Quote:
Originally Posted by t-maxxracer32
o ya yes patrick is it for school! it only has to go 10 feet but any more than that is extra credit
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10ft! That's easy. We had to do 15m (49.2ft) with speed, so going just for distance and not speed you could easily get 60ft+ I think (as long as the surface it's on is nice and smooth, and it goes straight).
If I was going to do one again I think I would go down to my LHS or hardware store and get some 5 or 6mm diametre aluminum tube to use as the frame, axles and lever. It will be strong, light, look good and you should be able to get some that will fit standard size rc bearings.
I'd use CD's for the rear wheels and possibly the fronts (make sure you put them on the axle as straight as you can). Bigger wheels will accelerate slower, but you'll get more distance/top speed out of the same number of axle turns. Once your spring has finished powering the car the big wheels will have more momentum than little ones and will keep the car rolling for longer. CD's are a good size though.
Use a long lever like you have, but think of it like the lever is a pinion and the axle that you wrap the string around is your spur. Big pinion/lever and small spur/axle = slow take off, but high top end, and in this case distance (if you have the power to use all the gearing). Small pinion/lever and big spur/axle = Quick take off, but not much top end, and less distance. So like rc you have to find the right combo for how much power you have (spring force in this case) and what you want it to do. I like B15's idea of using a stepped axle for the string. If you get if working right I'll be like an auto 2 speed. Wind the string onto the smaller part first (second gear), then onto the bigger part (first gear).
Make sure it goes straight and smooth. How well it rolls is very important, since it doesn't have much power. I'm pretty sure that the cars that won the comp I was in, the spring finished powering the car at about half way and they rolled the second half (this was 1999 though so I could be a bit off). Mine finished powering the car at about 10m (32ft) and rolled the rest, but their's got to full speed quicker.
I'd have the end of the lever basically in line with the rear axle, but better to be slightly in front than slightly behind. Should help you get the best leverage. And if it is in front slightly then the lever shouldn't hit the axle when fully pulled back.
Now get designing, I don't want less than 50ft
