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|Aspect of the base (geometry #1) integrating the servo controller printed circuit board (optical or hall mode)||Test jig multi-geometries, from 1 to 8 field coils, 1 to 2 servo controller pcb (optical or hall mode):|
|What is hidden inside the Hammond box (photos page)||Aspect of the test jig configured for geometry #2a (optical mode), 4 field coils and 1 servo controller pcb|
|Making a Geometry #1 by using 3 identical brass tubes. The 3 tubes contain the same magnets sizes. those 2 tubes are mounted on one plexiglass plate.
"hall" mode: possibility to meet the criterias #4, #5 & #6, no difficulties for the alignement of magnets.
|Test jig for Geometry #5 connected to a 3 channels board.|
|Can be hidden inside a box.the material of the top of the box can be aluminium, brass, copper or any plastic.
Special attention must be done in case of using copper or thick aluminum (Contact).
|Levitation stabilized in "hall" mode, differential or not.|
More details on this configuration [.pdf]
|Test jig aspect, configured for geometry #2a (optical mode), 8 field coils and 2 servo controller pcb:
"the big luxury", this configuration permits more longitudinal and transversal stability, means more resistance to draught, shock, etc. (the system is inoperative against your cat !)
Note: we can imagine the floating object as the mobile part of an linear motor extremely sensitive, unloaded, practically without any energy loss (no friction) and sollicitated by longitudinal, transversal and vertical forces which are absolutely not linear...
|Basic constituents of an electrical servomechanism model:
a geared reversible motor which the high torque output side drive in synchronism, the mechanical load and one potentiometer generating the angular position information.
after everything has been connected to the servo controller printed circuit board, under voltage and motionless, supposing that the potentiometer body are free to rotate under a negligible torque. If we make a rotation in any direction of this body, for example: 12 degrees, immediatly
|>>> the "high torque output" rotates by 12 degrees and return at stability state. Note that not only the angular position is transmitted to the load but also the angular speed of the request (inside the limits of the system characteristics). That's, we get nearly a mini electrical power steering. From this model, a lot of realizations are possible for an amateur.
Note: from more than two centuries, physicists, mathematicians, mechanical / electrical / electronics engineers and many others have imagined, elabored, defined, put in mathematical form and built many type of servomechanism, regulation system and servo control of all kind and of all size, the relating literature is abundant.
Utilization of servomechanism board "in the way of ..."
Direct reading of white letter on compass card (for example: the first vertical line of letter [N]orth) of a car accessory compass, and transfom weak torque in usable hight torque reproducing the magnet compass headings in the way of... a gyrocompass (read the position of gyrosphere containing the gyros and transfer the heading value outside for mechanical purposes, ex. synchro-transmitter).Note: the board configuration is exactly same as for levitation purposes.
|Demonstration model ("opto" mode)
see the additional shield around the motor and note the plastic gear box.
|Watch the dynamic behaved of this (curious looking) assembly, for practical demo the white disk as been synchronized at 187° of North instead of 0°.
Compass at 187° (white disk mark), ship heading at 152° (rotating plate mark, 187°-35°)
|After plate rotation: |
compass at 187° (white disk mark), ship heading at 222° (rotating plate mark, 187°+35°).
A video 79 Ko - 10 s duration (.AVI - wmv9) can be viewed by clicking on one of the 2 pictures.
... or tracking the Sun, or even of the Moon
Study of a Sun position sensors very simple: We retain the gimbal described in the page "Something else", we add a servomotor on each axis freedom, these motors are connected to the output of 2 servo controller boards, we mount on the gimbal "elevation" the light sensors, each connected at the input of the corresponding servo board.
Both axes are equipped with a dial angle for measuring the azimuth and the elevation of the Sun, in addition, a magnetic compass is added on the top of azimuth gimbal for calibration help.
|Aspect mounting demonstration
1. The frame oriented to the sun in a clear sky (morning)
2. The frame oriented SW with cloudy sky (afternoon)
If the sky becomes uniform, the system just stops in minimum power consumption (fly over the picture)
The motor of azimuth (vertical axis) and the motor of elevation (horizontal axis) are used in mode "axis fixed, stator mobile".
The first use of gimbal "elevation" is the mounting of a solar panel (evidently more large), it includes the both sensors "azimuth" and "elevation".
object of the experiment: The purpose of the experiment was to evaluate several optical sensors of different types, their arrangements and the servo board input type to be used, to make a solar position sensor (or light source sensor) very simple.
There is really to much UV ! Never look at the sun with the naked eye or through any optical device: risk of irreversible damage to the eyes (blindness) (fly over the picture)
At the left hand of the "elevation" gimbal the sensors "elevation"
at the bottom in the center of this gimbal the sensor "azimuth".
For tracking the sun the photoresistances mounted "in bridge" seem very effective, one oriented toward the past, the other toward the future, so as not to face the sun in normal operation, the signal of unbalance of the values of brightness initiates the mechanical negative feedback of the servomotors, bringing back the bridges at state balanced.
