Pinewood Derby 2025

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  • LCHIEN
    Super Moderator
    • Dec 2002
    • 21459
    • Katy, TX, USA.
    • BT3000 vintage 1999

    Pinewood Derby 2025

    It is time to help the Grandson again this year which means I'll probably enter a car into the Family member division to channel some of the ideas I have instead of making his car for him.

    One thing that has gotten old for him and me (HIS FOURTH, MY 6th)car is polishing the nails they give you for axles. Time consuming and kind of boring. I chuck them up in a slow running drill and then sand them with progressively finer strips of sandpaper - usually 220, 400, 600, then some polishing paper scraps I got from work long ago for polishing fiber optic connector ends. Probably 1000 to 4000 grit. The idea is a smoother axle allows the wheels to run with less friction. Times are decided with .001 ms resolution so yeah every bit counts.
    This year I decided to try for me some prepolished axles they sell on Amazon and the internet claimed to be.
    The commercial axles are rounder and they have a groove so that the wheel runs with less contact area.
    But overall, from three different seller, none of them had as good a polish as mine.
    The picture shows on the left side, the stock BSA (boy scouts) axle, the stock axle I polished,
    and on the right, three axles costing $2 per axle.

    Click image for larger version  Name:	Comparison stock and three brands polished axles.jpg Views:	0 Size:	106.2 KB ID:	860212
    Its hard to light highly polished round surfaces, but you can see the roughness in the reflective area how smooth and uniform the light reflection is.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions
  • LCHIEN
    Super Moderator
    • Dec 2002
    • 21459
    • Katy, TX, USA.
    • BT3000 vintage 1999

    #2
    Trying something new...
    Pouring melted lead into a measured routed cavity for getting the car to the max allowed weight of 5.00 Oz. With thin, aerodynamic bodies, you need a lot of weight. I've had in the past 1 oz bodies needing 3.5 oz of lead weight (1/2 ounce for the wheels and axles).
    Bottom of the car, for look's sake.
    Click image for larger version  Name:	20250113_155129.jpg Views:	0 Size:	281.3 KB ID:	860214 Click image for larger version  Name:	20250113_155133.jpg Views:	0 Size:	286.1 KB ID:	860215

    My dentist friend gives me the lead foil backings from his bite wing x-ray films.
    Last edited by LCHIEN; 01-15-2025, 02:48 AM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

    Comment

    • leehljp
      The Full Monte
      • Dec 2002
      • 8552
      • Tunica, MS
      • BT3000/3100

      #3
      In making pens with CA finish, I use 4 ft very bright overhead LED 5000K lights and just as you wrote - the shine shows the perfection or imperfection.

      There are some/many 4 ft lights that have non continuous lighting, or 3mm dot LED squares spaced every 4 to 5 mm. These create a sparkle of sorts and does not let one see the continuous shine as in your pict of the Grade A above, and therefore hard to distinguish the imperfections.
      Hank Lee

      Experience is what you get when you don't get what you wanted!

      Comment


      • LCHIEN
        LCHIEN commented
        Editing a comment
        This is a USB microscope, it has built-in ringlight for shadowless illumination.
        As with most high magnification, the working distance is so small its hard to get direct lighting on it without the camera and lens casting major shadows over the work and a very steep incidence angles.
        Last edited by LCHIEN; 01-15-2025, 01:19 PM.
    • LCHIEN
      Super Moderator
      • Dec 2002
      • 21459
      • Katy, TX, USA.
      • BT3000 vintage 1999

      #4
      Click image for larger version  Name:	image.png Views:	0 Size:	1.35 MB ID:	860222

      TOP: "Polished" Axle After I polished it four more times
      BOTTOM: "Polished" axle from vendor

      Little better lighting.
      Note: the wheel rides on the raised part
      Races are decided by a few thousands of a second.
      Last edited by LCHIEN; 01-19-2025, 11:58 AM.
      Loring in Katy, TX USA
      If your only tool is a hammer, you tend to treat all problems as if they were nails.
      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

      Comment

      • LCHIEN
        Super Moderator
        • Dec 2002
        • 21459
        • Katy, TX, USA.
        • BT3000 vintage 1999

        #5
        Grandson Trying something for his car that's new to me... Hydro dipping.
        They did this test piece yesterday to see how it worked
        Man, I think its really neat looking!

