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Maglev Project

Discussion in 'General Electronics Discussion' started by f22lightning, Aug 27, 2012.

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  1. f22lightning

    f22lightning

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    Aug 27, 2012
    Okay so me and my friend want to build a maglev train, as far as how this will be setup we have it handled, the part I would like some help with is where I want to create a circuit or maybe even a pcb that would allow me to program a microcontroller to switch the polarity of the magnetic coils that we are building, I was told to use an H-bridge of which I know nothing about, I want to use a PICAXE so if you they have a chip with H-bridge built in then it would be great if not how can I go about creating an H-bridge circuit that is controlled with a picaxe chip, as much as you can would be great.

    (if you think there's a better way to go about this without an H-bridge than please by all means let me know)
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I assume we're talking a model, and not a real one :D

    You are probably better off spending some money on rare earth magnets and arranging them in such a way as to provide lift for your carriage.

    When you start talking electromagnets, you start talking high power and (in the real world) often superconductors.

    If you need to control magnets, it is best done for control purposes rather than for lift (at this -- presumably small -- scale)
     
  3. f22lightning

    f22lightning

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    Aug 27, 2012
    Yeah we are using magnets for lift and magnetic coil to drive it forward, which doesn't need much power and yes its a model at a small scale and I which to know the best way to change the current
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    An H-Bridge allows you to reverse the current in some load.

    Making an h-bridge from 4 mosfets (for low power) is pretty easy. Just make sure you don't turn on both mosfets on one side :)

    Google should give you the general idea.

    Come back and ask if you need more info.

    I have some chips that contain "half bridges". They're essentially just 2 mosfets in a small package. There are probably other chips too.
     
  5. f22lightning

    f22lightning

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    Aug 27, 2012
    okay so I found this https://www.sparkfun.com/products/315 and it seems simple enough, correct me if I am wrong but can I connect this to a PIC and tell it to just send high and low to the logic pin and be able to switch the current around?

    P.S. I think its like H L H for like one direction and H H L for another
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yeah, that chip allows you to power up to a 36V load with inputs compatible with your PIC.

    Consider if you'll want more than forward and reverse. Might you also want stop as well?
     
  7. f22lightning

    f22lightning

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    Aug 27, 2012
    Stop could be a possibility but how would I go about doing the stop on a magnetic coil or on the chip for that matter?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Well, current can be flowing in one direction, the other direction, or not at all. Actually the last has 2 possibilities, firstly that the coil is open, the other that it is shorted.

    All 4 give useful effect.

    The chip you've found has 4 half-bridges. This means you'll have 3 inputs to handle, one each for the half bridges, and the enable input for the pair.

    If the enable is pulled low, all the transistors in the half bridges go open. This gives you the "coil is open" condition.

    If the enable is pulled high, and the other two inputs are in opposite states you will get current being driven either one way or the other. This gives you the another 2 states.

    Lastly, if enabled, and the H Bridge inputs are at the same logic level, the coil is effectively shorted. This is the last state.

    The first and last states (open and shorted) are very different if there is any magnetic field inducing a current in your coil.
     
  9. f22lightning

    f22lightning

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    Aug 27, 2012
    Okay so if for example the I programmed the pic so that one output tells the enable to go low the coils will no longer have power and essentially just stop, while the other output can tell one part of the h bridge to go in either direction, right?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It will almost certainly be more complex than that.

    You're going to have to switch direction of the current in the coil to allow it to provide pull and push from fixed magnets in the track (or coils in the track).

    With the coil open, the train will coast. Shorted it will brake (you can also brake it by manipulating the current through the coils to similar (and in fact stronger) effect.
     
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