My First Commission

[Rob Will]

Sorry.....that was sooo bad.

Actually, my nephew who lives far away wants to come visit so I can help him cut out his (Boy Scouts) Pinewood Derby Car.

Anybody have any LOOK GOOD/GO FAST design tips for my first "commission"?

Thanks,
Rob

[matt dumney]

The best design is low and flat. Polish the axles and the tire surfaces with 300+ sandpaper or steel wool...use graphite to lube the axles. Also make sure the axle slots are parallel and the car tracks straight. Weight must be exact to the standards...can't remember what they are.

There are lots of sites that cater to this and provide the information to make it super fast.

[Scott Banbury]

I'm working on this one right now.

I've had more than 2 dozen cubs through my shop in the last 2 weeks cutting out cars, polishing axles and lathing the outside diameter of wheels.

I'm glad the derby only happens once a year

[Danny Heisner]

One thing I read about on the Internet that seemed to work pretty well was to seat 2 opposite axles deeper than the other two so that the car only travels down the track on 2 wheels. Less friction means more speed and with only 2 wheels touching the ground, there is less friction.

My experience is that the shape of the car doesn't really matter much. Axle prep is everything. Besides putting graphite on the axles, I also polished them with car wax prior to assembly. Not sure if that worked, but my son did place first at the pack meet and second at the district meet.

My two cents.

Have fun!

Danny

[Rick Gifford]

I don't have to make any more derby cars... thank goodness. I was making two a year, and sometimes 4 when the boys wanted a different design between races.

The size of the car, flat, large, square, rounded... means absolutely nothing. The track isn't long enough for areodynamics to worry about.

I have seen champion cars as large as the block of wood it starts with. In fact I saw one that was just the block of wood out of the kit as-is and it was a winner.

The key is smooth axles, smooth wheels, and properly places weights.

The car should be the absolute maximum weight allowed. One trick is to purposely have too much weight, and when the inspectors call you in to fix it you start taking weight off until you just qualify. All scales are a touch different so you never know how the "official" scales will be.

Extend the wheel base will help the car run straight. Every time it rides against the center rail it slows down some. Just turn the kit wood over and cut new axle slots and then shape the car... which will remove the old slots that are now on top.

As long as the wheels do not extend past the front of the car your ok. If you look at the block from the kit the slots are not the same distance from the front/rear.

While this is not set in stone, the placement of the weights makes for a huge discussion and sometimes arguments.

Personally I have found by placing most of your weight just in front of the rear axle (inside the wood of course) and maybe a small amount of weight in the nose (to prevent chatter when the car is going down the steep slope) seems to work well.

You have two options. Weight in the front, and the car goes down the slope faster than the others but will slow down on the straight track. Weight in the rear, and the car goes a bit slower down the slope but gets a rear end boost from the weights on the straight track.

Watch the races. You'll see one car lead more than half way, and the other seem to kick in a turbo boost and pass it for the win on the straight track. It has weights in the rear.

Smooth the wheels. There are molding marks that need smoothed off. The axels, i.e.nails, need smoothed and the burs removed under the heads.

Don't know if your rules allow wet lubrication or not. Ours never did. I used graphite powder to grease the axels/wheels. Whatever you use, lube it like crazy.

I might have a file at home on how to build a pinewood derby car with tricks and help tips. If you want it, and I can find it that is, I'll email it to you.

While its true you can mess with the axles to get the car to ride on 3 wheels (only two and the car will rock), good examiners will look for that. Our officials were very watchful of that cheat. You will have to fix it or be disqualified. Fixing it at the last minute might mean you have to bend the nail to get the wheel down, if so your pretty much screwed. The car won't run well afterward.

Proper weights, excellent polishing of the wheels and axles, good balance from left to right on weight placement are key.

Some folks even sand the inside of their wheels to remove material to lighten the car that much more so they can add it back in lead weight inside the car.

Oh, dunno about your area, but here we had some folks so interested in winning they would purchase their cars online from professional pinewood derby builders. Anywhere from $35 up. Pitiful and sad. We knew who they were. They certainly didnt get any respect that way.

