Goldman of the Georgia Institute of Technology. “This rover has enough degrees of freedom that it can get out of jams pretty effectively. By avalanching materials from the front wheels, it creates a localized fluid hill for the back wheels that is not as steep as the real slope. The rover is always self-generating and self-organizing a good hill for itself.”

This particular gait could provide a blueprint for future rovers tasked with navigating difficult terrain on the Moon or other planets, with the team now hoping to put it to the test using larger wheeled robots.

“This combination of lifting and wheeling and paddling, if used properly, provides the ability to maintain some forward progress even if it is slow,” Goldman said. “Through our laboratory experiments, we have shown principles that could lead to improved robustness in planetary exploration – and even in challenging surfaces on our own planet.

The research was published in the journal Science Robotics.

Source: Georgia Tech

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