Need advice for pinewood derby project

Discussion in 'The Projects Forum' started by strantor, Mar 21, 2012.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    My company has an annual pinewood derby. It is on April 12. I have the kit & I want to make a record breaker. I will be in the outlaw powered class. That means I can put a motor or whatever kind of propulsion on it. I can't use compressed air, C02, or combustibles. I don't have to use the regular pinewood derby wheels either.
    A coworker gave me a decently high powered ducted fan that runs on 5V; I think it was from a PC CPU that he was going to use but now he's decided not to compete. The top performers have usually been ducted fan cars, but I don't think that using thrust against air is the best option, when I can use thrust against the track. I think it would be better to power the wheels - but, since the wheels would be prone to slippage on the slick track, I thought about making a tracked vehicle. May be as simple as cutting a groove in the center of the wheels and stretching a large rubber 0-ring from the front wheel to the back wheel. Also I though it would be an advantage to make it teardrop shaped. Does any of this sound like a good idea? I've never built a pinewood derby car and not sure. just looking for ideas.

    'There was a team of engineers a couple of years ago who made one that set the record. I wasn't there, but people who were there said that it had no visible propulsion system and it's internals were some big secret. The only clue was that it had an LED on the front. Rumor has it, it will be competing this year. I want to beat it.
     
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Make a rail gun car. You will beat everything going.

    More practical a model rocket motor. Maybe combined with a maglev system? :)
     
  3. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    I actually could make a rail gun car, but I would need a launching base. Launching bases are allowed, but the weight of it counts towards the weight of the car, and the car has a weight limit. I couln't get help on AAC with that too :(. I will have to see what weight I have available for the base.

    Rocket motor has combustible propellant, not allowed
     
  4. JoeFromOzarks

    Active Member

    Apr 14, 2010
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    I love Pinewood Derby cars!! (Built several, even built a competitive track.)

    Do you have the rules in PDF you can post here, or a link?

    :) joe
     
  5. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    No, it's on the company server, but I can cut & paste:

     
  6. BSomer

    Member

    Dec 28, 2011
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    Pinewood derbies seem to have come a long way since I did it in the boy scouts...
     
  7. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    well for boyscouts, it's probably still the same. Keep in mind, this is for a company event; a company that prides itself in it's engineering prowess.

    There are 3 classes. This is the most extreme class. The first class is the same as boyscouts.
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Way back when I competed the biggest speed killers were wheel wobble on axles and wheel scrub on the track. I wonder if small guide wheels in the undercarriage on vertical shafts would be a good way to prevent wheel scrub. Lot's of people worked hard on aerodynamics but that never seemed to be much of a factor.
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    What about using a wind up spring setup as your "motor"... Wind it up..and let it go.. you're down the track in a few seconds if that.. Traction will be important.

    It can't be tough competition if "ducted PC fans" are last years champs. You are right..Thats not the way to go..

    How long is the track?
     
  10. JoeFromOzarks

    Active Member

    Apr 14, 2010
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    What components of the “kit” you obtained are required on the finished car? Can you scrap the kit and build entirely from scratch? If so, I’d look into a custom carbon fiber chassis. As “pretty” as the body can be decorated, it is cosmetic and adds weight. Though, having a “body” can legally get you past the rule “P2. You may not use any car body that competed in a previous year’s event – the car body must be built for this year’s event.” You may then perfect the chassis from year to year, depending on the intent of Rule P2.

    How tall are the lane separation guides? If the separation rails are only half an inch tall, “four inch wheels” (P3A) would probably hop right on over. (grin)

    KJ6EAD is correct, aerodynamics doesn’t play much of a role at those speeds. One year, a hollowed out Pinewood Derby car shaped and painted like a full sized flat nosed school bus took grand prize. But “sleekness” has its place.

    I hope the judges use a real scale for weigh in. One year, the hosting troop used a kitchen dietary scale which was so out of whack most racers spent the pre-race time shaving weight. (We built our car using an extremely accurate balance scale!)

    Slightly angled foam glued to the bottom of the vehicle makes for an excellent brake and is very light weight and durable. You'll have leeway in ground clearance.

    Are you permitted to attach a tiny magnet to the “starting peg?” (P9) That would give you a trigger to operate a tiny reed switch on the front of the car. I don’t know if I’d rely on a mechanical contact switch. Depending on room lighting, one might consider a tiny LDR against the peg.

    How many times does your car race? If only once, running a 1V motor at 5V (windings smoking as the car flies down the track) (grin) may be a consideration. We’re hopping into the complex aspect here, but ramping speed from start may be important. “Givin’ ‘er all ye got” out of the gate may cause ‘er to wheelie and flip over. Semi-rigid rubber tires comes to mind, time to study the R/C parts websites.

    You don’t have much time, April 12 is right around the corner. Get a neighbor to build you a single lane test track, you don’t want any unanticipated surprises come race day! Our test track was made from inexpensive counter-top “plastic laminate” scrap from the lumber yard. It goes without saying, our cars were not powered. (grin)

    How come none of the places I ever worked had fun events like this? (I ate some fouled potato salad at a company picnic one time, but let’s not count that!)


    :) joe
     
  11. John P

    AAC Fanatic!

    Oct 14, 2008
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    Do the rules actually allow powered wheels of any kind? I think that's why people use rockets and CO2 cartridges--it's not that they haven't thought of driving an axle with a motor.

    I wonder what the brilliant engineers' "mystery drive" was.
     
  12. JoeFromOzarks

    Active Member

    Apr 14, 2010
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    I don’t know if I’d bother with powering the axle, instead couple the motor right to the tire and have a solid both-rear-wheels-driven (posi-track type) axle. Battery could counter-weight. Just speculatin'. :)

    The confidentiality of “trade secrets.” (grin) Security of that drive train is probably up there with the President’s “football!”

    :) joe
     
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