Race Cars and Motorsports

It's been brought to my attention that a great many BritishV8 guys started their hot-rodding careers by building toy cars to race at Cub Scout pack meetings. That... and also a lot of people have helped sons or grandsons build these cars. Let's see some photos!

Here's one of my old cars... circa ~1975 and partly inspired by Jaguar E-type (but also Corvette and Datsun Z).



The trick detail of this car was that thin pieces of wood were glued to the sides of the official Cub Scouts wood block. A groove was routed into the bottom, and melted lead tire weights were poured into that groove to bring it up to the 5oz (?) weight limit.

Were any of your cars styled like British cars? Were they painted "British racing green"? Did anything identify them as "V8" or "V6" powered such as dual "exhaust pipes" sticking out the back end? Were they fast?

When I was a lad we didn't have the Pinewood Derby so that's one I missed out on. I did help my neighbor's handicapped son build one years ago when our street rod club sponsored a small derby at one of our events. Ours resembled a mid 50s F1 car similar to the Ferraris or others. We painted it red, but the body was a lot like this Connaught F1 taken at Goodwood.

You asked for it Curtis... both my boys have been in scouts for several years & they have a blast with the pinewood derby cars. We did some research early on & have our formula down pretty well now. They have 9 trophies between then including a couple of Pack Grand Champion trophies (fasted car across all the cub scout levels in the pack -- usually about 100 cars).

Here's a sampling of the cars they've made...


Younger son made this car this year & took 1st place in the Weblo's division earlier today. He was the 2nd fastest car in the pack by .03 seconds...


And older son made this one (the white one in front) - a replica of his cell phone. He's in Boy Scouts now so raced in the "siblings" division. He took 1st place too!

Here are a few cars that are from prior years... This one is we called the "Limberger Lamborghini"...


This 3-wheeler was a learning experience... it was fast, but jumped the track twice & was disqualified... I'm going to try it again next year (we have an adult's division) but with the forward two wheels closer together to keep it from wiggling so much...


This last one is like Curtis' in that it has wood glued on each side of the original block to make it wide... I don't even know where my kids saw Starsky & Hutch, but one of them decided to make the Torino from the TV show...

I really like all these cars - VERY, VERY creative, Rob!

The black three-wheeler is particularly intriguing. I can't understand how it can work! (I'm surprised the rules allow a three-wheeler.) By eliminating a hub, it should have less friction and thus have a big speed advantage on any 2D surface. But isn't it inevitable that it should crab to the right if the surface is concave, or become unstable (driving on two wheels) if the track has an abrupt transition between inclined and flat sections?

This is my "old number one" - a little faster than the black car (from the following year). This orange car was Pack 157's overall winner, but Eddie Morris (who came in second place overall that year) got the trophy for "Best Styling" on account of his car had a nicely carved engine and rear wing.



Come on guys. I know there are more old Pinewood Derby racers out there!

Thanks Curtis. All of our cars only have 3 wheels that touch the ground... we always put one front wheel about 1/16" to 3/32" higher than the other front wheel. Nothing in the rules says you have to have 4 wheels or that all 4 have to touch the ground. That minimizes friction so faster. If you look close at the 3 wheel car, you'll notice two wheels are spaced closer & the 3rd wheel is further away. It was designed for the two closer wheels to be @ the back (that's where most of the weight is), but w/just one wheel up front, it went side to side too much & jumped the track as noted above. After the race was over we ran it backwards so the two closer wheels were up front it went fine -- just not as fast because the weight wasn't in the back. Next year is our last year in cubs so i'm going to make one like that for the adults division... i've never made one for myself, just helped the kids so figure that'll be my last shot. I'll mention to them you complimented their designs... they come up with the ideas & I help them figure out how to do it.

Yep, that's an old Pinewood racer trick.

[royalrangers.ag.org]

We need to get a physics professor to step in here and set us straight, because something doesn't add up.

