Getting a robotic explorer to another world is an amazing accomplishment, but it won’t be worth much if the mission comes to an early end because it gets stuck in the soil. NASA has partnered with the Georgia Institute of Technology to investigate ways a rover might be able to cope with crumbling or loose materials. The school constructed a prototype vehicle called Mini Rover with nifty “wiggling” wheels.
Sending robots to explore a place like Mars has many advantages, not the least of which is robots are much more hearty than humans. However, controlling a machine from several light-minutes away is tricky. Operators can use images from the rover to plan courses, but they can only guess about the consistency of the surface. Attempting to climb a hill with loose gravel could be disastrous when there’s no one in millions of miles who can right a flipped rover. Even seemingly safe flat surfaces can be dangerous — the Spirit rover met its fate after becoming stuck in a patch of loose sand. A better understanding of a branch of physics called terradynamics could help avoid this.
According to Georgia Tech physicist Dan Goldman, a rover wheel with higher degrees of freedom can help a robot cope with almost any slippage as it navigates across alien landscapes. The Mini Rover uses a wheel maneuver the team has dubbed “Rear Rotator Pedaling.” The front wheels continuously push material back toward the rear wheels, which creates a slope less steep than the real slope. The rear wheels “pedal” to walk up the gentler slope. Thus, the rover creates multiple small hills to get over a large one. If the rover sinks into loose material, the same pedaling motion can pull the wheels free and inch them forward.
Georgia Tech built the prototype in collaboration with Johnson Space Center using 3D printing and commercial off-the-shelf parts. Since it’s easily repaired, the team was able to subject it to harsh conditions without fear of ruining it. This also allowed researchers to test types of locomotion that could never have been tested on a full-sized rover developed for a real mission. They found the careful pedaling movement was the most helpful, and in general, going slow is the best approach.
NASA could choose to integrate similar wheel designs on future rovers, but construction work has already wrapped up on NASA’s next major rover. The Perseverance rover will launch this summer and land on Mars in early 2021. It will have a helicopter drone that may help to map out its course, but an unexpected sand trap could still prove problematic.
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