It is not my intention to present a complete description of the principles governing the operation of the Dirod. Moore's Electrostatics does a more than adequate job in this regard. But a brief analysis is in order as it will aid in the proper construction of the kit. First, it is important to note that any sharp metal surfaces will suffer corona losses which will limit the ultimate voltage and current produced by your Dirod. While metal edges can't be eliminated entirely, Dirod #6 makes every effort to round all metal edges. Whereas Dirod #5 used 1/4 inch copper tubing, Dirod #6 uses 1/2 inch tubing and suffers much lower losses than the previous model. Copper fittings add modestly to the cost, but provide for much lower corona losses than if the tubing had been cut or bent. In all of your considerations in building and using your Dirod, remember round metal components are better than sharp ones.
The Dirod conductors can be divided into 3 zones, each insulated from the others. The zones are separated from each other and from the disk by a square foot of acrylic, the corona shield. Without this shield, electrical current would flow more freely between the zones and the voltage produced would be limited.
Two of the zones lie above the corona shield, each consisting of a collector and an inductor. The collector makes contact with the rods via a brush that extends through the corona shield. Let's follow a rod as the disk spins. As each rod passes beneath the collector, it finds itself in a Faraday cage and gives up that charge to the collector. Let us suppose the front collector is negative. As a rod leaves the collector and approaches the inductor, electrons in the rod are repelled by the negative inductor.
As each rod passes beneath the inductor, electrons leave it via a brush to the neutral connector, the third of our zones, lying beneath the corona shield. As the rod leaves the inductor, now carrying a positive charge, it passes beneath the opposite collector, giving up that charge to the (now positive) collector via its brush. Now passing beneath the positive inductor, electrons are attracted to the inductor. Where will they come from? From the rod on the other side of the disk which is simultaneously passing beneath the negative inductor. Connection is made via a brush on the neutral connector.
The rod leaves the inductor carrying a negative charge. When it reaches the negative collector, it delivers up that charge via the collector brush and we have completed our cycle. Which collector will be negative and which positive is a coin flip. In fact, each time a spark snaps, the collectors reverse polarity.