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Pinewood Prius?

Discussion in 'Gen 2 Prius Main Forum' started by efusco, Jan 2, 2007.

  1. viking31

    viking31 Member

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    My son when he was 9 or 10 entered the Pinewood Derby that featured about 30 or so cars and won first one year and second the next (although I thought he could have had a chance at first again because the scoring was not quite right, but I didn't raise a stink about it; it's for the kids!).

    Firstly, you have to use the parts supplied in the official Pinewood Derby kit. That's the plastic wheels, nails, wood axles, and body. There are min and max weight restrictions and usually the cars on the light side tend to place higher. I let him do nearly all the work himself. The car wasn't necessarily super aerodynamic (standard flat wedge design), the paint and other items were what you would expect from a 9 year old. We used lots of powdered graphite to lube the axles (important!). No other prep on the nails or the plastic wheels.

    Shortly before the race and during the weigh in, I discovered only three wheels contacted the ground. He inadvertently put on the front axle on a little askew so only one wheel in the front contacted the ground. I thought then for sure he was doomed to be at the bottom of the pack. Too late for a fix now! Nonetheless, he took first.

    Turned out, that after doing research on the internet, by building the car so only three wheels touch the track you may gain a slight advantage by having less friction and the car is less likely to wander back and forth on the track.

    Rick
    #4 2006
     
  2. IsrAmeriPrius

    IsrAmeriPrius Progressive Member

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    <div class='quotetop'>QUOTE(efusco @ Jan 3 2007, 06:35 AM) [snapback]370045[/snapback]</div>
    Come on Evan, lighten up. I was just teasing you. I am a UCLA fan. My team did not even come close to being competitive in the Emerald Bowl.
     
  3. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(IsrAmeriPrius @ Jan 3 2007, 04:24 PM) [snapback]370364[/snapback]</div>
    I should have thrown in a smiley or something, I wasn't really angry at you...you were just "hatin' on my boys" kinda thing. ;) <-- Mandatory smiley
     
  4. hill

    hill High Fiber Member

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    <div class='quotetop'>QUOTE(efusco @ Jan 2 2007, 11:54 PM) [snapback]369860[/snapback]</div>
    The last time I built a pinewood derby champ, Evan, it was modeled after a '63 Maserati ... boy I just dated myself.
     
  5. Bigsk8r

    Bigsk8r New Member

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    Evan,

    I just e-mailed you a tip guide for decreasing rolling resistance and proper build methods. As for the shape, some competitions have strict dimensional requirements. If your pack uses a photo-transistor gate at the finish line, there will likely be a height limit.

    My suggestion would be to take a Prius side image as suggested by others and use a photo editor to reduce it in the Z axis. If you set the X axis to the length you need prior to this, a good cut and decent paint job should give a look that is acceptable all at a height that will still yield good aero properties.

    Some other folks here have made statements about weight (mass). If you take the same exact car at 3 ounces and time it, then add 2 ounces to it, it will be faster every time. You are a smart guy you do not need a physics lesson on that.

    Good luck sir!!

    Bigsk8r
     
  6. efusco

    efusco Moderator Emeritus
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    Just so everyone knows the status, I did use one of my profile shots of my own prius and adjusted the size in photoshop to 7" front to back. The 'blank' for the pinewood derby car is exactly 7" long. Interestingly the pre-cut axle slots on the derby blank are exactly the same distance as the axles on the Prius photo...so that part will be easy.

    I think I'll have to glue on another blank to get the high though...the peak of the roof is almost a full block higher.

    I think I'll try to photograph the entire process so others can reproduce and/or modify/improve my design.

    Oh, and thanks for all the tips. Seems there are some really good PWD memories out there and some folks who really got into it.
     
  7. Godiva

    Godiva AmeriKan Citizen

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    <div class='quotetop'>QUOTE(Bigsk8r @ Jan 3 2007, 10:49 PM) [snapback]370532[/snapback]</div>
    Isn't there a diminishing returns thing that happens once too much weight is reached? Isn't the trick to balance the weight, friction and resistence?

    (No, I never built a pinewood derby car. Never entered a soapbox derby either. In fact, didn't take physics in High School either so maybe I do need a lesson. Be gentle with me.)
     
