pinewood derby

You, a master builder with a 100% win record, ask US for advise??

Preferred lubricant seems to be dry PTFE powder. Micr> Hi,

Here's what I did: On the night of the big race the car still has to be weighted. 1/4" dia lead fishing weight works well. I did not want my son drilling the holes as the drill could pass completely through the car and into his hand. Instead, I drilled the holes and was the one getting the wound cleaned and stitched up. Save your child from this outcome and let your brother drill any holes so you can watch the race with your child. ERS

Polish axles, and make sure there is no stamnping or press marks evident (like the marks around the head of a nail from forming)...Ensure your wheels are in alignment, as alignment is a big drag and every little bit helps.....Get the weight dead on the max. Even if you have to buy another kit, make sure wheels rotate freely but not wobbly. PTFE is the lube I would go with. True up the wheels cirucmference and eliminate any mold flash etc.round is much more efficient than egg shape when it comes to wheels...You can possibly machine a V shape to the wheels profile so the tread is the point of the V, which will eliminate even more frictional loss.....

Sounds like a lot has changed s>>Hi,

On Wed, 25 Jan 2006 17:15:17 -0600, Rex B wrote in rec.crafts.metalworking:

Profile the wheels so that they are the same shape and that you have a minimum contact patch with the track. (less rolling resistance.) Use the round "dowel" type weights, you can find them at hobby shops that have the Pine wood derby accessories. Drill holes in the car to mount the weights at a 20+ degree angle from horizontal with the weight pointing down toward the front of the car. (weight transfer from the bottom of the hill to the flat part of the track.)

Radius the axles and the wheels where the axles head retrains the wheels to match and have good clearance. Put a ton of PTFE there. That is the big friction point.

Line up the wheels to the car to try and get them as much in the same plane as possible and in a good relationship.

If you really want to be a smart ass get some brass tubes, some steel balls slightly smaller than the tubes. Seal one end of the tube, put in the balls and then fill with oil, seal the other end of the tube. Now you have a movable weight system that won't rattle. Mount that assembly at an angle in the car...low point toward the front. This works great...but is considered a cheat in most scout troops.

Oh..test test test....keep adjusting the car and running it down an test truck and time it. Micro seconds count in pinewood derbies.

Won a 2nd place first time out, 1st place the second year.

I just got finished helping my son do his Boy Scouts pinewood derby car. From helping other dads over the years I can tell you that the previous posts were right on the money. If you can, true the wheels. I pushed the wheel on a .099 gage pin and took very light skim cuts in the Hardinge to true the OD to the center hole. There are ridges on the nails from the cold heading process on both the diameter and most importantly under the head (like a parting line). I skim cut these off with a thin bit in the Hardinge to clean up the ridges and parting line and then polished the OD of the nails where the wheels will contact. I don't use the saw slots for the nails. Instead I predrill .078 diameter holes for the nails in the Bridgeport to insure absolute perfect alignment. Do drill up to high or the car won't clear the 1/4" high track guide. The best lube is spray on Teflon. Do the nails and wheels but tape the ends of the nails so they won?t slip out of the car when you drive them in. Lastly, add enough weight (anywhere) so you are right at the limit. For the Boy Scouts that?s 5 ounces.

Is this a sanctioned event? Pinewood derby (Cub Scouts) use 5 oz weight. Need max weight by adding lead. Verify on Postal scales. Suggest Max weight and take a little cordless drill to take weight off if necessary (will help others do the same) Car should be slightly rear bias on weight. Axles on pine derby cars have two rough edges that need careful deburring and polishing. Wheels need as much space apart as possible to prevent scrubbing the guide rail. True wheels seem to work as good as regular wheels as they wobble so bad. Rules won't allow wheel bushings or oversize pins.

Rules require dry lubricant. Most use dry graphite to lube the axle. Take extra. The little ones will try to run the wheels off of it, this will screw up the alignment. Need to roll straight.

