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Can Repelling Magnets Replace the Spring in a Pogo Stick? (kjmagnetics.com)
292 points by mhb 4 months ago | hide | past | web | favorite | 142 comments



Seems like electromagnets could help compensate for distance by drawing more current when far apart, and less when close together. A microcontroller could essentially make the force linear like a spring. Of course, then you need wires hooked up to your pogo, and that might be scary if the microcontroller has a bug (or somehow fails) since you are now essentially hopping onto a railgun.


About as scary as my Tesla on autopilot going around a curve at 75mph. Every time I ask myself, what if there is a bug or if it turns off...


I know exactly what you mean. I will admit at 20mph over the speed limit going over a poorly maintained curve on the Mass Pike I usually just disengage for a moment and then switch it back on. It can take the curve, but it doesn’t feel good to let it.

I’ve had it lose tracking on the highway. It just leaves the wheel in the last position and beeps very urgently to let you know to take over.

I find autopilot helps me become more aware and less fatigued while driving. It’s a level 2 system. There is never a question of losing engagement as an active driver like what happens with level 3 self driving.

It will keep a clearly marked lane better than I can (it’s very precise with staying in the exact middle of the lane and doesn’t cut corner like humans tend to). For stop and go traffic it’s a blessing.

It sucks at zipper merging. I’ve had to brake for merging cars more than once, even though they are visible coming into my lane on the HID. That part needs work. And I don’t really trust it to change lanes as I feel like the blind spot detection isn’t quite there either.

All said it’s pretty much the most amazing driving tech ever, and the TM3 is most definitely the most amazing driving machine I’ve ever had the pleasure of owning. Just orders of magnitude better handling than I realized was possible. Curves rated at 25mph that I used to take at 45mph in my Infiniti previously with some tire squeal, it can silently tear through at 65mph. I don’t know what the skidpad rating is, but it feels unflappable and body roll is just nonexistent.

Actually it’s a bit tricky because you literally feel no complaints or judder or roll all the way up to pulling 100% of traction the tires have to offer. It is quite well mannered once it does start drifting though.

Sorry, sorry, I can’t help it. You can guess I’m thrilling at parties.


I rave about how awesome it is too. In stop and go traffic it’s wonderful and rarely asks me to touch the wheel. I don’t like it for lane changing either so I always take over.


> It will keep a clearly marked lane better than I can (it’s very precise with staying in the exact middle of the lane and doesn’t cut corner like humans tend to).

Anyone have experience with the lower Westchester County section of the Taconic Parkway? There are some serious curves, and the lanes are very narrow. In the left lane, you're maybe 2-3 feet from the box-beam center divider.


I just saw someone reverse their TM3 into their garage with their phone. Pretty neat! Definitely will be my next car to make my long commute bearable via autopilot tech.


The ratings on corners (at least in Australia) are rated based on visibility, not some complicated traction calculation.

They factor how far a head you can see, and how much time you need to react. Lots of cars/bikes can obviously tear through them faster. But that means they are just taking much more risk.

That said, perhaps auto driving can respond quicker, but I’d imagine that doesn’t change most of those ratings give. The time needed to avoid accidents is largely due to physics not reaction speed.


Pretty much every critical system in a vanilla Toyota is already software-controlled, not to mention the legion of critical systems involved in air travel, elevators, medical equipment (e.g., pacemakers), etc. Not sure that this should bring comfort, but at least you need not be particularly frightened by your Tesla. :)


Elevators use simple physical safety systems.

Which is why you see headlines like: "Skyscraper elevator plunges 84 floors — and everyone survives" https://www.cbc.ca/news/world/elevator-plunge-chicago-1.4913...


Every link i’ve seen to this story annoys the hell out of me because they don’t explain HOW the elevator eventually stopped. That’s literally all I want to know.


It reached the bottom. Probably hit one of these: http://elevation.wikia.com/wiki/Buffers

Note that it wasn't descending particularly quickly; one cable snapped but other safety systems were still operable.


The article says it went from the 95th to the 11th floor. It appears it stopped before reaching the bottom buffer.


The best book ever for understanding how Elevators work is a wonderful late 20th century work of fiction called The Intuitionist by Colson Whitehead, which was described by its author as what you would expect to happen if you let a child grow up reading elevator manuals.


Entering “elevator safety mechanism” into google will bring up several links with explainations. The first link for me references this story.