If you lift one front wheel off the track surface, obviously it stops bearing any weight - but that weight still exists and in fact it's almost all transferred to the other front wheel (since the cars are usually relatively long). When you double the weight on the remaining front wheel, by definition you also double the equal and opposite "normal force". When normal force is doubled, then the automatic result is that the kinetic friction is also doubled. So, in fact, the total amount of kinetic friction should be the same for a car with both front wheels touching as for a car with only one front wheel touching.

I have an alternate theory why lifting one wheel MIGHT make a pinewood derby car run a little faster.

First though, I want to question something I think is wrong on the Royal Rangers website: I believe there's no appreciable friction between the wheels and the track surface because the wheels are rolling (not slipping. To be clear, there's probably some slipping at the track surface, just not much.) So long as the wheels are round (e.g. all burrs have been removed), the friction that matters is between the wheels and the axles.

To make a car really fast, I think it's key to polish the axles carefully and lubricate them appropriately.

Why do some cars seem faster when you test them with one wheel raised a tiny bit off the track surface? Because inevitably the two front axles are unequally polished. If they're unequally polished,. then there's a fifty percent chance you'll raise the worse one and make the car run faster. In other words, I'm proposing that perhaps the "coefficient of friction" of the two axles are appreciably different, and THAT'S the real difference, NOT the normal force.

Incidentally, the car's dynamic weight distribution over its three (or four) wheels might not behave as people expect. I strongly suspect that if you lift the left-front wheel, you'll end up with relatively little weight being carried by the rear-right wheel, at least on the inclined part of the track. Why? If static weight distribution isn't biased heavily to the rear, if the the track is steeply inclined, if the CG is relatively high, or if the car is decelerating because it's rubbing against the track's center guide strip, then the car's weight distribution will transfer toward the diagonal line defined by the right-front and left-rear wheel. If the CG crosses that line, the right-rear wheel will come off the track.

Comments?

You're way past my two semesters of general physics -- at least whatever's left of it after the beer I drank in school & about 25 years!

All I can tell you is I've not seen a car with all 4 wheels touching the track get a trophy in our pack.

I agree with you that there's no appreciable friction between the wheel & the track. A lot of guys graphite the "tread" part of the wheels; we never have & my boys have several trophies including an overall pack champion and a 2nd place overall -- both in a field of 80 or so cars. We do smooth the wheels by chucking them into a drill press (using a jig that holds the wheel) & sanding with 220, then 320, then polishing rouge on a dremel tool... so the wheels are true & smooth. We also polish the inner edge of the wheel & hub since they touch the sides of the car so are sources of friction. Some people shave down the hub so only about 1/2 to 1/3 of it touches the car, but that's against our rules so we can't do it. Similarly, some people crown the "tread" surface but again, that's against our rules so we don't do it.

We do polish the axles... similar to the wheels, we chuck the nails in a drill press & use a small file to file away the flashing between the head & the nail itself. Then sand w/220, 320, & then polishing rouge... looks like chrome when they're done. We have found that leaving some of the file scratches (e.g., sanding the high spots but leaving some of the grooving) on the shank of the nail seems to make the car faster. I think that has less to do with reducing the surface are rubbing between the nail & the wheel & more to do with the fact that the grooves hold some graphite so there's fresh graphite falling out throughout the heats. Just a theory though. We douse the axles & wheels in graphite using a small tube with a needle that lets us get the graphite right where we need it, we give it 2-3 good "puffs" & spin the wheels to work it in... back of the hubs, front where the nail is; on each wheel -- we probably do that at least 15-20 times before turning the cars in.

As for where the weight is, it's as far back & high up as we can get it... the longer it's on the incline pushing the car, the better. With about 4.15oz in the back & .85 in the front, the car doesn't chatter & has most of the weight pushing the car. Doing that leaves the center of gravity about an inch from the back of the car.

Well mine...it's around here somewhere, I think when I last saw it, my boy was relocating a platoon of GI Joes with it. I can't wait to build one with him in a few years. Mine was a chairs style ferrari inspired racer, that placed 1st in the pack that year. I'm glad to see there's some proud scout parents out there. Any space derby crafts out there? - Phill...Eagle Scout