You cannot create continuous motion using permanent magnets. They do not *generate* any energy, merely store it, like springs. You can make something vibrate for a while, until that energy gets dissipated and it comes to equilibrium, exactly like the spring pendulum in a watch winding down.
You can generate motion with electromagnets, but that's because you have an outside source of energy (chemical reactions in a battery, mechanical motion of a generator, light from the sun, etc.) which is powering your motor.
Not continuously without a changing input.
After reading your comment about the PC fan, every time a blade travels around, it will be attracted to the magnet pulling it forward and then backward as it passes. You'll end up pushing it just as fast as you pull it. It's like trying to speed up a merry-go-round at the park by pushing it but not letting go and pulling as it goes by.
Let me pose a different idea to you though:
**What if your external magnet(s) moved as the fan blade magnets passed by?** That way you can get the push without the pull, vice versa, or even both a pull then a push?
This is like pulling the merry-go-round when the bar is behind you and *pushing* when it's ahead of you. Any kid at a playground knows that's one way to get a merry-go-round spinning.
*Ah-ha!* Now we're getting somewhere right? That would surely cause the rotor to spin faster and maintain it's motion. But you'll notice that it requires a changing input. You need to flip that magnet over, and that requires you put some energy into the system, which makes sense right? We can't just break the laws of thermodynamics because of *magnets*.
So how are we going to flip that magnet back and forth? If you're using an actual magnet, you need to physically move it. That means an external moving part on your motor, and if you keep going down that path it gets really complicated really fast. Next thing you know it'll be magnets all the way down. So what else can we try?
Well instead of an actual magnet on the outside, what if we just used a magnetic field? Magnetic fields can be generated and manipulated using electric currents. [Here's a cool diagram](http://www.learnabout-electronics.org/ac_theory/images/Solenoid-Bar.jpg
) of what a magnetic field created by a wire coil will create. Very similar to the magnet right?
Well it turns out we're now in the process of designing an electric motor. First, lets start with a DC motor. DC is Direct Current, which means the electricity always flows in the same direction. Well if we just swapped your external magnets for an electric coil and powered it up do you think we'd see a difference? Probably not at all. It's pretty much the same magnetic field except a coil instead of a magnet.
One thing that electricity is good at though is turning off and on very easily. Magnets dont turn off and on, but electric coils can. So what if you sat there and flipped a switch as the magnets spun by? Well that's not very practical and your timing would be all off. How can we time it better?
Well what if we put the coin on the fan blade instead? Surely the best way to time a spinning part is to *use the spinning part*. This is exactly how *brushed DC motors* work. They have an electric coil on the spinning part inside that's not directly connected to the power source (e.g. a battery), and stationary magnets on the outside part (called a stator). Also on the stator are metal brushes that connect to the power source. When the inside coil spins around, the brushes contact a metal section on the rotating part and allow current to flow while they're in contact. This "powers up" the magnetic field in the coil. If these are in the right places, the field created will oppose the stationary magnets on the outside, and then as it spins around the brushes will lose contact and cut power to the coil before it starts pulling back.
This ends up being a merry-go-round where the kids all stand on the merry-go-round and push at the same time with one foot each.
It's a very simple type of motor that doesn't require many complicated parts. You can actually try making something that uses the same concepts yourself. Every toy you've had with a battery powered motor probably uses a brushed DC motor. They're cheap and simple to make and can run off simple DC batteries.
So how fast will it go? Brushed DC motors will pretty much go as fast as they're allowed. The higher the current going through the coil, or the higher the voltage pushing that current, the harder the motor pushes. The motor speeds up, the brushes make contact more frequently, and eventually it gets to the point where the resistance against rotating matches the force the power source can push in. In this case the resistance would be two things: 1) Friction, 2) The load on the motor i.e. the air the fan is pushing.
There are brushless DC motors as well, but those have other more complicated parts I don't want to talk about.
But lets talk about AC now, or Alternating Current. The power in your home uses AC. This is current that doesn't just flow in one direct, but switches back and forth very quickly. In North America, our AC is 120V and 60Hz, meaning it switches back and forth 60 times per second. This ended up being a really efficient way to send power because it can be transformed to different voltages and currents very easily. It's also the reason many of your electronic devices have a black box on the power cord. Those are doing up to two things: 1) Transforming it into a more appropriate voltage, and/or 2) converting it to DC current. But motors happen to really like AC current.
