Pinewood Derby

"f86sabre" (f86sabre) 01/11/2014 at 10:27 • Filed to: Pinewood Derby

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This Sunday the Cub Scout den I lead starts on their Pinewood Derby cars. This is our first time building them. So, I know some of you have been down this road. What are your tips? What stupid stuff have you seen?

John Norris (AngryDrifter) > f86sabre 01/11/2014 at 10:30

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Debur the nails (axles), put the weight up front.

Edit: Actually, its been a while, it may be weight in the rear is the key. Definitely makes a difference though.

getchapopcorn > f86sabre 01/11/2014 at 10:32

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Man, you lead a cub scout den and get to play legos with your boy... I would like you life now, please.

John Bulzacchelli > f86sabre 01/11/2014 at 10:33

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Graphite on the axle does wonders as a dry lubricant. (you can use ground up pencil "lead")

Ramblin Rover - The Vivisector of Solihull > f86sabre 01/11/2014 at 10:40

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Reduce profile, obtain lead. Debur the axles, but for final assembly, use some type of mild adhesive into the body. It's okay for you to be able to remove the axles, but if they slip in the body lightly enough, they'll pinch the wheels and retard speed. (E.g. handling the car may mess it up, either by you or track operators. Ask me how I know this)

Structurally speaking, one of your best bets to reduce overall profile is to reduce the car to a U-section. []\__/[]

That leaves you two side rails strong enough around the axles that they won't splinter, a place to insert some of your weight (drill the rails), proper blending in of the wheel air flow, and enough wood that adding weight isn't prohibitive. I helped a younger brother build basically an open body single tube frame styled to look like a lizard, but getting the thin stick of wood with outriggers back up to weight required basically a car-sized sheet of lead, and the outriggers were fragile.

If you have access to the track, you can experiment with ride height - if you don't don't mess with it. In fact, if you need to add weight under the body (steel plate, etc.) you may want to lift the axle pin location. A lot of PW derby tracks risk scraping even on a standard block, and there are variances between the tracks. It's fairly common for a left track to have some leftward crown, right track have some rightward crown, middle track have a different arc, etc.

Bad Idea Hat > getchapopcorn 01/11/2014 at 10:46

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Or you could have a daughter(s). I'm pretty sure Turbeaux's daughter is going to be jumping from girls scouts to boy scouts when she finds out they get to race cars.

Someone else has daughters (forgot who), and I foresee the same thing for them.

leicester > f86sabre 01/11/2014 at 10:46

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From my recollection when I was a scout (back when we had the 'spear a cave bear' merit badge)...
Smooth the mold burrs off the wheels with Emery cloth. Put the wheels together on a single rod, and put it in a drill to spin as you smooth them.
Same thing with the axle nails. Smooth any burrs using the same method.
When nailing in the wheels, make sure not to overdrive . Also make sure they are all square with the body (although my best car only had three wheels that touched the ground)
As close to 5 oz as possible. Not sure that the location of the weight makes a difference, I put mine forward.
I'm sure there is a Pineboxlopnik site out there, too with big forum arguments on the best methods.

With-a-G is back to not having anything written after his username > f86sabre 01/11/2014 at 11:10

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Assuming reducing tread width and changing axle locations are illegal....
Fake a spring suspension by band-sawing a bit of clearance around the axle mount, using a long stalk of body wood as both "trailing arm" and "spring." This is a rarely used but effective trick. Even 1 mm of spring travel does wonders.
Rear weight adds potential energy on the start position, but too far back leads to a speed instability and bad friction loss. 30-70 f-r weight balance, concentrated in a slug low in the body rather than distributed. Aero downforce is almost negligible at these low Reynolds numbers, but some people swear by front wing downforce and rear lift.

But if it's your first time building cars, then sanding the wheels with a drill spindle, using graphite on the bearings, and coming in close to max weight are the low-hanging fruit.

EDIT: in case the spring suspension idea is unclear: http://www.goaskgrandpa.com/flex.htm

speedygopher > f86sabre 01/11/2014 at 11:29

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Don't forget the NOS, bro.

Frank Grimes > f86sabre 01/11/2014 at 12:02

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Here is a car I made. I tried making a AutoUnion streamliner. My suggestion dont try to build an ambitious car in one day. Also dont attach the wheels at the last minute or it will be a good looking car that flys off the track. Also paint it instead of a last minute aluminum foil insulating tape job like I did.

Local Miata Bro > f86sabre 01/11/2014 at 12:11

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When I was in scouts my father and I made the AE86 from Initial D, but with little success we cheated my last two years and used pre-made cars from hobby lobby...

55Buick, Oversteer Scientist > Bad Idea Hat 01/11/2014 at 12:28

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My 2 sisters used to do something called "Indian princess." It's something the YMCA does, and it's much better than Girl Scouts, in my opinion. They do pinewood derbies, camping out in the woods, pumpkin carving, etc. I think it's nationwide, because it's put on by the YMCA. Take a look, it's pretty cool!

Your boy, BJR > f86sabre 01/11/2014 at 12:52

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I made the yellow police car from mad max, a lowrider, and my grandpa's ford taurus wagon police cruiser when i was in scouts.

f86sabre > getchapopcorn 01/11/2014 at 19:03

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I count myself lucky every day.

f86sabre > With-a-G is back to not having anything written after his username 01/11/2014 at 19:07

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Thanks and high five for mentioning Reynolds number.

ttyymmnn > f86sabre 01/21/2014 at 21:37

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Back in about '75, I was living with my mom and her husband. David was an electrical engineer, and when I brought the kit home from a pack meeting, he was certain he would be able to design the winning car. After all, he was an engineer . Rather than carving, he used a belt sander to round off the nose and taper the rear. It looked pretty good. He drilled out the cockpit to insert a lead weight, and devised a system whereby you could add or take away wood screws to get the car up to the greatest total weight without going over the limit. I painted it blue, but my mom detailed it with a slick red-on-white racing stripe. Aside from painting the car blue, my only other contribution to the process was picking this wooden Playskool guy as my driver. I thought the pot on his head was a nice touch.

The car looked great. And it came in last place in every race it ran. I won the Square Wheel Award, which was a plaque with half a derby car, uncarved, glued on the front, with both wheels sawed flat.

f86sabre > ttyymmnn 01/21/2014 at 21:48

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It has been tough with my first time scout. We discussed the design. He sketched it out, is smoothed it a bit and cut it out of the block. He sanded it for five minutes until he got bored. I masked an area and he drew flames. I cut the masking tape and he painted it. First time with a spray can for him. He helped hammer in the wheels and placed a large number of flaming skull stickers on it. Nothing says tiger scouts like flaming skulls. I need to get it weighed tomorrow.

ttyymmnn > f86sabre 01/21/2014 at 21:49

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No wings? ;-)

Good luck!