Engineering
Designing Soft Robots That Squeeze Through Tight Spaces
Quick fact
Soft robots made of silicone rubber can squeeze through openings only 10% of their normal cross-sectional area by using pneumatic pressure to drastically change their shape—a capability no rigid robot can match.
Why this is interesting
Imagine a robot that can flatten itself like a pancake to crawl under a door, then reinflate and keep moving. How do engineers make a machine that squeezes through gaps smaller than its own body?
Read the full explanation
Understanding Designing Soft Robots That Squeeze Through Tight Spaces
Traditional robots are built with rigid bones and joints, so their size is fixed. Soft robots, by contrast, are made from compliant materials like silicone rubber that can stretch and compress. To squirm through a narrow gap, the robot relies on three design pillars: materials, actuation, and morphology. The material must be soft enough to deform elastically without breaking. Actuation provides the force to change shape—often by pumping air into internal chambers (pneumatics) or pulling tendons. Morphology means the robot's body shape is deliberately designed to create anisotropic deformation, so it can elongate to squeeze through a tight space and then shorten or expand to anchor itself. For example, an inchworm-inspired robot uses alternating expansions and contractions along its body, allowing it to move like a worm while its cross-section shrinks. The same principles let a robot slip through rubble in search-and-rescue or navigate inside the human body for surgery.
A deeper explanation
The key mechanism is controlled compliance. The robot's body is a continuous elastic structure. When an external constraint (like a narrow gap) applies pressure, the robot's compliant material deforms to match the gap's shape, reducing contact forces. This is different from a rigid robot, which would jam. The ability to change shape comes from actuators that create internal stress, causing the body to bulge, contract, or elongate. Pneumatic actuators work by increasing air pressure in internal chambers: if the chamber is surrounded by a stiffer layer on one side, the softer side expands, bending the robot. Coordinating these actuators in a sequence—e.g., contracting the tail, extending the head, then anchoring the head and pulling the tail—allows locomotion. The material's elasticity ensures that after the robot passes the constriction, it can recover its original shape. Designers also optimize the robot's cross-section: a circular cross-section deforms uniformly, but an ellipsoidal one can flatten more easily under vertical compression. This is why many squeezing robots have a flattened or 'soft' shape that naturally conforms to gaps. The governing principle is that the energy supplied by actuators is used to overcome the resistance of the environment, and the compliant body distributes stresses to avoid damage. This capability is uniquely enabled by soft materials, which have a lower Young's modulus (stiffness) compared to metals or rigid plastics, allowing large strains without failure. Understanding this mechanism is crucial for designing robots that can navigate cluttered or tight environments, and for predicting their behavior before building them.