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Simple electric motor help

  1. May 22, 2004 #1
    I've been trying to build an electric motor for my 11th grade physics class and I'm having some problem.

    I'm trying to stay away from using a reed switch because my teacher hinted at a better grade for motors using a split-ring commutator (and because I couldn't find a reed switch anywhere). I've looked through several websites (at least 20) and I can't seem to find any kind of guidelines. All I found were sites explaining the theory and how the split ring commutator works.

    If anyone could answer a few of my questions and even go beyond that in helping I would appreciate it.

    1. How does the direction of the wires being wrapped affect the motor and which direction should they be wrapped?

    2.Will the motor be affected my the nail attracting magnets before a current is run through the wire?

    3.Along with the magnetic wire, what other types of wire should be used?

    Thanks to anyone whom helps.
     
  2. jcsd
  3. May 22, 2004 #2
    Not sure what you mean by 'nail attracting magnets'. I assume you have a wound field coil also and not just a wound armature? Unless your motor has permanent magnets, nothing will attract to anything until the current is turned on.

    A few notes on winding: I assume you have a large nail or bolt for the armature. It needs to have the wires wound the same direction all the way. I don't know what the instructions say if you have any, but when I built mine (a long long long long long time ago) I used doorbell wire wound in two layers around a 1/4 inch bolt. The shaft of the motor was a wooden dowel. I started winding at the dowel and worked towards one end of the bolt and then back again. Then the wire continued by jumping over the dowel and was wound in the same direction on the other side and back to the center. Use washers on the ends of the bolt/nail so the wire can't slip off the end.

    I don't know what you are using for a 'field coil' but if it is wound you need to do the same thing. What will work best is if you have some steel rod or maybe 1/8 inch thick strap bent into the shape of a U. It is wound the same way. If you have nails pounded into a wooden base it doesn't work as well as if the field coil assembly is all one piece. I helped my nephew build a motor and this is what we found. To remedy it at the last minute we wrapped some wire back and forth around the bottom of his nails. This 'completed' the path for the magnetism. If you do this, DO NOT use copper wire. The wire needs to be magnetic. The best thing is still something in the shape of a U. As far as actual winding of the field goes, same thing as the armature. Wind each one so that if you kept winding around the bottom (assume U shape) then you would just keep winding on the way up the other side. You may want more than 2 layers of windings on the fields. My motor only had 2 and it worked, but it used a U shaped field. My nephews did not and the last minute patch up I mentioned helped, but more wire would have been preferred.

    There is also a right and wrong way to hook the wires on the armature to the commutator. I'll let this sink in and you can ask me any more questions you may have or give me any more details you think I need.

    Glad to help.
     
  4. May 23, 2004 #3
    It sounds like you're making the kind of motor that has permanent magnets as the field magnets. Each time the rotor comes around the direction of the magnetic field in the rotor will be switched through the commutator. The polarity of the field magnets, obviously, always stays the same. The nail will be attracted to the magnets when the motor isn't running, but that makes no difference whatever.

    Making a split commutator is not too hard. You can actually make it out of the ends of the magnet wire itself, if that's all you have. Start off by making sure you have stripped all the enamel off the ends of the magnet wire that forms your rotor. If the shaft that is going to have the commutator is made of metal you will have to wrap some electrical tape around it before you put the commutator on to insulate it from the circuit. Hold the stripped ends of the magnet wire so that they are on opposit sides of the shaft from each other with the stripped part over the electrical tape. Then tape them into place so they stay there. You already have a crude commutator with this set up. You can try running the motor. It will be necessary to adjust the position of the two wires such that they contact the brushes at the proper time. The best position for them is where the motor runs the fastest.

    One improvement may be to flatten the wires gently with a hammer to increase the area that the brushes make contact with. Take them off the shaft before you do this and hammer them on some hard, relatively clean piece of metal. Copper is pretty soft and this shouldn't be too hard. Then you will need to give them a curve to match the shaft. The best way to do this would be to find a nail that is about the same diameter as the shaft and tap them against it. (You'll have to hold the nail in a bench vice.)

    The more elaborate alternative is to find a short tube of metal that will fit over the end of the shaft, cut it lengthwise with a hacksaw, and use the two halves as the commutator. If the tube is a little bigger than the shaft you can increase the diameter of the shaft by wrapping masking tape around it. The important thing is that the two hales cannot touch each other when mounted (glued), they have to make good contact with the wires, one wire to each half, and they have to be oriented on the shaft so that they make contact with the brushes at the proper time.

    You shouldn't have any problem using magnet wire for the whole thing, if that's what you already have. There is another kind of very flexible, fairly thin, stranded wire with plastic insulation that I like to use for anything that's going to be run by flashlight batteries. Unfortunately, I dont know the proper name for it. But any thin, flexible wire with plastic insulation is perfectly good.You ought to ba able to change the direction that the motor goes in by reversing the + and - connections to the battery.
     
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