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Author Topic: Self accelerating reed switch magnet spinner.  (Read 289920 times)

conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #240 on: October 30, 2013, 08:56:36 PM »
@Conradelectro,

Quote from you:

"We will soon all eat the same gene manipulated and poisoned food out of gigantic factories".

Consider moving to Costa Rica; Pura vida!

There must be some very nice tropical areas in Puerto Rico and growing food should be easy with may be two harvests per year. Agriculture should still be more natural than in central Europe. The travel agencies call Costa Rica a tropical paradise and recommend hiking and trekking tours.
 
As an old man I would probably not support the climate very well and getting used to the situation there would require more strength and adaptability than I have left. Never uproot old people, they tend to die.
 
Greetings, Conrad

synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #241 on: October 30, 2013, 10:21:45 PM »
       "The small tropical nation of Costa Rica celebrated 65 years without a permanent standing army this past December, and now, they’re moving toward another important milestone: A legal framework for becoming a 100% GMO-free country".

conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #242 on: November 07, 2013, 10:35:22 PM »
I am still playing with the LM311 because more modern Comparators and OpAmps which I ordered did not arrive yet.

After learning about offset and hysteresis I changed the circuit and could reduce oscillations. But there still are are few ups and downs when the drive coil is switched off (see the attached scope shots).

After much testing I came to the conclusion that the back EMF spike of the drive coil causes these few remaining oscillations of the LM311 although I cut off the back EMF spike with a reverse LED. Just the presence of the drive coil in the circuit (between positive rail and collector of the internal transistor of the LM311) makes it prone to self oscillations.

It is a bad idea to switch the drive coil with the LM311 (a separate robust NPN transistor should be used) but I wanted to test offset (pins 5 and 6, BALANCE) and hysteresis (positive feedback) in a minimal circuit.

I also think that one should create an external offset between positive and negative input of the OpAmp (as TK is doing it in his TL082 circuit) instead of using an internal BALANCE, it gives more flexibility.

The 100 pF cap between positive and negative input of the LM311 is very necessary to stop oscillations when driving a coil (cap can be between 100 pF and 1 nF). Offset (BALANCE) has to be set in a position which keeps the internal transistor in the off state in case there is no signal from the trigger coil.

If I switch only a LED with a 2 K resistor (no drive coil, no reverse LED) as indicated in the circuit diagram I get absolute clean switching and the 100 pF cap can be removed. By help of BALANCE (offset) I can set whether the LED is on or off in case there is no signal from the trigger coil.

I hope this makes sense, for me it was an exercise in OpAmp circuit design.

Greetings, Conrad

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #243 on: November 13, 2013, 12:49:39 AM »
I'm amazed at the distance you are getting. The op-amp sense system can be made very sensitive, but the drive coil coupling to the magnet rotor is what is really amazing. That is some respectable distance there.

Meanwhile, here's another version of the same kind of circuit, using a Cd-S photoresistor and ambient light, to detect the shadow of "something"  ;) and trigger a high-current electromagnet. The 7809 voltage regulator keeps the op-amp sense circuit stable when the mosfet fires, and the "boost" power supply allows the electromagnet to use a much higher voltage than the sense/control circuit needs. The mosfet is a 55 volt, 110 amp part in a small TO-220 package. The mosfet runs cool, no heatsink seems necessary at the moment. The DC resistance of the electromagnet is about 29 Ohms, with wire scrounged from a TV deflection yoke ferrite wound around a u-shaped core of mild steel rod.

conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #244 on: November 17, 2013, 12:16:49 PM »
I'm amazed at the distance you are getting. The op-amp sense system can be made very sensitive, but the drive coil coupling to the magnet rotor is what is really amazing. That is some respectable distance there.

Meanwhile, here's another version of the same kind of circuit, using a Cd-S photoresistor and ambient light, to detect the shadow of "something"  ;) and trigger a high-current electromagnet. The 7809 voltage regulator keeps the op-amp sense circuit stable when the mosfet fires, and the "boost" power supply allows the electromagnet to use a much higher voltage than the sense/control circuit needs. The mosfet is a 55 volt, 110 amp part in a small TO-220 package. The mosfet runs cool, no heatsink seems necessary at the moment. The DC resistance of the electromagnet is about 29 Ohms, with wire scrounged from a TV deflection yoke ferrite wound around a u-shaped core of mild steel rod.

@TK:

I am still playing with OpAmps which open up some interesting "trigger" possibilities, as your latest circuit shows.

From the capacitors and the 7809 voltage regulator in your latest circuit I deduct that you have problems with self oscillations. What ever I try, there are self oscillations which have to be worked out carefully.

My latest idea is that a trigger coil has to be AC-coupled. At the moment I have little time, but I will post the circuit soon.