For clear sky this state is the position of the sun at this time, if the sky is cloudy, the panel is pointed to the most luminous zone (average), which is always better than no orientation at all ...
The best and simple arrangement seems to be: two phototransistors with hemispheric lens under the control of one photoresistance for luminosity correction.
Note: The calibration has been done with the help of the freeware Helio V3.2, donwloaded from the site: www.petermeadows.com
If one don't like the electronic, one can try some green solution ...
Relays: R coil>400 Ohms
if unclear drawing: contacts NO 4-5 (extremity), NC 6-3, COM 2-7
Example of hand wired interface board (60 x 100)
Both terminals 3 points at hand left and at hand right are not part of description
at the top:
- terminal 2 points: input external power source
under it: the bridge B1 (capacitors C1 & C2 are not installed).
- terminal 3 points: servo output to motor
at the bottom:
- terminal 3 points: positioning signal input from servo control board and above that, between relays K1 & K2: J5-J6 then J7-J8
- Diodes D1 & D2 are wired on soldering side.
Running mode choices:|
Servomotor drived in normal analog mode (interface board connected but not in function):
- J5 & J6: closed;
- J7 & J8: open;
- no external power supply source on J1.
Servmotor powered on external source during the approach course, then switched to analog mode near the final balance position:
- J5 & J6: closed;
- J7 & J8: closed;
- one adequat power supply source to J1.
Approximate positioning one bit only:
- J5 & J6: open;
- J7 & J8: closed.
- one adequat power supply source to J1.
Servo control board, before ±12V regulation;
External, independent or not, regulated or not ±12V nominal, the using of the onboard regulated 12V is possible but not advantageous: only the output stages avoid the extra power losses. Excepting special cases, the best is to apply to J1 the same servo board main AC supply source
External, independent or not, in 10-15 Vca range. (C1 & C2 values selected accordingly). The first logic choice is to use the servo board AC supply (13VCA, 800 mA).
Particular useful case: during the adjustments period of a new delicate or fragile system, this interface board used in mode #2, with the external power source adjustable from zero volt, is very effective against excessive mechanical reactivities.
Details & generalities
|Suggestion for to assemble the hall sensor for the first tests:
A1302 with devices for connecting and positioning. In flyingmagnet, the hall sensor mode is only a step for get accustomed with the system (criteria ,  are not met), aesthetic aspect has not be take in count, but if we want use this more intensively it can be judicious to embed it, in tiny plastic box by means of epoxy.
This can be use as mechanical stop in right side during the adjusment of optical sensor (it's good also to add temporary a mechanical stop at the left of optical sensor...), the mounting spacer, the screw and nut must be none magnetic, 2 pieces, back to back of prototyping board glass/epoxy, grid 0.1" and 2 three points headers.
If we choice definitively the "hall" mode instead of the "opto" mode the positionning of the hall sensor will be different.
Page PHOTOS1, geometries #1, 2, 3 & 5.
|At left: The flyingmagnet in geometry #2. Two identical tubes as than used for geometry #1, ("Photos" page) and mechanically linked give the base of a platform. The rolling stability in #1 is not directly controlled but established by the assembly particularities (magnets bonding, unbalance, parallax, off-centre magnetics poles, etc.) giving a final erratic roll free. In geometry #2 this problem is fixed by principle, indirectly the performance are improved.
At right: the derived geometry permits the examples named flying carpet and skateboard
page PHOTOS1, geometry #2.
|Test jig aspect, configured for geometry #3 (optical mode):
2 times 2 pairs of field coils, each two pairs at 90° of the other, 4 pairs of lift magnets, 2 optical sensors and 2 servo controller boards. This setup is equivalent to 2 basic flyingmagnet (geometry #1) linked at their middle and at 90°.
|Disc platform for #3 (cross) or #4 (3 legs stars or triangle) geometries.
To note: the 4 permanent magnets positionned on each quadrant for geometry #3, the external rectangular windows at 120° allow the disc to be configured for #4 geometry.
The others windows are for to lighten or for to read the disc position.
|Suggestion for to assemble the reflective sensor with connection and positioning device. A hole will be drilled in the horizontal part of guide and an other in the base for to secure the sensor after the correct position has been found (one inox metal screw).
To note: the separate IR bias diode allows the sensor sensitivity linearizing in fonction of ambient light.
|Reading of magnetic compass in "opto" mode by reflection:
through the liquid, (reading of white letter on black background is easy) all hardware must be absolutely none magnetic material (also the gear box in plastic material) and the permanent magnets motor must be shielded by external casing, reclosing also the top end around the output shaft, at this state the motor assembly become only a passive error factor (corrigible).
|Test jig for geometry #5 (mode hall)||If we can put the elements in a "star" we can certainly put them into a "delta".|
|Coils setup looking like a "star"
6 coils for fields correction, 6 ceramics permanent magnets ajustable in height (sustentation and static attitude control), in the center: the optional coil for elevation, under control or not, and 3 hall sensors (differential mode) mounted on a plexiglass disc, adjustable by rotation around his axis.