There was an elevator hacking talk that went into the buffers at the bottom of the elevator. You may have seen them in elevators that have glass on the outside of the shaft like in malls and hotels. The elevator never rests on those. Those are to take the impact of an elevator that crashes. Inspectors will often test the buffers as well as part of routine maintenance:

https://www.youtube.com/watch?v=ZUvGfuLlZus


The basic theory is that between the car and the wire there is a spring connected to brakes. When the car hangs in the wire this spring is loaded and the brakes disengage, if the wire breaks, the spring returns and brakes engage. All this is mechanical.

What I never understood is how elevators can travel downwards so quickly without such a system engaging. Can they block it somehow or are they never accelerating fast enough down?


I’d also like to know what they meant by “plunges”. How fast did it descend? Was it in free fall?


You can easily tell that it wasn't in free fall, because if it fell 84 floors in free fall and then stopped, the passengers would have died.


It could have slowed down gradually and stopped. The articles I’ve read don’t do a good job describing anything.


If it slows down gradually, it's not in free fall.


Guess again. The cable could break at floor 84, and the elevator car could travel through the next 50 floors, and not slow it’s descent until the 34th floor, at which point, given ten vertical feet per floor, it would still have a total stopping distance of nearly 200 feet, or 2/3 (66%) of a football field.

So, 500 feet of freefall is still substantial. That puts the situation on par with a bungee jump.


What's deadly is the other type of failure, where the counter weight causes the elevator to shoot upwards, like what happened in that elevator in Chile. There's a video of the guy confused as the doors continued to open/close at each floor. He had severe injuries.

Apparently if that ever happens, your best bet is to lay flat on the floor with your hands covering your head, as the impact will launch you upward.


Thats how I usually approach stressful situations, so I should be fine.


Aren't brakes and steering mostly manual? I don't think it's the right advice to tell people to trust Autopilot when it's failed in several egregious ways.


They are manual in the sense that there is a physical connection: the steering wheel is usually mechanically coupled with the steering rack, brakes usually through through hydraulics.

That said there are probably 5-20 systems in a car that can completely control these systems without any human input. Think of automatic emergency braking, traction control, vehicle stability control for the brakes, and autopark + powered steering for the steering.

Most of these systems have multiple redundancy and isolated monitors (eg, if autopark is on and the vehicle speed is > 10mph, the monitor will intervene) but there are still probably some theoretical situations where this could occur


Steering is electronic.


Electronically assisted, but still mechanically coupled for 99% of consumer cars. I've completely lost 12V on a car before and still managed to bring it safely to the side of the road.

Inifinity tried steer-by-wire but ended up retrofitting traditional hydraulic steering back.[1]

[1] https://en.wikipedia.org/wiki/Drive_by_wire


sterring is electric, but there's always a backup system in case the electronics fail: https://youtu.be/em1O8mz7sF0?t=276


Driving a car on the road with other cars is - factoring in the age of the tech, lack of regulation, involvement of humans and the consequences if it goes wrong - more difficult that what's mentioned on your list.


there's a huge complexity difference, however.


I have used Tesla autopilot on twisty cliffside roads (my hands hovering an inch away). The question in my mind was, when there is "nothing" there, is that a place it thinks is okay to go? Or is it a place a place where it should absolutely not go? I wish it could just tell me that.


It doesn't know about dropoffs. It only knows about lane lines. It's really good at following lane lines. Sometimes right into an obstacle.


It knows about the driveable areas even outside the lane lines where it can go in the case of an emergency.

See: https://www.youtube.com/watch?v=il6LV4064bI


>what if there is a bug or if it turns off

Right? I have an irrational fear of laser eye surgery because I'm afraid some random component in the machine will fail and cause some sort of over-powered pulse.

It's far more realistic a component would fail in a car though and cause the 'brain' to take a shit on itself. Still pretty out there but it would be a very real concern of mine.


You let it go round a curve at 75mph, or is this hypothetical?


I think he's referring to a curved piece of highway, not a turn.


The downside risk is never worth it for me. I'm always hands on, and curves I treat it like a drivers' ed situation: You better do the right thing.


Yeah, I tell people that I treat it like a well-mannered 15-year-old driver - I expect it'll do the right thing, but I'm here to take over in case it finds itself out of its depth.


Consider not going on a modern airliner. Every commercial passenger jet since the A340 has been fly-by-wire.

(military jets have been so longer).


