  In many robotic systems, the holding state consumes power, limits operating
time, and increases operating costs. Electrostatic clutches have the potential
to improve robotic performance by generating holding torques with low power
consumption. A key limitation of electrostatic clutches has been their low
specific shear stresses which restrict generated holding torque, limiting many
applications. Here we show how combining the Johnsen-Rahbek (JR) effect with
the exponential tension scaling capstan effect can produce clutches with the
highest specific shear stress in the literature. Our system generated 31.3
N/cm^2 sheer stress and a total holding torque of 7.1 Nm while consuming only
2.5 mW/cm^2 at 500 V. We demonstrate a theoretical model of an electrostatic
adhesive capstan clutch and demonstrate how large angle (theta > 2pi) designs
increase efficiency over planar or small angle (theta < pi) clutch designs. We
also report the first unfilled polymeric material, polybenzimidazole (PBI), to
exhibit the JR-effect.
