Author Topic: Axial DC motor project  (Read 1958 times)

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Amish_Fighter_Pilot

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Axial DC motor project
« on: August 19, 2017, 08:10:54 AM »
Hello everyone. I'm planning to eventually create our own power systems around this property instead of the gas generators we're currently forced to use. We're being denied utilities by the city and power company so we've had to be creative...

Anyway, the motor I really want to build is a axial flux type motor, but I do not want alternating current. I know that DC axial flux motors are absolutely a thing because many electric vehicles use them. What I don't see is people building DIY versions as generators. So getting the information I need is proving harder than I'd hoped.

So, my plan for a test version of this general idea will probably use hard drive magnets. They're by far the easiest magnets for me to get and I will be creative to make them work even though they're oriented the wrong damn way for most things. I will be putting them on an axle and then I'll spin them over my stationary windings. I plan to take the same pole for all the magnets and orient it so the disk they are on makes one big ring magnet basically. Its going to look really weird because the drive magnets are curved, but that will be fine for a test model. I'm using recycled motor wire for the windings, so this thing will be quite the recycling project.

Wiring the armature is more of a complicated topic though. What I think I want for best copper density is two rows of windings, one forming a smaller "inner track" and one "outer track". The exact shape and configuration of the inductors is definitely somewhere I need help. I'm assuming the wedge-style inductors common on DIY wind turbines here would be acceptable. I'm assuming air core is probably best for this job, but I'm open to suggestions. Wire gauge, number of turns, and exact dimensions of the coils is still undecided. I was considering wiring the coils in parallel, but maybe in groups of series parallel. It would be nice to keep the output in the 12V range, but even up to 48V is pretty workable. If the output potential gets a lot higher than that, I do have a magnetic DC transformer I invented that could be used(though I don't know how efficient it is yet).

The first version of this motor will be tested by compressed air through a "Tesla Turbine", so the rotational speed should be pretty consistent at a given pressure. So, basically the rotational speed can be set to whatever I want and kept there.

hiker

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Re: Axial DC motor project
« Reply #1 on: August 19, 2017, 10:51:39 AM »
Some of those H. D. mags have a n. S. Pole on the same side..they snap in half fairly easy..use a vise or a pair of vise grips...easyer to do if you score one side with a hack saw..been a few members here that have built wind gens with h.d. Mags..check out the search box ...top right ?
WILD in ALASKA

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #2 on: August 19, 2017, 11:47:43 AM »
I did find quite a post where the guy was cutting them in half. That's certainly a much easier-to-handle size even despite the slight curve. I may try that.

Any thoughts about sandwiching my coils between moving magnets on both sides of the disk? I've seen this configuration on commercial products, but all the DIY versions are AC that I can find. I'm pretty adamant about getting low-to-no-ripple DC out of this thing.

joestue

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Re: Axial DC motor project
« Reply #3 on: August 19, 2017, 01:19:52 PM »
you can't get dc out of a changing magnetic field.

the only way to get ripple free dc power is the homopolar motor. its a practical option for a few tasks, such as making 1 volt at thousands of amps for electrowinning copper, before the invention of the diode. that's about it. there are superconducting homopolar motors being used for ship propulsion.

anyhow, 3 phase is sufficiently ripple free once you add an inductor and capacitor to the rectifier. if you need better, there are some practical options, such as 5 phases.

computer hard drive mangets are about ideal for an axial flux machine, on the order of 6 magnets, so that would be 12 poles. yes you can break the magnets in half and then cluster them together to make a larger machine, or increase the pole count beyond what is practical.

as far as the size of the coil: hard drive manufactures are interested in the highest angular acceleration they can get that read head moving for the least mass of copper: which means the coil is actually very close to ideal in terms of diameter, inside and outside diameter ratio and thickness.

if you want to make a compact axial flux motor, copy the profile of that coil and make (i think, 18) similar coils. squash the coils together so you get the overlapping, 2 layer, 3 phase coil structure, and make an axial flux machine from the magnets pulled from 6 identical hard drives. plan on finding more than 6 identical hard drives because some of the magnets will break when you pull them off the mu-metal backing.
« Last Edit: August 19, 2017, 01:24:06 PM by joestue »

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #4 on: August 19, 2017, 01:37:05 PM »
I'm not planning to make a changing magnetic field. I'm confused by what you mean by that.

