Burrowing Mole-Bot Could Characterize Other Planet’s Soil

Burrowing under soil opens up a whole new world, especially when that soil is on other planets. Getting under the top layer of regolith on a world such as Mars could give access to a world still extant with life, whereas, on the Moon, it could lead to discovering a water source. So, for almost 30 years, scientists have been developing robots based on that most well-known burrowing machine here on Earth – the mole. Unfortunately, the models that have made it into space so far have failed for various reasons, but that hasn’t stopped more research groups from trying to perfect their own version of a mole robot. A paper from a research group at Guangdong University of Technology in China describes their efforts and frustrations in mimicking one of nature’s more unique but capable specialists.

To be fair to the development teams working on previous versions of “mole” robots, the failure was not always their fault. The Planetary Undersurface Tool (PLUTO) robot was fitted to Mars Express and had a hammering mechanism unlike anything seen in nature. It made it to Mars but was not successfully tested because the Beagle 2 lander that Mars Express was attached to failed to deploy its solar panels properly, ending the mission before it began.

Insight, another mission to Mars, carried another probe with a similar mission. The Heat Flow and Physical Properties Package (HP3) probe was designed to burrow 5m down into the Maritan soil and measure the heat coming from the interior of Mars. Unfortunately, it ran into unexpected soil conditions and wasn’t able to burrow as intended—as we reported extensively. After multiple failed attempts, that part of the mission was eventually abandoned.

In other words, burrowing on other worlds is hard. But that didn’t stop the team in Guangdong from trying. Their robot is meant to be much more similar to an actual mole than either HP3 or PLUTO was. The existing missions both used forms of drilling techniques, whereas the new robot uses actions intended to mimic what actual moles do.

There are two types of digging motions used by different types of moles. The first, and the one most commonly depicted in media, is shoveling away dirt from in front of them by using their massive forearms. Another, less commonly known method is using their huge teeth to bite away at the dirt and using their arms to push it underneath them. 

We know this because much research has been done into the kinematics of mole burrowing behavior. Those assessments showed the importance of the front and hind legs for mobility and moving the dirt around the mole’s body.

Understanding kinematics is only the first step, and the team from Guangdong took the next step in building a prototype, which, admittedly, looks like a mole, though maybe not a cute and cuddly one. It has distinct forearms and hind legs, and its head is shaped like a mole’s, though given its lack of eyes, it almost looks more like a shell casing. Advanced electronics, power systems, and motors are hidden inside the robot’s body, allowing it to mimic the overall shape of a mole more fully.

To test their prototype, the researchers made a bed of plastic particles to simulate the size the robot would expect to see in lunar or Martian regolith. The robot successfully burrowed itself into the particles. However, it had difficulty moving forward and creating the kinds of tunnels that moles are famous for. That seemed to be because of more complex coordination between the forearms and hind limbs, which was modeled in the current iteration of the prototype.

That first prototype is a step toward a more complete model that might someday be used in another world. Future research would include developing techniques to allow it to burrow, crawl, run, and even swim, allowing the locomotion of this bot to become genuine”y “multi-mode,” as the paper describes it. It might be hard to find another world off Earth that would need all those capabilities, but as biomimetic design improves, expect to see more bots shaped like cuddly and furry things back home exploring new worlds.

Learn More:
Zhang et al – Mole-Inspired Robot Burrowing with Forelimbs forPlanetary Soil Exploration
UT – NASA Has Given Up on Trying to Deploy InSight’s Mole
UT – It Looks Like it’s Working! NASA InSight’s Mole is Making Progress Again Thanks to the Arm Scoop Hack
UT – InSight’s ‘Mole’ is Now Completely buried!

Lead Image:
Different orientations of the mole robot prototype.
Credit – Zhang et al.

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