Centered solenoid design

Discussion in 'General Electronics Chat' started by #12, Jan 15, 2014.

  1. #12

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    Is this how you would make a centered magnetic concentration on a rod magnet?
    Is this how you would wind a coil to make the rod assembly move left and right, depending on the polarity of the current flow in the coil?
     
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  2. inwo

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  3. #12

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    It's for strantor. I'm trying to come up with a 2 way solenoid that does not have a moving coil design. Like a speaker, only the other part moves.

    Nice link, but the drawing of how to orient the coil doesn't show up on that page.
     
  4. MaxHeadRoom

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    How about a simple iron rod with a strong button magnet on each end?
    The alternative common in solenoid vales is a spaced double coil?
    Or check out directional proportional valves, they do exactly that with one coil.
    Max.
     
  5. inwo

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    Rats, I can't find my cow magnet to test.:(
     
  6. strantor

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    Hooray, pictures!

    I've been looking at voice coil designs, it seems there is an option which part moves; the coil or the magnet. It just depends what end you mount to terra firma. The question that pops into my head goes like this...

    Here's a voice coil actuator:
    [​IMG]
    Could the force strength be increased by making the entire outer structure out of magnets? The inner core, stacked neodymium button magnets. The outer core, stacked neodymium ring magnets, the base, flat puck neodymium magnet.
     
  7. inwo

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    The reason that moving coil was picked is that it has less mass?


    Interesting experiment (for me).

    Center is neutral, either polarity.

    "How about a simple iron rod with a strong button magnet on each end?"

    Same as a long magnet!

    A non-magnetic rod though.
     
  8. MaxHeadRoom

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    I thought it worth considering for economy reasons?
    Max.
     
  9. strantor

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    OK, now that I've seen the pretty pictures and thought about it, here's what I think (someone please correct me):

    The reason a solenoid can only go one way is because the electro-magnetic field is acting on a non-magnetized object. It can only attract, the large hunk of Iron.

    And that's where the voice coil is different; you have an electro-magnetic field interacting with a permanent magnet field, and the actual location of the poles is of little or no consequence (I have no idea if that's correct; please confirm or deny).

    So, what you've drawn is essentially just a voice coil that has its poles concentrated in the center instead of at the ends, and I think that the operation would be the same as a regular voice coil except it would have more mass.

    Opinions? Facts? Anybody?
     
  10. inwo

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    If it's any help.

    #12's works fine as shown. Just not centered.

    I don't communicate well.:) Here's a picture.

    One polarity shoot rod magnet out the end.
    The other polarity pulls rod in until flush.
     
  11. strantor

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    That doesn't seem exactly like #12's design. The key of his design is the iron cups that divert the magnetic path back around.

    What you have there, seems more like a regular voice coil, except inverted.
     
  12. inwo

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    That works!

    Both outer ends must be the same pole.

    No neutral.
    Push/pull with polarity reversal.

    ps.
    Very pronounced with larger buttons.
    Full range of motion both ways. Button to button.
     
  13. strantor

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    Directional proportional valves use a voice coil. Or maybe a servo sometimes. I've taken apart an pneumatic I/P transducer and it has a voice coil in it.
     
  14. strantor

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    This thread isn't already post-mortem is it?

    Without further input, I'm going to assume that voice coil diagram in post #6 displays the most efficient design, and that it can be improved upon by constructing the entire armature out of neodymium magnets. I don't know what stroke length or force I need yet, as I have to print out and build the hand (in progress) to work out the leverage ratios and such, but for now, for messing around on the bench, this is what I'm considering purchasing to make a 3" stroke, 1" diameter high-force voice coil:

    [​IMG]

    I want a tiny hole straight through the center, so that my cord can run through it, and pull in both directions.

    Is this a stupid idea? It wouldn't necessarily be an expensive mistake, but it would be an unfortunate waste of time and money.
     
  15. #12

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    The hole in that configuration won't hurt anything.

    I was hoping somebody could be real clear about which way to take the idea I came up with or show a simple way to make a speaker-like design that moves the magnet instead of the coil. Inwo said "both ends the same magnetic polarity" and I have no clue whether he is right or wrong. That's why I posted this as a question.

    I can't take this aspect of the design any farther due to ignorance.
    It might be a good idea or a bad one. It might send you in the right direction...or the wrong direction.

    Just trying to be helpful, but you know what they say, no good deed goes unpunished. I rely on our previous interactions to persuade you not to be angry (much) if I'm wrong.

    and remember, you just have to get it to move. Power will come later.
     
  16. strantor

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    No worries, #12. This is R&D. **** doesn't always go according to plan. I know that. An unfavorable finding is still a finding.
     
  17. #12

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    Are you going for the, "found 1000 ways that don't work"?

    Unfortunately, a project this sophisticated will probably accomplish that. :D
     
  18. strantor

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    If I were anywhere near the level of Tesla or Edison, I'd probably be somewhere between them; call it "500 ways that don't work"
     
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  19. strantor

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    I've got the main part of the hand done, and I'm printing the middle finger (because it's the strongest, worst case scenario) as we speak. I will measure the full force I can generate with my own middle finger, then I will assemble the hand and see how much force is required on the pull-cord to get the same force at the fingertip that I am capable of. Then we will have half the story. Later, probably this weekend, I will print the forearm and determine how much space I have to work with. Then there will be some real design parameters. Thinking logically, I should hold off buying anything until I have the design parameters. But, I am an excited person, so I cannot make any guarantees.
     
  20. strantor

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    Sorry for the rapid-fire posting. I'm watching a 3D printer; it used to be captivating, but I've seen it enough to be able to focus on other things now.

    So, these neodymium magnets have a pretty low max operating temp (80C). If I'm going to be trying to squeeze maximum performance out of minimum space, I'm probably going to find it painful to not overheat these things.

    This takes me back to an idea I had earlier, about an all-copper voice coil. Would that be possible? Wound field DC motor vs. Permanent Magnet DC motor analogous to Wound Armature Voice Coil Vs. Permanent Magnet Voice Coil?
     
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