More details (.pdf)
|Coils setup looking like a "delta"
Idem as the precedent setup but with only 3 coils for fields correction. It uses the same sensors assembly as the star setup but with different behaviours for the couple sensors/coils.
This setup permits to get a maximum of performances in cost, stability and heigth of levitation.
Vidéo 75 Ko, 10 s duration (.AVI - wmv9).
back to PHOTOS2
|Test jig geometry #5-6, "hall" mode, "induction" mode or "opto" mode (laser)||Handy accsessory for to tune the mode hall (any geometries)|
|Domain closing, attitude control and longitudinal trim (weak) of the object.
Two square barrels of ceramic (10x10x48 mm) magnetized transversaly, located at each extremity of the jig, ajustable in height and in angle ensuring the closing of the domain. The vertical adjustment of the barrels controls the horizontal positionning and their rotation the attitude of the floating object.
Other type of floating object: (fly over the picture)
Test jig for geometries #5-6, positioning by induction
From the bottom to the top of the flying object we find:
1 ) induction coil
2 ) floating magnet
3 ) 2 batteries 3 Volts stacked
4 ) oscillator circuit (50 kHz)
|Handy tool for tuning in hall mode.
In some geometries, the relative location of the elements [hall sensors - field coils - magnet in levitation] requests to compensate the effect of the negative feedback introduced by the stabilization field surrounding the hall's signal. This is the case for the geometry #5-6a (except the 3 coils in delta base). In this one, the hall's sensor is strongly coupled with the field coils, reducing drastically the loop's gain, consequently the stabilization becomes weak or impossible.
(for each channel involved, one in the case of the first configuration).
Assemble on a piece of rigid material :
– one auxillary field coil connected to the servo controller output;
– one mobile hall sensor, positionned in the field coil, the signal of this sensor will be added (+) to the others "hall" signals at the summation point of the servo board. (to connect the coil adequatly).
If everything is in working condition, it's probable that the magnet in levitation will start to go in vibrating mode: reduce the coupling with the hall sensor until the vibration stops, inversly, if the magnet in levitation is under a weak control reduce the distance between the sensor and the core.
Move the hall sensor for to get the strongest stabilization without any trend to the "vibrating mode" - Keep a safety margin.
At the end of the tuning process we can replace this external temporary setup by a hall sensor directly coupled to the core of one of the field coil.
Opto mode (laser) : A chip laser pointer modified (keychain) used as transmitter and one opto sensor OPB704 used as receiver, positioned at each extremity, connected adequately to the servo board are enougth. (the criteria , ,  can't be meet).
Mode "induction":The positioning by induction permits to control the object on any kind of trajectories, straight or curved, the concept is totally reversible:
- either the floating object contains the inductor, the whole "sensor/guiding" is located in the base (left picture)
- either the inductor is located in the base and the system "sensor/guiding" is located in the floating object (maglev toys for example). this permits also to avoid the coupling between the sensors "hall" and the field coils as it's happens in mode "hall".
back to PHOTOS2
|Test jig for geometry #6 : view of peripheral and central sensors (mode hall).||Test jig for geometry #6 without peripheral sensors|
| 2 configurations "hall" have been tested (not really usable):
a - static positioning setup
12 field coils, 24 hall sensors & 3 servo controller boards (1 master et 2 slaves).
b - dynamic positioning setup
12 field coils, 2 hall sensors, 4 servo controller boards and 1 small geared servo motor (for tracking the levitated magnet).
Configuration without sensor "hall":
Positioning by induction (like in geometries #5, #6), 12 field coils, there is several possibilities for servo controller like for the configuration: a -.
Notes : The 3 setups allow the moving or the positioning of the levitated magnet at any place on the circle materialized by the 12 field coils, the 3 sensors at the center are not used in those setups.
This geometry requests imperatively accuracy for: sizes, angular positions, centers geometric, uniformity of magnets and the coils , etc.
Setup of the geometry #6 for platform or geometry #5
Levitation of a platform by means of internal and external magnets crown, the control of the stability is done by means of the magnet located at the center of the platform.
geometry #5: At the center of geometry #6 we find a geometry #5 (magnets crown, field coils).
Notes : (fly over the picture)
In both cases the control of stability is done by means of the 3 sensors "hall" located at the center of the test jig (differential mode).
We can find the principle of the control of stability by looking the colors dots on the coils and those between the sensors (the dots between each sensors indicate the signal differential corresponding to the set of coils of the same color.
back to PHOTOS2
Another example of positioning by the mode "induction" (geometry #5).
This principle, plus a special implantation of the coils fields allows with the identical coils to increase significantly the levitation altitude.
(It is not the case in this example not optimised, makes for practical reasons at the center of the test jig geometry #6 totally inapropriate.)
from the bottom to the top of the flying object, we found:
1 ) Induction coil mounted around the magnet
2 ) two stacked batteries 3 V (6 V)
3 ) oscillator circuit (50 kHz)
The reading head is linked to the servo board by means, in this case, of 2 interfacing circuits.