I always let my kids design their cars, sand them, paint them, help polish the axles/wheels. I operated the power tools.

Good luck with your build!

[Bill Wyko]

Don't forget to graphite the axles

[Jeff Booth]

Well, there seems to be at least 2 camps in our cubscout pack. The look good camp and the go fast camp. And of course some people are maybe trying both.

At our pack there are races by den and by the pack. Also out of 35 kids we give out 12 design awards that are voted on by parents and siblings of the cubs. In other words we hand out 9 speed trophies and 12 ribbons for nice artwork and original design and so forth.

The other component is that this is supposed to be something that the kids are involved in building. The degree to which the child participates is entirely subject to the conditions. We see lots of cars entirely constructed by parents. Most are a hybrid of kids and parents. THe first year my 6 year old had no concepts and little interest. So I built him a very simple car that he decorated. But I was careful with the critical details related to speed and he easily won. That got him interested.

This recent year he contributed a lot of input and did about 40% of the work and 95% of the decoration. It did not win any design awards but took 1st in den and pack in speed again.

As the previous person noted, there is a wealth of information on the internet as well as a ton of vendors for books, machined wheels and axles and the like.

At the same time you should carefully review the rules as each pack is different. I think our pack is fairly typical. We do not allow that the wheelbase may be modified, you must use the original provided axle slots. We do allow that nails may be polished, but they must be original BSA provided nails. We allow that wheels may be ever so slightly smoothed, but no substantial removal of mass or narrowing of the profile that engages the track. No washers or extra parts in the region of the nails and wheels. Also the car body should stay within the footprint of the provided block. The car must weigh no more than 5 oz. Only dry lubricants may be used.

I myself am a engineer that works pretty heavily on the theory side of heat transfer and fluids. So naturally I studied every possible angle for weight placement, wheel treatment and so on. At the same time I am interested in working with my son and not around him. So this year he picked out a less aerodyamic shape than was optimal for speed, we discussed that and arrived at some sort of compromise between his original imagined form and something that had a chance of doing well in the race.

Every kid seems to really want to win at least a few race heats, most are content not to win them all. I think therefore applying some care to a few key points will achieve that goal.

a) get the car close to 5oz (say 4.95 or greater, but do not be too obsessive, some parents hover at the scale making last minute adjustments for hours to get the last thousandth of an ounce, honestly better results can come from other places). I know this because I officiate the weigh ins, I have seen more than one car hit the floor during this jumbled cycle of trying to adjust the weight to the last milligram, it is nonsense. The weight should produce a center of mass about 1cm forward of the rear wheels, low in the car - close to the track. I use tungsten welding electrodes, tungsten more than as twice as dense as copper and steel etc.

b) the nails need clean up on the inside under the head, typically there is a webbing between the shaft and head that will catch on the wheels, clean that with a jewelers file. The nails also have some ridges on the shaft from the forming process right under where the wheels spin, typically these are only on one side and therefore do not present a problem, simply install them in the car with the ridges facing up and the wheels will not contact the ridges. But spinning the nail in a cordless drill (in a vise) with some metal polish will help reduce friction on the underside.

c) the wheels are injection molded plastic, the runner sprue is right on the tread and will leave a nib that is up to 0.005" proud of the surface, you need to sand that off

d) as the last user said you need to get the nails in straight, I use an arbor press to set the nails, but others have luck drilling a nailhole using an undersized bit. THe nail should be set so that the wheel has about 1/16" of play side to side, once the car runs true and straight and all 4 wheels are touching the ground then you should epoxy those nails in place, kids tend to drop those cars a lot, also sometimes racing itself will work them free

e) if the kid allows, then a doorstop type wedge design is pretty good aerodynamically, the back of the car is maybe 1.5 cm high - perhaps a little more

f) apply lots of flake graphite between the wheels and nails, spin the wheels several time and repeat (5 times)

g) My son sands the car, drills holes for the weights, inserts and glues in the weights, polishes the nails and decorates the car. I cut the block, true the wheels, do the final tuning of it going straight and glue in the axles.


Most of all, have fun with the kid. We discussed a lot about sandpaper grades this time around. He was into that.

Good luck.