In these pages, I have discussed using my Dirod #8 to drive electrostatic motors. Can we understand how Dirod and the motors work? Perhaps we should first summarize qualitatively some aspects of static electricity.
Static electricity exists because there are two types of charge, which we call negative and positive. Examples of negative charges are free electrons and negative ions. The latter consist of atoms or molecules which have picked up an extra electron and remain stable for least a short time. Protons and positive ions are examples of positive charges. A positive ion is an atom or molecule which has lost an electron and remains stable for at least a short time.
There is a force of attraction between negative and postive charges, and a force of repulsion between charges of like sign (positive or negative). These forces play a fundamental role in understanding how the motors work. Like the force of gravity, the electrostatic forces vary inversely as the square of the distance separating the charges. Strong forces exist when charges are close together, and rapidly weaken as the distance increases. This ability of charges to influence one another at a distance is is described as the electric field, in analogy to the gravitational field.
Materials can roughly be catagorized as insulators or conductors. Insulators, such as the Styrene or plastic sheets covering the outside of a motor's rotor, have the interesting property that charges may be induced on them. An example is rubbing a length of plastic pipe with a cloth. Since the insulators are do not conduct electricity, the induced charge remains in a fixed position on the body. Furthermore, the induced charges are of opposite sign to the charges that have set up the field. Thus the body with the induced charges is attracted to the body which induced the charges. In this way, we understand why the moving beer can stator in our motor was attracted to the rotor, after we started Dirod.
Conductors are metallic materials which contain free electrons. When a conductor is placed in an electric field, the free electrons migrate to the surface of the conductor. Since the electrons tend to repell each other, they distribute themselves over the entire surface of the conductor.