  8. Bigsk8r

    Bigsk8r New Member

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    <div class='quotetop'>QUOTE(efusco @ Jan 3 2007, 11:09 PM) [snapback]370542[/snapback]</div>
    Hey!! :eek:

    I resemble that remark! :D
     
  9. Bigsk8r

    Bigsk8r New Member

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    <div class='quotetop'>QUOTE(Godiva @ Jan 3 2007, 11:13 PM) [snapback]370545[/snapback]</div>
    I wish I could remember all the physics that go into it!

    The basic version though is that straight down, in a vacuum, a 1 Ton hunk of lead will fall at the same speed as a feather. However, the moment you introduce any friction at all, the difference is stark.

    You are correct about the diminishing returns once the load limits of the axles and wheels are reached. As soon as the axle flexes or the wheel distorts, you have just upset the friction balance of the vehicle. Until that point though, mass is king on equally built cars.

    If Evan can get the shape he wants, can get the cars center of gravity to be about 1" in front of the rear axle, and be very close to 5 ounces, the car will run good. I can't wait to see it!

    Good night all,

    Bigsk8r
     
  10. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    actually overcoming the drag of friction on the wheels are the hinderance to speed. so more weight simply overcomes that initial startup and gets it going faster. as the speed increases, the additonal weight provides more momentum which in turn, makes any drag caused by the wheels to have less and less effect.

    i do remember about a dozen trips to the post office because they were the only ones that had an accurate scale that would weigh ounces accurately.
     
  11. darelldd

    darelldd Prius is our Gas Guzzler

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    I think the PWD should keep pace with modern society. Why not allow electric propulsion? Mine would have LED headlights. :)

    Back when I actually did this as a kid, mine sucked. Look really cool though!
     
  12. Bigsk8r

    Bigsk8r New Member

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    Evan,

    Where is our update on the Pinewood Prius Project?

    ;)
     
  13. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(Bigsk8r @ Jan 20 2007, 12:15 AM) [snapback]378164[/snapback]</div>
    Due to terrible weather this past week the race has been postponed for a week...good news for me since I've been away for a week on vacation and have done little on the derby Prius. It's coming along though. The side profile is spot on....but due to the dimensions I have to work with it's narrow and doesn't look quite right from the front or top.

    I've taken some pics of the early process. I'll take one just after sanding. One after painting. And some of the finished project...hopefully before next Saturday's weigh in.
     
  14. efusco

    efusco Moderator Emeritus
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    The local Pinewood Derby is complete. For it being my first year as the head builder and considering that I had to build 3 cars I think it went pretty well. My son Brendan was in a run-off of the two undefeateds for the Tiger Cubs and lost 3/4 heats....after I looked at the car at home one of the wheels/axles was slightly off and wobbling, a tiny push got it straight and I think he could have won had I had a chance to 'tune' it before the heats.

    My other son, Heath, did OK, but he had weight placement issues and didn't really let me work on the aerodynamics much.

    But, for those who've been waiting, the Prius came out pretty decent. My painting skills leave a lot to be desired, but all in all I think anyone who knows what a Prius is would recognize it as such. I was in the middle of the pack for the 'over-the-hill' race, but hadn't really expected it to be fast, just wanted it to look somewhat like a Prius.
    [​IMG]

    [​IMG]

    More photos at:
    http://www.flickr.com/photos/efusco/sets/72157594428688334/
     
  15. David Beale

    David Beale Senior Member

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    And if aerodynamics do have an effect, from my schooling days, aerodynamics are more important at the -rear- of a vehicle than the front. In other words, most modern cars are more efficient going backwards than forwards! As I remember, it was about a 30% difference (aerodymanics is 30% more effective on the rear than the front).
     
  16. Bill Lumbergh

    Bill Lumbergh USAF Aircraft Maintainer

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    My pinewood racer was based off of an Alfa Romeo. Yeah, it lost, but I gues I'm lucky it didn't break down halfway down the track.
     
  17. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    hey nice Prius. bit longer and lower, but gotta work with the piece of wood given. but my criteria is easy, just like any other unmistakeable Prius on the street, your pinewood racer is unmistakeably a Prius. very nice job!