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.

1. Electromagnetic force effect

An electromagnetic force, also known as the Lorentz force expounds the idea of how both stationary and moving charged particles interact with one another via electric and magnetic forces. As an electric current produces a magnetic field, the reverse is also true: an electric current can be generated through a changing pattern of magnetism [4]. The latter point is the reason why we have electricity. For example, if a coil of wire is placed inside a magnetic field and the wire is spinned around to fluctuate the magnetic field, then electricity will flow through the wire. Figure 2 illustrates this.

Specific Tasks

• Step 1: Film the construction and operation of the motor.
• Step 2: Use Ansys Maxwell to simulate the motor to see if you can investigate what happens in simulation.
• Step 3: Characterize the motor. Using an encoding wheel and a tachometer, plot curves of torque versus angular velocity of the motor.

Method

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 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 component. The liquid metal will also act as a fluid heat sink to minimise degrading 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

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

References and useful resources

• Method to measure torque
  • https://www.youtube.com/watch?v=NIpspXaPVcs

Figures

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  Figure 1: Gallium experiment setup

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  Figure 2: Ball bearing motor experiment setup

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  Figure 3: Tachometer's laser lined up with encoder wheel. Left - encoder wheel with 0 rpm, Right - encoder wheel with 1951 rpm

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  Figure 4: Torque arm pressing against load cell

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  Figure 5 - Part 1: Arduino torque code

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  Figure 5 - Part 2: Arduino torque code

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  Figure 6: Magnet passsing through coil of wire on Ansys Maxwell

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  Figure 7: Simulated current behaviour of Faraday’s Needle

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  Figure 8: Physical setup of the Faraday’s Needle experiment

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  Figure 9: Magnet being pushed through coil of copper wire

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  Figure 10: Graph of the multimeter’s current readings vs. time

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  Figure 11: Metals one hour after being submerged in gallium

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  Figure 12: Gallium after one hour of being in contact with the corresponding metals

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  Figure 13: Setup of the Gallium experiment with the ball bearings on the inside

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  Figure 14: Torque vs. Time of the ball bearing motor with respect to current

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  Figure 15: Angular Velocity vs. Time of the ball bearing motor with respect to current

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  Figure 16: Torque vs. Angular Velocity of the ball bearing motor with respect to current