        Click image for larger version  Name:	Hydro Dipped test item.jpg Views:	0 Size:	190.7 KB ID:	860224
        Loring in Katy, TX USA
        If your only tool is a hammer, you tend to treat all problems as if they were nails.
        BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

        Comment

        • leehljp
          The Full Monte
          • Dec 2002
          • 8552
          • Tunica, MS
          • BT3000/3100

          #6
          That looks GOOD! Very GOOD!
          Hank Lee

          Experience is what you get when you don't get what you wanted!

          Comment

          • LCHIEN
            Super Moderator
            • Dec 2002
            • 21459
            • Katy, TX, USA.
            • BT3000 vintage 1999

            #7
            Click image for larger version  Name:	20250117_175138.jpg Views:	97 Size:	130.7 KB ID:	860232
            How I put a screwdriver slot in a nail head.
            Mount the dremel.
            install a thin abrasive disc
            chuck the nail into the drill press without turning it on
            Lower the nailhead onto the spinning abrasive disc until the slot is cut

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            Click image for larger version  Name:	20250117_201639.jpg Views:	82 Size:	147.1 KB ID:	860235

            The nail is bent a degree or two. Turning it allows me to adjust the front end alignment so it runs straight to counteract any tendency to go right or left rubbing against the guide rail.

            Click image for larger version  Name:	20250119_222140.jpg Views:	81 Size:	164.9 KB ID:	860234

            Last edited by LCHIEN; Yesterday, 03:45 AM.
            Loring in Katy, TX USA
            If your only tool is a hammer, you tend to treat all problems as if they were nails.
            BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

            Comment

            • LCHIEN
              Super Moderator
              • Dec 2002
              • 21459
              • Katy, TX, USA.
              • BT3000 vintage 1999

              #8
              cars tuned and weighted and finished
              Attached Files
              Loring in Katy, TX USA
              If your only tool is a hammer, you tend to treat all problems as if they were nails.
              BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

              Comment

              • LCHIEN
                Super Moderator
                • Dec 2002
                • 21459
                • Katy, TX, USA.
                • BT3000 vintage 1999

                #9
                This car deserves a video, called Midnight Lights
                Attached Files
                Loring in Katy, TX USA
                If your only tool is a hammer, you tend to treat all problems as if they were nails.
                BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                Comment

                • LCHIEN
                  Super Moderator
                  • Dec 2002
                  • 21459
                  • Katy, TX, USA.
                  • BT3000 vintage 1999

                  #10
                  why did I make 2 cars?
                  Because I have multiple ideas and probably too much time being retired.
                  The Money one is faster apparently but the Midnight Lights one lights up which I think is unique.
                  I apparently can only enter one in the Family division. Last time I entered one under my name and one under my son-in-laws name and they were not happy.

                  Not sure which I should enter. Go for speed prize or design prize?

                  Click image for larger version  Name:	image.png Views:	0 Size:	1.38 MB ID:	860270
                  Last edited by LCHIEN; 01-22-2025, 04:21 AM.
                  Loring in Katy, TX USA
                  If your only tool is a hammer, you tend to treat all problems as if they were nails.
                  BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                  Comment

                  • LCHIEN
                    Super Moderator
                    • Dec 2002
                    • 21459
                    • Katy, TX, USA.
                    • BT3000 vintage 1999

                    #11
                    Results.
                    Grandson won third in his age class.
                    They didn't announce overall winners for Family group but here's three captures of a race with both of my cars (Right two lanes) finishing 1-2
                    Attached Files
                    Last edited by LCHIEN; 01-26-2025, 01:22 AM.
                    Loring in Katy, TX USA
                    If your only tool is a hammer, you tend to treat all problems as if they were nails.
                    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                    Comment

                    • leehljp
                      The Full Monte
                      • Dec 2002
                      • 8552
                      • Tunica, MS
                      • BT3000/3100

                      #12
                      Congratulations on all the great work you put in and the results that were garnered.

                      Loring, A question for you that I have mulled over and over the past two days: When the bend the nail as in post #7, 3rd picture - how or where do you put this nail and what is the orientation to make the car not hug the rail? I can understand it being an axle and changing the orientation of one wheel, but that doesn't appear to be an axle. I haven't figured that one out. Thanks.
                      Hank Lee

                      Experience is what you get when you don't get what you wanted!

