Electromagnetic Induction

[CasimirFX]

Good Planetary Day Everyone,

I hope this thread will serve as a platform and reference for actualizing a simple inexpensive diy induction dynamo, and 'motorless' assist and EM-brake.

First, let me introduce myself, feel free skip to next paragraph for on-topic. I'm Casimir and after lurking/reading the ebike forums for a couple of weeks just joined this fine, fine board with intent of attempting climbing its the informational ladders towards a inexpensive 2kg assist for bike tours, but I would also like to explore alternative models of transforming electric current to kinetic bicycling energy. Namely the-frame-as-stator-and-the-wheel-as-the-rotor -pipe-dream-subtype (atm). This inspired by two things: my mothers induction-oven-top, and the induction dynamo. I have somewhat good understanding of the electromagnetic theory, and just a little practical electronics experience. I live in Finland as a freelacer artist-type and love art, biking, computers, design, electronics, freedom, funk and.. Ah, on to the topic.

Induction dynamo. A dynamo that can power bicycle lights without any (additional) mechanical moving parts or friction.

The working induction dynamo -models I have seen achieve this simply by placing two or more magnets on the spokes and one coil on the frame along their circular path. This produces a pulse of current from the coil every time a magnet passes it by. This should be easily transformed to dc for a led or four (with a rectifyer & cap). Such as the one from Reelights or this one:

http://www.youtube.com/watch?v=BM6abzny0zQ

Basic theory can be read here: http://books.google.com/books?id=dZG7EFaOPSMC&pg=PA329&dq=induction+generator

In couple of months one is going to need good lights around here once daylenght falls under 22 hours here near the polar circle. So, with that in mind, practical experimentation with induction dynamo is in order in order to learn more, and hopefully this will become a simple experimentation platform towards propeling wheels around with EMF's.

Aside from powering bunch of LED's, induction as a phenomenon is very intriguing... for transferring electric energy to kinetic energy - moving a wheel directly by means of induced electromagnetic field or at least assisting the movement. Using the rear bicycle wheel as the 'rotor' Would this be possible?! After all this already happens in the "electric motor" ppl posting here use! Maybe a modified rim or... Could be your average stainless steel spokes or alu rims simply wont allow for this, and kilos of permagnets would be needed around the wheel, but - 'I want to see it with my own eyes'. So, onward!

I have just recovered a bunch of 24V old relays from a dumpster and thus have lot of coils. I was hoping the coils would have magnets in 'em, but no. Instead these latching relays create MF via a stack metal strips in the middle of a coil to trigger a switch and include a return spring for re-set. This very much brings me back to the question presented by wheel-as-stator -idea (or stuff-on-pokes/rim-as-stator if you like).

What kind of alternatives to permanent magnets are there when producing a magnetic field? Or should one ask primary EM field (without applied current). Maybe in other words: can current be induced in a coil with some material other than 'permanent magnets'?

Also, this path has probably been traversed before by others. Any pointers welcome.

C

 

[fechter]

Welcome to the Sphere.

The idea of turning a bicycle wheel into a brushless motor has been discussed a few times in the past. Yes, it would take quite a few magnets attached to the rim to make it work, but it may be possible. One problem is the likelyhood of the magnets attracting junk from the road and sticking. Another problem is spoke deflection at high loads possibly causing rotor contact.

While in theory, you could induce magnetism into a rotor without permanent magnets the same way an AC induction motor works, but you still need a large mass of iron and copper in place of permanent magnets.

Permanent magnets are likely to be much more efficient.

Making a dynamo to power lights is quite a bit easier than moving a bike. Much lower power level.

 

[bobmcree]

to get any appreciable power you need the magnets very close to the coils. i cannot see this working on a bicycle wheel, and i don't see the point when you can get a perfectly good hub dynamo.

if you are doing it just for fun i will be interested to see how far you get. i tried building a generator a few years ago and found that until i got the coil to magnet spacing down below .5mm it was almost useless. with that spacing dirt is going to be a problem.

the simple solution is room temperature superconducting magnets. just stay away from any ferromagnetic materials like cars which will draw you toward them and stick you to their steel bodies like glue. that and there aren't any, but when space and time are just illusions that should not hold you back.

