THEORY

According to Faraday's Law, if B is the flux density of a constant magnetic field and conductor is moved at this velocity V, and EMF is generated in the conductor such that:


E = B x V

If the conductor is part of a complete electrical circuit with a resistance R, then the EMF will produce a current in the conductor such that:
I = E/R = B x V/R

If a conductor of length L carrying a current I is placed into a magnetic field B, a magnetic force B is created such that:
F = BLI sin A

* where A is the angle between B and I, since the force F is perpendicular with both B and I

Obviously, to create an efficient DC motor, we need more than just a single current-carrying wire in a magnetic field. We also need to have a different structure that allows the motor to run continuously.

A viable motor consists of a coil in a static magnetic field of flux density B. The current is conducted through sliding contacts (commutator brushes) connected to the current source. The brushes ride on the ends of the coil wires, thus conducting current through the coil. Figure 2, 3, 4 and 5 illustrates the coil of the single-coil motor in a static magnetic field of flux density B at angular positions of 0 degrees, 90 degrees, 180 degrees, and 270 degrees.


At 0 degrees, the ends of the coils are contacting the "brushes", and current flows through the coil. The current will interact with the magnetic field B in the coil segment AB to generate a downward, force, as shown in the figure. The current I in coil segment CD will also interact with the magnetic field to create a upward force, F. The forces F generated by both coils are of the same magnitude but of opposite directions There are no force generated by the current in segment AC since the current is parallel with the magnetic field B.




The coil will rotate until it reaches the 90-degrees position, where ends of the brushes slide off the brush ends. Current will be cut off and no force will be generated by the coil. However, the inertia of the coil will keep it rotating in the forward direction, past the 90-degree position, and the brushes will again touch the other end of the other coils.



In the 180-degees position, current will again flow in the coil segments AB and CD, although now in opposite directions. The current flowing in coil segment AB will now generate an upward force, while the current in coil segment CD will produce a downward force. Again, there are no forces generated by coil segment AC since the current is parallel with the magnetic field B.




At the 270-degree position, again, no current flows in the coil, and the coil continues to rotate only due to its own inertia. Past the 270-degree position, the coil will return back to its original position, and will continue to rotate until the current source is turned off.






To increase its effectiveness, more coils are added to the motor, to increase the total force generated by the current in the coils, and create a continuous rotation.