Derby Talk

Simply put, as a PWD car rolls down the track, it rotates about the center of mass (starts angled down, and rotates until it is level). The COM is almost always between the axles, or the car will be unstable (pop wheelies) The further away from the center of mass the weight is, the more energy is co...

I've discovered a few interesting things while doing "thought experiments" about adding weight to a PWD car. I thought I'd share them, and maybe solicit some responses. I started with a presumption that you had hollowed out an area in the block that was shaped like a rectangular prism to b...

Pennies weight varies quite a bit

FYI-
Prior to 1982, pennies were made from copper.
In 1982, they switch to zinc, with copper plating.
Zinc is less dense than Copper, so pennies 1982 and later would be lighter.
This might help explain your variance, if you took a random sample from a penny jar.

I was trying to justify to myself if I were going insane, have a really poor memory, or there were forces I didn't understand at work. I'm happy to report that I'm not insane, and my memory serves me well. I replicated my test setup again. And again, the back wheels move IN-IN (or from out to in, fo...

If anyone can learn from their mistakes, I should be pretty knowlegable in this area by now. I've come to believe that the precision required to get a PWD car to roll perfectly straight cannot be acheived with the types of material/tools typically used to build a PWD car. You can get it close (sound...

This statement just doesn't make any sense to me I was using drilled axle holes, not slots. I am now able to visualize the results from shimming, but I was mixed up before (thanks for setting me straight). Now I see that the shims cause the axle (nail) to rotate about the point of the nail. I could...

Just to clarify, I never said the car didn't roll straight. It rolled perfectly straight on my 4' test track (card table) right from the start. The problem was the wheels slid from outside to inside on the axles. Following the alignment procedure, I started with 3 wheels, then moved to 4. I'm certai...

I think that if you use the search function, you will find the answer to most of your questions already posted. There's a really neat tip about using a dremel cut off wheel to remove the axle burrs. That worked great for me this year. There's tons of theories about 3 wheelers - draw your own conclus...

I guess I think now, that I didn't fully understand the shimming process, as I was under the impression the axle rotated about point where it met the car body (near the center) and now realize it rotates about the point of the nail head. Also, I remember kicking myself for not filing down the nail h...

Let me start over. I realize I introduced too many issues, and it clouded what I really wanted to find out. Last night's experiments produced completely different results. Let's assume that what I observed before the race was either remembered incorrectly, or was the result of the axles being too fa...

Sorry, now I see the mistake in my earlier posts. Let me clarify. I seemed to get the same results whether I rolled the car frontwards or backwards, and on all four wheels. I thought I was able to correct the problem on the front wheels with 4 shims or so (on the bottom of the axle -what I thought w...

In the back, we drilled two 1/2" holes just above the axels, and just below the top surface to fill with weight. Since the thickness in the back is nearly 3/4", and the axle holes start 1/8" above the bottom, the axel holes come close to the 1/2" holes. They may actually have pun...

We heavily favor the drill press. I got a small scroll saw at a garage sale. (approximately 4" x 1/8" blade, that moves up and down on a flat surface) I feel pretty comfortable letting my son use this to shape the car, keeping his fingers away from the blade. He doesn't like it though. He'...

I didn't spend too much time with wheel alignment prior to adding weight. (why bother?) Just a quick check on the hardwood floors, and a visual inspection. I felt pretty good (got some neat tools for Christmas!) that this year we had everything square and straight. Once I got the card table set up, ...

I'm reluctant to post something on a public forum that may be taken as criticism of the way my pack runs the pinewood derby. I blame myself for waiting until too late this year. Maybe if I had started in October, instead of the Christmas break, things would have been better. For several years in the...