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Some magnet reading with a gauss meter.

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  • Some magnet reading with a gauss meter.

    Thought I would show some readings I took off of some pancake magnets with my gauss meter.


    Starting off with some old stock T jet type magnets followed by some of the larger stock AFX type, then Dash ceramic,

    then some poly magnets. The neos, (not shown), measure about double what the Poly's read and I have yet to find them useful in any car.
    The old T jets read about half of the AFX and Dash ceramics read with the poly's reading almost double what the AFX read.


    [url=https://flic.kr/p/2fcCnMW]Old T jet


    [url=https://flic.kr/p/2fcCnNs]AFX


    [url=https://flic.kr/p/RvWErH]Dash ceramic


    [url=https://flic.kr/p/24EJWAM]Poly

  • #2
    Have you ever checked to see how adding traction magnets affect the magnetic strength of the motor magnets?

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    • #3
      A car's motor and traction magnets have to interact to some degree. Traction magnets would move the center of the magnetic field towards the rear of the car. When I was building Wizzard cars I could center the armature without any traction magnets installed. That was the procedure recommended by Bob Lincoln, however with the traction magnets installed the armature would want to move further back if there were no shims to keep it centered on the motor magnets. With the traction magnets in place the armature would be hard up against the rear shim, which might create extra drag. I liked to center the armature with both the motor and traction magnets in place, I never got around to doing any track testing to see which configuration was better.
      Last edited by RichD; 04-03-2019, 05:19 AM.

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      • #4
        I have not checked the magnet strength with traction magnets installed but I would pretty much guarantee they would have some effect on the motor magnets.

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        • #5
          Something folks overlook is that the rear axle, typically being carbon steel, is attracted by the magnets, creating additional drag against the rear axle bushings. Enough that you can see it when you try spinning an axle without the gears engaged, with and without magnets.

          There may also be some small amount of braking due to eddy currents induced in the rear axle.

          The simplest fix I can think of is replacing the stock axle with one made of a non-magnetic grade of stainless steel. That will keep the axle from being pulled toward the magnets, but not remove the eddy current braking. The only way to get rid of both would be to use a non-metallic axle. Carbon fiber anyone?

          Aluminum is another possibility, but I suspect it will be too easy to bend. And, since it is conductive, there would still be eddy currents.

          Actually, the fact the diameter of the axle is so small means eddy current braking should be quite tiny. My guess, not worth worrying about.

          Ed Bianchi
          Last edited by HO RacePro; 04-02-2019, 11:57 AM.

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          • #6
            Hasn't been overlooked. People have already been using titanium both as a wight saver and because it is not magnetic. The problem has been that they wear quickly although Wizzard is supposedly selling ones that have been coated and have better wear.

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            • #7
              KVA stainless would be lighter and stronger than normal axles... probably last longer too - who knows if it'd be less magnetic...?

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              • #8
                Isn't stainless steel always non.magnetic?

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                • #9
                  There are magnetic grades of Stainless Steel. I don't remember the alloy numbers/designations off the top of my head. Just checked, 304 and 316 grades are magnetic.

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                  • #10
                    While most annealed stainless steels are non-magnetic, "Cold Work" can make some stainless steels magnetic. "Cold Work" is the deforming of the metal at room temperature.

                    From Kimballphysics.com -- "Magnetic Response of Stainless Steels".

                    "Grades with higher amounts of austenite forming elements nickel, manganese, carbon, copper and nitrogen form less martensite when cold worked, so do not become so strongly magnetic. This can be evaluated as the ratio of austenite former elements divided by ferrite former elements, or simply as the Ni/Cr ratio. Grade 316 products usually only become slightly magnetic and 310 and 904L are almost totally non-magnetic no matter how severely cold worked. Grade 301 on the other hand has a lesser amount of nickel and work hardens even more rapidly than does 304 . and becomes strongly magnetic after even a small amount of cold work."

                    You are unlikely to find 310 or 904L stainless steel rod or tube in diameters which could be used as slotcar axles. The most readily available grades of stainless steel are 304 and 316. Stainless fasteners are commonly available in 18-8 stainless steel, which is mildly magnetic.

                    Axles will need to be hard to resist bending and wear. "Hard Drawn" axles would have a high amount of work hardening, and so could have significant magnetic properties. It is not clear whether heat treating would also develop the magnetic properties of stainless.

                    The best source of stainless material I have found that can be used as axles is the precision tubing commonly used for hypodermic needles. These tubes are magnetic, but not nearly so magnetic as common slotcar axles, both because they are stainless and they are hollow. While stiff, straight and hard, they are more easily bent than solid axles, due to their thin walls. Given that, they are still good material for making axles.

                    https://www.mcmaster.com/precision-tubing

                    Ed Bianchi





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                    • #11
                      I used to make axles out of thin-wall 316 SS tubing with a carbon fiber core. Made and sold quite a few of them, but haven't made any in years. I modified a RCBS handloading press, developed a die, and then used a pull-trusion technique to carbon fiber/resin core the SS tubing. One foot lengths were easy, but I did work up the process to do one meter tube lengths. I still have the tooling around somewhere.

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                      • #12
                        More info on stainless steel and its magnetic properties here: https://www.scientificamerican.com/a...gnets-work-on/

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                        • #13
                          > I used to make axles out of thin-wall 316 SS tubing with a carbon fiber core.

                          *************
                          Oh cripes Gerry! Is there anything you haven't done?!?

                          I am curious as heck... How did they perform? My first impression is the pull-trusion process would break up the carbon fiber. But if that didn't happen, I'd expect the carbon core would be under extreme compression, while the stainless would be under radial tension. The combination would make the composite much stiffer than the tube would be alone.

                          I'd also expect the composite would rebound somewhat as it emerged from the die -- growing a bit larger in diameter.

                          Do you have any of that material left?

                          Ed Bianchi

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                          • #14
                            with meters, you can play with the mags a lot. ie.. upside down or not to get the stronger side rack facing or the 3 spots on the face to play with what I will call timing. match the opposite ends of the 2 motor mags to increase or decrease the initial pull of the motor.

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                            • #15
                              I have axles left. Back in the day, I filled an order for 1,000 of them. They ended up at a different manufacturer/reseller and were sold as if they were their product with no credit given to me. So I stopped making them. The SS tubing I used only had a wall thickness of 0.005". By pull-trusion, I started a dry carbon fiber "thread" bundle up through the tube. Once it was through the tube, it was continually pulled through at a controlled rate while simultaneously intruding a resin matrix under pressure through the tubing. The end result was a SS/carbon fiber matrix filled tube that was then cut to axle lengths. Once I figured out the process including the viscosity of the resin and how much pressure to apply, I could get a guaranteed 100% fill in the tubing. I've never bent or broke one, just wore them out on the bearing surfaces.

                              I also used the process to make custom, non-bendable R/C helicopter main shafts. You could totally destroy the heli in a crash and the mains haft would be unscathed.

                              I have a surprise for you that I have to get off of my fat Irish *** and mail down to you. I'll include some axles in the package. It might be a week or two before I actually get the package out.

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