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #5 on: August 19, 2017, 01:44:59 PM »
To get a better idea what I am talking about with regard to the magnets, please take a look at a floppy drive motor. They have a big flat disk magnet above a radial set of coils. I want a magnet configuration like that, but with axial coils instead of radial ones.

joestue

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Re: Axial DC motor project
« Reply #6 on: August 19, 2017, 02:13:32 PM »
To get a better idea what I am talking about with regard to the magnets, please take a look at a floppy drive motor. They have a big flat disk magnet above a radial set of coils. I want a magnet configuration like that, but with axial coils instead of radial ones.

they run on ac, 2 or 3 phases digitally generated by a microprocessor..

a series of north and south magnets moving past a wire makes a changing magnetic field.

Mary B

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Re: Axial DC motor project
« Reply #7 on: August 19, 2017, 03:53:47 PM »
DC is your car is generated by an alternator that produces AC, it is rectified then filtered by the batteries capacitance/inductance. Just use some diodes and big capacitors out of computer power supplies. If they are high enough voltage you can string a bunch in parallel to get the clean DC. My ham radio gear AC power supplies take 120 volts AC and convert it to 13.6 volts DC with no ripple(any ripple = hum on the transmit signal).

So nothing wrong with building an AC generator and rectifying it. It is how things are done.

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #8 on: August 19, 2017, 06:10:49 PM »
To get a better idea what I am talking about with regard to the magnets, please take a look at a floppy drive motor. They have a big flat disk magnet above a radial set of coils. I want a magnet configuration like that, but with axial coils instead of radial ones.

they run on ac, 2 or 3 phases digitally generated by a microprocessor..

a series of north and south magnets moving past a wire makes a changing magnetic field.

You raise a good point. I should have been more clear with my thread title that I'm trying to generate power rather than have a motor I can control. I suppose what I am envisioning is a more complex homopole motor.

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #9 on: August 19, 2017, 06:19:46 PM »
DC is your car is generated by an alternator that produces AC, it is rectified then filtered by the batteries capacitance/inductance. Just use some diodes and big capacitors out of computer power supplies. If they are high enough voltage you can string a bunch in parallel to get the clean DC. My ham radio gear AC power supplies take 120 volts AC and convert it to 13.6 volts DC with no ripple(any ripple = hum on the transmit signal).

So nothing wrong with building an AC generator and rectifying it. It is how things are done.

Its very possible that may be what I end up doing. I already have an alternator and can maybe get more of them soon. I still really want to build what I guess will be a homopolar motor, only reversed from how its usually done. I will be turning the magnets with a Tesla turbine.

joestue

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Re: Axial DC motor project
« Reply #10 on: August 19, 2017, 07:31:40 PM »
I will be turning the magnets with a Tesla turbine.

they don't work that way. you turn the disk (or cylinder) inside the magnetic field..

when you rotate a magnet on its own axis.. the magnetic field doesn't rotate.

dnix71

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Re: Axial DC motor project
« Reply #11 on: August 19, 2017, 09:20:29 PM »
Tesla turbines operating from compressed air will be horribly inefficient because compressing air and using it to drive a motor is horribly inefficient. When you compress air it heats up. Then the heat radiates away and you lost most of the energy you spent compressing it.

If you need to make power off-grid, solar PV is cheap, safe and easy. If you have absolutely no money, then you might have to improvise. If you are already buying fuel for a gas generator then you must have some money.

It would help if you could tell us the kw hours of energy you need, what applainces you have to run, etc., plus your local climate. Direct thermal solar hot water is very easy. If you have lots of sun you can cook with reflective parabolic solar ovens for basically nothing.

Living completely off the grid requires thinking different.

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #12 on: August 19, 2017, 10:20:48 PM »
The Tesla turbine is just to test it with since I have easy access to compressed air and it's quieter than some other options. Electricity is at a premium on our property right now.


they don't work that way. you turn the disk (or cylinder) inside the magnetic field..

when you rotate a magnet on its own axis.. the magnetic field doesn't rotate.