 

[CasimirFX]

Ah, thanks to the instructables -page below, I now have found an inexpensive source of magnets - used hard-drives. I think these should be easy to come by in quantity.

fechter - Thanks for the Welcome. 8) Just now I am trying to figure out a way in my head to 'temporarily magnetise' just the parts close to the the stator.. Very much 'concept'/imaginary stuff, hah, something like the hubless wheel...

bobmcree - What kind of generator were you building? I would be interested in hearing more. What were the magnet materials I suppose is one important q here.

AFAIK theoretically generator is just the same as a motor, but I am not speaking from pragmatic perspective :wink: My reasons for not using a conventional electromechanical bicycle dynamo include: no moving parts, no friction, no noise, no batteries, no stealables (well, hex'd on frame), possibly lighter weight, learning and having a simple platform for making induction experimentation and measurements on.

Interesting to hear about the magnet spacing problem. The Reelight -'indyctnamo' ppl have their model working from a 3-5 mm distance, if I remember correctly from their instructional video. And then there is this diy kit which recommends 0.5 cm gap (see bottom of page):
http://www.freelights.co.uk/install.html

I found this diy guide which pretty much does the footwork (although I'd like to work out on the physics on a spreadsheet given the time and energy)
http://www.instructables.com/id/Contactless-dynamo-powering-bike-safety-lights/

Afaik the output power is function of magnetic field density (or is it intensity or strength in english). Thus a low density magnetic field would need to pass by closer to the coil. Also I think, according to my physics classes, that the current gradient (word?) will be positive when the magnet approaches the coil and negative when it is moving away from the coil, and thus a rectifier bridge similar to ones in AC-DC transformers is needed. Whew, I hope all these terms mean what I think they mean in english.

Edit: oh, ok. The plot thickens: http://www.freelights.co.uk/how.html - effective function is achieved trough the fact that the magnets on the spokes "push around" a magnet inside the coil which then induces current. Clever...

 

[Reid Welch]

Your English is super-excellent.

I really appreciate you guys for going through these deep waters, explaining to lunkheads like myself
(I am intuitive, not scientific-brained).

It is also a great help in following the arguments (that's not the right word, pardon),
when you do as you all do, and break the lines into bite-sized paragraphs.

A big mass of black text is hard for this reader to follow.

For me, with my weak eyes and widescreen monitor, short lines,
plus highlighting key points by standing the key point alone, grabbing the eye,
makes it easier for a person like me to follow the thought-leaders' points here.

At any rate or style, what a great thread.
I wish I could add even a single, cogent thought.

However, funny thing: today I was reading a practical mechanics magazine of 1881.
There is an article about the various kinds of electric motors, dynamos, "magnetos",
as brushless AC generators were termed then, or soon after.

The very early workhorse motors all fell into one of three basic types.
I just about bet that if I were to transcribe the article at hand to this page,
some of you would say, "Wow. Those very early electrical men knew their motors."

Nothing much has changed, but for the vastly improved permanent magnets available today;
not at basis.

Thank you, gents, for this thread.
I'm learning a bit, just a bit, and even that bit of new understanding is,
personally, exciting my field ha ha (a very bad pun)!
I should be banned for that last line.

Cheers,
Reid

++++++++++++++++++++
I see in first posting but not having previewed,
that my line breaks, some of them, are odd indeed!
That is not the look I have in the posting comp window.

So I will fix the line breaks to look right on this 22" widescreen monitor.
I don't know the technical cause...but I do know how to say "crap!!!!" :lol: :lol: :lol:
Tip to myself: use "preview" before posting.

The video below, irrelevant to this thread. Stop reading now.
PS: world's first plug-into-the-mains electric motor, ever.
It was ours, and is gone now. Series wound, you will see it run for the first time EVER on AC.
There is a serious error in the overlaid text: Curtis was not the "financier"; he was an equal partner with Crocker.

