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Thread: Cub Scout Pinewood derby loss

  1. #1
    Join Date
    Feb 2002
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    Default Cub Scout Pinewood derby loss

    Got invited to go to a Cub Scout pinewood derby last night, so I made a car from a kit and got beaten pretty easily by a car built by a machinist friend of mine. He refuses to tell me what he did to make it go fast.

    It came with plastic wheels, nails for axles and a pine body. I polished the nails but the wheels still squeaked a bit. The lube was some white teflon powder stuff and I sanded the wheels round. His car even had a winged spoiler on top that should have increased the drag, but his car just ran away from mine.

    Any ideas on how to beat this guy next time? We race again in March and I want to win this time.

  2. #2
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    yeh start at the top of a steep hill and use my 550 pound sister as ballest.put a blowtorch at her backside and get her to fartAlistair
    Please excuse my typing as I have a form of parkinsons disease

  3. #3
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    Do a Google on pinewood derby. I remember reading someplace, all sorts of nefarious skullduggery that one can do. I don't remember the details though.

    One thing was, to make sure the wheels track exactly straight, i.e. the axles are parallel. There was also stuff about weight distribution and undercutting the front end of the car so when the starting block pivots forward, your car starts moving immediately.
    ----------
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
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  4. #4
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    LOL... Wow! That sure brings back memories. I "helped" my daughter build one about 25 years ago but that was with AWANA's. As I recall, there's a maximum weight of the cars and a carved up body comes in under weight. Soooooooo.

    1. Add weight to the front of the car to bring up to maximum weight.
    2. Polish axle nails and remove irregularities under the head.
    3. Use graphite and polish the wheel holes over the nails.
    4. Polish the wood where the wheels contact the body.
    5. Cut the wheel treads so that only a narrow razor-edge makes contact with track. (At the center of the tread)
    6. Make the body aerodynamic and shinny.
    Added:
    7. Pre-drill for nail holes to make sure they are straight.

    Good luck.

    By the way, my daughter took first place in the race and "best of show".
    Last edited by CCWKen; 01-10-2007 at 02:02 PM.

  5. #5
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    Weight in the front? I'd think the back might be better, as it would then have slightly more potential energy (it would be going down the slope for the maximum amount of time) ...but what do I know....
    ----------
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
    Law of Logical Argument - Anything is possible if you don't know what you are talking about.

  6. #6
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    Hmm. Before offering suggestions it would be a good idea to brush up on the rules.

    1. The car weight shall not exceed 5.0 ounces. The official race scale shall be considered final.
    2. The overall length of the car shall not exceed 7 inches.
    3. The overall width of the car shall not exceed 2 inches.
    4. The car must have 1 clearance between the wheels.
    5. The car must have 3/8 clearance underneath the body.
    6. The wood provided in the kit must be used. The block may be shaped any way that is desired.
    7. The wheels supplied with the kit must be used. The wheels may not be cut, drilled, beveled or rounded. You may remove the seam from the wheels.
    8. The axles supplied with the kit must be used. They may be polished or lubricated.
    9. Wheel bearings, washers or bushings are prohibited.
    10. The car must not ride on any type of springs.
    11. The car must be freewheeling, with no starting devices.
    12. No loose material of any kind, such as lead shot, may be used.
    Free software for calculating bolt circles and similar: Click Here

  7. #7
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    This site http://www.pinewoodderbyphysics.com/lectures.shtml has some information that one may or may not want to believe....
    ----------
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
    Law of Logical Argument - Anything is possible if you don't know what you are talking about.

  8. #8
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    For my daughter's racer, I don't remember polishing the axles so much as making sure that they tracked straight. There is some slop between the bore of the wheel and the axle, so I made sure of minimum clearance between the side of the wheel hub and the side of the car, and between the side of the wheel hub and the head of the nail, er..axle. Then tweaked the outboard ends of the axles fore and aft until the car tracked straight.

    Took first place, easily, but it was in a group of technical innocents. Sort of like: In the land of the blind, the one-eye'd man would be king.

  9. #9

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    Things to do to make a Pinewood Derby car fast:
    1) Make the weight of the car as close to the max standard as possible, i.e. 5.00 oz. Add weight to bring the car weight up to 5 oz. This gives the car enough inertia to overcome axle friction and rolling friction in the straight.
    2) If the distance between the axles is X, the CG should be positioned about 75% of the way aft toward the rear axle. The aft CG increases the potential energy of the car which is converted to kinetic energy in the straight. If the CG is too far aft, the front wheels start to bounce off the edge of the track causing the car to slow down.
    3) The axles should be polished. Any burrs on the nail head on the inside should be carefully filed down and polished.
    4) The wheels should be placed on a mandrel and turned true so the car will not bounce.
    5) The axles should be run in in a drill press, i.e. hold the wheel in your hand and turn the axle with the drill press chuck. Tap graphite into the wheel until the inside bore of the wheel and the outside face which mates with the axle head are coated.
    6) Though in general, aerodynamics is a secondary effect, most of the fast cars I have seen are very low profile.

  10. #10
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    SGW, that's a good site, the one you posted seems to give an informed explanation of the physics. I googled a few where they are telling nonsense, advocating making the centre of gravity as high as possible, because since the weight is at a higher elevation obviously it contains more kinetic energy. which of course is true but irrelevant to the competition.

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