Ball bearing motor

Producing significant torque typically requires so much power that the bearings are heated to several hundred degrees.

[1] In 1965 Electronics and Power magazine published a letter by RH Barker asking for an explanation of how this type of motor worked.

[2] 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.

[4] However, H. Gruenberg has given a thorough theoretical explanation based on pure electromagnetism (and neglecting the thermal effects completely).

[5] 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.