Pineword Derby - its on now!

[41magsnub]

So, helping the girlfriend's son with the pinewood derby.  He goes to a 7th Day Adventist school.  When we asked about the rules over a month ago they said the followed the BSA rules.  Tonight was practice night, the race is next weekend.  Nope - not following those rules.  All they are restricted to is 5 oz, no propulsion other than gravity (sorry Scout), and 4 wheels.  There were a couple of metal frame cars, lots of wheel reprofiling to reduce rolling resistance, that kind of thing going on. 

We have a week...   We are not going to change cars, we made a snake shape that I think is going to win the style competition.  However, I now am going to spend a bunch of quality time with the wheels and axles with the dremel tool.

The weight balance is already about right and the overall weight will be dead on at 5oz.  Currently its 5.2 oz, and once they do the official weigh in on the official scale I'll drill out some wood to bring it right to the limit.

Any other tricks out there?  At this point I doubt we can win a straight race against some of the "cheaters", but I bet I can get us to just behind them.

[Andiron]

What lube are you allowed?

[41magsnub]

At this point, anything I can get in the time constraints.  I have graphite with moly in it right now.

[Scout26]

Two questions:

1)  Is her son doing most of the work, or has this become a "Dad" competition?

2)  Are you still doing the Big Brother thing ?  Is he in scouts?

[41magsnub]

It's become a Dad thing unfortunately.  At the practice, all the kids were running around the gym while the dads were working on cars.

This has nothing to do with my little brother in BBBS (who is not in scouts).

[griz]

One of the guys at work got in to that.  He said the biggest thing is polishing axles and profiling the wheels.  I had guessed that alignment would be important but he said it was easy to get it straight.  Good luck.

[T.O.M.]

When I ran a Cub Scout pack, we had a race for others,  meaning dads could go nuts so long as the weight and size rules were followed.   

In my experience,  it's all about the weight, the axles, the wheels.  Make it weigh 5 oz straight up.  Center the weight, maybe a bit toward the rear.  Polish the axles until they are mirror finish.  But also make sure the head of the axle also has no spurs andgets polished.  Chuck the wheels into a bit (they sell one) which can go in a drill or Dremel.  Some guys thinned their wheels. I just smoothed and rounded mine.  There are two lubes available, a white teflon powder and the traditional graphite powder.  After you mount your wheels (be careful not to push in too tight and create drag between the wheel and body.  I used to fold an index card and use the double thickness as a spacer.) put a bit of glue on the axle to hold it in place.

Some guys claim you can balance the car on three wheels to increase speed.  Some claimed you could use a round file to create a low spot in the axle which you could load with graphite.

My son's Web I year, he made a black SUV looking thing.  Added wood to make it taller.  Anyways, it was aerodynamic as a brick. Hollowed it down to 5 oz.  Polished the axles, worked the wheels.  He won 3rd in the pack (we had around 80 Cubs).  Best was he did most of it on his own, and the car looked like it.  Some upset engineer dads...

[AJ Dual]

Put all the weight in the back you can. It's potential energy is just a bit higher that way.

Also, do you have to ROLL on 4 wheels, or just HAVE 4 wheels?  

If you can bend/lift one of the four wheels so it doesn't touch or roll, you've eliminated 25% of rolling resistance no matter how the wheel is profiled or how well the nail/axle is polished.

[41magsnub]

Put all the weight in the back you can. It's potential energy is just a bit higher that way.

Also, do you have to ROLL on 4 wheels, or just HAVE 4 wheels?  

If you can bend/lift one of the four wheels so it doesn't touch or roll, you've eliminated 25% of rolling resistance no matter how the wheel is profiled or how well the nail/axle is polished.

That part is done, one of the front wheels is about a 1/16" above the others.  The weight is about 3/4" in front of the rear axle.

[bedlamite]

Make the car as heavy as possible.
CG should be about 1-1 1/4" in front of the rear axle.
Wheels should be as light as possible.
Aerodynamics. Small frontal area is key.
Polished axles. Don't bother with slotting them. the increased pressure of the bearing area negates any advantage of slots.
1-2 degrees of negative camber on the rear wheels  to keep them away from the wood.
Lift one front wheel, align remaining wheels so it turns 4" toward the lifted wheel for about 8' of travel
Graphite.

