LEARNING TO CRAWL: Origami Robot Moves Like an Earthworm

A team of engineers at the University of Illinois at Urbana-Champaign built a new kind of crawler robot. The wheel-less design takes inspiration from two unconventional sources: origami and the earthworm. Assistant professors Aimy Wissa and Sameh Tawfick, along with a team of graduate and undergraduate students, used “Kresling” paper-folding principles to create buildingblock actuators (Figure 1).

The Kresling origami structure — a chiral tower with a polygonal base — couples its expansion and contraction to longitudinal and rotational motion, much like the turning of an ordinary screw. The University of Illinois robotic design utilizes a skeleton made from the buckling origami tower. A servomotor rotates the origami blocks, initiating expansion and contraction from the turning motion. The robot then takes on the gait of a crawling earthworm.

The university researchers hope to someday integrate the paper design into small, scalable, and cheap robots as well as deployable adaptive structures. According to the researchers, “the ability to produce a functional and geometrically complex 3D mechanical system from a flat sheet introduces exciting opportunities in the field of robotics for remote, autonomously deployable systems or low-cost integrated locomotion.”

Motion Design spoke with Assistant Professor Aimy Wissa.

Motion Design:

How does your robot move?

Prof. Aimy Wissa: The robot uses origami building blocks. You can think of them as actuators, or mechanisms that convert rotation inputs into motion. We have a servomotor that turns the internal origami building blocks, and that gets translated into longitudinal extension and contraction to move forward. The idea is similar to a screw.

Motion Design:

How are the robots powered and controlled?

Wissa: Perri, the larger robot, is powered using a lithium polymer (LiPo) battery that is mounted on the robot. The battery powers a servomotor, which turns the base of the origami tower. The robot is controlled with an Arduino board, also mounted on the robot. Thus, the robot is untethered, with all its power source and controls onboard.

Poly is a much smaller robot, about a quarter of the size of Peri (Figure 2). Peri is powered using an external power source and is also controlled using an Arduino board; however, the control board is not mounted on the robot. Unlike Peri, Poly is tethered. Part of our current work is to create a control architecture so that the robots are autonomous.

Motion Design:

How are the robots like an earthworm?

Wissa: The robot mimics the gait of earthworms, or peristalsis. Peristalsis is the motion strategy that earthworms use where contraction in the circular muscles leads to forward motion. This is mimicked in our robot because circular motion and rotational input at the base of the origami tower lead to expansion or contraction in the longitudinal direction, which causes the forward motion.

We’ve also mimicked the function of the setae, which are the little bristles on the bodies of earthworms. Inspired by those setae, we designed directional feet, enabling the robot to move forward, but not slide backward.

Motion Design:

What led you to use origami folding principles?

Wissa: Professor Sameh Tawfick walked into my office and he had a Kresling tower of origami. He said, “Look at this! You can think of it as a screw or a ‘mini’ actuator.” I looked at him and thought, “We can really design a great crawl robot using this.” An origami tower uses buckling instabilities, so very little rotational input gives you a large longitudinal jump, or contraction.

Motion Design:

How do these buckling instabilities appear in the robot?

Wissa: The buckling instability that we are exploiting in our design is a structural property that allows a small input to lead to a large and fast output, referred to as a snap. The snap-through buckling occurs when the energy input to the system is enough to move the structure through an unstable equilibrium and into a stable equilibrium. The origami cells that make up the internal Kresling towers in the robots are bi-stable, meaning they have two equilibria and can snap from one equilibrium to the other with small variation in the input, which is the rotation angle at the base of the origami cell.

Motion Design:

What applications are possible because of this design?

Wissa: Because the body is deformable — and the origami is made from paper and is soft — we can really go into tight spaces. So, we can use this for pipe inspection, for example. Pipes have different kinds of diameters, and you want something that can fit in there with ease.

Because of the repetitive folds of origami, we can build metameric structures — structures of any segments, in series, and they all have the same function. So, now you can move as one single unit, or you can break into smaller segments, do multiple tasks, and then meet again. If you want to survey a large piece of land, for example, you can collect data separately, and at the end, you can gather all those robots into one.

Motion Design:

How does your robot compare to conventional wheeled robots?

Wissa: Wheeled robots are great. But when you go on uneven terrain, legs are better. I can envision launching this robot after an earthquake, or where there’s rubble or uneven terrain. The robot’s feet can grab onto different surfaces and move forward.

Motion Design:

What’s next regarding the development of the technology?

Wissa: We want to expand the modes of locomotion. We can go forward, and we can turn left and right. We want to explore other modes of locomotion: rolling or jumping.

Motion Design:

Are there durability concerns with a material like paper?

Wissa: Paper is a suitable material for origami structures because it can sustain folds without compromising its structural integrity away from the folds. The strength and durability away from the folds is a result of the fibers that were pressed together to produce the paper. That being said, we will continue to explore different materials to expand the application possibilities for these robots.

The robotics project was originally a collaboration between two labs at the University of Illinois — the Bioinspired Adaptive Morphology Lab (led by Wissa) and the Kinetic Materials Lab (led by Tawfick). The project is now expanding to include a third lab (Alleyne Research Group) to enable a more sophisticated and autonomous controls strategy. Learn more about the origami-inspired crawler robot at mechanical.illinois.edu.

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