Projects:2019s1-142 The Ball Bearing Motor Mystery
Contents
Supervisors
Honours students
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 were as follows:
- T=ki2 (1)
- i2=(k0/k)+(k1/k)=a+b (2) [2]
From substituting equation (2) into (1), implies that torque is directly proportional to the square of angular velocity - suggesting a squared relationship between the two.
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
Results
Conclusion
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.
- Method to measure torque
Figures
Figure 1: Gallium experiment setup
Figure 2: Ball bearing motor experiment setup
Figure 3: Tachometer's laser lined up with encoder wheel. Left - encoder wheel with 0 rpm, Right - encoder wheel with 1951 rpm
Figure 4: Torque arm pressing against load cell
Figure 5 - Part 1: Arduino torque code
Figure 5 - Part 2: Arduino torque code
Figure 6: Magnet passsing through coil of wire on Ansys Maxwell
Figure 7: Simulated current behaviour of Faraday’s Needle
Figure 8: Physical setup of the Faraday’s Needle experiment
Figure 9: Magnet being pushed through coil of copper wire
Figure 10: Graph of the multimeter’s current readings vs. time
Figure 11: Metals one hour after being submerged in gallium
Figure 12: Gallium after one hour of being in contact with the corresponding metals
Figure 13: Setup of the Gallium experiment with the ball bearings on the inside
Figure 14: Torque vs. Time of the ball bearing motor with respect to current
Figure 15: Angular Velocity vs. Time of the ball bearing motor with respect to current
Figure 16: Torque vs. Angular Velocity of the ball bearing motor with respect to current
Current and magnetic field distribution of each ball in the ball bearing for zero and first order fields. Ref [x]
