Prajna

Watching from the sidelines with avid interest...

Splendid. Now all I need is for someone like @exchemist to translate this into simple terms that I can comprehend. I am still studying the wiki, btw, in the hope that I can get to a broad-brush understanding of how magnetism works.

You might note that an electric motor will not run until you flick the switch. Although it doesn't take much energy to flick the switch and the real energy that is running the motor comes from the power supply that switch needs to be turned on for it work. Here the operator is turning the rotor, effectively just switching fields in the magnet array, rather than any direct application of force to the rockers, which are what send work to the output. You may well understand how the linkage operates between the switching of the fields and output from the fields (and, apparently, the inviolable recovery of energy back into the field to balance it, if that is what happens) but it's far from clear to me. It seems to me that the connection is via magnetic attraction and repulsion of the switched magnets and by eddy current drag on the rotor tabs or fingers, but quite how that connection operates and how to begin to analyse it is beyond my current knowledge. If you can help me towards an understanding of that then I will be delighted. Leave aside any thought of it being any kind of perpetual motion/free energy/overunity device and look at it as just a transmission system: how is the work done on the rotor translated into work done on the output? You might like to analyse it in terms that a fellow engineer on the welding forum I frequent observed, "That's a very complicated system for what is effectively a brake." I particularly like the way @exchemist has approached analysing the device, I find it clear, logical and easy to relate to. Perhaps his specialisation is not physics but, for me anyway, I appreciate the way he has stated things.

True enough, it is only an animation, perhaps even a simulation though not necessarily accurate. I'm not sure I have advertised it in any particular way apart from being a curiosity. As a thought experiment surely I have presented enough to spark a discussion on (at least hypothetical) energy exchange. Thanks for continuing with your attention and thoughts.

Well your expertise is (probably) physics and mine is more geared towards engineering. I could divert my attention to studying physics but really my interest is in approaching this from an engineering point of view. If you can help me to understand how the energy exchanges occur in this device, preferably in simple terms, then I will be very happy for that. I can understand any frustration you might have in dealing with a physics-naif who could resort to studying physics rather than asking questions the answers to which might be obvious and intuitive to one with a deep understanding of physics. I hope you will at least admit that this device presents an interesting problem of analysis and the energy exchange is far from obvious (to most people anyway and, I guess, even to some physicists).

Here is the updated animation. I have modified the cam groove so that it matches the cam pin movement and generally improved the animation so that it is smoother and less glitchy.

Sorry to have been quiet, I've been redoing my animation to better represent movement (or approximated movement) in the device. @exchemist, I do hope to ask for some more detail regarding your analysis, particularly regarding what you consider as Stroke 4 in your analogy. @sethoflagos, I am also interested to explore hysteresis further to estimate what part it plays in the dynamics of the device. @swansont, thanks for the further response. It seems to me that you make bare assertions, such as, "Magnets don't do work" and the above, "The energy for doing stuff with magnets is not contained in the magnetic field." Now, most likely you are right and it just remains for us to research deeply enough to understand your assertions but it would be much more helpful if you would offer some explanations to go along with your assertions. Thank you.

There were very helpful comments today.

Thank you. Anyway, I hope there's nothing stopping me being able to do it tomorrow.

Excellent analysis, both of you. Sorry, I have no more reaction points available today or you'd both get a +1. This is exactly what I came here to explore. All I have to do now is re-read both comments carefully to make sure I understand. Thanks.

I did add a rather conspicuous wink but thanks for the clarification.

Sorry, I'm not sure of the dynamics yet. The rotor is rotated at whatever angular velocity, the tabs are spaced at 20 deg so the spacing will be varying. At the starting position one or the other side of the device will have a tab/finger centralised between the magnets and the other will have tabs spaced evenly above and below the gap. The magnets are prevented from closing completely on the tabs by a cam groove on the output flywheel. So, at the starting position the magnets with a tab in the gap will be at minimum separation.

In the current design the tabs or fingers are arranged every 20 degrees around the rotor. There are nine tabs and the rotor axle is co-planar with the centre line of the magnets, so when there is a tab central to the gap between the magnets on one side there is a space on the opposite side. The magnets are 10mm x 2mm neodymium (N52?) and the tabs centres are at approximately a 35mm radius. The 'bulb' on the tabs that lies between the magnets is 5mm radius to match the area of the magnets. This may be more or less optimal as far as effectiveness in switching the flux and suffering eddy current drag, I don't know yet. This is somewhat arbitrary and is just my first best guess of what might work. I wish you guys would stop with the perpetual motion slur, I'm rather hoping for over unity!

