When heated, popcorn can expand more than 10 times in size, change its viscosity by a factor of 10, and transition from regular to highly irregular granules with surprising force. These unique qualities can power inexpensive robotic devices that grip, expand, or change rigidity.
Simple robots are less prone to failure and wear; many can operate autonomously over a long period of time. Popcorn is inexpensive, readily available, and biodegradable. Since kernels can expand rapidly, exerting force and motion when heated, they could potentially power miniature jumping robots. Edible devices could be ingested for medical procedures. The mix of hard, unpopped granules and lighter popped corn could replace fluids in soft robots without the need for air pumps or compressors, which tend to be more expensive, and add weight and expense to a robot. With popcorn, only voltage needs to be applied to get the kernels to pop, so it would eliminate the bulky and expensive parts of the robots.
Since kernels can’t shrink once they’ve popped, a popcorn-powered mechanism can generally be used only once, though multiple uses are conceivable because popped kernels can dissolve in water. The researchers experimented with Amish Country Extra Small popcorn, which they chose because the brand did not use additives. The extra-small variety had the highest expansion ratio of those they tested.
After studying popcorn’s properties using different types of heating, the researchers constructed three simple robotic actuators — devices used to perform a function. For a jamming actuator, 36 kernels of popcorn heated with nichrome wire were used to stiffen a flexible silicone beam. For an elastomer actuator, they constructed a three-fingered soft gripper, whose silicone fingers were stuffed with popcorn heated by nichrome wire. When the kernels popped, the expansion exerted pressure against the outer walls of the fingers, causing them to curl. For an origami actuator, they folded recycled Newman’s Own organic popcorn bags into origami bellows folds, filled them with kernels, and microwaved them. The expansion of the kernels was strong enough to support the weight of a nine-pound kettlebell.