Chapter 1. Introduction

Certainly one of the finest books ever written for amateur scientists was A. D. Moore's Electrostatics, recently reprinted by Laplacian Press, This book should be considered a prerequisite to the current text. What you are holding is simply a construction manual. You should consult Moore's book for explanations of the principles of electrostatics. That said, I have tried to make the instructions thorough enough to be followed by someone without access to that excellent text.

Moore introduced to the world a variety of influence machine which he dubbed a Dirod, the name stemming from the combination of a disk with rods. He described two kinds of Dirods, the first having rods perpendicular to the disk, and the second, radial Dirod having rods parallel to the disk face like the spokes of a wheel.

I must confess I have become hooked on Dirods. Static electricity generators tend to be at the mercy of atmospheric humidity, but the Dirod is amazingly robust, both mechanically and electrically. While Moore gives instructions for the construction of four Dirod models, it is fun to tinker with the design, trying to get the most out of each system. For myself, I was interested in a design along the following lines:

I have made one major departure from Moore's radial design by mounting my disk horizontally rather than vertically. This design provides a little table for adding accessories like capacitors and motors. Wires and connectors are a potential source of corona loss and the horizontal design minimizes the distances to be covered from generator to accessory.

Models #6 was an extremely satisfying and reliable design. Dirod #7 is really nothing more than a big #6 with slight modifications to the inductors and collectors, and 48 rather than 36 rods. Because #7's inductors and collectors are farther apart, it's ultimate voltage, and hence spark length, is approximately double that of #6. Model #8 returns to the footprint of #6, but because its collectors are farther apart it has very nearly the spark length of #7.

For all of my Dirods connections are made to the Dirod using 1/2-inch copper tubing, which drastically cuts corona losses compared to smaller diameter conductors. I am making #8 available primarily as a kit of pre-cut parts, though some may wish to buy the instructions alone and cut their own parts. Most of the raw materials are easy to get at any hardware store. My rods are cut from aluminum welding rod, the acrylic parts from 1/8-inch stock, the conductors are 1/2-inch copper tubing with plumbing fittings to fit. The belt is a sewing machine belt, and the neutral connection is cut from HVAC duct tape. If you cut your own parts, the dimensions will depend on those parts. However, as a rough guide, #6 uses a 6-inch disk, 36 2.5-inch rods, and a 12-inch square base and corona shield. #7 uses a 10-inch disk, 48 3-inch rods, and a 16-inch square base and corona shield. Model #8 uses an 11.5-inch disk, 36 2-inch foil "rods" and a 12-inch square base.

The most important material needed for Dirod construction is the brush material. This material must be thin, flexible, durable, and electrically conductive. I have experimented with a variety of materials, but the best so far has come from a kind of anti-static bag used to ship electronic circuit boards. My brushes have a resistance of about 25K ohms/inch. Feel free to experiment with different brush materials. If you find a better one, please let me know.

I hope you have as much fun with your Dirod as I have had designing it. Happy Sparking!