Magnetic Levitation Anamoly Needs Your Explanation
Magnetic Levitation Anamoly Needs Your Explanation
(OP)
I have a short video of a magnetic levitator I built and am trying to explain a curious effect.
www.youtube.com/watch?v=fWRJL3Nbb-0
Notice the washer oscillating side to side without touching anything? Can someone please explain what this can be attributed to?
Theory 1. Flux density: If the return path for the flux is biased in one direction (i.e., through the
back of the visible setup), then the washer tends to rotate so as to minimize
the path length in air.
Theory 2. Irregularities in the surface of the washer cause the sensors to see it in different spots, causing it to oscillate like a limit cycle.
Theory 3. Video is faked. Change career to film editor immediately. :)
Thanks,
Nathan
Short explanation of operation:
When a current passes through a wire, a small magnetic field is generated. When that wire is coiled around a ferromagnetic core, a very strong magnetic field is created. This magnetic field provides the lifting force to cause ferric metal objects (e.g. a steel ball) to rise towards the electromagnet. The IR diode and IR phototransistor measure the location of the ball. With the essential phase lead circuitry, a control signal is generated that drives a power transistor. The power transistor turns on or off the electromagnet. The timing of when to turn off or on the electromagnet causes the ball to rise and fall so fast as to appear to be levitating. Just before the ball is outside the controlling distance of the electromagnet, the current is sent through the coil and the ball is pulled back up.
www.youtube.com/watch?v=fWRJL3Nbb-0
Notice the washer oscillating side to side without touching anything? Can someone please explain what this can be attributed to?
Theory 1. Flux density: If the return path for the flux is biased in one direction (i.e., through the
back of the visible setup), then the washer tends to rotate so as to minimize
the path length in air.
Theory 2. Irregularities in the surface of the washer cause the sensors to see it in different spots, causing it to oscillate like a limit cycle.
Theory 3. Video is faked. Change career to film editor immediately. :)
Thanks,
Nathan
Short explanation of operation:
When a current passes through a wire, a small magnetic field is generated. When that wire is coiled around a ferromagnetic core, a very strong magnetic field is created. This magnetic field provides the lifting force to cause ferric metal objects (e.g. a steel ball) to rise towards the electromagnet. The IR diode and IR phototransistor measure the location of the ball. With the essential phase lead circuitry, a control signal is generated that drives a power transistor. The power transistor turns on or off the electromagnet. The timing of when to turn off or on the electromagnet causes the ball to rise and fall so fast as to appear to be levitating. Just before the ball is outside the controlling distance of the electromagnet, the current is sent through the coil and the ball is pulled back up.





RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
You should be using a ball bearing to avoid this type of behavior.
TTFN
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RE: Magnetic Levitation Anamoly Needs Your Explanation
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Magnetic Levitation Anamoly Needs Your Explanation
To test the theory you could attached a light piece of tissue to the washer to try to increase the air damping effect. If the oscillations get less with time the point is made. If you can estimate the mid-point of the oscillation, you could try starting it at this position, ie giving it less of a moment in the first place.
I’m not buying IRstuff’s theory because the sense circuit/feedback is vertical and does not apply any sort of torque to the system.
RE: Magnetic Levitation Anamoly Needs Your Explanation
Putting it simply: Align the coil (probably move it forward a tiny bit) so that its axis exactly passes through the axis of the optical sensor.
The torque arises quite naturally from the offset combined with the shape of the washer.
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
The video shows the hanging end of the paper clip being drawn upward.
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
Since this was published in the September Design News you should expect a flurry of responses from both of the other readers.
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
I love the theories, but start with the simple causes before going complex. Here are the possible keys to the motion explanation, that was much more obvious when the light receiver was a half inch wide.
1. The suspended object is going to start being moved by the slightest breeze or magnetic influence since it is a nearly friction free mounting.
2. The shadow cast by the suspended object varies as it rotates. If your light receiving area was wider you would see the washer visibly rise and fall.
3. Every time it reaches a certain angle where the shadow starts to obscure the receiver differently, you will see a change in coil current. When the shadow gets "larger" the washer would get a bump of extra pull to keep it from "falling". This causes an imperceptable rise in height and potential energy. The washer willingly drops back down this energy hill and changes direction.
4. Try a hemispherical plastic cover over the washer (1/2 a ping pong ball if IR opaque) and you can separate the optical from the magnetic influence.
Let me know how far wrong I am.
Thanks for the memories.
RE: Magnetic Levitation Anamoly Needs Your Explanation
But where’s Nathan now? Has he learned anything about this in the last three months or is he content to collect his five hundred dollars and move on?
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
at the ruben h. fleet space theather science center in san diego, one of the displays is a large pendulum. the pendulum is a large brass ball at the end of about about a 4 meter filament. this pendulum will, over the course of several hours, precess around a circular pattern on the floor while swinging back and forth (forming a large flower petal pattern). the reason given for this complex motion is the earth's rotation. the rotation imparts a side-force that is higher on one side of the weight than the other, thus causing the precession motion about an inscribed circle.
the washer in question is suspended in the magmetic field, freeing it from the forces of gravity, but not those of the earth's rotation. with the earth's motion imparting vertical plane forces on sides of the washer, it begins to rotate about the vertical axis. however, the washer soon encounters weak magnetic flux line differential forces from the suspension system (probably due to the imperfections in the construction of the electromagnet and the presense of the optical sensors interfering with the lines of flux). these weak flux line forces overcome the earth's imparted rotational forces, swinging the washer back the other way. this equalibrium process is repeated at the other end of the vertical axis rotation, and the oscillation is sustained.
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation
RE: Magnetic Levitation Anamoly Needs Your Explanation