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Nut will not stay on the bolt.

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  • J Tiers
    replied
    of course, the item was assembled as piecework by some family on the kitchen table, who were paid almost nothing per unit....... Which is one reason it sells for $1.99....

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  • Joel
    replied
    My 1.99 version already made it here from China. The fit and finish are quite good - definitely better than expected, and all of the parts are made from brass.

    I am about half deaf, but in a quiet room I can hear it. Holding it by the head and not the shank makes it somewhat quieter, but with no ambient noise, I am sure it would be easily heard by young ears. However, with just a little distance and a little background noise, it shouldn't be a problem.
    The (actually useful) instructions say "Putting the magnet close to the head of the bolt makes the switch turn on and the vibration motor starts moving. This vibrates the bolt and consequently the nut comes off."

    It spins the nut rapidly and covers an inch in about 3 seconds (M6-1.0).
    We live in a magical world - how something as complicated as this can be manufactured and delivered to my door for 2 bucks (brass, with 2 batteries, tape and a super magnet) is beyond me.

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  • MaxHeadRoom
    replied
    Update:
    Device was delayed through customs and came with a sticker "Goods not Fulfilling the conditions laid down in articles 28 & 29 of the treaty on functioning E.U."
    Device is made in China and a Knock off of a device first made by Kreis of Japan.
    It comes with a password for the Kreis website that advises it is bogus item that is no longer produced by them.
    As to the device, it works pretty slick and is well made, the vibration mentioned is only experienced by the holder and not heard, at least on mine.
    The battery has to be inserted in the head with the correct polarity.
    I believe the result is of a kind of Faraday effect, just a variation of it.
    Max.

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  • chemist6.02e23
    replied
    Originally posted by kc5ezc View Post
    Great looking trick. Joel, what was the amazon item number. The one I found was about 10 bucks
    Thanks
    Just search "magic bolt"on Amazon and you'll find quite a few, including the $1.99 version.


    Sent from my iPad using Tapatalk

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  • PStechPaul
    replied
    It's available for about $4 from:
    https://www.banggood.com/Nut-Off-Bol...l?rmmds=search

    The reviews seem to indicate that there is a motor in it, and it's rather loud, so the pager vibrator is probably the trick.

    Leave a comment:


  • kc5ezc
    replied
    Originally posted by kc5ezc View Post
    Great looking trick. Joel, what was the amazon item number. The one I found was about 10 bucks
    Thanks
    ]

    Found it! My google fu on amazon is corroded. Found it a few minutes after I posted.

    Leave a comment:


  • kc5ezc
    replied
    Originally posted by Joel View Post
    I think it is to push the false head of the bolt off for maintenance.

    Thanks for posting this OT Max. I found them for 1.99 shipped on Amazon and know a couple of folks who will really enjoy them.
    Great looking trick. Joel, what was the amazon item number. The one I found was about 10 bucks
    Thanks

    Leave a comment:


  • MichaelP
    replied
    Thanks Joel, it makes sense.

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  • Joel
    replied
    Originally posted by MichaelP View Post
    What's the purpose of the spacer?
    I think it is to push the false head of the bolt off for maintenance.

    Thanks for posting this OT Max. I found them for 1.99 shipped on Amazon and know a couple of folks who will really enjoy them.

    Leave a comment:


  • MichaelP
    replied
    What's the purpose of the spacer?

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  • PStechPaul
    replied
    I watched the video again, and there is a spring inside the bolt that connects to the battery. Thus, the current will flow through the helix, and its magnetic field will be along the axis of the bolt. The permanent magnet is applied at 90 degrees to the axis. Thus (I think) there will be a force acting on the conductive nut. But I'm not sure if it is acting as rotational torque, or linearly along the axis of the bolt.

    It is possible that the magnet operates a reed switch to conserve battery life when not being used. Thus the current would produce two orthagonal magnetic fields producing torque on the nut equally along the length of the thread.

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  • Barrington
    replied
    The comment that the device is noisy in operation suggests to me that it might simply be something vibrating the bolt cyclically and the nut is just precessing off. The most obvious candidate would be a pager motor - there are plenty of very cheap ones small enough to fit inside that size of bolt.

    The magnet is then a covert means of operating a switch and nothing to do with the action whatsoever.

    Cheers

    .

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  • J Tiers
    replied
    The field will weaken at the far end of the bolt, but the nut seems unaffected by distance.

    The weakened field will have less torque.

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  • PStechPaul
    replied
    From the Wiki article, here is a diagram showing current, magnetic field, and forces for a simple homopolar motor made from a dry cell, magnet, and two loops of wire:


    By Ths1104 and Smial - File:Motor_homopolar_flux_force.png (File version without logo), Public Domain, https://commons.wikimedia.org/w/inde...curid=24882076

    So there must be a conductor on the axis of the bolt which conducts current opposite in direction to that through the hollow cylindrical walls of the bolt. The video shows the magnet placed on the side of the bolt, rather than on the end as shown in the diagram, but it might not matter. I think there will be significant current flowing through the nut to provide torque, especially if the bore is large enough to make the walls very thin. To test that hypothesis, try coating the threads with non-conductive oil or paint.

    https://upload.wikimedia.org/wikiped...1_smial_wp.ogv
    Last edited by PStechPaul; 06-25-2017, 02:28 PM. Reason: More info

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  • J Tiers
    replied
    Originally posted by Jaakko Fagerlund View Post
    Explains it fully, as the video shows everything needed for a homopolar motor.
    .....
    Not quite.....

    The rotating part of a homopolar motor has a current through it, RADIALLY, with an axial magnetic field . That nut has NO radial current in it, so it is not the same thing. and that magnet does not set up an axial field. Look up the homopolar motor and see.

    In fact, it is hard to see how any current will flow in the nut, since one would expect the brass bolt to carry the majority of the current, the thin nut would not get much if any.

    it may be that the principle is similar, but if so, the actual homopolar rotor does not seem to involve the nit, which rotates evenly despite its distance from the small magnet. presumably there is something else inside.

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