Most have adult and Jr. division as well as outlaw (no rules). Some are judge in different categories. Best of show, most original, fastest, prettiest, whatever. When we did it we made sure everyone won a certificate identifying their car as special in some category.

Hard to have fun when your trying too hard. Keep in mind wins are usually in just inches but having fun is priceless.

Easiest car to fab and polish would look like half a football. Kinda like the cars they used on the salt flats made out of a aircraft fuel tank except cut in half.

Sorry, I can't help you with your predicament, but you might like this story:

Good luck!

R, Tom Q.

I'd take a different approach...

Rig only two wheels in contact - opposite front and back.

Less drag is less drag, you know...

Richard

Narrowing the tire tread to a V has three benefits:

You've heard most of the tricks already. The only one I'd add would be to keep the weight to the back. Since the cars start on a slope and end on the flat, there's more drop at the rear.

Streamlining should be a plus, but I've seen some real clunkers win.

And whatever you do, remember that your daughter is the boss. The father of one of my older son's friends insisted that the weight would be best taped underneath the car (flat piece of sheet lead). The son thought that it might drag on the center strip. When the race started and the car wouldn't move, you can imagine how both of them felt.

Whatever happened to powdered graphite?

John Martin

I was actually disqualified from my Cub Scout pinewood derby competition in

Anyhow, all those mods helped, and I'd recommend the modern equivalent of them all. Powdered graphite was the hot setup friction reducer in my day. Weight and aero are obvious.

I've wondered where the weight should be centered. Obviously you'd want to reduce instability and have the car run a straight line down the track. If the weight was in the center the car would be less impacted by rubbing against the side or center rail, but might be less stable. Hmmmm...

On-board webcam

Technically, we cannot make this type of modification. A little truing up we can get away with but major changes like this to the wheels are expressly prohibited in the rules included with the kit. Besides: According to the experts air resistance has been discounted as irrelevant at these speeds . I don't buy into the lower rolling resistance theory. The only one I'm buying is the rotational inertia effect but I'm going to double check with the expert (chief engineer).

Good point, that's makes a lot of sense.

Apparently, according to the experts, the speeds are to low to make an difference.

It got replaced by Teflon. Sometimes newer is actually better.

Keep the weight in the back....it will fall longer....it has been debated forever...trust me....the longer the majority of the weight is falling, the faster the car goes. Center of balance should be about 1" in front of the rear axel...further back, and the front wheels move around too much.

Polish the axels.....to a mirror finish.

Some sites to look at....

This takes me back a few decades. I remember a fellow at the lab who turned the axel rods (nails) on a microlathe, deposited lubricant on them, and then drove them in crooked, and wasted it all.

First suggestion. Do not do anything that you cannot do with your child. That is the entire purpose. Having a winning car and alienating your child is the wrong thing to do. Work with him/her. If this is the introduction to machine tools, make it a positive introduction. IF you cannot describe why you are doing something to the child, then it should not be done.

The design [color, pattern, coolness] is much more important than the mechanics. This is their design. Let them do it, and you just help them.

Remember this is a kids project. Have your own fathers section if you must, but let the kids learn and have fun Bert

SNIP

Thank you for the great story. I can relate, having been raised by a working mom.

James

Let your kid build the car. Any work you do is robbing her af a fun experience. And any cheating robs all the other kids.

Our Cub Scout pack got so out of control with dad-built cars that we added a seperate class for them. It was sad- some of the boys couldn't pick their own car out of a line up- they had never seen it until race day.

And for all those theories as to why one car wins and another doesn't- they are all bullshit. When we rebuilt our 5 lane track (and added a high speed finish line clock), we tested it with a variety of cars, running each car through each lane 5 times. After 25 runs, none of the cars was a consistant winner, nor did any lane come up faster or slower than the others.

There is one tip- build the car a little heavy (the limit is 5 oz) in case the official scale is off a little- it's easy to take weight off.

-Carl

Maybe. A few decimals down...

At these speeds air resistance is a small part of it.

I think this is the one that matters.

However you can get away with it...

Richard