Hybrid Armature Design Based on Compliance Matching with C Armatures

Abstract

The most common metal armatures used in an Electro-Magnetic Launcher (EML) are the C-armatures and the multi-fiber brush armatures. A brush armature has a shorter current path and thus has a less ohmic loss. Nevertheless, brush armatures lack compressive stiffness to provide mechanical contact forces at the current ramp-up and ramp-down periods. Also, by construction, brush armatures lack the mechanical strength to accept extreme mechanical loads during operation. This article presents a hybrid armature design that incorporates qualities of both C-armature and brush armature projectile technologies. The design starts with a monolithic solid block armature to provide a short current path. Compliant mechanism design methods are then applied to provide mechanical compliance at the contact surface equal to a C-armature. The resulting hybrid armature provides mechanical pressure for current conduction when electromagnetic (EM) forces are insufficient, but the current path inside the armature is also minimum to reduce Ohmic loss. Plots are provided that compares contact pressure distribution, contact surface current density, muzzle velocity, and efficiency of the hybrid armature and a C-armature. The resulting hybrid armature has 33% less parasitic mass that delivers 22% higher kinetic energy to the payload.