Hobby Electromagnets

Discussion in 'General Electronics Chat' started by thanchantnichols, Sep 21, 2016.

  1. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    Hi Ive been searching for small electromagnets (or Im happy to modify other products, like solenoids) for a project I have involving modelling - train sets, that sort of scale. Anyway, Im looking for low power, maybe 200mA or so, say 12V, and have some reach to pull at objects or other magnets to a cm or so range. but doesn't need to lift weights or anything like that. Think train set sized things like tiny doors or model cars. Ultimately I'll have a number of magnets directed by microcontrollers, with strength and polarity control. The electronics and software I can handle, but finding a supplier of small hobby electromagnets is surprisingly difficult. Wondering whether anyone can point me in the right direction? (I'll say please!)
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Solenoids and servos are easy to apply, but I can understand that you do not want the plunger or actuator to be visible. I don't have a lot of experience with small, low-current electromagnets, but I suspect getting action against any sort of resistance from 1-cm away might be difficult.

    Some other thoughts:
    1) Memory wire (Nitinol) can be used for hinges and is used in micro indoor models. Here's one link to making hinges: http://l3d.cs.colorado.edu/~ctg/pubs/programmable_hinge.pdf

    2) Sub-miniature servos can actuate flat surfaces and be entirely hidden. The trick is to use a bent wire rotation in a slot/pocket. Here's a picture from the Internet to give you the idea. They are called RDS in the hobby.
    upload_2016-9-21_5-20-48.png

    John
     
  3. ci139

    Member

    Jul 11, 2016
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    Last edited: Sep 21, 2016
  4. DNA Robotics

    Member

    Jun 13, 2014
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    You can attach a lever to the moving arm in an automotive relay to get more stroke. You can adjust the stops a little to get more stroke but it gets weaker. You can disassemble them and just use the coil to pull an iron rod thru the center.

    relay_inside_lrg.jpg

    Relay-Single-2.jpg
     
  5. AlbertHall

    Well-Known Member

    Jun 4, 2014
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  6. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    Thanks all! Im experimenting with taking the frame off a solenoid and giving it a solid metal core, its just a matter of finding a size and type Im happy with. One project I have in mind is to arrange a series of electromagnets under a model roadway and manipulate the fields to draw a car toy along it. The car would have a small rare earth magnet in it. So the pulling force can be very low, probably under a newton, and I shouldnt need a lot of current draw. I like the idea of hacking a reed relay, I'll give it a go.
    I haven't had a lot of luck with relay magnets - perhaps they are too well designed and keep the magnetic field close to its surface, or like many solenoids draw a significant amount of current.
    The servo hookup is ingenious, thanks John.
    Memory wire.... wow I recall that from many years ago! Id forgotten it existed. Cool.
    I'll keep trying and keep up the suggestions!
     
  7. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    In that case the electromagnet should not have an iron core otherwise the magnet might prefer to be attracted to that rather than move on to the, further away, next electromagnet.
     
  8. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    You might be able to move the car with the electromagnets by having a piece of aluminium fixed underneath the car and then activating the magnets in sequence thus generating a moving field which the aluminium would want to follow as in an induction motor. That might produce a smoother movement.
     
  9. MrSoftware

    Active Member

    Oct 29, 2013
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    Maybe take the rod out of something like this:

    http://www.kr4.us/solenoid-5v-small.html

    That said, if you're moving things by dragging them using a magnet that is under the surface they are sitting on; instead of a magnet that turns on/off, what if you used a plain old neodymium magnet, but have the magnet control mechanism pull the magnet away from the surface to "release" the object, and closer to the surface to grab the object? In my head I'm picturing a game board (monopoly, chess, etc...) and you're dragging objects around the top of the board using magnets located under the board. Maybe my vision isn't correct, but this is what I based my suggestion on. Good luck!
     
  10. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    Good point. Which gives me another idea - let the car be attracted to the metal cores and apply a reverse polarity to get things moving. I have much to look into.
     
  11. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    You know although Ive been thinking "no moving parts", the simplicity of having a line of solenoids under the track is appealing and simple.
     
  12. MrSoftware

    Active Member

    Oct 29, 2013
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    Are you moving the objects on a track, such as with a model train, or are they able to move in all directions such as on a flat surface? I just now caught that you're trying to move objects without other any moving pieces. ;)
     
  13. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    For this project I'm thinking model cars, matchbox car size, on a track which can guide them. Being free wheeling they don't need a lot of magnetic attraction, particularly if they happen to have a magnet in them. My original idea was place electromagnets in a row under the "road", which can be very thin, and drag it along by changing intensities and strengths of the fields. Like a linear motor. I see there are various DIY linear motor ideas on the web so Im looking at that at the moment. But Im open to any ideas.
     
  14. MrSoftware

    Active Member

    Oct 29, 2013
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    I think some superconducting electric trains are moved this way, but sequentially powering magnets. Check out how they did it.

    I'm no expert in the field, but you might have better luck with a plastic track. If you use a metal track,I'm wondering how much of your magnetic field will be absorbed by the tracks before interacting with your cars. But that challenge aside; I would say try some magnets in the bottoms of the cars and electromagnets in the track that you just turn on and off sequentially to drag the cars along. Timing will be important. Cool project, let us know how it goes.
     
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    For realistic, rather than jerky, movement of the cars you will need the electromagnets to be very close together. Perhaps pole piece extensions would help, so that the bulky coils can be positioned away from the path of motion.
    If it were my project I think, instead of electromagnets, I'd try a single drive-belt-carried permanent magnet below the 'road'.
     
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  16. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    That's my plan. Still haven't found appropriate magnets yet, so still searching for the right size and type.
     
  17. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Interesting idea! Hope you post the final outcome at least of a simple but working design.

    If it becomes too efficient, be careful that moderators could consider it a coil gun in disguise and close the thread...:p :)

    Let hear from you!
     
  18. MrSoftware

    Active Member

    Oct 29, 2013
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    @atferrari - You gave me an idea.. If the moderators don't yank this, the end actually shows what might be a solution for you, depending on your power requirement.

     
  19. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    I like this guy. I want to be like him when I grow up. Yeah, I know, hes a lunatic, but I can live with that.
    Anyway thanks for that!
     
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  20. thanchantnichols

    Thread Starter New Member

    Sep 21, 2016
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    Im back. Im still looking...... to repeat myself, I need a low voltage electromagnet with a local field strong enough to pull an object, whether metal or another magnet, from say 5mm away with a weight of maybe 2g. So only a few newtons. In this case a wheeled toy car. I pulled a solenoid apart and it worked as long as I gave it a core to concentrate (to use an old phrase) the lines of force. I won't need a high rate of flux change, maybe 1 Hz at most. Unfortunately for me the one suitable solenoid I found.... Im having trouble locating a similar one, as it came out of my junk box. And we all have one of those. The little "mini" or "micro" solenoids won't cut it. And I certainly don't want to require 1A+ to run a single lower power magnet like this, as I might have dozens active at one time. Lets see, 200 or 300mA? maybe 12V, or 24V if need be? Hoping the team here which have a whole lot more experience with small electromagnets can point me in the right direction. Maybe I'll have to wind my own.
     
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