Sorry, I don't understand. Unless you mean it's a win that I'm belatedly reading about magnetism and you don't need to be involved in analysing the device. By the way, I stumbled back on the article about monopoles, for anyone interested, it was in Popular Mechanics: https://www.popularmechanics.com/science/a60079037/magnetic-monopole-hematite/

It's not so unusual though for magnetic fields to be sharply bent, a keeper on a horseshoe magnet does this when placed across the poles, providing the shortest possible low reluctance path for the field and containing it, effectively neutralising the magnet. By the way, I've just taken a look at the Ferromagnetism page on Wikipedia and am finding it very helpful in understanding magnetism. Soon I may be able to drop my naive model and speak intelligently about it.

That sounds completely reasonable and is just what I was angling for a competent analysis of. I do recall the eddy current demonstration of dropping a magnet down a copper tube, a very impressive demonstration of eddy current drag. Certainly it is my estimation that the fingers will get sucked into the gap and resist being pulled out again but I think (may well be mistaken) that these two forces will cancel each other. However the eddy current drag may be what correlates the input force to the output power. It may be that whatever reconfiguration to reduce the eddy drag will also have an equal impact on the power output, satisfying input >= output. Only my gut tells me that there might be an input < output while my head tells me that cannot be. Thanks for that, @sethoflagos, that is a very useful comparison.

This is exactly the conversation I hoped to have here, @exchemist. Yes, my preliminary experiments showed that with magnets in repulsion a steel sheet, in this case a steel rule, inserted into the gap caused the magnets to be attracted to the rule. My guess at what is happening there is (if you'll indulge my less-than-physically-exact language) the magnets in repulsion, because their competing fields offer a very high reluctance to the other's flux path, try to complete their circuit by adopting (and attracting) the steel rule, a much lower reluctance path, into their circuit. When the rule is removed the magnets again face an unacceptable high reluctance to their circuit and therefore attempt to mitigate it by moving apart.

Thanks, @Mordred, I recently read a headline suggesting that someone has found a magnetic monopole but can't remember where I saw it. I seem to recall reading that Maxwell's equations are not actually Maxwell's, that Maxwell expressed his equations as quaternions but didn't publish them before he died. It was Heaviside who published Maxwell's equations, having converted them all to vectors, so really when we talk about Maxwell's equations we are talking about Heaviside's equations and neglecting Maxwell. But then it might have been some renegade astronomer who wrote that, I can't recall exactly.

Regarding the sliding of a magnet off a sheet of steel, I guess that what is really happening is that you are not feeling the same force you feel when you try to lift it directly, you're not working directly against the magnetic field. Once you get to the edge of the sheet the area of the magnetic contact reduces, and with it the force holding the magnet to the sheet until finally the magnet is clear of the sheet. Triboelectric generation is looking more and more interesting these days. Won't be long before the free energy cranks are baffling themselves with that. Hmm, come to think of it, I've done nothing about adding generation to my device, ... reciprocation, triboelectrics, ... hmm ...

Ah, ok, you were talking with regard to the device and I was (at that time) talking with regard to the thought experiment. Cross purposes, sorry for the misunderstanding. Yes, I'm sure that at some point I will need to consider distortion in the fingers/tabs but engineers often just over-engineer things, add s fudge factor, rather than fuss about such details. This particular design is just a proof of concept and the objective was to make it easy for people to grasp the principal of operation. The rotor is designed so that the number and geometry of the tabs can be changed easily in order to test different configurations. That provokes images of some structure bowing down to hoist a tiny metal sheet up into the air. Sure, to some barely detectable extent a solid structure will distort due to the forces involved in the thought experiment I described but really, is it really fair to say in this situation that the structure is doing all the work and the magnet is doing none? That is a very strange way to describe the situation in my view.

Ok, the situation in the device though is that the magnets are not moved closer nor separated by the operator, rather the magnets move under the effect of their changing state of repulsion or attraction governed by whether there is a finger or no finger between them. So, in my view, energy is being exchanged between the magnetic fields on one side of the device and the fields on the other. Is this a reasonable description? The operator is not moving the magnets, not even by poking them with a stick, he is merely turning the rotor that determines which side of the device has a finger in the gap and which doesn't. Maybe I should rename my 'fingers' to 'tabs' to avoid the idea that there is any poking of the magnets going on. I don't see where there is any direct link between the work or energy or effort required to turn the rotor and the work or energy or effort produced by the switch state of the magnets, unless there is some reason to suggest that the eddy current drag is directly related to the output. The drag will certainly depend on the strength of the magnetic field on the side of the device that the finger/tab is passing through and the speed of the finger/tab through that field and, I guess, on the area of the tab that's in the field, perhaps even other things I have yet to consider.

