A ball bearing motor or ball-race motor consists simply of a small ball- bearing assembly with provision for passing current radially between inner and outer tracks to produce circular motion.
Explanation
A ball bearing motor is an unusual
electric motor
An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
that consists of two
ball-bearing
A ball bearing is a type of rolling-element bearing that uses ball (bearing), balls to maintain the separation between the bearing (mechanical), bearing race (bearing), races.
The purpose of a ball bearing is to reduce rotational friction and ...
-type bearings, with the inner races mounted on a common conductive shaft, and the outer races connected to a high current, low voltage
power supply
A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...
. An alternative construction fits the outer races inside a metal tube, while the inner races are mounted on a shaft with a non-conductive section (e.g. two sleeves on an insulating rod). This method has the advantage that the tube will act as a
flywheel
A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...
. The motor rarely starts without assistance, having effectively zero static torque, but once rotation begins the motor will accelerate until it reaches a steady speed, the direction of rotation is determined by the initial spin. Although ball bearing motors can reach reasonably high speeds they are very inefficient. Producing significant torque typically requires so much power that the bearings are heated to several hundred degrees.
Theory
In 1965 Electronics and Power magazine published a letter by RH Barker asking for an explanation of how this type of motor worked. At the time various explanations had been offered.
S. Marinov suggests that the device produces motion from electricity without magnetism being involved, operating purely by the resistance heating causing an asymmetric thermal expansion of the balls in the bearings as they rotate.
The same explanation is given by Watson, Patel and Sedcole for rotating cylinders (instead of balls).
However, H. Gruenberg has given a thorough theoretical explanation based on pure electromagnetism (and neglecting the thermal effects completely).
Also, P. Hatzikonstantinou and P. G. Moyssides claim to have found an excellent agreement between the results from the electromagnetic theory and the experiments measuring the total power and efficiency of the motor.
See also
*
Homopolar generator
A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and th ...
*
Homopolar motor
A homopolar motor is a direct current electric motor with two magnetic poles, the conductors of which always cut unidirectional lines of magnetic flux by rotating a conductor around a fixed axis so that the conductor is at right angles to a s ...
*
Faraday paradox
The Faraday paradox or Faraday's paradox is any experiment in which Michael Faraday's law of electromagnetic induction appears to predict an incorrect result. The paradoxes fall into two classes:
* Faraday's law appears to predict that there wi ...
References
External links
The Ball-Bearing electric motormotor torque calculation
{{Electric motor
Electric motors
Rolling-element bearings