Squishy motor powers robots that can take a beating

The motor features a soft rotary actuator inside the wheel and axle assembly(Credit: Xiangyu Gong)

In recent years robots have gone soft – literally – bringing with them a number of advantages. They are safer for humans to work with, can grasp different types of objects and now, may soon be better equipped to handle rough terrain. Scientists have developed a squishy motor that powers a soft rover across rocky paths and through water. They say such a vehicle could find applications in search and rescue missions and even deep space exploration.

"If you build a robot or vehicle with hard components, you have to have many sophisticated joints so the whole body can handle complex or rocky terrain," says Xiangyu Gong, graduate student at Rutgers University and lead author of the study. "For us, the whole design is very simple, but it works very well because the whole body is soft and can negotiate complex terrain."

Gong and his team crafted the rover out of silicone rubber, a material nearly one million times softer than aluminum. The four-wheeled vehicle is able to roll across rock beds and through water, handle falls of more than eight times its own height and is entirely free of metal so is suitable for harsh areas with electromagnetic fields.

But the real breakthrough lies in the engine room, more specifically, a soft rotary actuator inside the wheel and axle assembly. These were created using 3D-printed molds and soft lithography and were inspired by peristalsis, the contraction and relaxation of circular muscles like those in the esophagus that drive food down into your stomach.

By inflating and deflating air-filled pockets within the wheel, the researchers were able replicate the actions of the esophagus to drive an attached rotor, which then had the effect of converting peristalsic motion into torque to drive the vehicle forward. They say that, alternatively, the rotary actuators could be modified to operate a winch-like apparatus for an entirely different set of applications.

"The introduction of a wheel and axle assembly in soft robotics should enable vast improvement in the manipulation and mobility of devices," says Aaron Mazzeo, assistant professor of mechanical and aerospace engineering at Rutgers. "We would very much like to continue developing soft motors for future applications, and develop the science to understand the requirements that improve their performance."

The team imagines its soft motors finding applications in amphibious vehicles to explore lake beds, dangerous search and rescue missions and in deep space where shock-absorbing landers are needed to plonk down on other planets to explore the environment.

The research was published in the journal Advanced Materials.

You can see the soft motor and robot in action in the video below.

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