Solid copper commutation brushes for seawater use

Brush commutating linear motors are being investigated for underwater launching. Two key problems must be addressed before a brush system can be designed. These are: the life of the system and the operation of the brushes while submerged in seawater. The life of the current collector system depends on the type of commutation. Most DC commutating collector systems rely on arc to commutate the current. Arcing causes collector erosion. The erosion can limit the life of the system. Corrosion, biofouling, and brush lifting are three issues that must be considered when operating in seawater. In a recently completed program, we investigated the feasibility of using fingerlike, solid brushes for current commutation in seawater. We found that copper brushes have an acceptable corrosion rate and resist biofouling, and hydrodynamic and electromagnetic lifting forces are small compared to the required contact force. In this paper we present the key issues in using solid brush commutation in seawater and present the results of our tests and analysis.