A Squishy Motor for Soft Robotics

Engineers develop rotary actuators based on pneumatically driven elastomeric structures.

A small, squishy vehicle equipped with soft wheels rolls over rough terrain and under running water without breaking a sweat thanks to a new soft motor that provides torque without bending or extending its housing.

“The introduction of a wheel-and-axle assembly in soft robotics should enable vast improvements in the manipulation and mobility of devices,” said Aaron D. Mazzeo, assistant professor in the Rutgers department of mechanical and aerospace engineering. “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.”

In order to create the vehicle, Mazzeo and his team used silicone rubber nearly a million times softer than aluminum—somewhere between the softness of a silicone spatula and a human calf muscle, according Mazzeo.

The motors were produced using 3D-printed molds and soft lithography. The team has filed a provisional patent for this design. Soft lithography is used specifically for structures on the micro- to nanoscale and is referred to as “soft” because of the materials it uses, including elastomers such as PDMS (polydimethylsiloxane, an organosilicon).

According to Mazzeo, the soft motors represent the culmination of a number of recent innovations, including providing torque without bending. Other innovations from Mazzeo’s team include:   

  • A unique wheel-and-axle configuration that is not found in nature
  • Wheels that use peristalsis (wave-like contractions that move food through digestive systems)
  • 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 needing extra power

“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,” said Xiangyu Gong, a doctoral student at Rensselaer Polytechnic Institute who collaborated on the research while at Rutgers. “For us, the whole design is very simple, but it works very well because the whole body is soft and can negotiate complex terrain.”

Applications for the soft motors include:

  • Amphibious vehicles that can travel across rugged lakebeds
  • Search-and-rescue missions in extreme environments and varied terrains
  • Shock-absorbing vehicles that could be used as landers equipped with parachutes
  • Manipulating objects during magnetic resonance imaging

“We think these robots also would be useful for working around children or animals, and you could envision them being helpful in hospitals,” said Mazzeo. “There are opportunities also for toys and for creating educational science or engineering kits.”

For more on soft robotics, meet the 3D-printed autonomous Octobot.