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  • Mu Metal

    This was mentioned in the Viper Retro car thread.
    If I were to put a piece of this under the motor magnets of an Auto World Series III car that has the traction magnets removed, would the metal remove all magnetic attraction to the rails?

  • #2
    "would the metal remove all magnetic attraction to the rails?" Simple answer NO, it will not reduce ALL the magnetic force! It will reduce the magnetic attraction in a similar way that distance does. Distance is the way that the Viper Retro minimizes magnetic attraction to the rails. By placing the neo motor magnet in a plastic form that emulates the motor magnet, Viper increases the distance from the magnet to the rail to reduce the magnetic force to the rail. You would need to obtain some Mu metal and by trial find that level of magnetic force to the rail that you are looking for. I have used thin Mu metal to be able to pass the pin test on the HOPRA gravity class cars when using the small can motors which have neo magnets. A downforce scale would be one way to measure the reduction in down force as you apply different layers of Mu-metal. Hope this helps.
    Jim

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    • #3
      So the density of the material around the neos in the new Viper chassis does not reduce downforce?

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      • #4
        Any ferrromagnetic material placed under a motor will provide an alternate path for any magnetic flux that leaks outside the motor shell. It is that leaked magnetic flux that attracts the motor to the track's power rails. Just how much of that flux gets diverted away past the rails is determined by the thickness, width, location and magnetic properties of that material.

        In other words, a plate of magnetic material under the motor acts as a shield, preventing the motor's magnetism from reaching the power rails. No such shield will be perfect -- some magnetism will still be felt on the other side of the shield -- but a thicker shield will always work better.

        The lift-pin test places a limit on how much magnetic downforce a 'gravity' car can have. And it means to be competitive you'll have to set up your car to stay just this side of failing the lift pin test. The only true gravity car racing will be on tracks that have no steel in them -- tracks that use copper braid, copper tape, or some other non-ferrous material for power conduction. Aluminum, brass and some grades of stainless steel are potential alternatives, but copper is acknowledged as the go-to material for power conductors. (The only better conductor is silver, which is hardly ever used because it is too expensive.)

        It should be pointed out that while mu metal makes for a particularly good ferromagnetic shield, everyday mild carbon steel does a great job too. And the added extra weight of steel under the motor might just improve handling.

        Ed Bianchi

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        • #5
          That is correct.

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          • #6
            Originally posted by NicoRosberg. View Post
            So the density of the material around the neos in the new Viper chassis does not reduce downforce?
            From the pictures, it looks like the material around the Viper magnets is just a plastic holder. Plastic has no impact on magnetic fields. As jmacartney pointed out, the key features is that "Viper increases the distance from the magnet to the rail to reduce the magnetic force to the rail."

            There is no way to block magnetic fields. Mu Metal concentrates the field inside the material to reduce the strength outside the material.

            https://store-w4rbnih33r.mybigcommer...ds_effects.pdf

            https://magnetic-shield.com/all-about-shielding-faqs/

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            • #7
              I have no thin steel shim stock here to experiment with.
              What effect would a small steel pan under both magnets have on attraction to the rails?

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              • #8
                Originally posted by Wicker Bill View Post
                I have no thin steel shim stock here to experiment with.
                What effect would a small steel pan under both magnets have on attraction to the rails?
                It's likely to reduce magnetic downforce by some amount. Other folks here have posted about doing that with gravity cars. It's hard to say how much effect it will have.

                Here is another page talking about it: https://www.kjmagnetics.com/blog.asp...ding-materials

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                • #9
                  If you were going to add a flux collector from magnet to magnet it would be best to dig out some of the plastic and keep the outside of the metal as far from the rails as possible. You might get the best results by routing the metal shim from magnet to magnet across the top of the motor box.
                  .

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