What interests me most is the very low power demand of the ring magnet spinner I show further up in this thread http://www.overunity.com/13852/self-accelerating-reed-switch-magnet-spinner/msg376292/#msg376292 .

The LM311 consumes about 7 mA at 10 Volt, which leaves only 3 mA for driving the ring magnet spinner at about 2000 rpm. I ordered the MAX931 comparator which should only consume 4 µA. Together with magnet bearings I should be able to get a very low power draw for a ring magnet spinner. The MAX931’s unique output stage continuously sources as much as 40mA which is enough to drive my spinner without any other component.

Once I achieve the very low power draw (I hope for less than a 1 mW) I want to try various ideas for recuperating some energy into a drive capacitor.

Greetings, Conrad

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #245 on: November 17, 2013, 05:38:19 PM »
At the very low frequency I use the circuit above for, I don't really get any bad behaviour with the TL082 opamp. (Less than 0.5 Hz). I just sprinkled in the decoupling caps as "good practice", the circuit works fine without them.

The 7809 regulator is there to provide a stable reference voltage for the comparator as the run batteries run down or are drawn down by the power-pulse when the mosfet turns on. Without this stable reference voltage the setpoint control would have to be adjusted as the battery voltage varies. But with the regulator, as long as the run battery voltage is over about 10 volts, the photodetection system voltage and the setpoint potentiometer voltage remain stable and don't need to be readjusted. A better system would be to use an actual reference voltage chip, and some op-amps provide a stable reference voltage at one of their pins, but the TL082 is the simplest op-amp and doesn't have any fancy features like that. The 7809 draws a little more current than a reference voltage chip, and adds to the overhead, but it's all I had on hand and works just fine for my purposes here.

conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #246 on: November 26, 2013, 08:37:29 PM »
Magnet bearings, a question:

Finally I found the time to build a ring magnet spinner (the diametrically magnetised "ring magnet = cylindrical magnet" in the middle of the axis will be spinning).

The bearings on both ends are "magnet bearings" built with axially magnetised ring magnets.

It was very difficult to adjust the magnet bearings. They work fine, but the axis snaps away easily from the glass. The axis is a threaded brass bar. The nuts on the axis are also brass. All other bolts ar aluminium.

I wonder how to build magnet bearings? In the attached drawing please find indicated how it is right now and how one might do it in a different way.

What is the right way of implementing magnet bearings?

Greetings, Conrad

synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #247 on: November 26, 2013, 09:36:19 PM »
@Conradelektro,


                         Both schematics are incorrect. All the magnets face the same direction! The bottom four magnets definitely have all the north poles facing the same way, as well as the two magnets on the shaft. Take special note of the shaft magnet facing the glass wall; It protrudes a little more from the base bearings then the rear one! The top schematic would work fine if you turned the shaft around and repositioned the magnets a little!


                       Here's video number 1 from K&J Magnetics for placement of the magnets on the shaft:


              http://www.youtube.com/watch?v=ROEISzWDMdw


                        Here's video number 2 for placement and orientation of of the four magnets on the base:


              http://www.youtube.com/watch?v=LApuHTAo6K4

               
                          Here's video number 3 to wrap it up:


               http://www.youtube.com/watch?v=tsHVrFlO2BI


Pseudo-Levitation: In the first part, we focus on how to setup the pseudo-levitating shaft.  


Two D68PC-RB magnets in an unstable configuration Repelling magnets are not stable.  If you put the same poles of two magnets facing each other (north facing north or south facing south), you will feel a repelling force between the magnets.  If you try floating one magnet over another magnet, it is not stable in that position.  The upper magnet won’t just float in place.  Magnetic forces act to rotate and flip the magnet around to attract and stick together.

But what if we use 2 magnets underneath the floating magnets?  Won’t that make it stable?  It stabilizes it in some directions, but not all.  In the series of diagrams shown below, two magnets are spaced at some distance apart from each other with the north pole facing “out of the page.”  You’re looking at the north poles of the magnets.

For a third magnet placed above these two, there can be a sort of pocket of stability.  A third magnet can sit in this pocket, and be stable in the left to right direction, in the plane of the magnets.  It is not stable “out of the page.”
It doesn’t stop the floating magnet from simply rotating around.  It also doesn’t prevent it from moving in and out of the page.  In an unconstrained setup like this, the floating magnet will tend to shoot forward or backward.
But what if I use more magnets underneath to block it?  Sorry, it won’t work.  This is true for any number of magnets you place beneath it.  A mathematician named Samuel Earnshaw proved that this instability is true for any number or combination of permanent magnets; see Earns
« Last Edit: November 27, 2013, 12:09:51 AM by synchro1 »

conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #248 on: November 27, 2013, 10:19:40 AM »
There seems to be a difference between using four support ring magnets on the outside (as shown in the videos indicated by synchro1) and using two support ring magnet on the inside (as I do).

