How real electric motors work

John Storey

The ball-bearing motor: an explanation

How can a DC motor with no windings, magnets, commutators, or tricky electronics work? Over the years, folk have tried to explain this motor by invoking strange new interpretations of Maxwell’s equations, or by creating tortured descriptions of magnetic fields that are generated by a current-carrying conductor and then somehow end up doing what no other magnetic field ever does. Other folk have related the phenomenon to Energies Unknown To Science, and hypothesised that this might be a way of tapping into unlimited free energy. Some of these explanations have even been published in reputable journals, before being soundly demolished in even more reputable journals.

In fact the explanation appears to be very simple, if a bit bizarre. Think hot balls. The current through the ball bearings (100 amps or more, for the motor in the photograph) is enough to heat them up. The current is flowing radially through each ball, causing preferential heating along the axis of the ball perpendicular to the shaft. The ball therefore momentarily expands into an ellipsoidal shape. If the shaft is already rotating, this expansion can occur along an axis that is fractionally after the pure perpendicular, giving a little “push” to the shaft as it does so.

Following this up on the WWW is a good rainy-day project, but don’t believe everything you read!