A team from Harvard University, inspired by arthropod insects and spiders, has created a type of semi-soft robot made from drinking straws, which is able to stand and walk.
George Whitesides, a Professor at Harvard, was interested in the agility of insects and spiders.
"They can move rapidly, climb on various items, and are able to do things that large, hard robots can’t do because of their weight and form factor," he explained.
"They are among the most versatile organisms on the planet. The question was, how can we build something like that?"
He worked with Alex Nemiroski, a former postdoctoral fellow in his lab, to engineer robotic parts that could mimic nature.
"This all started with an observation that George made, that polypropylene tubes have an excellent strength-to-weight ratio. That opened the door to creating something that has more structural support than purely soft robots have," he said.
The researchers then took inspiration from arthropods to figure out how to make a joint and how to use the tubes as an exoskeleton.
This resulted in a simple joint, made by cutting a notch in the straws, which allowed them to bend. The scientists then inserted short lengths of tubing which, when inflated, would force the joints to extend. A rubber tendon attached on either side would then cause the joint to retract when the tubing deflated.
Using this simple joint system, the scientists built a one-legged robot capable of crawling, and moved up in complexity as they added a second and then a third leg, allowing the robot to stand on its own.
As the robot got more complex, they revisited the original joint and made modifications so it could exert more force or be able to support the weight of larger robots.
Eventually, they started making six- or eight-legged arthrobots, and making them walk became a challenge.
"We looked at the way ants and spiders sequence the motion of their limbs and then tried to figure out whether aspects of these motions were applicable to what we were doing or whether we’d need to develop our own type of walking tailored to these specific types of joints," Nemiroski said.
While simpler robots could be controlled manually using syringes, as the designs became more complex, the scientists put together a microcontroller run by Arduino that uses valves and a central compressor. They were able to replicate the gait that ants use, but found it harder to duplicate a spider's gait.
This is because spiders have the ability to modulate the speed at which it extends and contracts its joints to carefully time which limbs are moving forward or backward at any moment. But because the inflation and deflation of the tubing is binary, this level of control was not possible for the simple joint system.
Developing a system that can fine-tune the speed of actuation of the legs, Nemiroski said, would be a useful goal for future research, and would require programmable control over the flow rate supplied to each joint.
Other possible improvements include replacing the drinking straws with components made from a lightweight structural polymer that is able to hold a substantial weight.