Last edited by Chuck Thoits; 04-29-2009 at 10:21 PM.
It could be worse You could be on fire.
Chuck, the only thing that comes to mind is, go with very thin narrow wheels with ball bearings. I would make them out of plastic with a groove in the outer edge to roll a thin O'ring into to act as a tire. That would help it track better. Other than that maybe a compressed air nozzle to give it a better launch!!??
What goes around, comes around.
Many years since I was embarrassed by helping my son with a pinewood derby car. The first one didn't make it to the bottom of the track. We endured the harrassment, and the next time around we took 3rd in the regionals. Lessons learned. Actually, my son made the car, I provided the work on the things that let it go fast. If you have to stick to kit pieces (that was our rule), about all you can do is make everything as smooth as possible. Also use a forstner bit on the bottom to make places to add weight in strategic spots so the weight is right up at the max allowable (minus a smidge since you don't want to be disqualified because somebody's scale is out of whack). I put the axles in a drill press and smoothed them with steel wool and polishing medium. I also rigged a way to chuck the wheels in the drill press so I could use an abrasive to get them as round and smooth as possible. Can't remember how I did this, but it's also important to install the axles so the wheels are all tracking the same and not fighting each other. Sounds simple, but as I recall it was quite a bit of work. But it paid off. I don't think aerodynamics comes into play with something that small, but don't take my word on that. Maybe we would have done better than 3rd if I'd considered it, but my son had ideas about what he wanted it to look like, and actually it was his car. Good luck with that.
I wish I could help out, but we didn't win anything for speed. What I've read and been told breaks down to 1) geometry - wheels/axles square to the body and each other and 2) friction - polished axles and concentric wheels. We only did the basics to get the car down the track.
Good luck and have fun!
Chuck: my grandson's cub scouts did thiers two weeks ago. We had a blast. We finished 9th outa 11; but we did finish. The other two did not finish. My grandson insisted he build a truck so I cut and glued him a ford pu and he already has said next year it will a fast car.
When this thread is finished I will print it for him as a guide for next year.
It's all in the wheels and axles. My son's troop specifies that you must use the BSA wheels and axles and you cannot modify the wheels other than polishing to remove casting marks. They check that the molded "tread edges" remain.
Like Wes said - it's all in the rolling friction and geometry. I'd be temped to get the wheels perfectly round and fill them SOLID with some material. The wheels would have a higher moment of inertia (if all my physics is being remembered properly) and would/could maintain speed better in the flat.
Good luck -
compressed air? i'd go with a bottle rocket embedded in the car. remember, it if it's not disallowed in the rules...
benedictione omnes bene
alas.... no open flames allowed
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Instead of fenders, can you mount one or two horizontal wheels on each side, to run on the side rails of the track (in case your tracking isn't quite right)? Essentially roller bumpers on the sides.
When the going gets weird, the weird turn pro. - Hunter S. Thompson
When the weird get going, they start their own forum. - Vaughn McMillan
That's what I remembered as well Vaughn - weight as far forward as possible. BUT, I was informed the weight should be as far BACK as possible. Something to do with the center of mass and having gravity act on that mass as long as possible. Oh, and lead and zinc are now passe - they're using tungsten now because it's denser than lead allowing for more precise placement of the weight.
I do remember one of the winning cars had the slots for the axles re-machined accurately on the top (now the bottom) and ignoring the original slots.