But you have more time to react on a plane and switch to manual override. It's not like people fly with just a few meters distance to other airplanes. There's also a good distance to the only other thing you can crash into, the ground, as opposed to driving between walls or with a cliff to one side.


OP said "fly by wire", meaning there's no non electronic systems to fall back on. If the electronics fail there's no "manual override".


Of course there's a fallback. If the fly-by-wire system fails, there's another whole fly-by-wire system ready to take over. Usually this is safer than the old redundant hydraulics systems where all the lines ran close together, making them vulnerable to localized impact damage and fire.


I specifically said "non-electronic" fallback.


Reliably implementing a few control loops and exhaustively testing all possible input/outputs for bugs - difficult but manageable.

Reliably implementing image recognition from multiple cameras and AI that should respond to ever changing weather, inconsistent roads, signs, maps and other human drivers erratic behaviour within milliseconds - Not even in the same league.

Not saying aircrafts are simple but self driving is just orders of magnitude more complex. Otherwise we would have seen them on the roads already.

Aircrafts also have much stricter maintenance schedules, failure investigations and completely different economic, media and moral incentives.


Aircraft autopilots and fly-by-wire systems are vastly more simple than self-driving cars.


Depending on what fails how in a car, you may have less than a second to recover.

Apart from being hit with a high-explosive anti-air missile, I can't think of any failure mode in a plane that has such a narrow recovery window.


737 Looks like cables, air, and hydraulics to me.


737 is a much older aircraft. The A320 and subsequent Airbus jets and Boeing jets since 777 have been electronic.


The Embraer ERJ series does not have fly-by-wire, just to name one. So the assertion that every "Every commercial passenger jet since the A340 has been fly-by-wire" is simply false.


... So don't use it?


Not only that, but you can adjust the “springiness” by having a variable spring constant.


Using css animation-timing-function!


You can even make it jump by itself.


Maybe you can use regenerative braking to charge a battery, to avoid having wires and keep a bit closer to the spirit of the pogo stick.


Alternatively a lever system or non-circular gear arrangement could convert the force from fixed magnets into a linear response entirely mechanically.

...edited for sense


> you are now essentially hopping onto a railgun.

No, you're riding a coil gun. But your point stands.

https://en.wikipedia.org/wiki/Coilgun


You could have controls in the handgrips to change the shape and amplitude of the curve.

As far as bugs go, you could clamp the output in the good old fashioned analog way (i.e. via circuitry) so the worst case is you just fall/jump off which is already the case for the sprung ones.


Honestly, someone might want to hop on a railgun. Extreme pogo


Could you not hardcode limits in your circuit, such that the maximum power it supplies is never enough to be deadly?


Or hardwire? A fuse, just not having enough voltage, etc?


This is the best comment I have ever read


You don't have to think about buggy software to come up with death scenarios. What if a driver in the other lane is drunk or not paying attention? Another driver could kill you at any moment and there's nothing you could do to prevent it.


The dangers of operating a pogo stick on vehicle congested roadways are significant, but remain consistant across differing pogo technologies. This post makes no mention of making a pogo stick safer to operate on public roadways.


What are you talking about?


> For the 4, 5 and 6 magnet stacks, the outermost gaps tended to be a bit larger than the inner gaps. Why?

> As we add more magnets to the stack, the maximum pull force alternates up and down. If 2 magnets repel with some force, 3 is a little less, but 4 is a little more 3, but 5 is a little less than 4, etc. Why is this so?

Shouldn't these guys have figured it out pretty easily? Both seem to be readily explained by the fact that it's not just the adjacent pairs of magnets that interact. Given magnets ABCD, the A magnet is repelled by B and D but attracted by C. B is equally repelled by A and C, but attracted by D. And so on.


Seems like they missed a trick by arranging the magnets above three so that some of them are paired. You’d probably get more travel but not sure how the force would be affected and neither did they.

You could try A BC D, AB CD, AB C DE and A BCD E.


The core issue that's not mentioned is that we want a certain kind of a curve for deceleration because that what determines how the spring works. Little resistance first and lots at the end means it's not much different from just falling down!


Seem like an attempt of replacing a large, fine-tuned, atomic scale electromagnetically interacting system with a much simpler, less fine-tuned one.


The Universe is already running the best code for the job.


Fully compressed I believe the opposite poles fields begin to attract each other, counteracting the matching poles repelling one another, and explaining the alternating pull force.


