Lets here your pinewood derby tips

[HomeBrewerDude]

We'll do a weigh in tonight and I am planning helping him do the following:

adding weight to get as close to 5 ounces as possible
sanding wheels to remove any burrs
using dry lubricant on axles (allowed)

any other tips!?


TIA

 

[Aikouka]

Bring termites and accidentally leave by other competitor's cars.

 

[SearchMaster]

I have a ton of them but here are the ones that I think work the best.

- Put the wheels and axles in a baggy with dry lubricant. Shake them around a good bit then let them sit there for as long as you can.
- When you spin each wheel by finger, it needs to spin freely for at least 20 seconds. If it doesn't, you have too much friction.
- If you have a Dremel with a felt wheel, run it against the wheels for 5-10 minutes each - this wheel help the lubricant 'sink in'.
- The optimal center of gravity is about 3/4" forward from the rear axle

I have a picture from last year's winner that has a special trick as well, I'll try to post it later if there's interest.

 

[SearchMaster]

Also, don't just polish the wheels (both the axle part using a pipe cleaner and the part that touches the track) for smoothness...make sure you polish the axles themselves. Get several grades of sandpaper and put the axles in a drill, then shine them up starting with 400 grit then finish with 1000 grit.

 

[KMc]

Back in the day, I used to set one rear wheel just a fraction high so technically, the car would roll on only three wheels, thereby having less friction. With a little clever ballast location, it would roll stable and flat.

 

[paulxcook]

Can you carve out the front and fill with solder? That might mess up your weight I guess.

 

[SearchMaster]

Originally posted by: paulxcook
Can you carve out the front and fill with solder? That might mess up your weight I guess.

Actually you'd want to do it in the back (rear weight=better). It should be legal as long as you don't exceed 5 ounces. I hollowed out mine last year and put in lead shot from a shotgun shell until I hit the exact amount of weight.

 

[ric1287]

I won the PWD in second grade but they recorded the scores down wrong and gave me last place. That was the last time i ever went to a boyscout meeting.

 

[SearchMaster]

Originally posted by: KMc
Back in the day, I used to set one rear wheel just a fraction high so technically, the car would roll on only three wheels, thereby having less friction. With a little clever ballast location, it would roll stable and flat.

This is technically illegal, at least it was in our pack. All 4 wheels had to touch.

Nobody ever checked though, and I noticed several of the cars only had 3 wheels touching. I wanted to make sure ours was 100% legal so I made sure all 4 wheels were touching. We had the fastest overall time in our pack by a pretty good amount but neither me nor my son really cared about going to the regional.

 

[LordMorpheus]

the cars aren't going fast enough for aerodynamics to play a huge role, but any streamlining helps.

Making the wheels rotate well is the biggest thing. Make the the axles are straight, and the axles as well as the inner hole in the wheel are smooth. Lubricate with graphite liberally. Make sure clearences are good. When you spin a wheel it should freewheel for a decent amount of time before stopping.

The other tip is just physics. The only energy source these cars have is potential energy, and because you start them with their noses aligned on an inclined track, the farther aft in the car you place the center of gravity, the more energy it will have. When it's finishing on the straight, the car with the c.o.g in the back will have experienced a larger drop in potential and should therefore have more kinetic energy.

Other than that, don't get too competitive, and have a good time.

 

[Analog]

Dr. Pizza had some good tips in here:

http://forums.anandtech.com/me...id=38&threadid=2134764


BTW, the cars that were the fastest in my son's competition looked like skateboards. Not very appealing, but it what's you're after. My son won most realistic car.

 

[SearchMaster]

Here is the picture of last year's winner. It's not a super pretty car (though my son did all of the painting and such).

P1010006.JPG

Note the "front spoiler". The right column got torn off last year, but what this does is give you a jump start, assuming you have an automated track. The track's pin rests against the horizontal "spoiler". When the pin drops forward, instead of the front of the car being held back by the pin for a split second as it drops, the groove in the front of the car allows the car to move forward. It doesn't seem like much, but we consistently had about an inch of a headstart within the couple of feet or so of travel. In a short race, every little bit helped.

Also the grooves in the front alongside the wheels were designed to eliminate any friction between the wheel well and the body. This way only the axle hub ever touches the body.

 

[MotionMan]

My dad is an engineer, but both my brother and my cars sucked at racing. He let us do most of the planning and work, which, I guess is the point. They did look pretty cool.

My dad did add shot, but I think he put it too far forward.


When my son is old enough, we may build two cars: The one he wants to build and the one we are going to race

MotionMan

 

[drinkmorejava]

I found that a car with its weight concentrated in the back went significantly faster than with it concentrated in the front. That said, friction is still technically the same, however, due to aerodynamic affects causing a slight upwards force near the front of the car (lift) the total apparent weight of the car can be reduced, specifically with respect to the front wheels, thereby reducing total friction and possible lifting the front of the car off of the track. The problem with this is if the front of the car is actually lifted off of the track either a) the car will skip lanes b) it will actually slow down because there is increased drag. The point is to reduce apparent weight by using the lift and thus decreasing friction while still staying on the track.

If the weight is in the front, obviously, there is still the same amount of lift as long as the car is still on the track. However, you will end up with the front wheels being pushed against the track from the weight and the back wheels due to the streamlines (drag)(same concept as throwing a ball with a tail on it and the tail will remain co-linear with the direction of travel because it?s a stable configuration). This case will increase your friction because of the extra force on the back wheels.

As a kid I had no idea what was going on. I remember one year I put all of the weight in the front thinking it would ?drag the car down? faster, it wasn?t until a few years later I learned that gravity didn?t work like that. Thanks to my lovely aero/mech major, I?m actually learning how to quantify all of that stuff?which is kind of making the whole pinewood derby thing a little less fun than it should be.

 

[MotF Bane]

Remember that the scale they have at the derby is the final word on the weight. Bring along some small sticky weights, and slap them on if their scale tells you there is any weight room left. I managed third place once just by taking my first car and adding a few of those weights.