Projects:2019s1-142 The Ball Bearing Motor Mystery

Supervisors

• Prof Derek Abbott
• Dr Andrew Allison

Honours students

• Jayden Hayward
• Richard Saing

General project description

The ball bearing motor is a mystery because to this day as no engineer knows how it works! No one understands the physical principle at all. Your job is to do some experiments to investigate this motor and why it is that it rotates. Understanding the principle is important. It may not be useful for large motors, but it may be interesting for micromotors and micropumps that have numerous applications.

Abstract

Based on the Huber Effect, the ball bearing motor can be made to continuously rotate in either direction when supplied with either a DC or AC supply. This phenomenon was first observed in 1959 and has since motivated a number of theories to explain the underlying principles behind the motor's operation. This projects aims to test the validity of some of these theories by taking a modular approach to testing the ball bearing motor. An attempt to evaluate the electromagnetic behaviour is made with the use of the a simulation software called ANSYS Maxwell and the relationship between angular velocity and motor torque are also obtained by measuring a physical motor with the use of a load cell and tachometer. The completion of this project hopes to assist future research into the application of the ball bearing motor in micro electrical-mechanical systems whilst leading further research into the Huber Effect in the right direction.

Background

Ever since the Huber effect’s realization, many researchers have made hypothesis’ on how they believe the Huber effect works. Nevertheless, there has been no definite evidence to support any of these theories despite the diverse experiments, consequently the principle of the Huber effect remains unknown. The three main theories hypothesizing this effect are: the electromagnetic force effect, the thermal expansion effect and the electromechanical effect, all of which will be discussed here.

Electromagnetic force effect

The cause for the Huber effect that it uses the electromagnetic force effect, was first proposed in 1977 by Gruenberg - an electrical engineer in Canada. He states that inside each ball bearing there exists an initial current density, J0 with its corresponding magnetic field, B0. When the balls rotate with angular velocity ω, then a new current density, J1 will be generated due to the motion displacement that occurred in the initial magnetic field, B0. A new magnetic field B1 is produced as a byproduct of J1. As the ball continuously rotates then so does the process continuously repeats. The interchanges of between J0 and B1, and J1 and B0 is what causes a torque to occur. One remark is that the initial current density, J0 and the initial magnetic field, B0, is not sufficient to produce a starting torque, meaning that the motor is not capable of self-starting. A torque can only be produced once the motor is manually given a spin [2].

In the ball’s initial state without any external forces, the zero-order fields around the ball: J0 and B0 take shape as shown in part (a) of Figure 3. Once exposed to an external force causing the ball to spin, the fields around the ball in the bearing to take shape as shown in part (b) of Figure 3. Notice how the current density is now shifted to go along the “Y” axis and the magnetic field is shifted to go in the “Z” axis. This orientation of the fields is believed to be the cause of the continuous ball rotation. Through detailed analysis, Gruenberg concluded the relationships between torque, current and angular velocity was a squared one [2].

Figure 1: Current and magnetic field distribution of each ball in the ball bearing for zero and first order fields. Ref [2]

Thermal expansion effect

Thermal expansion is the increase in volume of a material as temperature is increased, typically expressed as fractional change in volume per unit temperature. Marinov hypothesized that the Ball Bearing Motor is a thermal engine, where it is able to produce motion from electricity without the use of magnetism. He states that the torque (or the main cause of the rotation) is from the thermal expansion of the balls in their bearings. That the contact points between the ball bearing and the races is where it heats up the most, causing the ball bearings to physically expand, yielding a small “bulge” at that point. Noting that not the whole ball becomes heated but only contact points of the ball as shown in Figure 4 with red dots. At these points is where the ohmic (junction between two conductors with linear current) resistance is much greater than the resistance across the entire ball [3].

Figure 2: Contacts of a ball with inner and outer races

This is where there ball dilates slightly, and since both the balls and races are made of firm steel; a slight dilation of the ball will create large torque. The motor will then rotate in the direction of provided initial torque. The motor undergoes its rotational movement through the repetitive heating of the ball bearing contacts with its electrical contact with the races. During the rotation, the ball’s “bulge” moves from one position to the next and the radius of the “bulge” becomes equal to the radius of the ball. This radius becomes bigger and bigger with more torque produced, resulting in a mechanical motion. There is not enough evidence to support Marinov’s theory, however the fact that the ball bearings become significantly hot and deteriorate, give reason to not neglect such a theory.

Electromechanical effect

In 1973, the physicist, Polivanov, proposed that Electromechanical was cause of this Huber effect. That the discharge takes place at the contact points between the ball bearings and the races, producing a force sufficient enough to sustain rotation. This force is produced by the applied voltage with an assert being that the current is prone to flow in the opposite direction to the applied voltage. The interactions between the current and the magnetic field causes a disturbance to the symmetry of the current and flux confined by previous contact points. As the points of contact are being continually established through rotation, the force is sustained [4].

In Figure 3, when the ball starts spinning, the old contact point shown in the green circle of part (b) is no longer the contact point. This in turn emerges a new current distribution without neglecting the old distribution, therefore the symmetry is disturbed. Hence the ball will continue to rotate from the momentum of the event of plasma discharge.

