Pinewood Prius?

My son when he was 9 or 10 entered the Pinewood Derby that featured about 30 or so cars and won first one year and second the next (although I thought he could have had a chance at first again because the scoring was not quite right, but I didn't raise a stink about it; it's for the kids!).

Firstly, you have to use the parts supplied in the official Pinewood Derby kit. That's the plastic wheels, nails, wood axles, and body. There are min and max weight restrictions and usually the cars on the light side tend to place higher. I let him do nearly all the work himself. The car wasn't necessarily super aerodynamic (standard flat wedge design), the paint and other items were what you would expect from a 9 year old. We used lots of powdered graphite to lube the axles (important!). No other prep on the nails or the plastic wheels.

Shortly before the race and during the weigh in, I discovered only three wheels contacted the ground. He inadvertently put on the front axle on a little askew so only one wheel in the front contacted the ground. I thought then for sure he was doomed to be at the bottom of the pack. Too late for a fix now! Nonetheless, he took first.

Turned out, that after doing research on the internet, by building the car so only three wheels touch the track you may gain a slight advantage by having less friction and the car is less likely to wander back and forth on the track.

Rick
#4 2006

 

<div class='quotetop'>QUOTE(efusco @ Jan 3 2007, 06:35 AM) [snapback]370045[/snapback]</div>

Come on Evan, lighten up. I was just teasing you. I am a UCLA fan. My team did not even come close to being competitive in the Emerald Bowl.

 

<div class='quotetop'>QUOTE(efusco @ Jan 2 2007, 11:54 PM) [snapback]369860[/snapback]</div>

The last time I built a pinewood derby champ, Evan, it was modeled after a '63 Maserati ... boy I just dated myself.

 

Evan,

I just e-mailed you a tip guide for decreasing rolling resistance and proper build methods. As for the shape, some competitions have strict dimensional requirements. If your pack uses a photo-transistor gate at the finish line, there will likely be a height limit.

My suggestion would be to take a Prius side image as suggested by others and use a photo editor to reduce it in the Z axis. If you set the X axis to the length you need prior to this, a good cut and decent paint job should give a look that is acceptable all at a height that will still yield good aero properties.

Some other folks here have made statements about weight (mass). If you take the same exact car at 3 ounces and time it, then add 2 ounces to it, it will be faster every time. You are a smart guy you do not need a physics lesson on that.

Good luck sir!!

Bigsk8r

 

<div class='quotetop'>QUOTE(Bigsk8r @ Jan 3 2007, 10:49 PM) [snapback]370532[/snapback]</div>

Isn't there a diminishing returns thing that happens once too much weight is reached? Isn't the trick to balance the weight, friction and resistence?

(No, I never built a pinewood derby car. Never entered a soapbox derby either. In fact, didn't take physics in High School either so maybe I do need a lesson. Be gentle with me.)

 

<div class='quotetop'>QUOTE(efusco @ Jan 3 2007, 11:09 PM) [snapback]370542[/snapback]</div>

Hey!!

I resemble that remark!

 

<div class='quotetop'>QUOTE(Godiva @ Jan 3 2007, 11:13 PM) [snapback]370545[/snapback]</div>

I wish I could remember all the physics that go into it!

The basic version though is that straight down, in a vacuum, a 1 Ton hunk of lead will fall at the same speed as a feather. However, the moment you introduce any friction at all, the difference is stark.

You are correct about the diminishing returns once the load limits of the axles and wheels are reached. As soon as the axle flexes or the wheel distorts, you have just upset the friction balance of the vehicle. Until that point though, mass is king on equally built cars.

If Evan can get the shape he wants, can get the cars center of gravity to be about 1" in front of the rear axle, and be very close to 5 ounces, the car will run good. I can't wait to see it!

Good night all,

Bigsk8r

 

actually overcoming the drag of friction on the wheels are the hinderance to speed. so more weight simply overcomes that initial startup and gets it going faster. as the speed increases, the additonal weight provides more momentum which in turn, makes any drag caused by the wheels to have less and less effect.

i do remember about a dozen trips to the post office because they were the only ones that had an accurate scale that would weigh ounces accurately.

 

I think the PWD should keep pace with modern society. Why not allow electric propulsion? Mine would have LED headlights.

Back when I actually did this as a kid, mine sucked. Look really cool though!

 

Evan,

Where is our update on the Pinewood Prius Project?

 

And if aerodynamics do have an effect, from my schooling days, aerodynamics are more important at the -rear- of a vehicle than the front. In other words, most modern cars are more efficient going backwards than forwards! As I remember, it was about a 30% difference (aerodymanics is 30% more effective on the rear than the front).

 

My pinewood racer was based off of an Alfa Romeo. Yeah, it lost, but I gues I'm lucky it didn't break down halfway down the track.

 

hey nice Prius. bit longer and lower, but gotta work with the piece of wood given. but my criteria is easy, just like any other unmistakeable Prius on the street, your pinewood racer is unmistakeably a Prius. very nice job!