You should really read this thread: https://www.physicsforums.com/threads/magnetic-field-rotation-or-not.805357/

Faraday himself did experiments that showed a disk of copper could have emf induced in it by rotating the axis of a magnet over it. Its possible because of relativity. The propagation of the field lags a bit the further out you go. Think Einstein light clock to get a feel for what I am talking about.

joestue

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Re: Axial DC motor project
« Reply #13 on: August 20, 2017, 02:32:56 PM »
here's a good video.

https://youtu.be/gduYoT9sMaE

btw, if you could get the magnet to spin by supplying current through the disk (or change the topology so you can get thousands of turns to get more practical volts).. wouldn't you suspect most motors would be designed this way? no brushes to wear out...

dnix71

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Re: Axial DC motor project
« Reply #14 on: August 20, 2017, 05:29:20 PM »
joestue

I was taught the the wire and magnetic fields had to move at right angles to induce a voltage. So if you rotate a disk magnet like the video showed, the magnetic field is not changing as it moves through the wire because the magnetic field is bipolar up and down.

But if the magnet was diametrically magnetized, flat across, then spinning it like the video would be the equivalent of spinning a bar magnet and that would induce a current. You could even magnetize more than one N and S pole.

http://www.magmamagnets.com/permanent-magnets/radial-sintered-magnets/ Expensive but now possible in quantity.

joestue

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Re: Axial DC motor project
« Reply #15 on: August 20, 2017, 06:03:27 PM »
I was taught the the wire and magnetic fields had to move at right angles to induce a voltage. So if you rotate a disk magnet like the video showed, the magnetic field is not changing as it moves through the wire because the magnetic field is bipolar up and down.

two ways to make voltage.. move the wire through the field, or change the value of the field. the field doesn't move, which is why you can't make voltage by rotating a magnet on its axis.


now obviously we can shoot a magnet out of a rifle, and argue that the "field" moved, but that's not what happened. rather than a source of magnetic flux that's dragged along with the magnet, think of the magnet as a superconducting coil of wire carrying a current. you moved the coil, not the magnetic field, which increased and decreased in value at any given point in space as the "magnet" travels by..
« Last Edit: August 20, 2017, 06:09:20 PM by joestue »

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #16 on: August 20, 2017, 08:50:35 PM »
It would appear the current flow and potential develop between the inside of the disk and the outer edge. Its the return path for the circuit that creates the design challenges, but I think I have a solution for that which wont involve slip rings or a commutator of some sort.

Homopolar generators already exist and apparently generate huge current but extremely low potential. Tesla wrote a short letter regarding the matter at one point, and suggested there may be ways to increase the length of the path from the center to the edge of the disk. He never got around to developing anything with it. I have a few ideas toward that end though.

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

dnix71

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Re: Axial DC motor project
« Reply #17 on: August 20, 2017, 08:55:30 PM »
The field of a magnet is small. If you move the magnet you are varying the field. The lines of force are not straight or infinite. All motion is relative.You can take a wire, hook it up to a voltmeter and move a magnet back and forth near it and generate voltage. It's the crossing of fieldlines that take energy and therefore makes electricity.

joestue

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Re: Axial DC motor project
« Reply #18 on: August 20, 2017, 09:58:19 PM »
There was some bs about using a spiral segmented disk to increase the "length" of the conductor, but when you understand what is going on you'll understand that they were probably duped by the lower eddy current, so it appeared to have more volts than a solid disk but if the magnetic field was more uniform they would have gotten the same result.



Anyhow i supect that man will invent a method to exert a force against spacetime itself ( as the supposed trapezoidal microwave resonant cavity supposidly does... lol!) But until you figure out how to do that, youll be stuck with homopolar motors which require slip rings.
« Last Edit: August 20, 2017, 10:05:40 PM by joestue »

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #19 on: August 21, 2017, 08:55:28 AM »
here's a good video.

https://youtu.be/gduYoT9sMaE

btw, if you could get the magnet to spin by supplying current through the disk (or change the topology so you can get thousands of turns to get more practical volts).. wouldn't you suspect most motors would be designed this way? no brushes to wear out...

