Brush Mounting as a Factor of Satisfactory Operation

That the brush is an ever present source of trouble on rotating electrical machinery is evidenced by the back numbers of our technical periodicals which are replete with innumerable articles on the subject. These articles cover practically all problems of material and application excepting that of the geometrical design. It is this phase of the subject that the following paper attempts to give. Undoubtedly these factors of geometrical design are known as they are readily discovered, their relations are relatively simple, but so far as I have been able to find they have not been published. The facts brought out by the following paper are: First, that the upper angle of the brush is a function of the lower angle and the coefficient of friction between the brush and the commutator, second, that the lower angle is a function of the pressure desired against the holder, and third, that the trailing brush has little to justify its use. These three conclusions are based on a design which eliminates a resultant moment acting on the brush which would tend to make it bind in the holder.