Curtis went on to invent the steam-electric turbine alternator still used today.
Crocker went on to invent, at the end of his life, early helocopters.
Wheeler invented at the same time as this motor was made, in the same shop,
the world's first mains-powered desk fan. No more battery motors, not in NYC, anyway:
real work to be done at low cost by tapping into Edison's new DC power distribution system.
I digress too much. But what a lovely, lovely motor:
the rarest, and this example of this model is surely the best-preserved of all two or five or so survivors;
still like new, but with patina, only.
Best with this low quality thing, is to doulbe click on the player window, and from there, choos "HQ"

it is not an HD upload by a far sight: cheap old digicam.
See the related video for an "HD" quality movie of the same motor ticking over?
To see the below-film in "HQ", you must double click on the player window, then select "HQ".
You'll get a somewhat better quality image. What's here below is poor for several reasons:
it's old, made with an old-style mini digicam, not HD at all. And YT compression, etc.
And the sound of the old digicam's inbuilt mic is grating to the ear.
~~~
See graphically how voltage and speed are interrelated;
how load increases current (power) draw,etc.

Motors are "simple". HP is torque times rpm, as all know already,
but I'm still hammering my own head with noob basics. 123 years ago:
[youtube]pkLyhUCIJW0[/youtube]
PPS: if interested at all, see the video response re-do of the demo;
gotta go to the actual YT page for that (double click on this player window right above for that, though)
I used a better camera and mics second time around.
In "HQ" playback, the second demo is far superior.

PPPS: here is a url leading direct to the last-ever public demo of the motor.
It was to be sold on eBay, and it did sell. This is my self-souvenir video of the grand old thing,
still as strong and unworn as when new, nearly.
http://www.youtube.com/watch?v=ctoUBMly1AE
SELECT HQ for best playback.
Dial up readers: Sell your first-born child if necessary and get some sort of broadband service
so you can seeeeeeeee VIDEOS and movies and all sorts of wonderful things.
This new age of internet is more important to mankind than even movable type, or the incandescent light! And we are yet in its crude, baby-steps infancy for now.
Truth!

 

[CasimirFX]

Reid Welch - What a beautiful piece of work! And to ramble a bit, yes, I can relate to your words about 'noob basics'. I am so there, despite physics, electronics and circuit design courses. Ah well, one day I hope I will understand reality.

On topic of brushless/induction dynamo:

To me it now looks like this type of 'magnet-in-spokes-er - uh-pushing-around-a-magnet-inside-a-coil-with-370-turns-of-wire' -design generator boils down to simply one thing. After all, attaching magnets to spokes using old spoke reflectors is as easy as making or reusing a coil. But most problematic part of this design, on paper, seems to be:

How to make the magnet inside the current inducing coil stay in the middle of the coil-cylinder, and rotate effortlessly? Gee, how does a rotor rotate inside a typical electric motor? Wait - I think I could make this out of an small used motor. I'll have to go dumpster diving for old floppy drives tomorrow. Or something with a typical electric motor. Reinventing the dynamo? I guess I will find out the 'catch' as to why bicycle dynamo's usually use mechanical wheel to actuate the rotor as opposed to pushing it around with a spoke or rim-attached magnets when I play around with it.

After that one can wonder if it would be possible to make each spoke act as a magnetic field source (again my favourite game-of-thought).

 

[bobmcree]

i first tried to make one of the kollmorgen brushless motors into an alternator by adding diodes, and it would not generate more than a few watts with a lot of power in from the small 4 stroke gas motor i tried to make into a gen. the magnet in these motors is a ferrite cylinder, so i thought if i put some N48 rare earth magnets on the steel drum to replace it that i would see a lot more power; i didn't. then i realized i had too much space between the magnet and the coils. i shimmed the magnets with some sheets of steel to reduce the gap, and it produced about 5 watts when spun with my electric drill. i gave up and bought a honda ex350, which is the smallest gen i have ever seen, and weighs under 20 lbs. i have used the gen on my trailer to keep the battery charged and extend range significantly. When you look inside a gen you will see the spacing is very small and not something one can achieve without a machine shop.

