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I just coudn't replicate it, no matter what, Help Noob

  1. Feb 1, 2010 #1
    Hello Friends,

    Here is the link to video to replicate.


    I have taken a circular cold steel shaft of 18mm dia and 1 ft in length, weight approx 400-450 gms attached 14 Nos 10mmx10mmx1/8 thick magnets on the top horizontally and 14 Nos on the bottom horizontally in opposite 1 line over the cold steel shaft. Please note these 2 lines of neo magnets are not touching each other as shown in video.

    I got a new 9v battery and applied the current to shaft by a thick 3 core wire. But the shaft is not moving at all :( where am I doing wrong ?

    Another issue is that I have a heavy duty battery as well which is used for my home inverter, but my battery vendor told me that if you apply + and - on a single shaft, the battery will explode or will get hot also ! :( How come they apply the plus and minus to the same shaft is puzzling me, I have not tried this setup on my home inverter battery yet. will this video setup run properly till the battery exhaust ? Is it good for battery health until the battery drain away ? or not ? I mean to say that if battery exhaust is the only problem then I can recharge it, but will battery explode or get hot ? is 9v sufficient for a cold steel shaft of my setup ? or higher voltage is needed for dc is another question.

    One more thing which remained to say, i have put such a pole over the steel shaft by which the magnet attract the steel shaft. (on the line above the shaft and the line below the steel shaft)

    OMG what is that blue colored wire below ? is that I am missing !

    Please help this noob.

    Thank you in advance.
    Last edited: Feb 1, 2010
  2. jcsd
  3. Feb 1, 2010 #2


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    Science Advisor

    Yes, that motor is very deceptive.

    The blue coil of wire under the rotating part is a field coil. You can briefly see the connections to it at one stage.

    The innocent looking shaft for the magnet rotor is an enamel coated wire with the enamel scraped off on one side and this is switching the field coil as it rotates because it is in series with the field coil. It makes contact with the bottom side of its support only and this is where the switching takes place.

    This means the motor is only powered for half a rotation of the magnets and half the magnets are there only to balance the weight of the ones that are being used.

    The current passing through the shaft with the magnets on it does not contibute to the rotation.

    There is a very common motor that uses a rotating coil above a magnet and this uses the same switching mechanism. This motor reverses the positions of the coil and the magnet and deliberately makes the operation deceptive.
  4. Feb 1, 2010 #3
    The shaft is rotating well. I just want to know my questions about the battery and if I place a coil below, will the shaft rotate, where should i connect both the coil ends to ? I want to generate electricity from the same. what are the flaws (if any) etc wrt to connecting the battery to shaft + -, comment about the voltages, is there anything wrong in connecting + - to the same shaft, what will be the status of battery, how to keep battery condition good from heating etc . Also please comment about voltage, is 9v enough of less, if less or more, what is the proper voltage to be given to my setup etc. please elaborate. Is this correct setup ? if not what is the correct setup to rotate the shaft ? please let me know. Maybe the person has done some mistake and is doing a faulty operation. If you know the correct operation, please let me know the connection diagram.

    Thank you in advance for your valued feedback.
  5. Feb 1, 2010 #4
    Hello Friend,

    Call this second video in this thread. Now please comment whether this below given second video is a proper connection.

    Your opinions are highly appreciated.
    Last edited by a moderator: Sep 25, 2014
  6. Feb 1, 2010 #5
    I wouldn't say the motor's deliberately deceptive...as the description says, it's intended to be very simple. Another type uses an armature coil with scraped enamel insulation as you describe, but this one simply bends the end of the shaft so that it only closes the circuit through the coil below at the right time...an ingeniously simple solution that's far easier to make and adjust.

    aspardeshi: Yes, the coil below is non-optional. The current through the shaft does nothing to move the motor, the shaft is only used to switch power on and off to the coil at the right time. That coil is what makes the magnet armature move, and it needs to be placed in series with the switch formed by the shaft.

    I'm not sure what you'e asking about the second video. It's not a common way to hook up a motor, no. The field magnets generally surround the armature and often have a larger number of poles, and of course real motors use actual brushes, not simple wires. Whether it's a "proper" connection or not depends on the type of motor what you're doing. For a simple demo as the video poster's doing, he clearly did it right, as the motor spun fine.
  7. Feb 1, 2010 #6

    I am doing a project of synchronous generator, for that I want to make a drive, So I was planning to make a DC motor and use it as a drive, but my requirement is that it should move the 400-450 grams of cold steel rotor with minimum current, speed is not a problem, i can adjust it with gears. but it should have minimum 1 NM torque. I hope you got it. I was finding the video 1 suitable as a setup, as in the second video i need to make a rotor that fat and also arrange for the flat plate magnet which is costly. I also have no knowledge of winding that fat coil.

    I thought the first video is better one and easy to make, can i make it at 9v dc ? I mean will shaft rotate in first video setup ?
  8. Feb 1, 2010 #7
    I still don't know what you're doing. Trying to turn a generator with a motor? You are aware this won't make more electrical power than the motor consumes, are you?

    The rotor mass is only relevant to changing speed. And your insistence on a certain torque while saying you can adjust RPM to fit using gear makes me wonder if you understand gears...if you increase RPM using gears, you will decrease available output torque. If you use gears to reduce RPM, you increase available torque. Any small DC motor that gives your desired output torque will use gear reduction to do so.

    No offense, but if you were trying to do what it sounds like you were trying to do, you've got a long way to go before you can successfully design and build a motor that's of any use. Those videos are essentially of lecture demos. They are not of any use for doing work. The first is simple but not useful for anything but being a simple motor. The second uses an armature from an actual motor, but again is mounted to demonstrate the operation of a motor rather than to perform useful work. In real use, it would have multiple permanent magnets or electromagnets positioned around and much closer to the armature.

    Just buy a gearmotor. You are extremely unlikely to build anything remotely as good as a cheap DC motor with integrated gearbox, and you can get one that is guaranteed to operate properly at the voltage, current, torque, and RPM you need.
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