No, I'm saying that theres youtube evidence you can arrange permanent magnets around the circumference of a disk and by applying repelling magnets around the outside you can make it spin. Free energy nuts use this to claim that they can power their homes off this free energy generator. Catch is, as soon as you start the thing spinning, it starts depleting the magnets and by the time you drain them down to nothing, you've wasted hundreds or thousands of dollars on neodymium magnets and the energy that you harvest from the short lived generator is FAR less than what it took to create the magnets, since magnet creation is a very inefficient process.

Wow, I'm impressed!!

You mean those motors work? (except for depletion)
Thought it was all bs.

ps.

Oops, may be on thin ice talking about this.

 

I'll let AAC play the role of Dr. Phil while I recount an experience from my childhood; maybe it will help you understand my stance on permanent magnets.

Back when my age was in the single digits and I had all my intelligence and imagination intact, I was quite the little inventor. I had a notepad (wish I knew where it was now) where I documented my ideas, like the 20ft snorkel with check valves, the electrocution water gun, and the infamous permanent magnet motor made from banana-shaped magnets.

I drew the idea up for my parents, and explained it in all its detail and they actually seemed convinced it could work; not being the technical types either of them, they encouraged me to propose my idea to someone who could help, but they didn't know anybody like that. So, my dad introduced me to news groups.

I was home schooled, very proper, and very well spoken (neither my writing skills nor my understanding of magnetics have improved since then). On top of being already more articulate than half the adults in America, I also consulted the thesaurus for every other word in my first post, in an attempt to not be taken for a child and dismissed. It worked like a charm; I presented my idea for the permanent magnet motor and was immediately flamed to death and back, being taken for a 40 y/o free energy nutcase. I had the concept of the first law of thermodynamics drilled into me with a rotary hammer. If you could find my 17 year old post, I bet you'd find that my words in post #60 are almost verbatim to what was said by the one semi-helpful soul who took the time to explain the intricacies of how magnets work (or don't work).

Since then I've lived with a phobia of magnets depleting. Ok, maybe phobia is a bit hyperbolic; an "acute awareness" of the potential for magnets depleting.

So, I may be a little off base with the whole thing, but I can't help it. It's ingrained in my soul.

EDIT: on a lighter note, my wires and magnets are here! hooray! See you guys later.

 

I know this is basically about solenoids/magnets for Strantors hand, but from what I've been reading almost no one in the real world is doing it this way now, they've moved on to better ways of doing it.

Using a motor and "differential pulleys". The differential pulley has two side, with the 'tendons' wrapped clockwise on one side and counter-clockwise on the other. In a thing called, "underactuated, flexible, tendon-driven hand".

From Google - https://www.google.com/search?q=+un...s=org.mozilla:en-US:official&client=firefox-a


And some PDFs to read -

 

I know this is basically about solenoids/magnets for Strantors hand, but from what I've been reading almost no one in the real world is doing it this way now, they've moved on to better ways of doing it.

Using a motor and "differential pulleys". The differential pulley has two side, with the 'tendons' wrapped clockwise on one side and counter-clockwise on the other. In a thing called, "underactuated, flexible, tendon-driven hand".

From Google - https://www.google.com/search?q=+un...s=org.mozilla:en-US:official&client=firefox-a


And some PDFs to read -

Thank you, this is very helpful for me. But when you say "almost no one in the real world is doing it this way now, they've moved on to better ways of doing it," what specifically are you referring to? The solenoids? Are you suggesting a motor be used? The information you've provided pertains to the mechanical aspect of making the finger automatically conform to the shape of the object being grasped, and makes almost no mention of the prime mover mechanism. It seems that all of the aspects of underactuated and differential mechanisms are unbiased as to what force actuates them. The role of prime mover is still up for grabs, and still warrants discussion. In light of what you've just turned me on to, I still feel that force-control is required, and that these solenoid-like devices being discussed are the way to go.

I'm really glad you posted this, because after speaking with my dad this weekend, I fear I may only be able to actually control 2 of the fingers and thumb. He said that his old prosthesis only had 3 sensors and 2 of the fingers were just rubber dummies to make the hand look natural. He said it was because too much tissue was destroyed and they were unable to locate signals for the other two fingers. I was contemplating ways to mechanically link the middle, ring, and pinky to act as one, in the same way described in your documents, only I didn't have the terminology. This gives me lots of ideas.

Actually, the inmoov hand I'm using already employs some of the described techniques, only not to the extent described. It can be modified though. I am excited to try it.

Thank you for spending time researching on my behalf.

 

No, I'm saying that theres youtube evidence you can arrange permanent magnets around the circumference of a disk and by applying repelling magnets around the outside you can make it spin. Free energy nuts use this to claim that they can power their homes off this free energy generator. Catch is, as soon as you start the thing spinning, it starts depleting the magnets and by the time you drain them down to nothing, you've wasted hundreds or thousands of dollars on neodymium magnets ...

Sorry Strantor, those videos are a hoax.

