Nasa has a 'mini' rover that won't get stuck on distant moons and planets

A new ‘mini’ Mars Rover can climb hills covered in sand and gravel, helping it avoid getting stuck on a remote planet or moon.

Nasa scientists – driven by the knowledge that the rolling hills of Mars are a long way from the nearest tow truck – constructed the ‘Mini Rover’, giving its wheels the ability to ‘wiggle’ so it won’t get stuck.

Using a complex move the researchers dubbed ‘rear rotator pedaling’, the robot can climb a slope by using its unique design – it has wheeled appendages that can be remotely lifted – to combine paddling, walking, and wheelspinning motions.

Professor Dan Goldman, from the School of Physics at the Georgia Institure of Technology, said: ‘When loose materials flow, that can create problems for robots moving across it. 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 localised fluid hill for the back wheels that is not as steep as the real slope. The rover is always self-generating and self-organising a good hill for itself.’

The research, published on the cover of journal Science Robotics, reveals that researchers built the ‘Mini Rover’ using 3D printers.

While a robot built by Nasa’s Johnson Space Centre previously pioneered the ability to spin its wheels, engineers at Georgia Tech recreated those capabilities in a scaled-down vehicle – with four-wheeled appendages driven by 12 different motors.

Siddharth Shrivastava, an undergraduate student in Georgia Tech’s George W. Woodruff School of Mechanical Engineering, said: ‘The rover was developed with a modular mechatronic architecture, commercially available components, and a minimal number of parts.

‘This enabled our team to use our robot as a robust laboratory tool and focus our efforts on exploring creative and interesting experiments without worrying about damaging the rover, service downtime, or hitting performance limitations.’

The rover’s broad range of movements gave the team the chance to test a number of different variations and calculations, using slopes designed to simulate the hills found on Mars and the moon.

Using a system known as SCATTER – Systematic Creation of Arbitrary Terrain and Testing of Exploratory Robots – the rover is able to tilt to evaluate the terrain it is tackling.

Andras Karsai, a PhD candidate at Georgia Tech’s School of Physics, added: ‘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.

‘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.’

In the paper, the authors describe a gait that allowed the rover to climb a steep slope with the front wheels stirring up the granular material – poppy seeds for the lab testing – and pushing them back toward the rear wheels.

The rear wheels wiggled from side-to-side, lifting and spinning to create a motion that resembles paddling in water.

The material pushed to the back wheels effectively changed the slope the rear wheels had to climb, allowing the rover to make steady progress up a hill that might have stopped a normal robot.

Professor Goldman said: ‘In our previous studies of pure legged robots, modeled on animals, we had kind of figured out that the secret was to not make a mess.

‘If you end up making too much of a mess with most robots, you end up just paddling and digging into the granular material.

‘If you want fast locomotion, we found that you should try to keep the material as solid as possible by tweaking the parameters of motion.’

Simple motions had proven problematic for earlier Mars rovers, which often found themselves becoming stuck in granular materials.

Professor Goldman added: ‘This combination of lifting and wheeling and paddling, if used properly, provides the ability to maintain some forward progress even if it is slow.

‘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 researchers hope next to scale up the unusual gaits to larger robots.

Professor Goldman said: ‘We’d like to think about the locomotor and its environment as a single entity. There are certainly some interesting granular and soft matter physics issues to explore.’

Though the Mini Rover was designed to study lunar and planetary exploration, the lessons learned could also be applicable to our own planet – an interest to the US Army Research Laboratory, one of the project’s sponsors.

Dr Samuel Stanton, a programme manager at the Army Research Office, said: ‘Basic research is revealing counter-intuitive principles and novel approaches for locomotion and granular intrusion in complex and yielding terrain.

‘This may lead to novel, terrain-aware platforms capable of intelligently transitioning between wheeled and legged modes of movement to maintain high operational tempo.’

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