Magnic Light: contactless bicycle dynamo light

[dougmc]

Putting potential principal working aside, such as at 0.0001% efficiency or 0.0001W power output, the considerations leave the scam as an only option for what is demonstrated in the videos. Incidentally, recent Popular Photography has a discussion of how to initiate a project on Kickstarter. The need to convince the Kickstarter to take you on might be one reason for such desperate measures as making a fake prototype.

Yes.

Though their design alone is cool. They could have just give you some magnets to mount your spokes near the rim and made this all plausible -- not as neat as promised, but real world. Instead, they've promised a product that that can never be delivered (unless I've missed something major here.)

Or, as I mentioned before ... maybe they do think it's possible, it's just that they need the money first to get to that point, and so they make fake prototypes to reach that goal? I don't know.

Their investors will be pissed if they've paid $200+ dollars for a cool light and either get 1) nothing or 2) a light that isn't anywhere near as cool as promised. And given the dollar figures involved if this gets funded ... these people then deserve to go to prison for fraud.

(Of course, before all that could happen, the thing would need to get funded, they get their money, they get some time to deliver on their promise and then they fail to do so to some degree. Given how fast their dollar figure has increased, it seems like they will reach their goal to get funded if something doesn't happen before that.)

 

[2_i]

In my idea, the magnetized disk has multiple poles along its perimeter. The edge of the disk is located near the rim, and the drag of the eddy currents drags it along with the rim, spinning the disk. Once the disk is spinning, it's a minor matter to place a coil and suitable flux path near the disk to make use of the changing magnetic field as the poles on the perimeter of the disk go by. Seems plausible to me. The only part that requires a bit of a leap of faith (for me) is that the eddy currents will cause a drag on the disk's poles. Since eddy current is used to produce drag in dynamometers and bike turbo trainers, it seems reasonable (to me) to think that there must be an equal and opposite drag/force on the magnets that cause the eddy current.

I think you are far here, Steve, from reality. When I position a state of the art magnet next to a rim spun by hand, 4-5 mm away - distance as in their video, the wheel nor magnet could not care less, no matter how the magnet is oriented. The only force I can detect is static magnetic, at the rim's joint where the rim is internally reinforced with steel or to the tire's wire bead if I try it with a rim with tire. Theoretically the power dissipation due to Eddy current braking is proportional to the square of velocity. When you refer to the turbo trainers, I suppose a plate is brought to high angular velocity by gearing and there is space there to put electromagnets around.

 

[Steve K]

I don't agree that I'm far from reality. There's no question that eddy current are generated with magnetic fields. The only unknown is what size magnet is needed to produce the desired effect.

I did throw a tubular front wheel into a truing stand and put a strong magnet near it (the magnet was scavenged from a hard drive). I could feel a bit of pull on the magnet, but not very much. It did slow the wheel a bit too. But, it didn't seem like enough force to spin a bottle dynamo by any means. I think the magnet had a single pole on the face that I had oriented toward the rim.

For comparison, I did have the opportunity to disassemble a low end mag trainer from Minoura years ago. It used an aluminum disc for eddy current drag unit, and it had a disc of magnets on each side of the aluminum disc. The discs of magnets each had six circular magnets, about 1" diameter, spaced equidistant around the disc. The magnets looked to be ceramic. They were set up to put a N pole on one side of the disc and a S pole on the other side, providing lines of flux normal to the surface of the aluminum disc. The mag trainer was capable of dissipating 100 to 200 watts, I'm guessing. Based on that, it doesn't seem that unlikely that a good magnetic design for my spinning wheel concept could transfer a couple of watts of power. I'm not that surprised that I don't get good results with the first magnet (or two..) that I pick up.

The problem of getting magnetic lines of flux to enter perpendicular to the surface of the rim strikes me as a challenge. Without magnets on the other side of the rim, the flux would bridge over to the nearest opposite pole, which would tend to make the lines of flux largely tangential to the rim surface.

