Off Topic: Pinebox Derby Advice?

I apologize for being off topic here, but I figured you guys might know something about this .... My son is in the Cub Scouts and we are about to build a Pinebox Derby car for an upcoming race. For those of you that don't know, Pinebox Derby cars are little cars carved out of a block of wood that race by coasting down a ramp. We must design and build the car ourselves and I was wondering if any of you had any advice on making the car fast. Things I do know: You should add lead weights to get the car up to the maximum weight (5 oz. I think). You can use a dry lubricant on the axles. Questions: Does the car need to be balanced in any particular fashion? That is, should the weight be distributed evenly around the midpoint or set to the front, etc.? Any special aerodynamic considerations as to the shape of the car? Anything else? Thanks in advance, Dave Ewing

Potential Energy (PE) = mgh where m is mass, g is gravity (constant) and h is your height. Kenetic Energy (KE) = 1/2 m(v squared) where m is mass and v is velocity while the car is at rest you have PE. When it moves this converts to KE, so PE ~= KE (accounting for friction loss) Basically, you can't change g or h as they are controlled by God (g) or the Cub Scouts of America (h). They are constant (while at rest). You can maximize your mass (m). This increases your PE which increases your KE which increases your velocity. What you will see between a heavy car and a light car (assuming equal friction loss), they will both come down the ramp at the same speed (remember Galileo), but at the bottom the heavy car will pull away from the light car as it has more KE. At least that is what it did for me in 1964 when I entered the Pinebox Derby.... :-) -Paul

On Tue, 05 Jan 1999 14:56:02 -0700, David Ewing

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>I apologize for being off topic here, but I figured you guys might know >something about this .... >My son is in the Cub Scouts and we are about to build a Pinebox Derby >car for an upcoming race. For those of you that don't know, Pinebox >Derby cars are little cars carved out of a block of wood that race by >coasting down a ramp. We must design and build the car ourselves and I >was wondering if any of you had any advice on making the car fast. >Things I do know: >Questions: >Does the car need to be balanced in any particular fashion? That is, >should the weight be distributed evenly around the midpoint or set to >the front, etc.?

I would say keep it in the middle in case there are bumps you can find some dry TFE at http://www.techspray.com/2414.htm. Other than that just remember that adding weight will only be effective after you have reduced friction to the minimum. All objects fall at 9.8 meter/sec/sec regardless of weight (umm... I think right Paul?) if they are not acted on by another force (i.e. drag). Drag can come from resistance to the air, the underside of the car rubbing on the track,the inside of the wheels rubbing on the track and the car , the wheels spinning on the axle , and the rolling resistance (I'm sure I've forgoten something) I don't know if it's "legal" or not but if you could lathe a high spot (ridge) on each the tires you could signifiganly reduce the rolling resistance. Maybe you could try some of that "frictionless" paint that all the NASCAR pundits claim J Gordon is using to cheat with : ) !! Just make sure that R.A.S. is the official sponsor and take pictures so that we can see it. Don't cheat and have fun.

Description of Pinewood derby removed. I remember when I raced, we used lead sinkers set in epoxy for ballast, and since our pack strictly adhered to the 5 ounce maximum, we set it slightly overweight (by about 0.2-0.3 ounces), went to the meet early and weighed it on their scale. We then drilled out enough weight to hit the maximum allowable. As to the previous response, having the maximum weight matters, since that is what overcomes the drag. As for "tricks," I remember that my cars were always angular (that was the easiest, just cut from the front bottom to the back top). Another trait of my cars was that all 4 wheels never touched the ground at the same time, mostly due to my poor craftsmanship, but this could reduce the resistance. Now for the real tricks. The most important thing is to reduce the axle friction. Take the nails that are being used for axles, and make sure you remove any burrs, ridges, or imperfections. After that, our Big Secret was to spray the axles and insides of wheels with.... Armor All! You know, the plastic protectant. I also am not sure if this is legal, but it does not need to be done at the race. Just spray it before you go, or the night before, it doesn't matter. Total weight and axle friction are the two most important factors. And try to make your pack follow the 5 ounce weight limit. Some may claim that is too technical, but it makes it fair. Just so you know if this really works, I got 3rd in my pack with graphite, then 1st with Armor All. My brother got first place, and I also got first place in an advisors race. Other families we have told this too have also reported excellent results. One caution: Don't tell other families until you are out of scouts. They might beat you. "Three options: Right, Fast, and Cheap. Pick Two." Like everyone else, I've changed my reply address. To reply, remove ._nospam_ from address.