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Rich's down force checker.

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  • Rich's down force checker.

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    interesting device you have there. My main question about it is:

    Do TJets read differently without pick up shoes and springs?

    Inquiring minds want to know.

    Scott
    Why doesn't my car run like that?

    Scott

  • #2
    DR. D's down force scale is a a modified version that the H.O.S.T. 1/32 club in New Hampshire used about 20 years ago when they raced on plastic track.
    The inventor made several for the club members & also shared the design with our rival club Shoreline.
    He even posted a "How To Build " on another forum so anyone could make their own.
    Of course after going to routed woods tracks our clubs didn't need it anymore.
    Curiously enough someone copied the idea & made the " Magnet Marshall ".
    I believe the inventor is a member of HRW and might still have that "How To Build " .

    There are many other down force scale builds on the 'net, this is one I use for my HO magnets:
    https://www.youtube.com/watch?v=BXLzgGgdf8Q

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    • #3
      I have not measured a car with the shoes and springs removed VS with them in place. The procedure is to put the car upside down on a place away from the steel bar and zero the scale. The car is then placed over the bar so that only the downforce is read. Using a device with rails would give readings closer to what you would get on the track. I deliberately designed the uprights that hold the bar in place so that shims could be removed to lower the bar and get lower downforce readings that would be more in line with testers that have rails.
      Shoreline Model Raceways used the same design when they still were racing cars with traction magnets, I don't know who came up with the original idea.
      The next time that I am prepping my cars for a race I will see if removing the shoes and springs makes any difference. The distance between the bar and the magnets would have to change for that to have any effect I would think unless the shoes also altered the shape of the magnetic field.

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      • #4
        The next time that I am prepping my cars for a race I will see if removing the shoes and springs makes any difference. The distance between the bar and the magnets would have to change for that to have any effect I would think unless the shoes also altered the shape of the magnetic field.
        I suspect that your scale is not going to be able to read fine (?) enough to see a difference. But the pick up shoe springs are trying to "push" the chassis "up". But then, it won't make a difference if the chassis is sitting on the front tires. One way to find out. I should think more first before I make posts.

        Scott
        Why doesn't my car run like that?

        Scott

        Comment


        • #5
          I built the scale with that massive steel bar for two reasons, one of which was that I could get more reproducible readings. The scale reads to the nearest 0.1 gram, the last digit is questionable. if your downforcce was 2.4g a 0.1g error would be 4.16%, if the downforce was 4.1g the error would be 2.44% and if it was 25.7g it would be only 0.39%. I just checked to see what would happen if the shoes and springs were removed. With the shoes and springs in place the car tared out at 22.0g and the downforce measured 27.1g. With the shoes and springs removed the tare was 21.6g and the downforce was 31.3g. With the shoes and springs replaced the tare was 22.1g and the downforce was 27.2g. It appears that the springs and shoes can have an effect on the downforce reading, for whatever reason.

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          • noddaz
            noddaz commented
            Editing a comment
            Thank you. Interesting results you have there.
            Scott

        • #6
          A few more comments, with this gage it is important for the car to be level, I use a bubble gage to check that. Since I built the gage I found that the wood part that supports the car was not perfectly flat and also wanted to move around on the scale. I put some tape under one corner to keep the support from rocking and added thick dabs of rubber cement to keep it from sliding around.

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