Self accelerating reed switch magnet spinner.

[TinselKoala]

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]

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]

@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

[conradelektro]

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]

@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.