New fluidic engine runs muscle-mimicking soft robots without external power

A team of engineers has developed a featherlight fluidic engine to power soft robots in assistive devices.

The new engine’s standout feature is its capacity to produce substantial force autonomously without reliance on an external power source.

According to researchers at North Carolina State University, their engine works on a principle of fluid dynamics. The new engine functions by directing oil in and out of a chamber within a soft robot.

High-force fluid engine

Soft robots powered by fluid engines, like hydraulic or pneumatic systems, can mimic muscle behavior in ways that rigid robots cannot. This makes them highly appealing for assistive devices aimed at enhancing mobility in the upper and lower limbs.

However, traditional fluid engines are typically tethered to external power sources, such as large air compressors, which greatly restricts their versatility.

According to researchers, previous attempts at fluid engines not reliant on external power sources have struggled to generate sufficient force, further limiting their practical application.

“Our work here addresses both of those challenges. Our fluidic engine is not tethered to an external source but can still generate up to 580 Newtons of force,” said Hao Su, an associate professor of mechanical and aerospace engineering at the University and the study’s author, in a statement .

Researchers’ fluidic engine features a pump powered by a high-torque motor driven by a battery. The resulting pressure allows the artificial muscle to produce substantial force.

This solution uses a two-part design. First, a direct-drive system with a motor , gear pump, and hydraulic artificial muscle (HAM) creates a compact, lightweight valveless setup. Second, a fluidic engine with a high-torque motor and custom gear pump generates high pressure to drive the HAM, delivering strong forces.

During proof-of-concept testing, the researchers evaluated the novel engine’s force-generating capability and efficiency in converting electrical power to fluidic power.

Efficient soft robotics

Tests showed that compared to traditional designs tethered to stationary sources or limited in force, the new design achieves portability (3.5 pounds) and high-force capability (580 N), crucial for compact, lightweight, and human-scale force applications in community settings.

Experimental results show it generates up to 0.75 MPa pressure with 15 percent peak efficiency, driving a McKibben muscle with 580 N force and 21 percent contraction ratio.

The team claims that by combining hydraulic compliance with electric control, the approach offers high-power density, which is essential for weight reduction in assistive and aerospace devices.

“We found that we were able to generate an unprecedented amount of force for an untethered engine, while still keeping the weight of the fluidic engine low,” And the maximum efficiency of our fluidic engine is higher than previous portable, untethered engines,” said Antonio Di Lallo, a postdoctoral researcher at the University and the study’s first author.

Researchers say that future studies will explore controlling two soft actuators antagonistically, potentially mimicking artificial muscles. Proof-of-concept wearable devices demonstrate the system’s potential for untethered deployment in lower and upper limb assistance.

The details of the team’s research were published in the journal Advanced Intelligent Systems .