The designer of the beefed-up bowling pin, Felsen´s first opponent, sits across a table from me in the hotel ballroom and grips my hand in an arm-wrestling posture. Mohsen Shahinpoor runs the Artificial Muscle Research Institute at the University of New Mexico and directs research at Environmental Robots. In a technical talk that day, he had shown videos of his devices in action. In one, a human skeleton pedaled a bicycle, powered by strips of artificial muscle.
Shahinpoor tightens his grip and tells me to push. As I start to win, he pushes back forcefully. His robot arm is programmed similarly: to add power when it starts losing. A sensor measures the angle between the arm and the table and increases voltage as needed.
Shahinpoor´s IPMCs consist of two metal-foil electrodes sandwiching a wet, Teflon-like plastic soaked with lithium ions. Just 12 volts—the equivalent of a car battery—cause the lithium ions, which are positively charged, to migrate toward the negatively charged foil layer, bulking up that side of the actuator and bending the IPMC. IPMCs are safer than dielectric elastomers because they use low voltages, and they´re stiffer, which enables them to exert more force per actuator. But they´re more sluggish because they´re triggered by bulky ions, not speedy electrons.
Environmental Robots spent $24,000 to develop the arm (more if you count Shahinpoor´s time). He tells me that he limited the machine´s voltage and force; he´s more concerned about demonstrating its potential, and about the human contestant´s safety, than about winning. When we finish talking, he heads to the event. Soon Felsen is pushing against his ´bot as a bemused crowd of about 150 looks on. She is using her arm, not her whole body, and she´s struggling.“Push harder!” exhorts the arm-wrestling champ. Twenty-six seconds into the match, she pins the robot arm. She flashes a big smile as the audience applauds. Now there are two teams left.