This is easily solved by including a minimal height spacer between the two magnets to prevent them from getting too close.


They spacer could even be a spring to add a bit of springiness.. Oh, wait.


Strong magnets are fragile. There are warnings about letting them hit each other (managed to break one of the HDD magnets I extracted that way).

Elastomer bumper should do the trick.


Loved the video. Didn't love the loud beep near the end, that's at about 3x the volume of the speaker the whole video...


YouTube desperately needs an audio compressor feature. Can't imagine why they haven't implemented that yet, it's more or less trivial.


I agree that they should, but it’s pretty reductionist and arrogant to call it “trivial”. There is no such thing as a one-size-fits-all dynamic compressor. You would also need a fairly sophisticated content detection system (don’t distort anything that is music, which is a huge use case on YouTube for example). Not to mention adding _any_ steps to their intake pipeline requires more processing power and data moving than you and I will ever touch in our lifetimes.


Speaking as a reasonably-experienced audio and DSP programmer -- and considering that the feature has existed in just about every home theater receiver for the past 20 years -- yes, it's trivial.

YouTube has the advantage of being able to preprocess the audio track in its entirety, although most implementations work on a block basis and don't need that. A 'night mode' feature would take about one weekend's worth of work from start to finish.

You would also need a fairly sophisticated content detection system (don’t distort anything that is music, which is a huge use case on YouTube for example).

No, you need a button that the user can press to turn the feature on and off. It should default to 'off.' For extra points, make it a slider.

Not to mention adding _any_ steps to their intake pipeline requires more processing power and data moving than you and I will ever touch in our lifetimes.

Compared to the work needed to process the video itself, it would be a total non-issue.


The audio compression / limiting can be done client-side, at playback time, offloading the cost of the operation


True, but that would involve modifications to the decode side of the audio codec. That's where the feature should be implemented (if not in the OS itself) but it's apparently not there. It needs to be supported on every platform, and deploying it wouldn't be anyone's idea of trivial.

On the server side, they could maintain a separate compressed audio track and switch to it when requested. They should have the ability to do that anyway for alternate languages and commentaries and such. Whether it would be more cost-effective to maintain a separate set of compressed tracks or to decode/compress/re-encode on the fly, I don't know.

It might be tempting to maintain caches of compressed tracks created on demand. That way they'd almost never incur a runtime penalty on the server, and also wouldn't have to pay a lot for storage. More than a weekend's worth of work at that point, though.


Even better, the whole limiting could be done client side, in OS or browser.


The response could be a closer approximation of linear by using six tubes, two magnets each, with varying initial distances. As the stick compresses, additional magnets contribute force, but not all at once.


Just have two fixed magnets and two moving ones:

[+- +-> ===== <-+ -+]

As long as the open-wide distance is capped you should have a smoother distance-energy diagram.


Unsurprisingly, an inverse-square mechanism can't replace a linear one over a wide working range.


I wonder if there’s a Fourier transform equivalent that’d let you stack up various inverse square curves to appropriate a linear curve?


yes. any set of complete functions form a vector space and can be used in a linear sum to appropriate other functions in the same space. the dot product tells you the value of the coefficients. The fourier transform is just a special case of this.


Inverse-cube for magnets


Could you use a lever to multiply travel distance while working with very strong magnets close together to make the force curve a bit more linear?


Where does the heat go? The spring will have a much larger surface area to dissipate the heat. Maybe surrounding the magnets with a copper tube will conduct some eddy currents.


A lot of science museums have a display showing how magnets and copper pipes interact. In short, because of Lenz's Law, the magnet's motion induces an opposing magnetic field in the pipe ... which suggests another possible way to make a pogo stick with the right kind of resistance curve as well as addressing the heat issue.


A mechanism that absorbs any kinetic energy would make for a very disappointing Pogo stick.


If it absorbed all of the energy that would be a problem, but any child who has seen one of those science-museum displays I mentioned can tell that's not the case.


You don't really want a pogo stick to absorb any energy, it'd be like trying to make a pogo stick out of mud.


This means the kinetic energy is lost to heat, which is not good for a pogo stick


Yes, but there will always be some heat loss, and the magnetism is lost with heat. I’m just assuming the pogo stick will drastically fail when the magnets get hot enough.


They should try this with electromagnets, and make the curve linear using electronics (and perhaps find the optimum curve in terms of fun when jumping around).


Wouldn't that consume a lot of electricity?