That video is just flat out wrong on this topic by the way. I watched it through and the info is just not correct. The field does spin, be cause each molecule of the magnet is a magnet in and of itself. While a bunch of magnetic molecules together, like a bunch of magnets together, form a larger field in effect, they're actually still just a bunch of smaller field sources.

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #20 on: August 21, 2017, 09:00:58 AM »
The field of a magnet is small. If you move the magnet you are varying the field. The lines of force are not straight or infinite. All motion is relative.You can take a wire, hook it up to a voltmeter and move a magnet back and forth near it and generate voltage. It's the crossing of fieldlines that take energy and therefore makes electricity.

Field lines are virtual. Unless you drop something like iron filings in the field, no "lines" form. Magnetic fields in general only really exist when they're being interacted with. They're very Schrödinger like that... Field lines basically don't exist, even though they seem to.

dnix71

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Re: Axial DC motor project
« Reply #21 on: August 21, 2017, 05:17:31 PM »
If you make voltage and amps on the disk I assumed it was eddy currents joestue. No disagreement there. Spinning a disk like that is the hard way to make electricity.

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #22 on: August 21, 2017, 10:05:19 PM »
If you make voltage and amps on the disk I assumed it was eddy currents joestue. No disagreement there. Spinning a disk like that is the hard way to make electricity.

Spinning the disk is a great way to make certain types of output, but not so much for producing good voltages. The reason the spinning magnets don't work in the classical Faraday Paradox test is that the EMF is induced relative to the return path, and so it was necessary to spin the disk to produce current. So the return path is a big deal, and the main reason the spinning magnet test doesn't work. Where there is a will, there is a way though. I have just the solution in mind.

joestue

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Re: Axial DC motor project
« Reply #23 on: August 22, 2017, 11:10:21 AM »
If you make voltage and amps on the disk I assumed it was eddy currents joestue. No disagreement there. Spinning a disk like that is the hard way to make electricity.

some of the early homopolar motors were laminated, I presume most of them are today. there is work being done to use them for ship propulsion, superconducting magnets of course..

anyhow, the reason spinning the magnet on its axis is because there's no emf generated anywhere.

Edit: when the magnet is a conductor you get voltage across the magnet when rotating the magnet...
« Last Edit: August 22, 2017, 03:51:09 PM by joestue »

Amish_Fighter_Pilot

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Re: Axial DC motor project
« Reply #24 on: August 23, 2017, 08:22:04 AM »
Think of this problem as one of those carnival gyros that spins all the people out to the edge using centripetal force. Imagine changing their path to the outside so they spiraled out. They would build up more momentum before reaching the edge if done right, but then if you wanted to channel a few of them back to the middle you'd be fighting the force pushing out. This is why there's no EMF measured with the even field. The back EMF kills the forward EMF. This is why the return path is everything. In the case of the spinning magnet and the disk, the EMF is created relative to the slip rings or commutators.

Just to be clear, I'm not some "Overunity" nut. I'm well aware this won't produce more power than it takes to turn it, no matter what configuration is used. This is just a pure fun sort of concept for now.

I just got a DeVilbiss GB5000 for 50 dollars and got it working, and we have a modified Alton 3500W unit, but these gas generators aren't good for constant use and we have already put 400+ hours on the Alton unit, and it's pushing 700 total lifetime service hours. We have no way to store power currently though and winter is creeping toward us steadily. Right now our biggest priority is getting our tiny mobile home finished.

joestue

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Re: Axial DC motor project
« Reply #25 on: August 23, 2017, 09:08:40 PM »
Think of this problem as one of those carnival gyros that spins all the people out to the edge using centripetal force. Imagine changing their path to the outside so they spiraled out. .

like a water pump centrifugal impeller? The problem is the electrons have no inertia. the mechanical analogy doesn't hold at less than relativistic speeds.


anyhow if you want to store energy in compressed air, it would be best to directly convert that compressed air back to useable shaft hp at the task you need it to perform.

air driven water pumps, even kitchen appliances have been used in the past.

MattM

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Re: Axial DC motor project
« Reply #26 on: August 23, 2017, 09:13:40 PM »
The phrase, "there is more than one way to skin a cat" comes to mind.

There are all sorts of unconventional methods that create identical results.  Nothing wrong with choosing your own path of least resistance.