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Thread: 12345

  1. #1
    Join Date
    Mar 2008


    Last edited by Chuck Thoits; 04-29-2009 at 10:21 PM.
    It could be worse You could be on fire.
    Stupid hurts.

  2. #2
    Join Date
    Oct 2008
    Kea'au Hawaii. Just down the road from Hilo town!
    Chuck, the only thing that comes to mind is, go with very thin narrow wheels with ball bearings. I would make them out of plastic with a groove in the outer edge to roll a thin O'ring into to act as a tire. That would help it track better. Other than that maybe a compressed air nozzle to give it a better launch!!??

    What goes around, comes around.

  3. #3
    Many years since I was embarrassed by helping my son with a pinewood derby car. The first one didn't make it to the bottom of the track. We endured the harrassment, and the next time around we took 3rd in the regionals. Lessons learned. Actually, my son made the car, I provided the work on the things that let it go fast. If you have to stick to kit pieces (that was our rule), about all you can do is make everything as smooth as possible. Also use a forstner bit on the bottom to make places to add weight in strategic spots so the weight is right up at the max allowable (minus a smidge since you don't want to be disqualified because somebody's scale is out of whack). I put the axles in a drill press and smoothed them with steel wool and polishing medium. I also rigged a way to chuck the wheels in the drill press so I could use an abrasive to get them as round and smooth as possible. Can't remember how I did this, but it's also important to install the axles so the wheels are all tracking the same and not fighting each other. Sounds simple, but as I recall it was quite a bit of work. But it paid off. I don't think aerodynamics comes into play with something that small, but don't take my word on that. Maybe we would have done better than 3rd if I'd considered it, but my son had ideas about what he wanted it to look like, and actually it was his car. Good luck with that.


  4. #4
    I wish I could help out, but we didn't win anything for speed. What I've read and been told breaks down to 1) geometry - wheels/axles square to the body and each other and 2) friction - polished axles and concentric wheels. We only did the basics to get the car down the track.

    Good luck and have fun!


  5. #5
    Join Date
    Jan 2009
    I live in Denton, Texas and ranched at Schulenburg, Texas.
    Chuck: my grandson's cub scouts did thiers two weeks ago. We had a blast. We finished 9th outa 11; but we did finish. The other two did not finish. My grandson insisted he build a truck so I cut and glued him a ford pu and he already has said next year it will a fast car.
    When this thread is finished I will print it for him as a guide for next year.
    Have fun.....
    Ray Gerdes

  6. #6
    Join Date
    Mar 2007
    Long Hill Township, NJ

    It's all in the wheels and axles. My son's troop specifies that you must use the BSA wheels and axles and you cannot modify the wheels other than polishing to remove casting marks. They check that the molded "tread edges" remain.

    Like Wes said - it's all in the rolling friction and geometry. I'd be temped to get the wheels perfectly round and fill them SOLID with some material. The wheels would have a higher moment of inertia (if all my physics is being remembered properly) and would/could maintain speed better in the flat.

    Good luck -


  7. #7
    Join Date
    Dec 2008
    falcon heights, minnesota
    compressed air? i'd go with a bottle rocket embedded in the car. remember, it if it's not disallowed in the rules...
    benedictione omnes bene

    check out my etsy store, buroviejowoodworking

  8. #8
    alas.... no open flames allowed
    Dragon's Paradox - ** working on updates ** Custom and One Of A Kind Heirloom Quality Hand Crafted Jewelry & Gifts

  9. #9
    Join Date
    Oct 2006
    ABQ NM
    Quote Originally Posted by Chuck Thoits View Post
    ...As of right now it weights in at 5 oz. That would be the limit for the boys. I have to get mine up to 10oz.
    The last thing to do is add another 5oz to my car but where front, back, top, bottom.
    I was also thinking about putting a tin body on it to cover the wheels. But don't know if that would eliminate enough drag to make a difference.
    If I remember right (now there's a stretch), I think low weight in the front will help your initial takeoff and help the car track straighter. My dad used to have bullet molding gear, so he'd drill holes in the bottom of my cars and pour molten lead into them to add weight. I have no idea how smart or dangerous this was, but that's how we did mine when I was a kid. Aside from my first car, the other several I did were for school-sponsored (not BSA) contests, so the weight and wheel rules were a bit more open.

    Instead of fenders, can you mount one or two horizontal wheels on each side, to run on the side rails of the track (in case your tracking isn't quite right)? Essentially roller bumpers on the sides.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

  10. #10
    That's what I remembered as well Vaughn - weight as far forward as possible. BUT, I was informed the weight should be as far BACK as possible. Something to do with the center of mass and having gravity act on that mass as long as possible. Oh, and lead and zinc are now passe - they're using tungsten now because it's denser than lead allowing for more precise placement of the weight.

    I do remember one of the winning cars had the slots for the axles re-machined accurately on the top (now the bottom) and ignoring the original slots.


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