Probably yes, but it would be an interesting experiment. By the way, they could use superconductor magnets :)


Maybe it's possible to apply a regenerative brake like mechanism?


I would still like to see someone build a pogo stick with many magnets with alternating polarity. This article indicates that it would work. Seven strong magnets with a 1" initial gap between each of them should work.


If you really wanted to do this, I reckon the way would be to have one set of magnets on the moving shaft and another set surrounding it, so the the repulsion tends to keep the shaft centered. Then you make the shaft surround taper towards the top, so that the further the pole is pushed in, the closer together the magnets are forced. You should be able to achieve any force curve desired with this setup by making the taper non-linear.


Just use current designs which, I would think, mechanically constrain the pogo stick except in one direction. Replace spring with powerful magnet (pair), and make sure there's a stop pin or something similar to keep the magnetic pogo stick from disassembling itself.

I think you're making things too difficult and expensive if you're trying to magnetically suspend and stabilize the pogo stick in multiple/all directions.

Also, magnetic radial stabilization would be stable only in a rough sense. The pogo stick handle would still wobble and be disturbingly/unexpectedly unsteady. I think for pogo sticks you'd really want a mechanically confined, piston-like design. You could still have magnetic stops on both extremes.


Although it's an interesting idea, I didn't mean to suggest only using the magnets to center it - I was merely clarifying the geometry.

Another advantage of my design is that it allows (requires, in fact) one to use many small magnets in place of a few large ones, which is safer and easier to engineer. But as for expense - I think that once you decide to replace springs with magnets in a pogo stick, you have left the path of economy anyway and might as well go for broke.


Maybe a series of magnet pairs, spaced at different heights, could approximate the spring effect. Each pair would be bound together (e.g. with strapping) with the negative charge being on the outside, since Earth has a negative charge. The bottom of the stick would have the strongest magnet, negative charge facing up.

-

+

+

-

The pairs could then repulse each other at a closer distance, approximating the spring function. I accept royalty donations :-)...but it's probably patented by now.


What about a hybrid system with springs for the longer travel but magnets for when you are about to bottom out?


I’ve often thought it might be interesting to replace the springs in a piano’s action with electromagnets so you could have control over the exact touch profile.


I don’t think pianos typically have any springs, everything is gravity powered with counterweights. The only springiness comes from striking the strings as far as I know. Only the really cheap electronic keyboards use springs. Even halfway decent electronic pianos still rely on counterweights.


I cannot speak about any piano, because I had chance to tinker with only one, but that piano had springs.

Keys itself return into their normal position because of gravity, but part of key action mechanism was powered by a spring. I discovered it while trying to fix some keys which was too slow to "recharge", to return to a normal position after a soft note, so I was unable to make a sequence of a short duration soft notes from the same key. I fixed it by stretching springs long enough for a plastic deformation to occur. Loud notes worked ok, because their "recharge" was driven fully by springness of the strings.

Though it was just one piano, I do not know how different the mechanics can be between different pianos.


I’m pretty sure even really nice uprights (Yamaha U3) have jack springs... maybe I saw the wrong diagram


I don't have a full text link, but definitely there's been some work done on at least the front end of this problem:

https://uwaterloo.ca/motion-research-group/publications/kine...


Or you could pay a piano tech a couple hundred, then have nothing to worry about for the next few generations


A guy named David Stanwood has a network of licensed piano techs all around the country who can replace the lead weights in the keys with magnets. One of the stated benefits is reduced key inertia.

https://www.stanwoodpiano.com


Would it be possible to put the magnets in some kind of tube which blocks magnetic flux, in order to get a linear relationship instead of the square law?


How can they stack three magnets with the repelling side facing each other on all three magnets? Isn't one side repelling and the other attracting?


You can do some interesting things with magnets. Consider the Halbach array ( https://en.wikipedia.org/wiki/Halbach_array ) often used for refrigerator magnets.

That said, the 3 magnet configuration would be:

NS - SN - NS

From the article:

> We added a third magnet, alternating which way the polarity faces with each magnet. Each magnet repels any adjacent magnets.


Can we make an electronagnetic-sprung mattress?


That would really suck in a power outage.


Or if you wet yourself


Ignoring other problems mentioned, what would the benefit of such a system be? I suppose it'd be very customizable, but probably expensive (both initial cost plus the cost of the electricity to run it).