[41magsnub]

Here is what we have to work with.  Dylan drew it (using a template from the internet) and I added the bump in front of the rear axle so there was somewhere to add weight,  I cut it and routed it.  He sanded and painted it in class.  So, he actually did a lot of work on it.

It is not really a speed build, if winning the race was the main objective I'd have pushed him into an aerodynamic wedge (not my first rodeo there, my Dad and I won the city in 1986 in boy scouts).

[Hawkmoon]

At this point, anything I can get in the time constraints.  I have graphite with moly in it right now.

Sounds good. I can't think of anything that might be better.

[Andiron]

Would a tiny nylon washer be allowed between the wheel and wood body of the car?


*Never did pinewood derby as a kid,  and don't have any of my own.

[vaskidmark]

*Never did pinewood derby as a kid,  and don't have any of my own.

Do you have any interest in renting one on a trial basis?

stay safe.

[Fly320s]

I'm still trying to figure out what a pineword derby is.

[41magsnub]

I'm still trying to figure out what a pineword derby is.

son of a...

[Andiron]

Do you have any interest in renting one on a trial basis?

stay safe.

I would, but I hear child labor laws are terrible these days.  Cost/benefit just isn't there. 

[BlueStarLizzard]

I'm still trying to figure out what a pineword derby is.

It's when the little boys in clubs race little toy cars. Usually the parents make the cars. Sometimes the boys make the cars.

I used to rant because the cub scouts got to do stuff like that and the girl scouts didn't. Then I realized that I didn't want to race little cars, cookies are tasty and flipping through a pile of cash from sales is much more satisfying than playing with toys, so I stopped ranting. 

[Fly320s]

It's when the little boys in clubs race little toy cars. Usually the parents make the cars. Sometimes the boys make the cars.

I used to rant because the cub scouts got to do stuff like that and the girl scouts didn't. Then I realized that I didn't want to race little cars, cookies are tasty and flipping through a pile of cash from sales is much more satisfying than playing with toys, so I stopped ranting. 

Read it again.  Carefully.

[Fly320s]

The thread title is, "PinewoRd Derby."

[BlueStarLizzard]

The thread title is, "PinewoRd Derby."

 


 

[zxcvbob]

Put all the weight in the back you can. It's potential energy is just a bit higher that way.

Also, do you have to ROLL on 4 wheels, or just HAVE 4 wheels?  

If you can bend/lift one of the four wheels so it doesn't touch or roll, you've eliminated 25% of rolling resistance no matter how the wheel is profiled or how well the nail/axle is polished.

Ding, ding, ding!

Put the weight as far to the back as you can and still have it stable.  Ballast just in front of the rear axle is probably about right.

I don't know if you can skeletonize the wheels to make them lighter, but you don't want flywheels here.  Too much energy goes into winding them up, and the track isn't long enough to get that back.  Three wheels is better than 4; I've never done one of these so not sure if the lifted wheel should be in the front or the back.

I doubt aerodynamics makes any significant difference, but reducing the frontal area couldn't hurt.  Insignificant differences can add up.

[CypherNinja]

https://www.youtube.com/watch?v=-RjJtO51ykY

[41magsnub]

Buncha non reading dudes in here...

[Scout26]

I have to agree with Chris.  The only reason I got so heavily involved in Robert's last Pinewood Derby is because he got tired of doing most of the work and losing to the some kids engineer grandfather who happened to have a woodshop that would make Norm Abrams cry.

Some hints:

1) Three wheels in contact with the track.  Having the fourth as ballast/balance is all it's good for.  And it should be a front wheel.
2) Weight 5.0 oz is the max, and it should be right on the rear axle.
3) Axles, polish and lube.
4) Wheels, round so the minimal amount is contact with the track. 
5) Check that rolls straight on level ground. (Just give it a good push).  if it's pulling to one side that will slow it down as it goes down the track.  Adjust wheels/axles to get it to roll in straight line.

And yes, there should be a "Family" category, for those hyper-competitive Dad's, Uncle, and Grandfathers.  Let the kids make their own cars as best they can and race those.    We also had various Style judging category so that even those that didn't come in the top three places in their dens at least got a ribbon for "Most scout like", "most colorful", etc.   We even had a prize for last place, a giant Hershey's Chocolate Bar, so one kid glued his wheels onto his car so he would lose every race and "Win" the chocolate bar.     

Make sure the kids have fun, and try to get him to do most of the work and explain how's and why's of what he's doing.