So.. in summary, I don't think it would be easy to make the idea work, but I'm also not going to say that it couldn't work. There have been too many people who have unequivocally stated that it would be impossible to build some sort of device, only to have someone build it in the near future. I'm just going to sit back and see how this Magnic light turns out!

Steve K.

 

[krienert]

Not an expert with magnetic physics... just my 2 cents.

When holding a quality neo magnet 4mm from a spinning rim, I get a once per rotational attraction when the steel inner-tube presta valve passes. I detect no other noticeable eddy current characteristics.
Note that the rim I am testing on is a triple wall, 30mm depth V-rim. So there is significant dielectric 'beef'.
I also tested a diametrically (opposing tube walls) magnetized neo tube threaded onto an old spoke.
When held in 4mm prox. from the spinning rim it begins to rotate only when the presta valve passes. At higher rpms, this does provide a very constant rotation of the tube magnet. Relating to what Steve K mentioned - maybe if I held a proper sized coil adjacent to the rotating tube I would see ac-voltage, but this current would have nothing to do with eddy currents of the rim...

I just read something on the groups main page... "Magnic Light works with all kinds of metallic rims (normally aluminum, steel or magnesium)."
Does Steel promote eddy currents as well?

I really hope that this concept of retrieving the 'waste' energy's associated with eddy currents is a new discovery. Even if its in the circuity aspects...
Something to look forward too, but I will have to hold onto what little money I have until its set in stone.
Cheers

 

[2_i]

I just read something on the groups main page... "Magnic Light works with all kinds of metallic rims (normally aluminum, steel or magnesium)."
Does Steel promote eddy currents as well?

All you need for eddy current effects is a continuous conductor. However resistivity matters. You get less effect with alu than copper, as resistivity of alu is larger and steel is really bad as its resistivity is nearly 6 times larger than of copper. In physics demonstrations you dip a conductor in liquid nitrogen to lower its resistivity and apply really big currents in electromagnets to make conducting rings jump.

Regarding other comments, human mind has a utility when it can make predictions and not wait time and time again for tests, such as in dropping a 1001'th reindeer off a skyscraper to test whether reindeer really can't fly.

 

[AnAppleSnail]

If all we want is a non-contact interface with the wheel, well...

Could the device contain a magnet-lined wheel? That is, there is a standard dynamo inside their device that couples to the induced fields of the bicycle wheel to turn? It's like an extremely lossy mag control ring...

 

[krienert]

thanks 2_i.
Gave me a bump to do some other reading on the subject...

 

[2_i]

Could the device contain a magnet-lined wheel? That is, there is a standard dynamo inside their device that couples to the induced fields of the bicycle wheel to turn?

I think this is what they could have done for the videos, i.e. taped their strong magnets to the inside of the rim and put a coil into the lamp, driving their LEDs. Their naivety might be in thinking that getting something similar done with Eddy currents is a trivial issue that they could e.g. get some external help with and, in the meantime, they should go forward and secure funds.

 

[krienert]

if the coil was somehow shielded from the magnets fields... what would happen to the eddy currents induced in the rim
with two static magnets reversed sandwiching the coil?

 

[2_i]

krienert, any stationary situation, where the permanent magnets have fixed positions relative to the coil and the rim is moving at a constant speed, will not produce a current in the coil. To get current, the magnetic flux through the coil needs to be changing. In your configuration this would be happening if the rim were accelerating or decelerating. Still, even in that situation the induced current in the coil would likely be very feeble because it is hard to produce a significant quickly changing Eddy current.

 

[krienert]

Thanks 2_i. Been reading the last couple days, without finding out how eddy current can alternate.
So as the top sketch shows, eddy currents are DC so the coil would not see them?

And the bottom sketch would suggest they would alternate, but it would not be significant enough an AC field for the
coil to notice?

 

[2_i]

The fact that the Eddy currents alternate when moving along the rim is not what is important for the coil. The coil cares only whether the magnetic field encircled by the coil changes as a function of time.

