Levitation static or dynamic



The levitation is defined as : "raising of a human body above ground without support and without material help" (). It is nearly antigravity (the weight of the object in levitation is not transfered to ground). Attending such a phenomenon could be very disquieting. In extending the definition to heavy material objects and redefining the condition "without material help" to "no support device" (which have a mass), a magnetic field that keep in position an object in suspension above the ground without any material between the ground and any point of the object put this object in levitation, the weight of the object is reported to ground. Thus an helicopter or a ball of tennis floating on a jet of water don't "levitate", the fluid that sustains them having mass. Nothing levitate alone in our planete and probably on many others.

Criteria for static levitation

In brief, for to produce a levitation experience well performed, amusing to contemplate, astonishing, one can agree on the following minimum criteria, all of equal importance:

[1] The object in levitation must appears heavy.
[2] The object in levitation must be totally motionless. (bolted in space)
[3] The object in levitation must be noiseless.
[4] The surface under (earth's plan) the levitating object must be flat.
[5] The space above the earth's plan and around object must be empty of any device.
[6] The levitation process must be discreet otherwise umperceptible.

Static magnetic levitation

The way to make levitation which is interesting for us, the well know process: the utilization of magnetic fields, precisely from permanent magnets in repulsive mode. Very simple in theory, but delicate in practice when we evaluate all of the criteria defined above, specifically the [4] [5] and [6]
Like everybody knows, if arrangements of permanent magnets permit to create repulsive forces, they don't permit self-stabilizing of the object in levitation (Earnshaw's theorem). To meet our criteria we must to define an adequate geometry which to comply with sustentation function and an analog servo controller for the stabilization function. The criteria #4 & #5 require to add electronic complements to these two basic functions.

Magnetic levitation in the way of...

In the way of... what it's can be done in the laboratories, in appearence of course. This system will put (by underneath) in stable levitation a magnetic object without sophisticated material at ambient temperature. With the addition of few volutes from cryogenic liquid, the illusion would be perfect.
The self stability isn't possible, but it is not prohibited to seek for a more favourable "geometry", this means a geometry witch the instability is more controllable. All geometries aren't self-stable but some are more or nearly... requiring less energy for object stability control and also how many escape axes and what kinds of trajectory involved ? for to meet the criteria [4], [5] and [6], six geometries have been studied, numbered from #1 to #6. The #5 & #6, have very different properties compared to the 4 others, the geometry #1 (pages "Photos" et "Tech's") is the original concept of the "Flyingmagnet".

Electronic and bases for stabilised magnetic levitation

These realizations require a minimum of skills in electronic and sheet metal or plastic work. it can be little bit difficult. Difficult or not, you can get the results defined by the criteria [1] to [6].

The tools and knowledge required:

  • tracing, drilling, cutting with enought accuracy (between ±½mm and ±1/10 mm) few aluminium parts of thickness between 1mm and 2 mm from a sketch and to assemble them;

  • to procure locally : aluminum or other none magnetic material sheet of 1.5 mm / 2mm thick : 220x100 mm minimum, angle (alu) 13x19 mm (1/2"x3/4"), nonmagnetic screws and hardware (3 mm, 4 mm, 4-40), (brass, inox), spacers, etc;

  • to procure locally electronic components (all components have been selected for the easiness to find them likewise their values have been unified as well as one can;

  • to assemble electronic components (good quality soldering iron 25 W, desoldering pump...).
  • to proceed to electronic adjustments (ruler, plastic and regular calliper, compass and magnetic compass, digital multimeter, trimming tool, etc.). To have access to an oscilloscope is a "plus" not only for troubleshooting but also for a better system understanding.
    To finalise the adjustments is the most funny part of this realization because it's the time "to levitate" finally...

Available elements for to help the achievements

  • Informations for electronic and bases plates sketches for geometries #1 & #6.

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Dynamic magnetic levitation

This is to levitate the moving objects.
What interest ?
The possible applications are more numerous, the experiments will bring new concepts.
We pass over the levitation of individual magnet or object built on a magnet but it draws for arrive to the ideas of "skates, mobile trays, vehicles, "maglev " (of modest sizes, we are not Alstom or Siemens). Before the criterion [2] was: "The object in levitation must be totally motionless" (bolted in space) we must now replace this by the criterion [12] and create few others.

But before, take a look to this exemple (sorry, for now, the videos are not very good): The idea of this setup is to experiment and make measures around the centrifugal and centripetal forces, orbitals movements simulation, etc.). In this experiment the centrifugal force, displaces, a mass along a pan tilted (without frictions) in order to observe the dynamic behaviors of this arrangement (ideal speed, in fonction of radius and slope angle etc.. Later, orbital movements around a central force (sphere).

