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Regulating T-Jet Downforce

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  • NicoRosberg.
    replied
    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?

    Leave a comment:


  • Dyno Dom
    replied
    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.

    Leave a comment:


  • Maddman
    replied
    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.

    Leave a comment:


  • Maddman
    replied
    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.

    Leave a comment:


  • smalltime
    replied
    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.

    Leave a comment:


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

    Leave a comment:


  • NicoRosberg.
    replied
    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.

    Leave a comment:


  • smalltime
    replied
    Originally posted by Maddman View Post
    The basic problem is the lack of a good reliable accurate scale. Without one any effort to regulate downforce is fraught with problems. For example most DMMs are accurate within 1% of a national standard when measuring ohms, and volts. From what has been posted on this thread the commercially available downforce testers are nowhere near that accurate.

    Find (or make) a good low cost widely available and accurate measuring stick and then you can have this discussion.
    I was wondering if we're making this too difficult.

    My track uses reed switches to sense a passing car.

    If you could regulate the distance a reed switch is from the underside of a chassis, and simply use a light hooked to the switch that comes on when the switch is made, then you have a very cheap, efficient way of checking downforce.

    Light up the switch, too much downforce.

    Any thoughts?

    Leave a comment:


  • NicoRosberg.
    replied
    I think Madd's comment is about getting multiple devices to give the same readings.

    He mentions 1% as a goal, where are the two commercial devices out there actually at?

    Leave a comment:


  • RichD
    replied


    My home made downforce tester uses a heavy mild steel bar. I was hoping that that would be less fussy about alignment than something that used actual rails. Soon I discovered that the whole works has to be level, so now I check that with a bubble gauge. The car also needs to be perfectly parallel to the bar to get reliable results. There is a 1/8th inch hole drilled in the bar to take a car's guide pin. The pin must not touch the edge of the hole. If I am careful about those things I find that I can always get reproducible readings.
    Once you develop a technique that gets reproducible readings you can measure a lot of cars to determine what a typical car should read and a car with bogus magnets would stick out like a sore thumb.

    Leave a comment:


  • Maddman
    replied
    The basic problem is the lack of a good reliable accurate scale. Without one any effort to regulate downforce is fraught with problems. For example most DMMs are accurate within 1% of a national standard when measuring ohms, and volts. From what has been posted on this thread the commercially available downforce testers are nowhere near that accurate.

    Find (or make) a good low cost widely available and accurate measuring stick and then you can have this discussion.

    Leave a comment:


  • Dyno Dom
    replied
    Hi Ernie, many of the guys are returning from the pandemic, and they are Fast. Yes, some have stretched the rules during the lax period, let's call it experimenting, but we're attempting to straighten that out. I hope all is well and to see you soon.

    Leave a comment:


  • NicoRosberg.
    replied
    I have found it very common that HO racing people are adept at tripping over their own feet!

    Leave a comment:


  • BIG E
    replied
    Originally posted by NicoRosberg. View Post
    Why isn't measuring them all feasible?
    Deane, you have no idea how crazy running in that group makes me. I enjoy hanging with the guys, and Dyno is one of the best people in the group, but sometimes I just wanna smash something, pack up my gear, and go home (and I have, minus the smashing). It was lots of FUN when Dom came up with the FRACAS concept and we raced on his beautiful 6 lane Maxx Traxx circuit. But many of these guys have stretched it out WAAAY too far. You would probably not enjoy the racing, it's very frustrating at times, whether I win, or finish down the field on a bad night. I am a paid shareholder in the club track, so I guess as a member I can vent once in a while. Haven't been back since the pandemic shut me down as far as racing goes, but I will be returning soon. --- Ernie

    Leave a comment:


  • NicoRosberg.
    replied
    Sounds like a plan.

    Leave a comment:

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