Squishy motor lets soft robots crawl over rocks

This soft, four-wheeled robotic vehicle is powered by a unique soft engine. (Credit: Xiangyu Gong)

Scientists have created a robotic vehicle equipped with soft wheels and a flexible motor. It can easily roll over rough terrain and through water.


Future versions might be suitable for search and rescue missions after disasters, deep space and planet exploration, and manipulating objects during magnetic resonance imaging (MRI).

The silicone rubber is nearly 1 million times softer than aluminum.

The most important innovation is the soft motor that provides torque without bending or extending its housing, says Aaron D. Mazzeo, assistant professor of mechanical and aerospace engineering.

“The introduction of a wheel and axle assembly in soft robotics should enable vast improvement in the manipulation and mobility of devices. 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.”

Vehicle innovations

  • Motor rotation without bending. “It’s actually remarkably simple, but providing torque without bending is something we believe will be advantageous for soft robots going forward,” Mazzeo says.
  • A unique wheel and axle configuration. The soft wheels may allow for passive suspensions in wheeled vehicles.
  • Wheels that use peristalsis—the process people use to push food to the stomach through the esophagus.
  • A consolidated wheel and motor with an integrated “transmission.”
  • Soft, metal-free motors suitable for harsh environments with electromagnetic fields.
  • The ability to handle impacts. The vehicle survived a fall eight times its height.
  • The ability to brake motors and hold them in a fixed position without the need for extra power.

To create the vehicle, engineers used silicone rubber that is nearly 1 million times softer than aluminum. They liken the softness to be somewhere between a silicone spatula and a relaxed human calf muscle. The motors were made using 3D-printed molds and soft lithography. A provisional patent has been filed with the US government.

“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, lead author of the study that is published in the journal Advanced Materials. “For us, the whole design is very simple, but it works very well because the whole body is soft and can negotiate complex terrain.”

Future possibilities include amphibious vehicles that could traverse rugged lakebeds; search and rescue missions in extreme environments and varied terrains, such as irregular tunnels; shock-absorbing vehicles that could be used as landers equipped with parachutes; and elbow-like systems with limbs on either side.

The Rutgers School of Engineering, the Department of Mechanical and Aerospace Engineering, the Rutgers Research Council, and an A. Walter Tyson Assistant Professorship Award supported the work.

Source: Rutgers University