Chatham: yes, there was a nuclear submarine port there, I believe. Sailing on the Medway is very interesting too, that sub being one fascination. Good, we're getting closer now. I think @swansont is still confused in thinking I'm talking about lifting something by attaching it to a magnet and lifting the magnet whereas I'm talking about the magnet being fixed and the object being lifted by the magnetic field. There's some ambiguity somewhere and I am not sure if it is in what I described or in @swansont's understanding of what I describe. No matter. I hope he can agree that in the thought experiment I described the magnet appears to be doing work as in W = fD. Certainly it looks like work is being done. Once we get this thought experiment done and dusted then maybe we can examine my proposed device and see how we correlate what is happening in it with thermodynamic laws. Maybe we can even discuss it in general terms without having to divert into obscure formulae. Can we say then, in this thought experiment with a fixed magnet attracting to itself, that work is being done by the magnet? Can we say also that the strength of the magnet is not depleted in the process of that? In that example some work must be done to remove the steel sheet from the magnet, if it is a permanent magnet, or the current must be interrupted to let the sheet fall if it is an electromagnet. So we can include that work and so on and develop the experiment further to include the mechanics of removing the sheet again etc. but let's leave that there and move back to the SMT. In the SMT the magnets are fixed at the end of rockers (levers really, on an axle at their centre). When a metal finger is rotated into the space between the magnets then the magnets will switch from repelling each other to being attracted to the finger. Obviously some work will be required in order to rotate the finger into the space. That work will be reduced, maybe even to some extent overtaken by the finger being attracted into the field in the gap between the magnets. Obviously the reverse will be true as the finger exits the gap since the field is still attracting the finger back into the gap and this will add to the work required to rotate the finger out of the gap. So these two effects should balance or cancel each other out. This is what I mean by 'symmetrical and why I disregard this effect since overall it neither adds to or reduces the force required to turn the rotor. There will be some eddy current drag on the finger as it passes through the magnetic gap, since any ferromagnetic material passing though a magnetic field acquires an induced magnetic field opposite to the magnetic field inducing it. How much drag will that be? Probably it will be proportional to the strength of the magnetic field that gives rise to it, that's logical and I'm happy yo accept that being the case. The magnets, in attraction to the finger on one side of the rockers and repelling each other on the other side, will cause movement, work in fact, on the rockers, causing them to rotate in a reciprocating manner as each magnetic gap encounters either a finger or a space. The force involved in that movement will depend on the strength of the magnetic fields which will vary dependant on the distance the opposed magnets are from each other - when the magnets are close they will exert more force, either in attraction or repulsion, and the converse; according to the inverse square rule. It may be that whatever the power of the magnets the eddy current drag will always be equal to the forces generated by the magnets in switching from attraction (to the finger) and repulsion (on the side that has a space rather than a finger.) Or maybe the eddy current can be reduced, perhaps by making the fingers small enough that they only just switch the magnets, perhaps by redesigning them to use some form of lamination such is done in transformers to reduce eddy currents. I'm not sure if you have noticed but when a magnet is stuck to a sheet of metal the force required to remove it can be much reduced by sliding it transverse to its field. In the SMT the fingers pass transverse to the field rather than in line with it and, like sliding a magnet off a sheet of steel, there may be less work required than if something was moving in line with the field. Thanks for further constructive comments, @exchemist Did I say the area of the plate was greater than the magnet? You're again talking about attaching something to a magnet and then lifting the magnet. I'm not. I'm talking about a SMALL plate of metal being ATTRACTED to a magnet that is in a fixed position. Do your stress tensors and Hookes laws and elastic distortions really contribute to what I'm discussing? Thanks for your interest but I really don't think what you've offered is contributing to illuminating what I was discussing.

Again, you're getting into marginally relevant details. Rather than go there, why not address in general and simple terms the exchange of potential energy? Anyway, I'm sure the upward force is not a point source at the centre of the sheet but is distributed in some way across the sheet.

Thanks. I'll look it up. Ok, "The Cauchy stress tensor is used for stress analysis of material bodies experiencing small deformations: it is a central concept in the linear theory of elasticity. For large deformations, also called finite deformations, other measures of stress are required, such as the Piola–Kirchhoff stress tensor, the Biot stress tensor, and the Kirchhoff stress tensor." I'm not interested in "small deformations" in this example. I think I have clearly stated what I am considering and "small deformations" is an aside to that conversation. What's happening in terms of changes in potential energy and how can that be simply and clearly described?

Ah, I think you misunderstand what I was referring to. I was describing an experiment where there is a table top, 30mm above the table is a magnet fixed to a support. Small sheets of steel are on the table. Pushing a steel sheet across the table top until it is situated under the magnet, the magnet will attract the steel sheet upwards til it sticks to the magnet. In this experiment I describe what is happening is that the magnetic field attracts the sheet so that it rises against gravity and, in the process, the gravitational potential energy in the sheet has increased. I'm not getting bogged down in deformation (which may, indeed, occur to some extent in this situation but is not a major factor in what is happening), simply I am looking at the exchange of energy and how that can be described. @swansont insists it can't be described as the magnet 'doing work' and that magnets 'don't do work'. Ok, then how do we describe it and if a magnet appears to be causing something to move via some force over some distance, if that is distinct from other forms ofwork then how and why?