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Creating large DC Motor for Funzies. Won't work.

  1. Aug 17, 2012 #1
    A picture I included shows how my motor is constructed. The basic science fair project looking engine. This engine is actually designed to do work, however, it will not turn over once DC is connected to it.

    The wire is close to 5/64 inch thick and the whole rotor is solidly soldered together. I had a heck of a time finding Magnets for the thing and finally found a circle magnet form a CB radio antenna. I was able to see some movement when 4 C cells were used as power, but no rotation was able to be achieved.

    What have I done wrong folks? Thanks for you're help if you help me ;)
     

    Attached Files:

  2. jcsd
  3. Aug 17, 2012 #2

    dlgoff

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  4. Aug 17, 2012 #3

    Bobbywhy

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    Re: Creating lare DC Motor for Funzies. Won't work.

    Flyingwing12, Welcome to Physics Forums!

    If your motor doesn’t rotate then there is some mistake in the construction or electric power connection (or both). You may compare yours with these to find the error:

    Your drawing looks a lot like this one:
    "How to build a simple electric motor":
    http://www.hometrainingtools.com/build-motor-project/a/1605/

    Magnet Motor Kit:
    http://www.miniscience.com/projects/magnet_motor_kit/index.html\

    Hundreds of photos and images of simple dc motors:
    http://www.google.com/search?q=simp...gG93YDQBQ&sqi=2&ved=0CFEQsAQ&biw=1223&bih=619
     
  5. Aug 17, 2012 #4
    Re: Creating lare DC Motor for Funzies. Won't work.

    I am confused because the construction of my motor is just like the smaller ones. I have jumped up the volts, and jumped up the magnet. I am just curious as to why it doesn't work.

    There must be some reason?

    Check out the picture on the first post.
     
  6. Aug 17, 2012 #5
    Re: Creating lare DC Motor for Funzies. Won't work.

    If connected to a DC wall outlet converter the converter senses the short circuit and shuts off.

    A car battery causes the wires to melt, and a 12 volt power supply does the same thing.

    These devices are averaging at about 8 AMPERES. Could the Amps be ruining my experiment?
     
  7. Aug 17, 2012 #6
    Re: Creating lare DC Motor for Funzies. Won't work.

    Can you post a picture of your setup?
    Wires melting is clearly a problem. Either use lower Voltage or huge thinner wires.
     
  8. Aug 17, 2012 #7
    Re: Creating lare DC Motor for Funzies. Won't work.

    Your design is also not good one. Using Coils would allow you to have much more torque by flowing little current. Also wire melting problem can be mitigated because, the long length of wire will reduce current flow.
    See Post #3 links, by Bobbywhy.
     
  9. Aug 18, 2012 #8
    Re: Creating lare DC Motor for Funzies. Won't work.

    Here is a picture of the motor. I chose this design because it shows the beauty of movement! All of the other designs are small and compact which don't interest me.

    Everything on the rotor is SOLDERED together. The tape is just to protect my hands form the pointy protrusions
     

    Attached Files:

  10. Aug 18, 2012 #9
    Re: Creating lare DC Motor for Funzies. Won't work.

    See the basic thoery
    F ~= B*N*I*L
    In your case no. of turns N = 1.
    Lots of design use at-least N = 15-20.
    So, you need to compensated your N=1 by increasing I by 15-20 times, provided you use magnet (B) of same capacity. You seem to be using alnico magnet, which isn't as powerful as neodymium magnets.
    The wires seem very sturdy, I don't think it melts with 8-10A. How long did you let it on?
    The only thing you could do is increase the current even more.
    But you need to make really sure that the support is friction free and the thing can rotate even with slight force.

    Once again, design change is what I suggest. You could easily scale up the 'compact' design.
     
  11. Aug 18, 2012 #10

    davenn

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    Re: Creating lare DC Motor for Funzies. Won't work.

    a number of problems some of which I_am_learning referred to
    one other is the magnet ... not what the manget if made of .... ''You seem to be using alnico magnet, which isn't as powerful as neodymium magnets.'' that I_am_learning also commented on, thats of least importance and your problems.
    The big problem is the shape of the magnet and its orientation to the coil. You cannot use a single magnet in the way you have shown
    Look closely at the drawing that dlgoff showed in his post above and particularly note that the coil sits BETWEEN the N and S poles of the magnet

    The single turn of wire as you have will not work .... although you may think you have multiple turns, you dont they are just single strips of wire in parallel with each other.
    You need an actual coil of wire with multiple turns that starts at one side of the upright and goes through to the other side/upright
    You will be able to make it work that way which is a variation on that drawing that has bother end of the wire coil coming out the same side

    Dave
     
  12. Aug 18, 2012 #11
    Re: Creating lare DC Motor for Funzies. Won't work.

    Could I wrap the entire thing in copper wire? Make it look somewhat of a sphere?

    I have a feeling that the wires are heating up because I do not have these coils of wire that you suggest. The multimeter does show low resistance.......

    I have made smaller models that have worked. They looked just like this. Although they had about 1-3 turns of wire.