                      Comment

                      • LCHIEN
                        Super Moderator
                        • Dec 2002
                        • 21459
                        • Katy, TX, USA.
                        • BT3000 vintage 1999

                        #13
                        Originally posted by leehljp
                        Congratulations on all the great work you put in and the results that were garnered.

                        Loring, A question for you that I have mulled over and over the past two days: When the bend the nail as in post #7, 3rd picture - how or where do you put this nail and what is the orientation to make the car not hug the rail? I can understand it being an axle and changing the orientation of one wheel, but that doesn't appear to be an axle. I haven't figured that one out. Thanks.

                        Click image for larger version  Name:	image.png Views:	0 Size:	11.5 KB ID:	860295
                        For all the wheels we use a 2.5 degree camber. With the top of the wheel tilted toward the car. That makes the wheel run to the outside and rubs against the polished axlehead and not the sticky painted body - less friction. Also only the edge of the wheel touches the track to reduce rolling friction. So I build a jig to tilt the body 2.5 degrees on the drill press while holding the body against a fence to drill repeated distance from the bottom of the car and perpendicular in the other direction. More than about 2.5° will cause the upper edge of the wheel to rub against the body of the car.
                        Click image for larger version  Name:	image.png Views:	29 Size:	1.34 MB ID:	860302
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                        One secret is to really make the car ride on three wheels - a tricycle. So I put the right front hole about .030 higher than the others and weight the car to the back so the right front wheel is off the ground. That allows the wheel to help steer the car with the center rail if need be, but the rolling friction and the energy to spin the right wheel are saved.

                        Click image for larger version  Name:	image.png Views:	0 Size:	5.1 KB ID:	860296

                        FInally, if your wheels are perfectly perpendicular to the direction of travel and all parallel, then it will roll straight down the track with no rubbing against the guide rail. But nothing is perfect and they have a tendency to wander either left or right over 40 feet. So this is where the bent axle comes in. I bend the axle a couple of degrees.
                        If the bend is up then the wheel is essentially parallel to the other wheels
                        If the bend is forward (as shown below) then the wheel has a 2 degree turn to the right
                        if the bend is backwards then the wheel has a 2 degree turn to the left.
                        Using the slot i milled in the head of the axle, I can rotate the axle to get a range of +/-2 degrees steering.
                        By running down a test track I can make the car run straight as possible to minimize contact with the center rail and the friction/speed loss it causes.
                        I say ~2° - I have no easy way to measure that but its about the smallest angle you can see by eye. I figure if I drilled the axles all perpendicular to the length of the car then the cumulative steering correction needed should be under a degree.

                        Click image for larger version  Name:	image.png Views:	0 Size:	11.5 KB ID:	860297
                        Last edited by LCHIEN; 01-31-2025, 11:52 AM.
                        Loring in Katy, TX USA
                        If your only tool is a hammer, you tend to treat all problems as if they were nails.
                        BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                        Comment

                        • leehljp
                          The Full Monte
                          • Dec 2002
                          • 8552
                          • Tunica, MS
                          • BT3000/3100

                          #14
                          That is brilliant! Thanks for the explanation! I appreciate you taking the time to draw up the picts with the written details.

                          Thank you!
                          Hank Lee

                          Experience is what you get when you don't get what you wanted!

                          Comment

                          • LCHIEN
                            Super Moderator
                            • Dec 2002
                            • 21459
                            • Katy, TX, USA.
                            • BT3000 vintage 1999

                            #15
                            delayed results... they ran out of time on race day so I got the 3rd place award family div, today.
                            My time was 3.12 sec (average of 6 runs)
                            Second place was 3.11 sec (apparently 6 ms faster)
                            First place was 3.08 sec.

                            Click image for larger version  Name:	image.png Views:	0 Size:	1.44 MB ID:	860308 Click image for larger version  Name:	image.png Views:	0 Size:	1.37 MB ID:	860309
                            Attached Files
                            Last edited by LCHIEN; 01-28-2025, 02:00 AM.
                            Loring in Katy, TX USA
                            If your only tool is a hammer, you tend to treat all problems as if they were nails.
                            BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                            Comment

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