Figure 3: (a) Cross-section of current distribution in a stationary ball. (b) Cross-section of new current distribution when the ball is rotated

Specific Tasks

• Step 1: Film the construction and operation of the motor.
  • https://www.youtube.com/watch?v=P-OtHLq0KVU
• Step 2: Use Ansys Maxwell to simulate the motor to see if you can investigate what happens in simulation.
  • Refer to Figure 8 in the 'Results' section
• Step 3: Characterize the motor. Using an encoding wheel and a tachometer, plot curves of torque versus angular velocity of the motor.
  • Refer to Figure X in the 'Results' section

Design

Previous works have shown that the ball bearing motor exhibited several self destructive behaviours when subjected to high currents. This has historically limited the measurements of the ball bearing motor as heating of the metal components expands and seizes the ball bearing races. One way to minimise these self destructive effects is with the utilisation of a liquid metal that submerges solid disks. This metal liquid will act as a slip ring that allow for current to be supplied to a solid disk. Not only will this method limit the heating of the ball bearing races but will allow for the Huber Effect to be investigated when the electricity is not being applied to a rotating but stationary component. The liquid metal will also act as a fluid heat sink to minimise the heating and expanding of the metal disks.

Liquid Metal

Gallium is chosen for this experiment due to its relatively low melting point (30 degrees Celsius) and its non-toxic behaviour which allows it to be safely handled. It is highly corrosive to other metals, however, it has also been proven to be an effective cooling agent with low viscosity making it very adequate for this project.

Galinstan, an alloy consisting or gallium, indium and tin, was also considered due the similar properties it shares with pure gallium. It was, however, dismissed due to its high cost when compared to gallium.

Solid Disks and Rods

A list of materials including; tungsten,copper,aluminium and stainless steel were tested against gallium to see which would be best suited for the manufacturing of the solid disks. Copper and aluminium showed obvious corrosion when placed in liquid gallium for 30 minutes. Whilst copper exhibited clear signs of becoming brittle, the aluminium rod that was tested completely snapped in half. Tungsten and stainless steel on the other hand showed little to no corrosion at all. Ultimately the solid disks were made out of stainless steel due to its relatively low cost and availability but the rods were made out of tungsten.

YouTube video showing how tungsten, copper and aluminium reacts with gallium: https://www.youtube.com/watch?v=nglK-_yMVz4

Figure 4: Metals one hour after being submerged in gallium

Measurement Method

To measure the torque of the motor, the shaft of the motor will be fitted with a peg like structure that will push against a load cell when the motor is operated. The peg (also referred to as the torque arm) were designed in Ansys Spaceclaim and 3D printed using polylactic acid (PLA). The load cell is a small steel bar with strain gauges attached onto its sides. When the load cell is bent, the strain gauges elongate causing its electrical resistance to change. This change in resistance causes a change in voltage which is amplified and measured using an amplifier and an Arduino board respectively. The Speed of the motor will be measured using a tachometer. To increase the accuracy of the tachometer, an encoding wheel also designed in Ansys Spaceclaim and printed using PLA. The encoding wheel is fitted onto the shaft and the tachometer is pointed directly at it.

Figure 5: Setup of gallium experiment

Figure 6: Tachometer's laser lined up with encoder wheel

Figure 7: Torque arm pressing against load cell

Results

Simulations

Ansys Maxwell was used to simulate a simplified, stationary ball bearing motor. Results show similarities to electromechanical behaviour described by Polivanov. Figure 8 shows that the current density at the point of conduction is at its highest and decreases as it moves closer to the center of the disc.

Figure 8: Magnetic field and current density behaviours. Left - Magnetic field around rail, Middle - Current density in solid disc, Right - Current behaviour described by Polivanov [4]

Experiment 1

Ball bearings outside metal discs

The setup is shown in Figure 4 was connected to a welder. An image of the welder is shown in Figure 9. It was hypothesised that applying a current through a solid disc would induce the same effect as if it was applied to a ball bearing. The discs were made of steel as it was one of the least affected metals with gallium. After applying current through the gallium and giving the shaft an initial torque did not cause the discs to continue spinning.

Figure 9: Welder

Ball bearings between metal discs

The ball bearings were moved in between the two solid discs and containers of gallium as shown in Figure 10. Applying the current through the gallium and giving the shaft an initial torque did not cause the discs to continue spinning. One important remark to take away from this is that the current needs to flow through the ball bearings for it to work, it simply can pass past the bearings.

Figure 10: Setup of the Gallium experiment with the ball bearings on the inside

Experiment 2

Regular Ball Bearing Motor

The welder was connected up to the ball bearing motor shown in Figure 11 and set to 58.5A. The welder was then turned on and the shaft was given an initial torque, the shaft then rotated at high speeds. The torque values and rpm values were recorded as described in method section. Both these sets of values were then plotted against time as well as against each other. This was repeated for the currents: 60A, 60.9A and 62.8A.

| width = 160
| image1 = Torque vs. Time of the ball bearing motor with respect to current.PNG
| alt1 = Torque vs. Time of the ball bearing motor with respect to current
| image2 = Angular Velocity vs. Time of the ball bearing motor with respect to current.PNG
| alt2 = Angular Velocity vs. Time of the ball bearing motor with respect to current
| footer = Relationships between torque, angular velocity, current and time

References and useful resources

[1] J.M.K.C. Donev et al.. Energy Education - Electromagnetic force, 2018 [Online]. Available: https://energyeducation.ca/encyclopedia/Electromagnetic_force.

[2] H. Gruenberg et al, "The ball bearing as a motor," Am. J. Physics, 46, pp. 1213-1219, 1973.

[3] S. Marinov, "The intriguing ball-bearing motor," Electronics & Wireless World, April 1989

[4] K. M. Polivanov, A. V. Netushil and N. V. Tatarinova, "Electromechanical effect of Huber," Elektrichestvo, No. 8, pp. 72-6, 1973.

[5] Integza (2019). DIY Torquemeter - How to measure torque! [Arduino & 3D Printed]. [video] Available at: https://www.youtube.com/watch?v=NIpspXaPVcs [Accessed 1 Jul. 2019].