 

[AnAppleSnail]

I think this is what they could have done for the videos, i.e. taped their strong magnets to the inside of the rim and put a coil into the lamp, driving their LEDs. Their naivety might be in thinking that getting something similar done with Eddy currents is a trivial issue that they could e.g. get some external help with and, in the meantime, they should go forward and secure funds.

Ah, I meant that the unchanging eddy current may be used as a non-contact coupling with the nonmagnetic bicycle wheel to turn a small dynamo inside their box.

 

[AndreyT]

The trouble here seems to be the assertion of no moving parts. If you have no moving parts and a uniform wheel-magnet separation, then the induced field will not move. With no moving parts to move coils through that stationary (to the device) magnetic field, no power can be produced. It's analogous to a marble on a tabletop - without any tilting, it won't get anywhere...

Actually, the fact that the wheel rim is rotating is already sufficient to produce power. I understand the intuitive feeling that make you to conclude that it is impossible. It feels like a paradox, and a very well-known paradox from the history of physics: so called "Faraday paradox". Wikipedia has a pretty good article on it

http://en.wikipedia.org/wiki/Faraday_paradox

The principle that makes so called "Faraday motor" to work, as well as makes the "Faraday generator" to produce electricity was puzzling theoretical physicists from the beginning of electricity. It reveals that in such cases the way we usually "imagine" the concept of magnetic field in our heads is not always appropriate (just like thinking of atoms and electrons as little spheres is not always appropriate).

In your post above you mention the importance of "uniform wheel-magnet separation". This is basically another way of saying that in such system (with "uniform separation") the magnetic flux through the rim does not change (even if the wheel is rotating) and therefore the system cannot produce power. The rotation of the wheel appears to be inconsequential. This is the same fallacy that trapped many physicists for centuries. That is the same fallacy that the above Faraday paradox is rooted in.

The fact that the wheel rotates matters and matters a lot, even if the distance between the wheel and the magnet remains constant (and magnetic flux through the rim remains constant as well). The explanation of how it works (several version of which is available in the above Wikipedia article as well as elsewhere) feels rather counter-intuitive for a person used to classic "everyday" concept of magnetic field.

It is interesting to note that people rarely question the validity of Faraday motor. I'm sure you all saw the videos on Youtube

http://www.youtube.com/watch?v=k7JTyRBfeF4

But at the same time people find it hard to believe that the same principle can be made to work "in reverse", to build a Faraday generator. Yet Faraday generator works too.

P.S. I'm not saying that the device discussed here is precisely a Faraday generator. I'm just saying that the intuitive difficulty that often prevents people from grasping the concept is pretty much the same as the one in case of Faraday generator.

 

[krienert]

AndreyT. wow.
cool reference.
Is what you saying, that the wheel represents the communicator in the homo-polar motor?
Wonder if there 'is' indirect contact with the wheel...(see photo below) circuit wise, in that the fork is a bridge between the hub-spoke-rim, and the mount on the brake... a long shot though...

-Cheers-

 

[Steve K]

Andrey's statement "I'm just saying that the intuitive difficulty that often prevents people from grasping the concept is pretty much the same as the one in case of Faraday generator" is basically what I was trying to say too... just because you can't explain how it works doesn't mean that it doesn't work!

The earlier reference to regenerative braking using eddy currents has made more sense to me since it was first offered. Like an inductive generator, it does require an applied rotating (or moving) magnetic field that is moving just a bit slower than the rotor itself. It's a clever enough idea when used with a rotor with discrete windings, but even more amazing when used with a solid rotor. Does each electron act as it's own little winding?? There's got to be some advantage to using discrete windings or no one would bother with it. Maybe just lower losses??

The complexity of this inductive generating using eddy currents suggests to me that it's not the technique used in the Magnic. I'm still leaning toward my earlier theory of the rotating magnetized disc drug/spun around by the drag of the eddy currents, but love hearing the various ideas thrown out by the CPF members! I hadn't seen that demo of the homopolar motor before, and am impressed by the bare-bones simplicity of it.