I have to use repulsion in opposite directions, the repulsion towards the glass has to be a bit bigger.

The attached drawing shows how it works in my recent build (only one support ring magnet on each side and axis goes through the centre of the two support ring magnets). I tried many magnet orientations, but only the one in the drawing works.

I will also build a contraption like indicated in the videos (two support ring magnets on each side, axis above the four support ring magnets).

Greetings, Conrad

synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #249 on: November 27, 2013, 02:18:42 PM »
@Conradelektro,


         Is the rotor axle making contact anywhere inside the upright holes where it passes through them on each end? The important facet of the pseudo-levitating shaft is that it vectors all the inherent instability in one direction, and one direction only, to the pinpoint on the wall. Note again the stability width diagram below, where the pocket appears in the space between the ring magnets to the right. Your setup appears to have too narrow a spacing between these base magnets.

conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #250 on: November 27, 2013, 09:01:17 PM »
In the first version I do not have "base magnets", just a smaller ring magnet on the axis inside a bigger ring magnet on the acrylic support (concentric ring magnets). The ring magnets are of course not touching but the axis is pressing very hard against the glass.

Now I have built a version with two base magnets. This version works much better because the axis is only pressing very slightly against the glass. All ring magnets are facing in the same direction.

See the attached photo.

Bigger ring magnets and a heavier rotor (axis) seem to be better. The ring magnets I use are a bit weak and the 3 mm axis is too light.

One only learns by building something. I always thought that concentric ring magnets are better, but it seems that two base magnets are easier to build and work very well. When I spin the rotor by hand it keeps turning almost a minute.

Greetings, Conrad

synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #251 on: November 27, 2013, 11:44:40 PM »

@Conradelektro,


            I realized I was making a mistake after my last post. Take a look at how Lidmotor handles the wall end of his levitator in the video below. I'm glad you achieved a great success with your latest build, it looks sensational!  


http://www.youtube.com/watch?v=VhKG4LPh3EQ

synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #252 on: November 28, 2013, 08:58:04 PM »
@Conradelektro,


                        The elongated coupled double rings at the base and on the shaft look like a novel innovation to me. I've never seen a permanent magnet pseudo-levitator built that way before. Your unique design may be a vast improvement over the existing approaches. Looks like you accomplished at least double the stability over the simple ring version. Very nice! I really doubt Lidmotor's ball bearing and attracting wall magnet would add anything to it.

conradelektro

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Re: Self accelerating reed switch magnet spinner.
« Reply #253 on: November 28, 2013, 11:39:36 PM »
@Conradelektro,
The elongated coupled double rings at the base and on the shaft look like a novel innovation to me. I've never seen a permanent magnet pseudo-levitator built that way before. Your unique design may be a vast improvement over the existing approaches. Looks like you accomplished at least double the stability over the simple ring version. Very nice! I really doubt Lidmotor's ball bearing and attracting wall magnet would add anything to it.

I had to use two little ring magnets because they are weak. They make a nice impression, but I doubt that they add any advantage.

I have some strong disk magnets (no hole in the middle, just disks with axial magnetisation) which could be used as base magnets. The plan is a 5 mm threaded brass rod as axis with a length of 250 mm carrying five ring magnets (diametrical magnetisation) in the middle and axial magnetised ring magnets at the ends. The strong disk magnets placed flat underneath the ends of the axis should hold up this long and heavy spinner.

I noticed some interaction between the diametrically magnetised ring magnet in the middle and the base magnets on both ends of the axis. A longer axis should help. And attached please find an idea to neutralise the effect of the base magnets on the ring magnet in the middle.

Greetings, Conrad

TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #254 on: November 29, 2013, 01:06:33 AM »
It will be interesting to see if the base magnets can be arranged so that the poles are vertical instead of horizontal. I haven't been able to do that. I use thin flat magnets polarized on their faces, very strong, for my base magnets in the electrostatic Mendomotor arrangement, but they have to be oriented so the poles are parallel to the shaft, and all are oriented in the same direction, so that the shaft magnets are repelled to push the shaft very lightly against the glass end-stop.

Lidmotor's magnet point of contact is pretty clever. My shaft is nonconductive, made from a phenolic tube, but I have an aluminum point insert in the bearing end and I could replace this insert with a steel one, and try the magnet suspension idea that way. I don't think it will give less friction than the sharp aluminum point against the glass, but reducing the number of permanent magnets is a plus.

The full-radial suspension with co-axial ring magnets is better for vertical shafts. It's hard to get a vertical shaft to balance and center properly unless you use full rings.