room temperature superconductors are not science fiction, but they are not quite science fact at a price any of us could pay. of course there would still be the problem of attracting objects with steel or other ferromagnetic materials in them. i have seen the campy 3w hub dynamo for under $100 and it is pretty cool.

 

[Reid Welch]

Bob is right. And thank you for the kind compliment of my windy post, CasimirFX of Finland.

I know nothing much of theory; can't do math. I self-taught what little I know by reading through every page of Scientific American magazine, from 1848 through 1945. I am a high school dropout. That's as far as my formal education went.

I witnessed, in those pages I still have, but must unload (give to the Google people, to put up online???),

I witnessed the birth and development of all the various batteries, magneto-electric machines, and watched the Statue of Liberty first tour the USA in parts, then to be assembled. I watched, month by month, the Brooklyn Bridge being built.

Fact: induction motors, brushless, AC, were in practical use in the 1850s.
They were most commonly used for electro-therapy: can generate high-enough voltages to give a shock,
but very little current; and this is long before the Rumkorph (sp) coil came to be well-known.

All the early motors depended on batteries to run, or a hand crank or steam engine to drive.
The electric light was not invented by Edison, but decades before, in the form of the arc lamp,
or "electric candle", which is a more apt name for it.

I am perhaps the only person to ever photograph and publish The Arc in actual operation.
It's on YT. I self-aggrandize but know nearly nothing in depth.

Anyway, the pure induction motor, or "magneto" was made by the millions.
It produces very little POWER, as a general rule.

But shocking, isn't it, that a fully levitating, actual train was made around 1910, fully perfected,
would go a hundred miles per hour, easily. But was never made in full scale, because of the magnet issue:
it required electro-magnets in series and parallel, in huge numbers, of huge size, and so, the train (they made scale models that would carry a child around a large room one hundred years ago), it was just too inefficient to consider making it full size; it would never, with that technology of yesteryear, be able to compete against the steam loco, which, at best, was only about two percent efficient at converting coal or wood into motive action.

Anyway. This induction motor, Casimir, appears to offer challenges worth trying to beat,
yet, it has surely been tried before and abandoned. Almost no idea of today was not tried many decades ago;

even semiconductors are about as old as the electric battery itself!
The transistor: now, that was simply but wonderfully, an analogue, solid state, for the triode vacuum tube;
itself a fluke invention that was not understood even by its inventors, not until about 1914, when someone realized that the triode could be used to AMPLIFY small potentials to control great, great amounts of power.

First ever (I think) video of the carbon arc flame. First and only good one on YT, at any rate.
Guess who made this vid below?
Be sure to see the accompanying video at YT; you'd have to double click this player
and look for the video response at the YT site, under the player over there.
"CRIminy!" That is a pun. Color Rendering Index. Also an Aussie term for "bejeezus hell!"
[youtube]Hi7uifnYFvQ[/youtube]

Of all the electrical lights ever made, only the carbon arc comes close to duplicating natural sunlight;
in fact, it has no "holes' in its ROYGBIV spectrum, unlike all other kinds of electric light.

I must stop 'jacking C's thread. Pardon me. I bow to the real genius because he WILL persevere;
I only dabble and fumble.

Direct link to "CRI-miny!" Watch it? Watch out for your eyes :wink: UVA, UVB, UVC, RF, and LOTS of visible light (in the original; the video is harmless).
http://www.youtube.com/watch?v=iJeJtDcHEww

