Pinewood Derby


 
Well I finally have the car complete I have the weight within .006 oz of max balance is 30/70 front to rear, axles have been polished and silicone treated as have the wheel hubs been treated to a silicone treatment. I tested it on the kitchen floor and it "FLEW" almost straight as an arrow. I think it may place REALLY well. It's not painted and I am almost thinking it should go naked as I think the weight is sooooo close it may go over or the paint may interfere with the low friction treatment I gave everything. I sure hope the weight checks out too. I adjusted it with this electronic scale and it literally could measure the weight down to a single #6 shotgun pellet so like down to .00x basically a thousandth of an oz

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Your scale and their scale.....wont be same always. Its their scale that matters....period. You do not want to be over. Although if the wood is unfinished you could just bring an exacto knife and carve some wood off to lighten it.

Id always stay under safely, no more than 4.95 or so. .Cut some pieces of aluminum muffler tape to add on bottom rear at weigh-in to hit exact.

Pwd, is down to a science. The compactness of the center of mass matters, which is why people buy tungsten wt and make rail cars. Less energy is lost in rotating thru the curve from incline to flat.

We built cool cars at pack level, we could win there easy enough. The cars for district and council were all out racing machines, with all the tricks the rules permitted.
 
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I guess around here we're not that advanced. Last year I bungled up the build very badly and he still went on to 2nd place in whatever the final race is called. This car I just finished is IMO a master piece. I have part of the weight just behind and on level with the rear axles, done by putting a 3/8" hole in back and placing a .223 bullet (not the whole shell LOL just the lead) in the hole pointy side to the rear and a .22 cal bullet in the hole, sealing with epoxy. On the side I milled out a 3/8" by 1" pocket just in front of the rear axles you see in the photos. In there and in the 3/8" hole just in front of it are nearly all the pellets from 3 standard 12ga #6 shotgun shells I cut open. and again held in place by JB Weld Epoxy. On the top you see 3 holes just in front of the rear wheels. There I placed 3 discs of lead I made by cutting a .22 cal bullet into 3 pieces and flattening them with a small ball peen.
I fully polished the axles and slightly reshaped the heads to sit correctly in the wheel hubs and than silicone treated the metal and plastic. I even silicone treated the body of the car where the wheel hubs will rub.
I really think this one will be da bomb. My daughter is taking it this AM to be painted and airbrushed by an artist she knows. On the top will be flames and on the sides the word "BULLET"
 
Well practice runs went fantastic last night he never came in less than 3rd and mostly 1st or 2nd. When they weighed the car for qualifying though it came in EXACTLY at 5oz even though my photos and my scale clearly show it slightly under. And I can attest to the accuracy of my scale thanks to it's ability to measure down to .00x oz and even can see the weight of a small piece of masking tape! Lesson for nest time. Don't go over 4.8 oz as my final weight before they left with the car was 4.976
 
LMichaels said:
Well practice runs went fantastic last night he never came in less than 3rd and mostly 1st or 2nd. When they weighed the car for qualifying though it came in EXACTLY at 5oz even though my photos and my scale clearly show it slightly under. And I can attest to the accuracy of my scale thanks to it's ability to measure down to .00x oz and even can see the weight of a small piece of masking tape! Lesson for nest time. Don't go over 4.8 oz as my final weight before they left with the car was 4.976
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Well, unless youve checked and calibrated with nist standard calibration weights, theres no way to know for sure whose is right. But regardless, only theirs counts...no matter what. Its unlikely a cheap scale is accurate to anywhere near what display shows.

A coworker of mine borrowed a $20,000 calibrated mettler balance from work for weighin of their district. They lived in rural area so i think pack level was omitted. Accurate to 0.001 gm, certifief routinely. So there would be no arguements.

I have 2 x100 gm certified calibration weights to calibrate my scale with. The calibration curve is basically a straight line, but electronics can show hysteresis, resulting in errors between calibration points. Mine doesnt though. Calibrated at 500gm, its dead on at 100 and 200 gm. To 0.1 gm. But pack, district, council doesnt go to that extent usually. What their scale says, is it.

You can use certified wts to make more of your own, by filling water bottle to get exact same reading. So a single wt...can make duplicates.. and check calibration at many points. Ie 50,100,150,200 gm.
 
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Too much trouble for me. Wife said the scale they used wasn't even as good as the one I used. And as for a $20,000 scale frankly if they disqualified a kid with that $20k scale and all the poor kid had was a cheap postage scale I would go ballistic on the official. Where is a kid supposed to come up with that kind of thing? Frankly the whole PW derby thing I think is over he top in some ways.
Now, as for how the little guy did he came in a VERY close 3rd. So close in fact the kid who came in second almost gave the position to him to take the design placement. Than changed his mind, so my little guy placed for design and will be moving on to some kind of finals
 
LMichaels said:
Too much trouble for me. Wife said the scale they used wasn't even as good as the one I used. And as for a $20,000 scale frankly if they disqualified a kid with that $20k scale and all the poor kid had was a cheap postage scale I would go ballistic on the official. Where is a kid supposed to come up with that kind of thing? Frankly the whole PW derby thing I think is over he top in some ways.
Now, as for how the little guy did he came in a VERY close 3rd. So close in fact the kid who came in second almost gave the position to him to take the design placement. Than changed his mind, so my little guy placed for design and will be moving on to some kind of finals
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your pack should usually make a weigh in scale available beforehand for people to check their cars who don't have one. Postal scales at the post office are also quite accurate and certified.

the standard mode of operation is to come in light and add weight at the weighin to get up to 5.0 exactly.

It's just all part of it. some people don't even know how to do it so we always kept a supply of various kinds of weights that they could glue on or stick on if wanted. some kids would show up several ounces under not having added any weight to the car at all
 
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Supposedly the weights must be integrated to be "integral" to the car not "stuck on" or taped on. I scoured the rules pretty darn hard. Which is why I went through so much trouble to mill out areas that could be filled with shot which allowed me to really fine tune the weight and balance. I think had I had more time to spend on the axles and experimenting with metal and plastic treatments and polishing he would have done even better. Next year will be better as I have an extra PW kit so I can start the build much earlier
 
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