Brushes

Two brushes help carry power to, and signal from the rotating video camera. The brushes used here are designed for use in motors like those in drills and other small power tools. This type of brush is made of graphite, and is variously called a carbon brush, graphite brush, motor brush, or just "brush". Brushes allow the flow of current between stationary and moving electrical components. Usually, the brush is stationary, and rubs against a rotating component called a slip-ring. In most motors that use brushes, the rotating surface is called a commutator. Two places where brushes are used which does not, strictly speaking, relate to motors, are rotating illuminated signs, and the spinning head in a VCR. In all cases, brushes address the problem of carrying current to parts of moving systems without wrapping wires around an axle (which would only be good for a couple of turns anyway).

There are many ways to implement a brush and slip ring mechanism. I started with a brush, a spring, and a length of square telescoping brass tubing which fit the brush exactly. After cutting the tubing to about 1-1/4", I used a Dremel to make a slit through which the brush lead passes. The spring is required to keep the brush pressed against the slip ring. The screw serves three purposes. It provides a backstop to keep the spring compressed. It provides an electrical connection point to attach a wire to the brush holder, and it serves the function of a registration pin to locate the brush holder in the insulating block. The holes through which the screw passes are threaded so that the screw can be tightened against the brass tubing.

To mount the brush holders in place and electrically insulate them from the frame, I cut a mounting block from Delrin (trademark Du Pont Chem.). Delrin is a strong, tough thermoplastic used in mechanical and electrical applications. Machining results in a smooth, accurate surface.

After getting the overall shape right, it was time to cut the grooves in the top and bottom blocks to clamp the brush holders in place, and then drill and countersink the hole for the screw which holds the pieces together.

After the pieces were assembled, a test fit was made on the mounting bracket, the brush holder was disassembled, final mounting holes were drilled, and the holder reassembled.

The brush holder is shown in final assembly on the slip rings page.