[Mike Betts]

Mclaren,

A few of your statements are either misleading or you have reached the wrong conclusions.

Four Basic Principles describe how magnetic fields are used in electromechanical devices:

1. A current-carrying wire produces a magnetic field in the area around it.
2. A time-changing magnetic field induces a voltage in a coil of wire if it passes through that coil (basis of transformer action).
3. A current-carrying wire in the presence of a magnetic field has a force induced on it (basis of motor action).
4. A moving wire in the presence of a magnetic field has a voltage induced in it (basis of generator action).

Items (3) and (4) are particularly important to DC motors and item (4) defines “back-EMF”.

The magnetic field between the rotor and stator does the work. Any spark on the commutation brushes is lost power (voltage times current), does not contribute to the magnetic field and does no useful work.

In fact, the brush losses are the main motivation for the “DC Brushless Motor” that has permanent magnets in the rotor and electrically commutated windings in the stator. The trade off is cost versus efficiency. Since the expense of most of our FIRST motors is of top concern, we usually use permanent magnet DC brushed motors.

Last item: Almost all AC motors have no brushes. The rotor currents are induced by a rotating magnetic field created by the stator windings.

Now that I have been critical, let me praise you and all of the students who are posting here for getting out, doing research and piecing together "The Puzzle”.