Universe Today
Shape Memory Alloy (SMA) is becoming increasingly common in space exploration applications. It has primarily been used in deployable structures, such as antenna booms or solar sail deployment. However, it also has a use case nearer the ground of whatever planet, moon, or asteroid it finds itself near. A new paper by Shufeng Tang and their colleagues at the Inner Mongolia University of Technology uses SMA to solve a problem in an area near and dear to space explorers' hearts—small space flexible robotics.
The paper, published in the journal Actuators, describes an earthworm-like robot that uses SMA springs to control a series of flexible joints. It combines the "on-off" features of SMA with a series of mechanical gears and a flexible skeleton that allows the robot to move while still being able to return to its original posture without the need for rigid control systems found on typical robots.
Using SMA springs has several advantages over traditional locomotion techniques. They're tiny and lightweight, making them ideal for robots designed to fit into small spaces. They are flexible, allowing them to be incorporated into a robot whose entire purpose is to flex as part of its movement pattern. And, perhaps most importantly for space exploration, they work even better at cold temperatures than on Earth.
Lava tubes on the Moon would be a great candidate for exploration by this robot.
The paper was split into sections covering the mathematics behind the kinematics of the robot and an experimental section that tested a prototype in various environments. Kinematically, the robot is complex, with the forces from the different springs interacting through joint connections. The authors ran a series of simulations modeling how the forces would interact before they moved on to building a prototype, and found that their design could extend, deflect, and move as predicted.
As with all physical implementations of models, though, the actual prototype didn't quite live up to expectations. It did manage some impressive feats - it could contract by around 25%, allowing it to use expansion and contraction as a form of motion. It could also deflect over 90 degrees off its original path, allowing it to navigate sharp turns. However, during a pipe climbing experiment, there were some errors due to a lack of heat dissipation, with the SMA springs not able to cool back down to their original temperature, therefore holding a shape slightly out of line with what was expected. Another test was run at cold temperatures, where the authors found they could decrease the "recovery time" it took the robot to return to its original form by 15% when it was subjected to cold conditions.
There were some limitations for the construction of the overall robot, though. It was limited to crawling through a 45mm pipe only, due to the size it was designed for, and the relatively small force output of the springs. That limited its payload carrying capacity, and the prototypes used in the experiments effectively didn't carry anything. Also, its power supply was run through a cable, and as the robot moved into a pipe, the drag force of that cable increased the force needed for it to move along. This could potentially limit its usefulness in exploring long distances in piping.
Fraser discusses how critical capabilities are to our space exploration efforts.
Overall, the experiments and modeling were a successful showcase of utilizing this exciting new material in a new space exploration application. The underlying structure of the worm's body could be used as a component in a larger flexible robot, such as a gecko or the snake-like ones we described before. As robot explorers start moving into ever more novel terrain on other worlds, there will be a place for those able to navigate small spaces, and an SMA-based movement style could certainly fit that bill.
Learn More:
S. Tang et al -An Extendable and Deflectable Modular Robot Inspired by Worm for Narrow Space Exploration
UT -NASA Tests a Robotic Snake That Could Explore Other Worlds
UT -Exploring the Moon with Biologically-Inspired Subsurface Robots
UT -The Next Mars Rover's Wheels Won't Get Torn Apart by the Red Planet
