How Fast Can a Robotic Drummer Beat Using Dielectric Elastomer Actuators?

Fast drumming presents a speed challenge to many robotic arms. To meet the simultaneous needs for speed, stroke, and force, we proposed and tested a new double-saddle dielectric elastomer actuator (DEA) as the artificial biceps for driving a lightweight robotic drummer. This work finds that fast force induction is instrumental to the fast drumming by a DEA-supported drumstick that makes a pivoted forearm. While a large pre-stretch and lateral reinforcement in a pure- shear series of DEA was good for generating a large isotonic stroke, it is not fast in isometric force induction. Instead, this work found a double-saddle DEA, which is a degenerated two- segment pure-shear DEA with a middle laterally buckled beam, managed to induce fast isometric force at down time constant of 0.5s when its ultimate actuation tapered due to substantial strain stiffening effect. As such, this double-saddle DEA-driven drummer suffered a less dynamic stroke decrement than the 8-segment DEA did. A 4.4-gram DEA managed to swing freely a 7.8-gram drumstick up to nearly 60 degrees at 5.5-6kV and a maximum tip speed of up to 0.45m/s. The drumming frequency upon 5.5kV activation was up to 2-2.5Hz. In comparison, an 8-segment pure-shear DEA-driven drummer fail to reach the drum when pulsed at 2Hz. Interestingly, a slower stroke can excite multiple drumbeats due to secondary bounces. To achieve a faster drumming to match human drummer, it is foreseen that a harder dielectric elastomer material will help drive a faster soft robot.