Magnets are springs, and only springs. Functionally either compression or tension springs.

You can't make perpetual motion from a wheel covered in springs.

Any energy released by the spring (to cause motion) must have first been put into the spring.

So bringing two N poles together takes energy, to overcome the springiness. Then when the two N poles repel and cause motion, they just release the energy that was previously put in.

Exactly the same as if you compress the two ends of a coil spring closer together, it absorbs energy. Then when released the two ends move apart, releasign that same energy.

There is nothing in any of that process than can cause continual motion, and if someone has ACTUALLY made a continually spinning engine from permanent magnets alone we're probably talking nobel prize type recognition. Same as if they made a spinning engine just from springs.

 

The question is not, "How do magnets make perpetual motion?". The question is, "Do the magnets become permanently weakened from being used as repulsion devices?".

 

Sorry Strantor, those videos are a hoax.

I concede. Now let us let sleeping dogs lie. Any more discussion about permanent magnet overunity motors should be in its own thread. It was a bad example, and a bad idea for me to bring it up.

 

The question is not, "How do magnets make perpetual motion?". The question is, "Do the magnets become permanently weakened from being used as repulsion devices?".

I forgot posing this question here on AAC 2 years ago. According to RB's response back then, I think his answer is "Yes."

I would argue that, the second part.

When i was a child the school science bar magnets came 2 to a box, with instructions to place the 2 magnets in N-S. Of course we used to put them away N-N (well the bad kids did, not me!) and as you can guess half the magnets in the classroom had barely any magnetism left so the kids would argue over who got the good magnets.

I can't think of ANY motor or electrical device I have seen over the years that ever had permanent magnets that were forced to oppose each other (forced "like poles"). Only motors etc that had perm magnets with iron poles acting as keepers when the motor was off.

 

http://www.kjmagnetics.com/faq.asp#time

I can't seem to find any other information confirming or denying the link.

 

As far as who is doing the underdriven thing, NASA, DARPA, University of Brazil(they have a very big prosthetics program) and many others.

Most of the ongoing research is using two prime movers, one for the fingers and one for the thumb. All four fingers are moved together.

I wasn't sure if you would be receptive to my adding to your project so I only gave one part of what I found. I'll post more of what led me up to the part I did post. The part on the differential pulley and motors. I clear my history on my computer so it may take a short while to find stuff again, but I will do it for you.

 

I know there are no magnetics experts here, so I post the following questions mostly as a checklist for myself to answer through my own research; I have to write this stuff down or I get distracted by shiny objects, and I thought recording it here might be beneficial if you guys know any the answers.

1. Concerning 2 magnetic fields interacting (permanent magnet + electromagnet, or permanent + permanent, or electro + electro); do the two fields need to be impedence-matched (for lack of the correct term). In other words, if the two fields are of equal strength and you increase the strength of one field over the other, does this increase the overall force of the actuator?

2. Is there any benefit to using a magnetic rod over an iron rod for a core? I have read that neodymium magnets have a permeability of 1.05, meaning just barely above that of air (1.0), so will the electromagnetic field of the coil even pass through the neodymium and contribute to the overall magnetic strength of the electromagnet? Or will it just be a neodymium magnet with a bunch of heavy copper wrapped around it, making it hot?

3. What is stronger per size/volume; an electromagnet or a neodymium magnet (assuming the electromagnet is not provided enough current to burn up)? Does it depend on scale? Other factors?

4. Will forcing magnets into opposition deplete them? (still unanswered definitively IMO). If so, how much/how fast, compared to in free air? answered, post 72

 

4. Will forcing magnets into opposition deplete them? (still unanswered definitively IMO). If so, how much/how fast, compared to in free air?

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magperm.html

A good permanent magnet should produce a high magnetic field with a low mass, and should be stable against the influences which would demagnetize it. The desirable properties of such magnets are typically stated in terms of the remanence and coercivity of the magnet materials.

When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the imposed magnetizing field is removed. The amount of magnetization it retains at zero driving field is called its remanence. It must be driven back to zero by a field in the opposite direction; the amount of reverse driving field required to demagnetize it is called its coercivity

http://www.magnetsales.com/design/designg_frames/designg_2.htm (very informative reference)

External magnetic fields in repulsion modes will produce a demagnetizing effect on permanent magnets. Rare Earth magnets with coercive forces exceeding 15 KOe are difficult to affect in this manner. However, Alnico 5, with a coercive force of 640 Oe will encounter magnetic losses in the presence of any magnetic repelling force, including similar magnets. Applications involving Ceramic magnets with coercive forces of approximately 4KOe should be carefully evaluated in order to assess the effect of external magnetic fields.

http://www.duramag.com/materials/neodymium-magnets-ndfeb/neodymium-iron-boron-technical-information/
Neodymium Coercivity ranges from 12-21 kOe depending on grade.

Strantor's final word: RB's magnets demagnetized from being put backwards in the box because they were inferior magnets with low coercivity. Neodymium magnets would probably be just fine in the same situation. Just make sure to buy the higher grade neodymium for peace of mind.