Test jig for centrifugal force geometry levmag N° 5_6 (temporary), guidding mode: opto laser
View of the drive plate built from a hard drive,
Test jig (cont.)
View of stabilized levitation zone.
Video: clic the picture.
No friction evidence :
 Sliding contacts, drive plate & sensor/dial for speed measurement  Zero friction zone: 8-12.75 cm (r=9 à 11.5 cm)
Preview of the assembly in rotation
Video: clic the picture.
  • Plate driven by weak or strong friction (servo motor);
  • Retainer of the levitation system;
  • Optical reading of the speed control device;
  • Sliding contacts (2): power for levitation controller;
  • Sliding contacts (2): signal: variation of kinetic energy of the object observed.
  • Inclination angle fixed at 4°;
  • Optical reading, 360 pulses/turn;
  • Levitation Controlled in mode opto, (diode laser + servo controller + air coils);
  • Main rotating mass: 830 g, balanced around the axis of rotation;
  • Mass of the object observed (magnet): 37 g.
Rotation speed and other settings for the centrifugal force are measured and calculated by Scilab or Matlab scripts.

New criterias

[12] The objet in levitation must be able to move on a straight trajectory, keeping is longitudinal axis parallel to the direction of the displacement.
[13] The trajectory of the object in levitation must stay inside the imposed trajectory.
[14] The space above the ground plane (base, track ...) and around the object must be free of any device (except particularities).
[15] The object in levitation must have provisions for propulsion and braking (except particularities).
[16] The cost must be weakly dependent of the lenght of the track, in clear, we will not using: coils, sensors, expensive magnets; etc, all along the track.
[17] After getting correct results we will try to apply the criterias 13 to 16 but for curved trajectories and this is tricky.

The levitation VS wheels for mobile objects

Advantages and inconvenients : We can imagine the following points :
  • the equivalent of friction coefficient is almost zero : hight speed with low energy lost for the propulsion (and why not for low and medium speed);

  • without noise and vibrations;

  • natural primary suspension, no high frequency mechanical vibrations.
These features combined with the control of the ramps, allow easy use of gravity for move silently an objects.
Note that the wheel has not said its last word : World's speed record the 3 april 2007:TGV Alstom : 574.8 km/h

The difficulties:
  • guiding, particulary the curves if necessary;

  • managing the ramps;

  • braking and emergency braking (in a real full size maglev);

  • the supply in energy (at least for a scale model or a toy);
  • the weight of the auxillary wheels system (in a real full size maglev).
In the design of the model, it's necessary to make difference between an heavy and high power system (real full scale maglev) and experiments concerning few hundred grammes on few meters.
we can't have magnets for sustentation all along a Maglev track, but this not a problem for a system of small size, even for an utility application (carrier tray), over distances of a few meters.

The levmag© geometry

One geometry among several, based on ceramic magnets, seems to meet all criterias.
Derived from geo#5-6, but more complex for the track (base) and for the object in levitation (vehicle) wich is "actif", mainly for the control of the front and rear axles.
Like the demos of levitation of static magnetic objects on this site, the electric consumption used for the stabilisation is minimal also the losses by eddy's currents are very low. For this concept this point is very important. This geometry can be apply also to individual bogies, or magnetic skates, integrated to a "carrier tray".

Magnetic levitation in the way of ...

This time one will try to replicate one of experiments using superconductors material and liquid nitrogen like e.g. : the old demo of: the physic's department of Sherbrooke University (Qc)

First step: evaluation of the geometry levmag© #1.

Test jig for geometry: levmag #1.
Side view.of "véhicle".
Test jig (cont.)
Front and rear view of the "vehicle", in the direction of "the rails"..
 Train's geometry model under test  Train's geometry model under test
Control of the front and rear axles by 2 channels, 2 field coils.and 4 hall sensors. The levitation height with the test jig incorporates the weight of electronic and batteries.

Second step: new test jig self contained, nearest the real model imagined (autonomous).

Test jig self contained for geometry: levmag #1.
Side view of "véhicle", sizes: 115x63x46 (mm).
Test jig (cont.): side view of the "vehicle" in levitation on his track.
The real levitation height is around 10 mm.
Total weight: 445 g if alkaline bat. or 420 g if Lithium bat.
Weight of sustentation magnets (4):82 g, weight of coils (2): 85 g.
 Real magnetic levitation train model  Test of home levmag model
The two channels are powered by two batteries 9 V (18 V).
The long wire at the left hand is used for the "in-flight refueling",
(for adjustments & measurements).

2 PCB stacked, specially designed for the dimensions of this model, constitute the vehicle "frame". The power supply is based on 3 regulators RECOM R-7812 - 0.5 for to extract the maximum of the two batteries. The auto-balance and automatic shut-off are functions which also contribute to the longevity of the batteries.
The virtues of a friction coefficient almost equal to zero:
The track is in two parts, forming 2 opposing slopes ("V" very flat, about 176 °, 65 cm), this "V" deviates from the vertical position (ccw) so the distance travelled is longer on the left than on the right. (at the first cycle, starting from the right side)
Video (700 Ko - duration 40 s, .AVI - wmv9)
The duration of oscillations have not been measured, maybe the batteries could not sustain the power as long. It's possible that a very small part of energy of transversal guiding is transfered to the longitudinal movement. Using the "in flight refueling" wire, the damping of oscillations is visible but still much much lower than that of a "4 wheels".

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