Steve K.

 

[dougmc]

AndreyT. wow.
cool reference.
Is what you saying, that the wheel represents the communicator in the homo-polar motor?
Wonder if there 'is' indirect contact with the wheel...(see photo below) circuit wise, in that the fork is a bridge between the hub-spoke-rim, and the mount on the brake... a long shot though...

I already mentioned a homopolar motor in post #20 and explained why that couldn't be it.

A homopolar motor requires a bushing on the wheel -- and they have explicitly said that this does not touch the wheel. Another problem is that there is not a good contact between the rim and the frame of the bike on most bikes -- on a typical bike, the spokes don't make good contact with the rim or the hub, the hub has lubricated bearings that make poor contact, there's probably paint on the frame where it holds the tire, etc. You can't rely on this to make a good connection. (You could modify your bike to make all this work, but that would remove the neatest thing about this light, how self-contained it is.)

Also, a homopolar motor involves a strong magnetic field across the entire wheel. In this case, there's a strong magnet (I assume) -- but it's in the light unit and nowhere else. To make a proper homopolar motor/generator out of this, you'd want strong magnets all the way up and down the fork -- and really, you wouldn't just want a line of magnets, you'd want them to cover the entire disc of the wheel -- though maybe the line of magnets would be good enough.

The Earth's magnetic field would allow it to make some electricity by itself with no other magnets if we had a bushing on the rim and good electrical contact through the rim, spokes, hub and frame -- but since the Earth's magnetic field is so weak, this would generate very, very little electricity. Also, even that tiny amount of electricity would go away when the bike was facing the wrong direction in relation to the magnetic field.

 

[dougmc]

The earlier reference to regenerative braking using eddy currents has made more sense to me since it was first offered..

A magnetic brake using eddy currents involves well understood physics -- the moving magnetic field causes currents in the metal, which retards the motion that causes the moving magnetic field and makes the metal get warmer. And if you replace the big hunk of metal with coils, you get a pretty standard generator.

I don't see where the word "regenerative" fits into this, however -- we're not regenerating anything. The creation of eddy currents retards motion and generates heat. If you use coils instead, it also retards motion and generates electricity -- and then we stop calling it eddy currents any more.

Any magnet in the light will generate its eddy currents in the spinning rim, and I see no way to get this energy back into the unit to power the light, not with the features they've claimed.

 

[minisystem]

Skepticism is good, but the insinuation that what they are doing is fraudulent seems a bit harsh to me. Declaring that the prototype is fake seems premature. It just seems so unlikely considering they are applying for a patent and are actively demonstrating the device at trade shows.

A request for more clarity on the exact theory of operation was adressed by the inventor in the comments section:

I hope you are satisfied with the following answer: We use a technique that provides alternating magnetic fields instead of a static magnetic field. So the same with the eddy currents which are alternating and the same again in our generator.
We are a small startup and try to start with this Kickstarter campaign- in autumn our technique will be published because of the time limits of patent laws but if we publish it now there will be companies that don't care for patents and start to copy.

My mantra is that extraordinary claims require extraordinary evidence and it would seem that the necessary evidence will be published this fall.

 

[Steve K]

I don't see where the word "regenerative" fits into this, however -- we're not regenerating anything. The creation of eddy currents retards motion and generates heat. If you use coils instead, it also retards motion and generates electricity -- and then we stop calling it eddy currents any more.

go back in the thread and look at the patent that is about regenerative braking for trains (IIRC) using eddy currents in the wheel. If you were willing to throw the same level of fairly complex technology at a bike generator, you could get the same effect as the Magnic. Other than the need to have two or three sets of coils in the stator, you also need to sense the wheel speed in order to create a moving magnetic field that is a bit slower than the wheel motion. Pretty complex, in my view, but it could be done.

Steve K.

edit: the post from 2_i had the link for the regenerative braking patent:
"This patent discusses regenerative Eddy braking"
http://www.freepatentsonline.com/y2003/0189380.html