Pinewood Derby

A disappointing 5th place finish out of 30 cars. There were 32 initial heat races with most cars racing in at least five of the 32 races. We were done with our five races by the 13th race (and we placed 1st, 2nd or 3rd in all five initial races) and even after the 24th race, on point count to get into the finals, we were tied for second.

As it turns out, the 1st place car was supra-fast, a good car length ahead of us (about 7 inches). It was shaped like a bus, but definately highly engineered and well made. It rolled dead straight with no wobble or deviation of any kind.

The 2nd place car was fast but only finished about 1.5" ahead of us. The 3rd and 4th place cars finished only 0.33" ahead of us. The 6th, 7th, and 8th place cars were all tied with us on point count and were less than 0.15" behind us. The rest of the field was pretty far behind, at least a car length (that's 6"). The 2nd to 8th place cars were all very, very low (looked like surf boards or wedges) just like ours. They also all had their weight in one large piece, near the back (just like ours). Some mounted the weight high, others low. All eight cars that were contenders had lots of graphite on the axles (again, just like us). We were the only ones who were using set screws to align the axles and we were the only ones who had a contending car that was more hour glass (like an Indy car) shaped than surf board shaped. Brad came up with a good idea, next year I'll try one car with integrated fender humps to reduce drag from the front wheels.

Next year, I'm definately going to pay even more attention to getting those axles perfectly straight. Kobe "Daddy, next year, instead of three cars, can we build five cars, will that be enough?" We'll get em next year.

You'll have to detail the regulations to me. I would be glad to come up with some concept sketches for an aerodynamic design.

Car length shall not exceed 7", includes all parts of the car.
Car width shall not exceed 2.75".
Car must have a minimum of 1.75" of clearance between the inside edges of the wheels when the wheels are pressed against the car body.
All parts of the car, other than the wheels, must have a minimum of 0.365" of clearance from the track surface.
The weight of the car shall not exceed 05.00 ounces (141.0 grams).
The Pack 252 scale used at race check in is the official scale and shall be considered final.
The official pine wood block must be used, but it can be shaped in any way desired as long as doing so does not violate any of the rules above. The block is nominally 7" long x2.75" wide x4" high.
The BSA axles must be used, but they may be altered, polished and lubricated with dry lubricant.
The official BSA wheels must be used. The wheels may not be cut, drilled, beveled, rounded or altered in any way except you may remove the mold seam and other manufacturing imperfections from the wheels.

So, there are the rules.

Could you measure the diameter and width of a BSA wheel for me? I'm attempting to do some drafting for you.

The official BSA wheels are approx 30 mm in diameter, 7.5 mm wide (flat part of the tread) and an additional 2 mm of width of curved sidewall. Looking at the interior of the wheel, the outside rim is about 3 mm thick.

http://www.pinewoodextreme.com/detail.asp?item_number=412700

Here's a good picture from a website that sells modified wheels.

ST

A preliminary draft in CATIA:

Trevor man,
I like it, yes, this is what I imagined. I have a dremel tool and I have a very steady hand, from the iso and front view, it appears the fairings for the wheels are higher than the upper surface of the car toward the centerline along the length. I assume that there is an aerodynamic reason for the 90 degree drop off from the high point of the wheel fairing to the lower surface of the car? In other words, either a concave or convex curve from the high point of the fairing toward the center of the car would cause higher drag, right?
Outstanding work Trevor...
Stuart

Actually, you are right. I should round those corners off a bit. Like I said, this is a preliminary draft.

Also, I had intended on putting a small radius fillet between the vertical wall of the fender and the horizontal main body of the car, but the shape was so complex that CATIA flipped out and wouldn't generate it. I figure you can shape that bit in easily enough yourself anyway.

I made the center bump fairly large, as I figured that would be the place to put your lead weights. Probably by drilling into it from the rear. You could also put weights into the fenders just in front of the rear wheels if the bump doesn't hold enough.

...for the same reason that making the outter edges of the tires has such a big affect, you want to keep the weight, all in as large a single chunk as you can. I was thinking of carving out a large hole 1" in front of the rear axle and casting a custom shaped piece of lead and inserting it from the bottom right there.

I could hollow out some of the wood under the fenders in the front to further reduce weight in the front so I can move weight (lead) toward the back.

Since you're allowed to apply decals, I guess that means you can also apply tape or something similar to cover any hollow spots, correct? If so, hollowing out wouldn't affect the aerodynamics and would be a very good idea.

Yes, tape can be applied to cover holes, on any surface of the car.

...can't find the car you were talking about, can you send a link to my home email or post here?
stuartmteramoto@aol.com

Sure thing:

https://www.youtube.com/watch?v=cZQ120GTD1w

oh, and if Durel and King Komodo play some more, you're going to have to change your sig line.