Remember our coil diagram? Well what do you think happens when the direction of electricity reverses? Simple: it reverses the magnetic field. Remember how earlier we said that it might be handy to flip the magnet over so that it pulls *and* pushes the magnet on your fan blade? Well AC is already doing that for you. It's flipping it's power back and forth, and if you hook a coil up to AC power, it will have a magnetic field that flips back and forth.
Before I go on: **DO NOT** just start connecting things to your home power. In fact, don't do it at all. If you want to play around with AC, go to an electrical hobby forum or something and start learning there. You can pick up a hobbyist power source capable of spitting out multiple voltages, currents, frequencies, and phase numbers of DC and AC. Start there.
If you use your home power, you're putting yourself at a huge unnecessary risk. With out properly inspected wiring and approved parts, you can easily connect a low or zero-load circuit, and hopefully your home circuit breaker can trip before damage is done. At the very least, you'll still get a nasty shock and you can burn all your components or worse - the wiring in the wall causing a house fire.
Using alternating current can work really well to get a handy pull+push in your motor. Since the AC current has a timing "preset" into it, it means you don't need to use the rotating part to time the motor speed. You can just use the timing of the AC. This lets us put the magnet back on the rotating part instead, and removes the need for electricity to get to the moving part. No more brushes, no more dirty electrical contacts that can fail. The power is always connected.
So how do we actually make it? Well you could put one magnet on the fan blade and a counter weight on the other side, and then put the AC coil on one side of the housing. Theoretically, it should spin at 60Hz (60 rotations per second) because the AC is able to push and pull it 60 times per second. If you go any faster or slower than that, it won't line up with the AC push and pull as the magnet swings by. If you try to go too slow, the coil will be moving back and forth very quickly when the magnet swings by. Imagine grabbing a merry go round and just pushing and pulling back and forth very quickly. It's not going to make a full circle if you keep pulling it back.
It would be almost impossible to get the fan spinning at 60Hz in the first place, but once it's there it will work as long as there's enough power to overcome the load.
But how can we make it more reliable? What if we had 4 magnets on the fan blade equally spaced out? Then the ac only needs to push *a* magnet 60 times/second, and you could have it spin at 15 RPS. That makes it much easier to get started and much more stable. Cool, now we're talking. There's still an issue with it though. The fan blade is only being pushed from one side all the time. Without a balanced force applied, over the long term you're going to have a problem with the motor being pushed to one side all the time. You'll have uneven wear on your bearing, and you might even cause your rotor to become imbalanced, which could make it shake and cause more damage.
Next improvement: 4 coils evenly spaced around the motor. This way, you can balance the forces out. Now we're talking about a nice reliable motor. Still an issue though. All 4 of your pushes happen at the same time, 60 times a second. That means that between each set of pushes, you're going to slow down a bit. So it's kind of like tapping on the gas repeatedly instead of holding it at the position you want. This causes your speed to fluctuate up and down with the pushes, and could end up being another source of wear.
Well we'll never get perfect, but we can get damn close. We could use 3 different AC powers at the same frequency, but offset by 1/3rd of a frequency or "out of phase" with each other, and triple down on our coils. This way, each magnets gets a push by 3 different coils in each quarter rotation of the fan. This is like having 12 kids around the merry go round who push 4 at a time. You get near-constant push.
What we're talking about now is called 3-phase power. It's AC that comes in three separate phases, each separated by 1/3rd of a full phase period. It's incredibly useful in industrial applications, and it's used in a few standard voltages. This lets motor manufacturers use standard designs.
Your home has dual or split-phase power, which is similar to 3 phase but is only 2 phases and a neutral.
So how can we control speed? There are tools we can use called Variable Frequency Drives. They're able to change the frequency that the AC operates at. By increasing the frequency, you increase the motor speed.
Seems to me he's talking the classic Perpetuum mobile...sigh...
But OP, no. And to understand why, you would not even need magnets. Say, you only have weights attached on the blades, not magnets. You could think now that gravity "pulls down" the weights, so from a certain logic, the fan should be spinning from gravity alone.
Of course we know, it doesn't work. And the perpetuum mobile with the magnets, it's basically the same thing.
Here is why all these ideas of perpetuum mobiles do not work: If it would really function, that is, the fan would be spinning (with or without a generator attached to it), it means it would create energy.
But energy must always come from somewhere, it can only be converted, it cannot be created. This is a fundamental law of physics.