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  • Regulating T-Jet Downforce

    Any suggestions on regulating club rules for T-Jet SS type chassis using AW/JL and Dash type motor magnets?? Scales differ for measurement but are there parameters if using a common scale??

  • #2
    There is the Doane DigiTune Magnet scale, and of course the Magnet Marshal 2 that this site sells.

    There is also resistance from long standing racers in both pancake and magnet racing circles to such scales, and classes defined by downforce - for obvious reasons.

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    • #3
      Dash switched to a different supplier because the magnets from his original supplier could vary quite a lot in strength. The earlier Dash magnets could be as much as 930 gauss, but the later ones were as low as 650 gauss. The newer Killer Bee magnets can also vary somewhat, I have only measured five pairs and those were around 900 gauss. Some people have complained that a few people were able to get magnets that were perhaps 950 gauss and would possibly have an unfair advantage. At that time it was proposed that the downforce of the cars should be measured as part of the pre-race tech inspection, but as far as I know nothing came of that. The DigiTune would probably the best thing to use for HO cars. I use a tester of my own construction to get relative downforce measurements.
      The obvious question to ask is how much impact does the strength of the magnets actually have on the performance of a T-Jet SS type car. You would expect that using more powerful magnets would result in a more powerful motor. My own testing has indicated that the effect of stronger magnets is not linear. I believe that is because stronger magnets result in more back EMF, so the effective voltage that the motor will see will start to go down. Too much magnet will reduce the top speed of a car for several reasons. Fanatic tuners will try magnets of different strengths to find what works best.
      The strength of the car's magnets would also have an impact on how much magnetic downforce the car would have. The amount of downforce would vary with both the strength of the magnets and the distance between the magnets and the track rails. Since that downforce varies with the square of the distance minor differences in tire OD would have a greater impact than you would expect. Some years ago I bought a Bacher built T-Jet SS car. The magnets were labeled 730 gauss. Some day I will have to take my own measurements, but they may or may not agree. In any case that is often my fastest car, but it has minimal downforce on my tester, 7.0 grams. A Dash chassis with ~930 gauss Killer Bee magnets is the fastest car that I have built myself, it measures 24.3 grams. Both cars use the same make and size tires and have the same front end and shoe tension. The Bacher car handles slightly better and the Dash car has a bit more power.
      It would not be practical to measure the gauss values of the magnets on race day. The DigiTune would give you downforce readings and those would be partly influenced by the magnet strength.
      I am not totally convinced that downforce readings would have a lot of value. If someone would take readings of a lot of cars it might be possible to get a better idea of what might be going on. As it stands now the readings would only tell you if someone was using illegal magnets.

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      • #4
        That in itself would be a big deal.

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        • #5
          Originally posted by Dyno Dom View Post
          Any suggestions on regulating club rules for T-Jet SS type chassis using AW/JL and Dash type motor magnets?? Scales differ for measurement but are there parameters if using a common scale??
          Wizzard is selling the "Doane DigiTune Magnet Scale". wizzardho DOT com SLASH doane-magnet-scale

          This scale sells for $75, and is based on a $13 Harbor Freight gram scale. The claim is that each scale is individually calibrated and that any scales should report similar values for the same car.

          ECHORR has adopted this as a standard for their SS class rules, which are nearly identical to the Fray Tjet rules. From echorr.com:

          Magnets:
          9. Downforce of car not to exceed 6.5 on the Doanes calibrated scale.

          The Wizzard page also mentions that the Ohio Cup and HOPRA are using it as well. I think this scale rule was adopted about a year ago by ECHORR. It'll be interesting to see if it sticks. I'm not aware of anyone else trying to regulate T-jet magnets in any other way, other than restricting the make/model of the magnets allowed.

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          • #6
            My favorite cheat:

            “there was no regulation on the size of the fuel line. Obviously, it didn’t take Smokey very long to capitalize on that non-rule. He made a fuel line that was two inches wide and 11 feet long, closer in dimension to an anaconda than a fuel line. Although it sounds pretty funny, the monster fuel line held an extra 5 gallons of gasoline, which made a very real difference on the track (until it was banned, of course).”

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            • #7
              Thanks, good info. Some in the club want a finite max # of 3.1 on club scale while others want to limit use for any Blue/White motor mags from AW/JL and Dash.
              I'm attempting to validate the 3.1 # among the span for the Blue/White mags??

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              • #8
                Have all the blue/whites currently in use at your club been tested?

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                • #9
                  Nico, the racers inventory have not been tested. There lies the contention for a specific # as the span for all B/W mags is wide.

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                  • #10
                    I guess some people don't want their magnets tested?

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                    • #11
                      The Doane DigiTune Magnet Scale has been promoted as a standard with all scales being close in readings. That is not the case in my experience. We have had 4 scales side by side and they all read different for the same the car. The clubs I race with have been checking downforce to get a sense for what is out there. For one club, we do follow the gauss measurements HOPRA has published and check magnets with a SpinDoctor Gauss meter, but those have the same issue as the Doane meter and do not always read the same.

                      To start with, I think you need to decide if you want to check gauss or downforce. If you are going to go by gauss, you will need to decide if you are going to measure the magnets in the car or out of the car and what spot you are going to take your reading. For the downforce, the Doane meter or something of that design will work. In either case, you'll want to start recording readings of the cars to build a database of measurements. From there you can set an upper limit. Since there is variance in the tools, it is best to have a single tool that everyone in the club has access to.

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                      • #12
                        Back when my 1/32nd club still raced cars with traction magnets we used homemade scales that were similar to the HO one that I built. Rather than bringing a single scale to each race each track had its own. In order to be sure that all of the scales would read the same a calibration magnet was used. Shims could be inserted or removed to adjust the downforce readings.
                        It seems to me that if a particular seller's magnets can vary greatly in strength simply specifying which make of magnet would be legal would not necessarily result in a level playing field. Look at the case of the early Dash magnets that were sold separately, those could be over 900 gauss. The magnets that came in the complete rolling chassis that I bought often measured as low as 650 gauss. 250 gauss is a big difference.
                        Using a magnetometer to determine the strength of the magnets would greatly increase the time that it would take to do the pre-race tech inspections. I have never tried to take readings of pancake magnets while they were still in the car, I will try doing that the next time that I prepare my cars for a race. Reading magnets with a magnetometer probe can be tricky. A Magnet Matcher type device might be easier to use, but the magnets would have to be removed from the cars.

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                        • #13
                          Yes, the club's intent is to check downforce with mags in car using a club scale. All other scales will simply take a differential of their scale vs. the club scale. I measured one of my cars on the club scale at 2.66 which measured at 4.86 on my scale (different brand) for a difference of 2.2. It was pointed out that there could be a wide span for strength among manufactured magnets and measuring all club members individual mags isn't feasible. My question for the accuracy of 3.1 as a max # would be as SSR suggested, simply record a database by checking many cars and deciding on a club mag # based off the measurements.

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                          • #14
                            Why isn't measuring them all feasible?

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                            • #15
                              When I raced 1/32 mag cars, they checked all cars for magnet down force. All that matters is the scales that they use at the race track. You may want to recalibrate your scale to match the club scales. It keeps it fair for everyone when all cars are scaled and held to a specific number.

                              Bob

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