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Regulating T-Jet Downforce

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  • #31
    Hall sensors maybe?

    The problem is that some racers just don't want this checking to happen.

    They enjoy what Dom gallantly referred to as 'experimenting'.

    I have always been appalled to see slot car racers admiring Smokey Yunick. To me he was just a cheat.


    • #32
      William Shatner went into space, you say we can't measure downforce? I guess the disagreement is where space begins and ends.


      • #33
        Originally posted by Eric Peterson View Post
        William Shatner went into space, you say we can't measure downforce? I guess the disagreement is where space begins and ends.
        Who said we can't measure downforce?

        From were I'm sitting, we've come up with numerous ways to do it.

        The bugaboo is getting a system that racers can have in their pit box that gives a very similar reading to the club unit.

        I simply was tying to provide a cheap, adjustable alternative, that's all.


        • #34
          They type of measuring device or technology used isn't the point. The availability, accuracy and repeatability of the measuring device is. A one-off homemade device is nice but doesn't make the cut. Currently the only widely available device is the one sold by WHP. They say that they are accurate and repeatable. Real world measurements say that they are not. Given that the device is a homemade modification of an inexpensive gram scale the likelyhood of multiple devices providing the same reading is laughable.

          Because of differences in resistor values, sensor values, etc. it is a well known fact that no two devices will provide the exact same reading. This is why devices have a tolerance. That +/- % of reading or scale is factored into the rules maximum or minimum allowable value. Note that % or reading is different than % of scale. You can test three or four assembled devices and develop a tolerance however, that is probably too small of a sample population for an accurate value. Ideally the tolerance should be provided by the manufacturer as they can test every device made or a large enough population so that the tolerance can be trusted.

          Posting pictures of your homemade device is nice but it avoids the issue unless you plan to mas produce the things or provide dimension drawings, parts lists and schematics so that all can make one. Suggesting different technologies is a different approach to diverting the discussion away from the most important point in any rules discussion.

          The various orgs are (or will be) having problems with measuring gauss as the widely available and inexpensive meter (that used a hall effect device) that was made by a hobbyist for the market is out of production with no replacement on the horizon.

          The other thing that should be considered is calibration drift. Another fact of life is that all devices drift over time. Magnets lose gauss. DMM accuracy changes. My Fluke DMM is certified to be in calibration for only a few years. Then if it is to be used as a standard the DMM needs to be returned to Fluke for re-calibration. Dragging your 20 year old Radio Shack DMM out of the box and claiming it is a standard is a joke.


          • #35
            My day job was keeping nuclear power plans online and in compliance with NRC, NEI, INPO and other organizations standards. Interpreting standards and developing compliance strategies can be a full time job. While I am not an I&C engineer I worked with them for over 30 years and am familiar with instrument accuracy, drift and setpoint calculations. I know my way around a rule book and have made or ruined many a rule book writers day.


            • #36
              A lot of very good ideas and opinions! The club has opted to use a single home made gram scale and somehow picked a max # of 3.1(I'm still attempting to receive an answer from club members on how that # came to be).
              It would seem all cars checked for that race and time would be accurate to that scale. My scale measures 2.2 higher than the club scale which would seem to suffice for my use as a comparison.


              • #37
                Originally posted by Maddman View Post
                They say that they are accurate and repeatable. Real world measurements say that they are not. Given that the device is a homemade modification of an inexpensive gram scale the likelyhood of multiple devices providing the same reading is laughable..
                What are the numbers?


                • #38
                  Originally posted by NicoRosberg. View Post

                  What are the numbers?
                  Way to give a homework assignment to an Electrical engineer.......don't you have a lawn to care for?
                  Last edited by smalltime; 10-17-2021, 01:39 PM. Reason: spelling, what else


                  • #39

                    What do you mean?
                    Last edited by NicoRosberg.; 10-17-2021, 01:41 PM.


                    • #40
                      How about Ohm's Law?


                      • #41

                        Ohms Law states that the current between two points is directly proportinal to the voltage across the two points. The usual mathematical equation that describes this relationship is I=V/R. Where I is the current through the conductor in amperes, V is the voltage measured across the conductor in volts, and R is the resistance in ohms. There are national and world standards for I, V and R. Your DMM is not one of those standards.

                        Previous posts in this thread have indicated that different WHP downforce measuring devices have provided different readings for the same car. That's enough for me. I don't have such a device. However, considering the materials used in the measurement device and the way is was manufactured it is more than reasonable to expect inconsistent readings from device to device.

                        Perhaps those orgs who have adopted a downforce measuring device have their own data that they can share on how they determined the accuracy of the device and the value of downforce listed in their rules.

                        My thoughts are that the goal of some posters is to divert, deflect and confuse. That is not my intent.


                        • #42
                          Originally posted by SouthShoreRacing View Post
                          We have had 4 scales side by side and they all read different for the same the car.
                          How much difference, in percentage terms?


                          • #43
                            Why wouldn't the house scale be accepted? Reason #21 why I didn't win the race, the Downforce scale isn't the same as mine. Really?
                            These type of rule discussions turn people off from organized racing.
                            Dom saw that back 20 posts ago I think.


                            • #44
                              People will want to build legal cars at home.

                              How can they do that if their scales don't read the same as the house ones?

                              It would be like having a 33.33mm width rule, but your calipers read different to the ones that would be used for tech on race day.


                              • #45
                                A person could compare the readings taken of his own cars with the club scale VS the readings of the same cars taken with his home scale. If the readings were not the same a fudge factor could be applied. The bar on my homemade scale can be shimmed to raise or lower it, the scales that my 1/32nd club used were the same. The scales were kept in sync by using a calibration magnet.
                                As far as the scales themselves go they only resolve 0.1 gram. If a car reads 28.3 grams the true reading could also be 28.2 grams or 28.4 grams. I designed a scale that gives bigger numbers so that small errors would be less significant. The scale that I use can be calibrated and I do have a certified calibration weight for it.


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