    Will try to improve it.
     
  13. Aug 18, 2012 #12

    Averagesupernova

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    Re: Creating lare DC Motor for Funzies. Won't work.

    Flyingwing12, before we go on I would ask you if you know what a commutator does.
     
  14. Aug 18, 2012 #13
    Re: Creating lare DC Motor for Funzies. Won't work.

    I know that it switched the current direction, right?

    UPDATE:

    Found magnetic wire in an old treadmill. Made a large 7 wind circle and got it to barely wiggle when 6vDC was applied.

    I think it is my magnet....
     
  15. Aug 19, 2012 #14

    NascentOxygen

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    Re: Creating lare DC Motor for Funzies. Won't work.

    Hi Flyingwing12. I have a lot of time for experimenters, being one myself, so it's interesting to see how you are going about the design of a model motor. You will learn a lot from this. As other have pointed out, there may be two problems: the magnet, and the rotor. :smile:

    To see whether you stand any chance of getting movement. disconnect power from the rotor but leave the rotor there, no need to move it. Now, between those wooden blocks temporarily sling a single length of flexible copper wire horizontally above the magnet—this will be like a simplified rotor. How to suspend it? Hang a short length of string from a drawing pin on each block to suspend the wire so it's free to swing up/down/sideways. This moveable wire will reveal any repulsion between it and your magnet when that wire carries current. Do you have some means to limit the current, as a thin piece of wire is likely to overheat and melt. Perhaps connect a 12v car headlight globe in series, if your only power source is a car battery.

    Should that single wire show no inclination to move when powered, then you are wasting your time trying to get your more elaborate "eggbeater" rotor to spin. It will be time for a rethink.

    Good luck with your demonstration.

    A very simple motor: http://m.youtube.com/#/watch?v=IQS1ZE0TVeo
     
    Last edited: Aug 19, 2012
  16. Aug 19, 2012 #15

    Averagesupernova

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    Re: Creating lare DC Motor for Funzies. Won't work.

    So does your motor have one? And if not why do you expect it to work?
     
  17. Aug 19, 2012 #16
    Re: Creating lare DC Motor for Funzies. Won't work.

    I proved today that a single wind of magnetic wire works. I was able to make a small 3 inch diameter circle out of mag. wire and make it rotate with 9v and the same support setup as the larger motor .

    The culprit in my experiment is my magnet. I notice that speaker magnets don't have a wide spread field like this little doughnut magnet I have.

    Tried hooking up the "eggbeater" to a 12v supply and it melted the wires. With magnetic wire I notice that it is non conductive with the coating on it, so sanding it made the smaller rotor possible to rotate. It did not rotate on its own, I had to get it started.

    Is there a formula I can use to determine the strength of a magnet that I need to get this " Eggbeater" to work.

    I know it is possible. It has to be.
     
  18. Aug 19, 2012 #17
    Re: Creating lare DC Motor for Funzies. Won't work.

    When you think of series are you thinking of this?

    It seems as if the lamp is acting like a resistor?

    I thought there is a V drop between resistors and base Voltage?

    Thanks for taking interest :)
     

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  19. Aug 19, 2012 #18

    NascentOxygen

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    Re: Creating lare DC Motor for Funzies. Won't work.

    Yes, the lamp is a convenient resistor. :smile: I suggested that you use it so it limits the current through the strand of thin wire. If you just connect a piece of wire across a car battery there will be a big spark, the wire will glow red hot and melt, thus ending the experiment. :frown: But with the lamp in series, the lamp will limit the current to a safer level. The wire may still get hot and start smoking, but the experiment will have served its purpose: do you see instant movement in that strand of wire or not?

    You must take the eggbeater out of the circuit for this single wire test so it doesn't steal the current from the piece of wire. Use a strand of wire that is flexible and hang it so it is free to move a bit, so that you can watch for movement. Because if you observe that the single strand does not move, then sure as anything neither will your eggbeater rotor!
     
  20. Aug 19, 2012 #19

    Averagesupernova

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    Re: Creating lare DC Motor for Funzies. Won't work.

    You really need a commutator. Suppose with a single loop of wire the current is split evenly through the upper and lower loop. In order for the rotor to turn the upper wire has to move in the opposite direction of the lower wire. One wire will fight the other. Remember the right hand rule when it comes to magnetism and current flow? The reason your single loop worked at all is because the field was small enough on the top compared to the bottom so the lower 'outpulled' the upper.
     
  21. Aug 19, 2012 #20

    NascentOxygen

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    Re: Creating lare DC Motor for Funzies. Won't work.

    I think you mean "it rotated a few degrees then stopped" don't you? It surely didn't keep turning and turning endlessly?
    So it melted the plastic-coated wires from the battery, or did it melt the egg-beater wires? (They look so thick that I'm surprised the 12v supply survived. Your eggbeater is no different from a short circuit.)
    Even if it is theoretically possible to get your homemade rotor to operate, it will first have to be modified a bit to give it commutator action. But I'm not suggesting you do that until we establish whether it stands any chance of working.
     
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