Ground

Carbon brushes carry +12 volts to and video from the rotating camera, but there are only two brushes. The observant reader will notice a missing conductor. Ground for the video camera power and signal returns through the bearing which supports the rotating camera axle.

Before this approach was proved feasible through testing, a ground system was devised patterned after a method used to get the signal from the spinning heads in VCR's. If a certain amount of force is applied to a large area, the pressure over that area is small. To get a good electrical connection in general between two pieces of metal, more pressure is better. So applying the same amount of force to a small area gives a cleaner connection. In the case of moving parts, the higher pressure also gives better "wiping action" to break through dirt and oxide in the connection area between the stationary and moving parts. Brushes always have a spring component to them, and in this case the brush is the spring. A section of 1/2" bandsaw blade was used because the steel from which these blades are manufactured is hard and springy. The steel is so hard, in fact, that the easiest way to cut out a length of it is to bend it in a tight enough radius that it simply breaks.

Bandsaw blade being squeezed in the vise, just before snapping in two

Removing the teeth

Breaking the blade in this way leaves a curled end, which was removed with the bench grinder. The teeth on the blade were also removed with the grinder. Repeatedly hitting metal with a hammer hardens it. Hitting metal with a ball shaped hammer causes the metal to curl up towards the ball. In this way the proper curve and stiffness were imparted to the grounding spring. At the end of it, my arm was pretty sore.

The grounding spring produces about 10 ounces of force when installed. To concentrate this force on a small area, the back end of the camera rotator axle was turned to a pointed taper on the lathe. Hardened metal cannot be drilled by conventional means, so the mounting hole was made with a grinding bit in a Dremel tool.

An insulated 16 gauge wire is soldered onto the grounding spring, and that wire is connected to the mounting plate which holds the stationary video and camera power connectors.

Initial testing showed this ground to give no improvement on the video quality. Ground through the bearing gave very good video quality, with no noise visible in the image with the camera either rotating or stationary. The grounding spring was left in the design however, and termed redundant, as insurance against future electrical noise which could develop in the bearing after wear.