Q: For noobs: what is the coiled nichrome wire for? This is AC powered.
But even if DC powered, the wire is required. Why?
What role does the series-connected resistance wire play?

r.

 

[liveforphysics]

The Agni motors use an axial flux-gap design.

Using the wheel itself seems like a problem for collecting debris, and normal wheel deflections could be an issue with tight flux-gaps.

I'm visualizing using a common disk brake type hub, and adapting something to the disk to extend it outwards to the desired radius, and afixing the magnets. Now we no longer have issues with spoke deformation, wheel flex alignment issues, and debris can be minimized by keeping the magnets at a fair distance from the ground.

Then a section of stator, which I would imagine wouldn't need to cover more than 1/6th of the circumfrence of the rotor could be mounted in similar fashion to mounting a disk brake caliper.

Best Wishes,
-Luke

 

[CasimirFX]

liveforphysics - that disk brake -type structure is very good idea. Close to the axle 3-5 mm tolerance is a lot.

I wasn't quite sure why you mentioned the Agni axial flux-gap motors, or what it was - so I ended up reading this:
http://books.google.com/books?id=jearIV8uVPoC&pg=PA4&dq=axial+flux+motor (Axial Flux Permanent Magnet Brushless Machines By Jacek F. Gieras, Rong-Jie Wang, Maarten J. Kamper)

Partitioned flux-gap alternator? The slic-a-pie dynamo? I think I will hit the bar now.... :lol:

 

[liveforphysics]

Yup, the slice of pie dynamo. That's exactly what I was getting at I see no reason why it wouldn't work.

 

[julesa]

You could just install a very small hub motor on a wheel and connect it up to rectifiers... unfortunately that wouldn't make use of your bargain coils so I guess maybe that idea's missing the point. Maybe you could build your own small hub-motor-style generator?

 

[CasimirFX]

Just before going out for the usual 3 hour bike ride, heavy downpour started so now I'm stuck inside.

julesa - Yes I could, well, or just get a hub-dynamo. But I want something that I can easily build (no shop).

I think bicycle wheel is strangely unexplored in its electromagnetic properties! Or perhaps I just cant find the material online. And how foolish it was to think I understood 'the basics'. I keep having to go back to reading what induction was again, even just simple stuff on force and work trying to understand if/why would(n't) something work.

Trying to gain theoretical upper ground I have been rehashing a lot, here are some of the pages I read

http://en.wikipedia.org/wiki/Faraday's_law_of_induction
http://en.wikipedia.org/wiki/Lenz's_law
http://en.wikipedia.org/wiki/Maxwell's_equations
(Maxwells original 1861 paper http://en.wikipedia.org/wiki/File:On_Physical_Lines_of_Force.pdf )
http://en.wikipedia.org/wiki/Magnetic_monopole
http://en.wikipedia.org/wiki/Lorentz_force
http://en.wikipedia.org/wiki/Electromagnetic_induction
http://en.wikipedia.org/wiki/Electrostatic_induction

http://www.physics.umd.edu/lecdem/outreach/QOTW/arch11/q218unipolar.pdf

Whats this I read about unipolar statorless motor?! No Lenz-law-losses? :lol:
http://www.stardrivedevice.com/over-unity.html

Plenty more where these came from

 

[CasimirFX]

To save money, time and hair, I decided I am going to do all the homework I didn't do at high school and HIT now. These I found were pretty good, or plain fun.

Faraday, Lenz, Induction Video lectures (physics, very good elementary stuff with demo's)

* MIT Physics II by Walter Levin, lectures 16 through 23
- Very good elementary stuff with demo's. Thanks MIT & Prof. Lewin!
http://academicearth.org/lectures/induction-faradays-law-and-non-conservative-fields

You can further pick and mix from these. Better than the prime time mush they show on TV!!
http://academicearth.org/courses/physics-ii-electricity-and-magnetism

Power, Energy, Batteries, Electronics (engineering)
* Energy and Power, MIT Circuits and Electronics by Anant Agarwal, lecture 24
http://academicearth.org/lectures/energy-and-power

Dynamics, Kinematics, Torque
- Stanford Uni Robotics by Oussama Khatib, a lecture with ebike related physics for calculating loads
http://academicearth.org/lectures/lagrange-equations

Tesla's Unipolar Generator
http://home.earthlink.net/~drestinblack/generator.htm or
http://www.bibliotecapleyades.net/tesla/esp_tesla_25.htm