 

I sent my 4 questions to K&J Magnetics (contactus@kjmagnetics.com) and was pleasantly surprised <1hr later with the following informative email:

1. No, I don't think you have to match the fields or strengths of an electromagnet and a permanent magnet to get them to attract or repel one another. A pair of magnets will exhibit forces between them either way, though the actual force you get obviously depends on the strengths of the 2 magnets.

Though it discusses only permanent magnets, you might find our Magnets Are Weird article interesting. It includes some discussion of using dissimilar sized magnets together.

2. If you are making an electromagnet, using an iron core is going to give you more strength than an air core. With the same size and shape number of windings of wire, with the same current running through it, you're going to get a lot more strength with an iron core.

Using a neodymium magnet as the core seems like it should be helpful, but your look at the permeability number reveals that it isn't.

If you are making a solenoid, or a solenoid like device that attracts to another object, you should probably use an iron core, and attract to a steel or iron plate. You could attract to another magnet, though this is obviously more expensive. The advantage of attracting to another magnet would be that you get more strength at a distance.

3. What is stronger, an electromagnet or a neodymium magnet? I'm not sure. Theoretically, an electromagnet's strength is related to the number of turns of wire and the current running through it. So, the physical limits come from keeping the thin wire (thinner wire lets you get more turns) cool enough to not melt.

So, the strength of an electromagnet depends very much on its design.

4. Neodymium magnets are much stronger than other magnet types. They also have a higher coercivity -- that's their resistance to getting demagnetized. You can demagnetize a neo magnet with magnetic fields; it just needs to be a lot stronger than other magnet types.

With ceramic or alnico magnets, you can demagnetize them just by storing them repelling one another. With neo magnets, as long as they aren't very thin shapes, you could literally store them repelling one another, clamped together for a decade, and not see much loss of magnetization at all.

Unless the magnetic field from your electromagnet/solenoid is really, really strong (like 2-3 times as strong as the field around your neodymium magnet), you're not likely to demagnetize it that way.

It's much more common to accidentally demagnetize a neodymium magnet with high temperatures than anything else.

Articles you might find relevant include our Surface Fields 101 article. Also check out our Audio Speakers article, which shows how a speaker is constructed (a coil of wire and a permanent magnet).

Best Regards,

Michael Paul
K&J Magnetics, Inc.
www.kjmagnetics.com

Quoted with permission from Michael Paul.

I have no affiliation with K&J magnetics. However, after this experience I will soon be a customer.

 

It looks like you have gotten to the heart of the matter and found a method to avoid simple mistakes. Congratulations and Thank You.

 

@Strantor, I spent most of the afternoon(retired and too cold to do anything else) looking for the links. I went down so many rabbit holes the first time, couldn't refind all the pages I wanted .

The one you should see is too big to post here, but here is a link to it -
http://scholar.google.com/scholar_u...AGBfm0N7w5C9Ppb-EvazeNrLV4zeGSXkg&oi=scholarr


Here are some more for you to look at. The bibliography at the end of the papers is some times a good link to other papers, when the papers are available to the public, not always available though.


This is a link to a Russian site for hands, it links to different projects all around the world. I didn't know there were so many places working on this.
http://mindtrans.narod.ru/hands/hands.htm

 

Reading more about voice coils, I see that their design is more different than what we are discussing than I thought. The permanent magnetic field in a voice coil actuator is perpendicular to the electomagnetic field (radial magnets). Their operation is explained by lenz's law. The designs and experiments we have discussed so far involve axial magnets; the two fields are in parallel, not perpendicular. But they still work. I'm not sure whose law explains what we are seeing, or why it works, or if it is possible to work as good or better than a radially magnetized scheme.

 

Check out this brain fart that I just wasted my evening on!

I wanted replicate inwo's experiment, but minimize the air gap between the coil and magnets, and also make it longer and slimmer like an actuator.

I was looking around for a thin-walled tube with an I.D. of just barely more than .25" (the O.D. of my magnets) to wrap my wire around. I couldn't find anything suitable so I decided to make something. I bored out this 3/8" bolt with a 6.7mm drill and it was almost perfect. I thought to myself it would be even better made of metal, that way there is barely any air gap at all! The metal is almost touching the magnets all the way around. So I went cross-eyed for an hour or so, making > 1800 turns, and it didn't work at all.

I sat there puzzled, trying different magnet configurations, different lenghts of bars, different currents and polarities. Nothing I did had any effect. The magnets always behaved exactly the same whether there was current flowing or not.

Started thinking of flux in terms of current, and air gap in terms of resistance, and DUH! I shorted the flux right past the magnets with the metal armature! Now I need to print a plastic bobbin one layer thick, with a .26" ID and try again.

 

Kind of two springs (one at each end) wouldn't they help?

I find the voice coil motors fascinating. And much more the price of the screws for linear actuators (moticont) even more !