I guess I was reading the other comments and thinking eminently customizable springiness - to the square-inch resolution. People pay outrageous amounts for Sleep Number beds. This would be the high-end version of that.


I literally can't wait for N-Gate's distillation of this thread.


permanent magnets tend to demagnetize when you beat them around, too


could some kind of conical shape offset the different power curve?


Don't magnets lose their magnetism with repeated drops?


TL;DR Yes but not very well. A spring made from magnets doesn't have a close to linear spring rate like a traditional coil spring does.


But is it linear, from the data? They had two datapoints and projected from that sparse data a regression line.


There are far more than two data points on all of the charts in the article. What chart are you looking at?


The youtube video mostly.


Hook's law[1] states that the force of a spring scales linearly with the distance it is stretched.

[1] https://en.wikipedia.org/wiki/Hooke%27s_law


And magnets repel with an inverse cube law. So there is no simple way to replace a spring with magnets.

You could "linearise" an electromagnet with distance sensors and code, but that's a bit of a Franken-Solution - not least because any delay in the closed loop could make the system unstable.

In this case a couple of minutes of research - or maybe asking a physicist - would have saved a lot of essentially rather pointless tinkering.

I mean - if you enjoy tinkering more than you enjoy producing an elegant solution, then tinker away. But this is noodling around for the sake of it, not solid engineering.


You coukd linearize it using a meta-material of small magnets, though it would probably end up being a cylinder lined with magnets of varying density.


You can also linearize it by making the displacement small enough -- which is how Hooke's law actually works.


No, it's linear from basic physics.


Within a certain operating region (stress and strain, i.e. the straight bit on the stress/strain graph), a spring will behave linearly e.g. F = kx.

In real life it should be pretty close to linear, but it would be worth checking as I could imagine there being non-linearity or time dependence of a spring under what is probably a decent amount of load being applied quickly and repeatedly.


Yes, that would have been fair. The electromagnets are also (close to) linear if you look at small intervals.


Coil spring + magnets = success?


You're fundamentally going to be limited by the fact that magnetic force is roughly exponential with regard to distance whereas coil springs are roughly linear. By stacking a bunch of magnets in the article they reduce the travel of any one magnet pair so it's closer to linear. If you look at short enough segment of a graph of an exponential equation it will look linear, this is basically what they're doing.


You mean quadratic, not exponential.


Actually, the answer is probably "it's complicated". https://en.wikipedia.org/wiki/Force_between_magnets#Force_be... gives an approximation in the x >> R case, but in the pogo stick situation we're not in that case, especially once we get to 5 magnets or so. But even there, if x >> L also holds (which it would in this case, since the magnets shown have R and L of about the same size), the force goes as 1/x^3 or so, because the 1/x^2 terms cancel out if you go through the small-L approximation. Which, again, is not relevant to the problem because our case has small x.

For small separations, the exact geometry of the magnets starts to matter. http://www.magnetsales.com/design/faqs_frames/FAQs_2.htm has some experimental results that show the field going up a bit over 3x when distance drops from 1 to 0.5, then ~2x when going to 0.25, then ~1.5x when going to 0.125 and only changingby 1/8 when going to 0.063... all distances in inches from _surface_ for a magnet that's radius 0.5 and length 0.5 in the same units. Note that this means that the distances from the _center_ are approaching 0.5.

All that said, the force is almost certainly not exponential, I would guess.


In the similar vein I wonder if exploding lithium ion batteries can be used as small rocket fuel


they did freedom units math! quite a feat


Yep, still quite hard to read.


The ability of permanent ferromagnets to resist (or survive) attacks on their permanent field orientations is related to their intrinsic coercivity Hci. In general, rare earth magnets are much more resistant, however, radiation, excessive heat, serious EM pulses, extreme magnetic field pressure as in this case, will degrade magnets. The degree of symmetry is relevant, as highly asymmetrical designs are much less resistant to magnetic field pressure such as in the case of Halbach arrays. I have constructed several Halbach arrays from N35 Neo magnets purchased from K&J magnetics 10 years ago that have lost approx 50% of their force compared to when newly built. Magnet manufacturers can produce a custom run of a high, extremely high, or even ultra high Hci magnets for a price. In past times this was done by increasing expensive dysprosium content, but now there are multiple ways, and I would suggest the Japanese lead in these efforts. I believe Ames Labs patented a form of nitrogen doped carbon which has an Hci that is rather astounding, but to date it is not a stable product.




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