Strong yet backdrivable robots through capstan-amplified electroadhesive clutches

Dexterous manipulation in compact robots requires combining high force output with passive backdrivability; capabilities that conventional geared actuation struggles to deliver. We introduce an electromechanical multiplexing architecture that routes power from a single drive shaft to multiple outputs and mechanically grounds them using capstan-amplified electroadhesive (EA) clutches in a load-transfer configuration. Wrapping thin-film EA clutches on cylindrical counter-surfaces provides exponential gain for EA braking force, while voltage pulse-width modulation yields sub-newton (<0.1 N) force resolution and low reflected impedance from the drive shaft, enabling compliant interaction. Force transmission behavior is explained by a mechanics-based model of curved clutches and supported by strain imaging showing a propagating, load-carrying slip front. Switching measurements under bipolar high-voltage drive demonstrate millisecond-scale release and effective operation near 1 kHz, enabling high-rate force modulation. Leveraging this clutch-level understanding, we realized a well-behaved system: a tendon-driven, two-finger gripper that transitions between highly backdrivable, cooperative grasping and firm, energy-efficient holding. By decoupling pulling from latching, the load-transfer design mechanically grounds the output without sustained motor torque, outlining a scalable route to compact, low-power robotic hands that maintain backdrivability while spanning three orders of magnitude in force.