pinewood derby

[Mike Kast]

Ok, do you think I can say my 5 year old daughter made this and get away with it?
the proportions are a little funny but I had to deal with what the kit came with. Not quite a 20,000 hour job but hell! I have a real one to deal with!

[Jim Smolka]

Looks like a fun project. There is a bunch of stuff and tricks to do to make the car as fast as possible. Good luck.

[Mike Kast]

well, fill me in Jim! They give awards for the fastest, the slowest and the coolest. My daughter said she doesn't want to try to be slowest, she wants a fast one, she wants a Porsche.
There is an adult division too, I already told her we have to make another one for her. I'll be racing with the big boys.

[911r_parts]

type in "pinewood derby tricks" at google and see all the links.

[SandyI]

Completely hollowing out the underside of your car and placing all your weights between the rear wheels helps your speed.

[azasadny]

Mike,

My son and I built one of these a few years ago, we drilled out the middle of the car then took apart some shotgun shells and loaded the hole with lead shot. We weighed the car carefully and left it an ounce or two below the allowed weight. We also polished the "axles" (nails) with steel wool, then put powdered graphite on them. The car ran really fast but was just barely beaten by two other cars. Have fun!!!

[Jay Zollinger]

The primary keys to pinewood derby speed are making the car as heavy as absolutely possible and carefully preparing the axles and wheels. You should polish the axles with increasingly fine-grit sand paper and pumice until they shine like a mirror, use the finest powdered graphite possible, sand any burs off the wheels, and make sure that everything is properly aligned. Good luck--and nice looking car!

[ZOA NOM]

Put all your weight out front. (see avatar)

[vash]

i did that when i was a kid. my dad was not as talented as you, and i ended up with more of a orange AMC pacer. i never did it again, but if i did i would recess the wheels in so that they didnt touch the rails on the way down. i cant wait until i have a kid so i can get really into it.

[ZOA NOM]

I think the track has two grooves on the outside where the tires ride, so recessing isn't helpful. I have heard that grinding the tires down to a sharp edge will help. They may have outlawed that these days, though.

[Mike Kast]

The rail is in the center. I actually added wood the thickness of the tires to have a recessed look. I had to have the SC flairs This is a YMCA thing so I still have to get the rules and give them their 2 bucks per car. This one is a cub scout leftover from my neighbors kid. I think they will be the same specs. If not this one is just practice

[earossi]

I had forgotten all about this topic! I had three sons go through Cub Scouts, and every one made multiple cars. The really competitive types make more than one car for each race season, and then race the fastest of their efforts.

The keys are to have the lowest rolling resistance and the greatest wieght. Moving all the weight to the rear could produce an instability in the car that will slow it down. So, front weight your cars.

Putting a knife edge on the wheels is one great idea. Another is to drill out the web of the wheels (lightening holes)........since the wheels have to go from zero to max rotational speed........you want to improve these ability to accelerate..........you do this by taking mass out of the wheels.

The axles are the next spot to focus. As stated above, they need to be polished to a mirror finish and they need to be "run in" on their axles. Finally, use lots of graphite for lubrication.

The last "trick" is to produce a car that rides "only" on three wheels! If you weight the car to the front, then "raise" one of the rear wheels so that the car will stand and move on the three remaining wheels.

Of course, it was my sons who developed such technology!

[Mike Kast]

Originally posted by unfixed
and i ended up with more of a orange AMC pacer.

Yea... dropping out of school and becoming a carpenter is finally paying off! BIG TIME!!!!
lol

[vash]

oh, the rail is in the middle. it has been a long time, i was in cub scouts. maybe if i did it again, i wouldnt even make it look like a car. maybe make it look like a wooden dog on wheels looks like a blast.
have fun, and good luck.

cliff

[ZOA NOM]

Another thing is the hub of the wheel. The surface area rubbing on the axle can be reduced by shaving off some length of the hub. Not too much, or the wheel will wobble. If the inside of the hub could be coated with teflon...

[Jim Smolka]

Make sure that the car rolls straigth. Temp position the axles and test the car on a flat table. Adj the axle if the car turns slightly.

[Jon Merck]

Hey Mike,
My son got into this last year and I found suprisingly a lot of adults were into derby cars too. I used a dremel tool by insterting the axles into the chuck and using fine polishes and a piece of cloth to get the mirror finish. Then we polished again using graphite on a piece of cloth. We tried several different weighting methods. Drilling a hole and filling with lead to get the weight allowed worked best. It was fun for both of us.
Jon

[ZOA NOM]

You need some way to add/remove small amounts of weight on race day. You'll never exactly match the scale they use. If I remember, there was a "weigh in" where you could fine-tune. I used clay to add small amounts, then they sealed it at the final weigh in.

[MotoSook]

The rules are very tight...as a matter of fact, the kit the our boys received (their pack derby was last weekend) had everything in it to compete. The "axles" had grooves already cut into the block of wood for the nail. You have to use the supplied wheels. No shaving the width of the tires. You can smooth the wheels where they touch the car to "deburr" them. Powder graphite helps.
An engineer's observation...the cars that had their weight concentrated toward the back were faster (as someone already said here). Simply physics...covert potential energy to kenetic energy. All cars start at the same height (nose height) with stops in at the top of the track holding the nose of the car. The further you can place the center of mass of the car, the higher your potential energy will be.

You can see the cars with less kenetic energy start to slow down at the bottom of the track. They then have to go another 30 or 40 feet. The ones that were well designed seemed to maintain speed all the way to the finish line.

All that said, it was our boys' first derby, and they really are not that competitive yet so I held back on the help. I cut the shapes they wanted, and they sanded until they got bored or tired.

I wanted them to fail (be as competitive as they know how..not how much I know) this time so they'd be more motivated next year. They give all the kids a trophy (crappy PC sheet..teaches them ntohing). The younger one got in the car afterward and said..."is this trophy for competing or for being competitive." Well, he was not happy when he realized it was for just competing...next year we'll engineer the cars!

You should have seen the parents at this thing...guys were working on there cars in the field house at the last minute...no sign of his kid(s)...but cordless power tools all around. You can work on your car after weigh in...you don't have to submit it on first weigh in. I'm as competitive as the next guy, but things like that takes away from the kids experience I say. Pine derby is not something to overshadow your kid's efforts. Have fun and let then do the work.

There is a "Master" competition where the dads and moms can build a car to compete.

[Mike Kast]

Originally posted by Souk
I'm as competitive as the next guy, but things like that takes away from the kids experience I say. Pine derby is not something to overshadow your kid's efforts. Have fun and let then do the work.

There is a "Master" competition where the dads and moms can build a car to compete.

I'm with you there. Me and my buddy have been talking about this for the last month. It kinda succs cause it obvious who built some of the cars. I'm talking about the cub scouts, not this YMCA thing, I don't know what this will be like. Extreme Yuppyness I suppose.
It's like steroids in sports, if five guys use them and get a huge edge, everyone who wants to remain competitive has to use them. It just screws up everything.
I'm just not sure how much a petite little 5 year old princess ballerina girl can do. She really wants it though. The girl loves speed, and I swear it's not my fault! LOL
I'll let her paint and sand, It's wrong for me to polish her axles?